Introduction

This section is for defending a planet from orbit. The next section is for attacking a planet by ground assault.

After all the interplanetary battles are over, and the defender's space fleets have been reduced to ionized plasma or fled in panic, the pendultimate stage is entered. The defenders orbital and planetary fortresses have to be neutralized, or at least neutralized enough so that ground troops can be inserted to set up a beachhead.

Orbital Fortress

The defenders remaining spaceborn assets will be in orbit around the planet. If the defender is fortunate enough to have a moon or two these can also be armed with defensive bases and weapons.

Orbital fortresses have far more punch than the equivalent combat spacecraft, kilogram for kilogram. This is because the spacecraft has to use part of its mass for propulsion, while the orbital fortress can use that mass allocation for more weapons instead. However orbital fortresses do have problems with heat radiators and supply.

Supporting the fortresses, the planet's orbit will probably be full of defensive assets such as small but deadly weapons designed to mission-kill invading spacecraft and any ortillery they drop. In the Strategic Defense Initiative, two concepts looked into were "Space-Based Interceptor" and "Brilliant Pebbles" (the latter were the heirs to "smart rocks")


When it comes to defending a space colony instead of a planet, you can attach weapons and defenses so the thing becomes sort of an orbital fortress that people live inside. On Babylon 5 this was called the "defense grid".

In Long Shot for Rosinante, Alexis Gilliland points out there are military implications. If you have several unarmed space colonies you will need a fleet of warships roving around to defend the colonies. If the colonies are then retrofitted with weapons so they can defend themselves, oh my! You suddenly have a spare fleet of warships that can be repurposed to military adventurism! Enemy colonies will become alarmed.

However the politicians of the nation which established the colonies may be unenthusiastic about the idea. For one thing it makes it harder to collect taxes from the colonies, since they can shoot at the tax collectors. It also makes it harder for the politicans to control the military, since the latter will be eager for some delicious military adventurism. Regardless of what those cowardly civilian politicans back home have to say.


The indispensable Future War Stories blog makes the point that there is a big difference between a Battle Station (orbital fortress) and a Military Space Station.

A battle station, mobile assault platform, or orbital fortress is basically a huge warship armed to the teeth that has no engine. It has lots of offensive weapons. Much like the Death Star from Star Wars, but used more to defend planets instead of blowing them up.

A military space station is a military base that just happens to be in orbit instead of on the ground. It is used to support troops, house spacecraft, administer logistical aid, and the like. Generally it only has defensive weapons, but may be protected by a space navy task force. They are much like the U.S. military bases located in the continental United States.

SPACE FORTS

We who have grown up with the bomb can hardly imagine a world without the Sword of Damocles hanging over our heads by a thread. Strategic warfare has been dominated by offense for over 30 years.

Even though it might take 20-50 years, advances in space might swing the balance back toward defense. Here are some wild speculations, hopefully based on engineering realities.

Don’t be surprised if the Department of Defense picks up the slack in NASA funding of mass drivers and solar sails. A mass driver is just what you need to bring most of an asteroid to the vicinity of the Earth by throwing away part of the asteroid for reaction mass. Solar sails would bring them back piecemeal. A million-ton asteroid in high Earth orbit would solve a number of problems such as providing hardening for certain advanced weapons systems and their heat sinks.

"Hardening" is the capacity to take a beating and remain functional.

Heat sink" is an engineering term which can mean anything from a tiny clip on a transistor to the Mississippi river. It's whatever is used to get rid of waste heat. On Earth, waste heat is mostly carried off by water or air and eventually radiated from the vast area of the planet into the cold (three degrees above absolute zero) universe. Some of you may remember the story by Poul Anderson about a rogue planet (Satan) that was thawed out by a close pass near a star and then kept warm as it sailed back into the dark by industrial waste heat on a grand scale.

Getting rid of waste heat without a planet isn’t hard, but it isn't cheap either. Waste heat radiators are a major factor in the design of space industrial facilities, habitats, farms and military bases. For all of these, including, in the long run, military bases, the Stefan-Boltzman law relating temperature and radiation rate and the fact that people and their machines function best around “room temperature" implies that the radiator surface area will be about four square meters for every kilowatt of waste heat.

Military fact #1: in the size we need, waste heat radiators will be very large. Radiators must be filled with something (substitutes for wind and water) to carry the heat. For both physical and economic reasons radiators should have walls no thicker than required to contain the filling material.

Military fact #2: radiators are unavoidably fragile. Something both large and fragile would make a lousy military heat sink. Nobody can cheat on physical laws, but with an asteroid, you would be able (for a while) to use the "Alice's Restaurant" method of waste-heat disposal. (Alice lived in the belfry of a deserted church and put the garbage downstairs.) Two weapon systems, particle beams and lasers, have the potential to end the current offense-dominated Mexican stand-off known as "Mutual Assured Destruction," or MAD. Lasers are getting about $200 million per year development money in this country, and particle beams are believed to be better supported in the U.S.S.R.

Both particle beams and lasers are line of sight, speed of light weapons. This could make for some mighty short wars! They are very similar in needing millions of kilowatts of power and large heat sinks (because they are not very efficient) and both work better in space. Either method, with enough power behind it and a good enough aiming system, could make short work of ICBMs, submarine launched ballistic missiles and perhaps even bombers and cruise missiles, thereby eliminating all three of the U.S. "triad" at one stroke.

Skip for a moment the moral and geopolitical implications: how does an asteroid fit into this picture?

First, it's by far the easiest way to get a hardened site into space. Hardening is absolutely essential if the opposition has a similar installation. Otherwise, all the advantages go to "he who shoots first," a much worse situation than MAD. An actively defended fort could most likely stop missiles, but there is no way to shoot down a laser beam. However, you need not worry about lasers if you are inside a multimillion-ton asteroid. An MIT study some years ago concluded that even to slightly deflect an asteroid (e.g. Icarus) would take a lot of the very largest hydrogen bombs people make. A laser that could wipe out missiles would just blow little pock marks in the surface of an asteroid.

Second, to keep the laser cool you need a monster heat sink that a hostile laser won't cut to confetti. Radiators are just too vulnerable, (see above) so the waste heat will have to be stored till the war is over and that means an asteroidal sized mass to store the heat. Even if the laser gasses only make one pass through the laser and then are discharged into space, a substantial heat sink would be needed for the auxilliary equipment and such things as cooling the laser mirrors. For the same reason, all the energy to fight a war will have to be stored inside.

How much energy storage and heat sink capacity would be needed to fight a hypothetical war between the major powers with space-based lasers zapping all the missiles? Unless you complicate things by having the forts try to fight each other to the finish, a few gigawatt hours of beam energy is sufficient to wipe out the warhead delivery systems inventory of the entire world. Altogether there are less than 5000 ICBM's and submarine-launched ballistic missiles. Five gigawatt hours of beam energy would give a little less than a ton of explosive effect for each one. Because lasers are only about 20% efficient,* and allowing for some safety margin, energy storage might be ten times the beam energy and heat sink capacity about eight times the beam energy. To get a feel for this amount of energy in standard military terms, one gigawatt hour is equivalent to about 900 tons of TNT.

(*If you believe in higher efficiency, plug in your own numbers. Free electron lasers might reach 50%.)

The next question is how big an asteroid do you need in order to absorb, say, 40 gigawatt hours? A simple general rule is that a kilowatt second will heat a kilogram of rock about one degree C. Forty gigawatt hours is 14.4 x 109 kilowatts, which means this much energy would heat a million ton asteroid 14.4 degrees C. Thermal stress rather than absolute temperature rise may turn out to be a determining factor. To keep a fort ready, you keep it cold.

How would an asteroid fort be constructed that could take considerable pounding from lasers and missiles and still be able to zap ICBM's. The best type, to start, would be the solid nickel-iron variety found in science fiction stories. Unfortunately, that may be the only place to find them. The processes (hotly argued over) that formed these objects may have left fracture-prone weak zones of silicate material between large blocks of solid metal.

For iron asteroids with fracture zones of stony iron (lumps of iron mixed with rock) the first job will be some outside shaping followed by drilling a lot of holes through the asteroid and stringing it together with steel cables. This would probably work with any asteroid that had as much compressive strength as concrete.

Next, a maze of coolant channels would be drilled through the rock or iron. Iron would provide an advantage here because of its much better conductivity. Either rock or iron would be fairly easy to drill through, but a mixture would be more difficult. The laser, control system and power storage would be installed in cavities dug out of the center of the asteroid. My guess is that energy would be stored in flywheels or fuel cells. Primary power could be nuclear reactors or solar cells. Either the solar cells or heat radiators for the reactor would hang outside and you could expect them to be shot off right at the start of any action.

Lastly, the surface would be covered many meters deep with foamed metal to soak up energy from a close nuclear blast or a short laser pulse. Much of the energy from a nuclear blast in space arrives in the form of X-rays which heat the outside surface so fast that a shock wave causes pieces to fly off the inside wall (spallation). A substantial layer of something crushable takes care of this problem.

To track targets and control the aiming of the laser would require a dispersed phased array radar too spread out to knock out with missiles and too hard to take out quickly with a laser. Verification of target destruction and some tracking would be done optically or with infrared. The radar information would be transmitted over redundant channels to a very large, fast computer in the fort. This part is within the capacity of present day electronics.

Like the Death Star in Star Wars, a space fort would have a vulnerable spot. It could be knocked out by a beam that went in where its beam went out. To protect its “Achilles Heel" each one might be surrounded with a flotilla of actively controlled mirrors: a fort could take bank shots with a diffuse beam at the other forts, while avoiding looking directly at them. (A fully focused beam would be so energetic that it would not be reflected, but would just vaporize the bank-shot mirror. The bank-shot mirror would refocus the beam more tightly.)

There are many counter and counter-counter strategies including shooting lasers at the forts from the ground, trying to disable all the enemy's reflector flotilla, hardening the bank shot reflectors, and slinging rocks at the forts. None look very promising. Attacking from the ground with lasers looks like it would bankrupt the country that tried it.

Why? Missiles can be destroyed by the energy equivalent of a few kilograms of TNT. A bomber can be wrecked by the equivalent of a few hundred kilograms. But an asteroid would take hundreds of megatons of TNT or millions of gigawatt hours. Not counting laser inefficiency, or the cost of the laser, a million gigawatt hours at one cent per kWh is $100 billion. The lasers would cost a thousand to a million times this much. Hitting a fort with another asteroid would be effective, but would take years due to celestial mechanics considerations. Also, it isn't easy to do secretly. Even the slightest ability of a fort to dodge would make it vastly more difficult to hit.

And a shoot-out between forts of similar size looks to be a real idiot's delight: “this hurts me more than you" really applies to space forts because four times as much energy as is in the laser beam must be dumped internally, and the vast majority of energy delivered by the laser beam would be reradiated; the remainder would do very little heating. Even with limitless energy available, an attacker using lasers would cook itself long before doing much damage to a target fort.

For the same reason, a small amount of hardening would protect a ground installation from attack by a space-based laser. The total energy available within a fort due to laser energy storage is equivalent to only a few hundred to a few thousand tons of TNT.

Schemes to put forts out of action would be less attractive if many countries owned several forts each. If only two countries owned one fort each, a fort being put out of action would leave the owner of that fort in a very bad fix, exposed to ICBM's without any way to retaliate. If a dozen countries owned several forts each, there would be very little point in keeping ICBM's active at all. Of course, some countries would still keep ICBM's around just to force others to spend money on defense. (A major effect of the U.S. bomber fleet is to force the U.S.S.R. to spend a bundle on air defense—money that would otherwise be spent on other military projects.)

Whether or not asteroid forts and very large lasers in space would have a major effect on ground warfare is a good question. I am sure tanks would be much more difficult to take out of action than cruise missiles or bombers. However, if the problems of shooting down through the atmosphere can be solved, it might accelerate the current trend, started by precision guided munitions, to quickly remove large, expensive objects from the battlefield. I don't think the troops will go back to swords and horses, but automatic rifles, hand-held rocket launchers and motorcycles might be the most expensive items practical on a year 2000 battlefield.

May the force be with you!

PYRRHIC

Belchar’s World, Battle of: The Battle of Belchar’s World – a term referring to Fourth Belchar’s, 6882 – while in most respects another of the minor squabbles endemic to the Shadow Systems, has attained a degree of fame through being taught in the majority of the Worlds’ military academies as an example of the problems that can result from close-orbital combat operations.

The battle was the last gasp of the Vile-Born Imperium’s attempted invasion of the freesoil Belchar’s World (Torgu Wilds). While a technical victory for the organized Vile-Born fleet against the irregular forces of the freesoil world, the majority of the battle took place in mid-to-low planetary orbit, resulting in extensive destruction of not only military craft, but also of civilian stations and other elements of orbital infrastructure – most significantly, the self-destruction of the orbital starport twenty-two minutes after Vile-Born boarding parties forced the docking bays.

Inevitably, the introduction of so much debris into this area caused a full-blown cascade catastrophe, resulting in mutual disengagement. After a number of attempts to penetrate the cascade zone with landing craft, all of which were lost with all hands, the Vile-Born fleet retreated from the system in good order.

(This was not to last: much of the fleet was subsequently destroyed in the Osquina Mutiny, instigated by a coalition of sub-admirals who preferred not to return to Vileheim and suffer the traditional sky-bath prescribed for failed naval officers.)


Winchell Chung: Would the "traditional sky bath prescribed for failed naval officers" include sky-diving without a parachute?

Alistair Young: Different kind, in this case: the Torgu Wilds are located uncomfortably close to a stellar nursery and other things contributing to an unpleasant radiation environment. The "sky-bath" involves being staked out under the open sky until the rads get you.

From PYRRHIC by Alistair Young (2019)
HABITAT LASERS AND MILITARY ADVENTURISM

(ed note: the Munditos are L5 colonies set in the asteroid belt (paired spinning habitats about 50 kilometers long, set inside conical mirrors). They are owned by their founding nation and must pay taxes. They are protected by military ships from their founding nation. Mundito Rosinante becomes independent, and decides to build a huge laser, energized by sunlight from the mirrors. Later they use the laser to power a large high-deltaV laser thermal rocket.)

     “Suppose we are preparing to defend against a future missile attack, like the one just past. Have you any ideas? I mean it's a little late to be brainstorming once the missile is on its way."
     "We might build a big laser,” he said at last. “I mean a really big laser, Governor, say 50 meters by 10,000 meters, or even 20,000. Nothing ultra-hot like the Navy uses, but continuous, you know? Pump it with the big mirrors."
     "Navy weapons doctrine calls for a power source to generate light, the hotter the better. We have the big arrays of mirrors for light. No need to use a middleman, as it were. We just build a cool, continuous gas laser, but very, very big. It ought to have an effective range of maybe 200,000 kilometers, and it could pick off a missile like nothing, don't you know?"

(ed note: Yes, lasers have to be pumped with monochromatic light and sunlight is polychromatic. Mundito Rosinante has a Japanese "dragon-scale mosaic mirror array" composing the two conical frustrums. The dragon-scale array is composed of tens of thousands of little mirrors, of three types. One type only reflects red light, one only blue, one only green. The mirrors are transparent to other colors. They coat the laser body with red and blue reflecting mirrors so only the monochromatic green light can enter the laser cavity. They also only use the green reflecting mirrors on the frusturms to send light to the laser.

Non-Japanese munditos use a monolithic aluminum mirror which reflects all colors of sunlight, and thus cannot be used to pump a huge laser. Monolithic aluminum mirrors are much cheaper. So Japanese munditos can have these lasers but others cannot.)


     "What about your idea to maximize the light density by using only one of the three colors of light our mirrors reflect?"
     "We've worked out the system for the green light best,” said Ilgen, running his hand over his crew cut. “We have that stack of mirrors—the red and blue mirrors left over from the quality-control work on making the big array—could we use them? How many do we have?"
     "The red and blue combined? Maybe 60 or 70 hectares,” said Skaskash. “That would give us a working length of maybe 16 kilometers. I think we really need 21 or 22."
     "Yes, 22 would take all the green light from one of the frustrums on the Don Q array-if we patched it up. But what about the cooling?"
     “Hey! Skaskash! If we built a pressurized jacket, oh, say one kilometer in diameter, the laser would be air-cooled except for the face, which would be silica! Then we could run a higher light-density and 16 kilometers would be enough! Hell! We could do it with 10!"

     "After the event, I ordered high-resolution pictures taken from Laputa."
     "This is the double frustum of Don Quixote during the cleanup,” she said, turning the print over. “This is almost the same view taken on January 20, showing the construction in the right-hand frustum in the interim. The technicians call it the Purple Shaft. Notice the support system, which can rotate the shaft in two planes. I imagine that if it was aimed at an object on the other side of the mirror array, a few of the mirrors could be removed."
     "This is an enlarged view of the same scene. It shows the Purple Shaft very clearly. We estimate that it is 1020 meters in diameter, 17,230 meters long. The outer surface is made of salvaged purlin tile mounted in salvaged purlin frames. The faint diamond pattern shows quite clearly."
     "It doesn't look purple at all,” said Hulvey. “Why do they call it the Purple Shaft?"
     "This is the device in operation,” she said. “A very short exposure time shows the inner structure vividly. It is a tube twelve or thirteen meters in diameter running the length of the structure. It is evidently covered with red and blue layered mirrors, so that it reflects purple light and passes green light into the gas mixture which the inner tube contains. In effect, you are looking at a huge gas laser pumped by an array of mirrors having an area of thousands of square kilometers."
     "The radiation data is consistent with methyl isopropyl mercury and carbon dioxide,” she replied, “but we don't know.”
     "Is it using the full power of the mirror array?” Hulvey asked.
     "No, on that shot they were using 30 percent,” she said. “We took a picture of the mirror, and had the computer calculate the angle of each mirror in the array. It gave us a false-color developed picture.” She pulled a print out of the pile. “Yellow is aimed at the laser, the red and red-purple are not. The little green rectangle was probably being used for something else."
     "Could they use the full power of the array to pump the laser?” asked Admiral Vong.
     "They've had it as high as 80 percent,” she said. “That is, we've seen them take it as high as 80 percent. It is a formidable weapon."

(ed note: the colony of Rosinante makes a treaty with Japan, and gives them the blueprints for the giant laser. The Japanese politicians are unhappy, since buiding lasers on their space colonies will make both the colonies and the the Japanese space navy harder to govern)

      "Rosinante has honored their agreement,” said Shinaka. “We have received their technical data for building the heat ray.
     "This heat ray,” said Shinaka, gesturing with his chopsticks, “it is a most troublesome thing. Why couldn't we have invented it ourselves so we could have suppressed it?"
     "It is implicit in the design of the Dragon Scale Mirror,” said Kogo. “I expect the reason we didn't invent it was because we consciously decided not to.” He ate a piece of tuna.
     "I was with the Dragon Scale Mirror project as a senior team manager back in ‘23 when it was getting started,” Kogo went on, “and the feature that most troubled the Admiralty at that time was the capability to use the mirror array as a defense against docking ships."
     "A short-range defense only,” said Shinaka. “Why were they troubled?"
     "A city wall is a short-range defense,” replied Kogo, wishing he could light up a cigar, “but when a city builds such a wall it may suddenly become more adventuresome in its foreign policy. The Admiralty feared the drift away from the Central Government. The habitats lend themselves to autarky very naturally. If they also become defensible, like castles, how will we be able to collect our taxes? The big laser was considered in that context, and we never went ahead with it because the Admiralty was afraid that such a powerful weapon in the hands of the habitat managers would make them impossible to control. That is what bothers you now, isn't it?"
     "Yes,” said Shinaka, eating a piece of octopus. “It diminishes our warships, also. Perhaps that bothers me even more."
     "It does not matter,” said Kogo, “the heat ray is there. Either we use it to advantage or we do not, but we cannot make it disappear. Consider that to use it one must have the Dragon Scale Mirror—which is standard on Japanese habitats, while only a small number of non-Japanese habitats have them. If we use it, we will have a significant military advantage for a significant length of time.” He smiled, showing his lower teeth. “I say build it!"
     "It is true,” conceded Shinaka, taking a fresh slice, “we would achieve a transient advantage with the device. What did you have in mind?"
     "Use it to free our Navy from defending fixed and scattered points,” said Kogo, “so that we can concentrate our forces for a decisive victory!"
     "The last time we did that was when we developed the Zero fighter plane at the beginning of World War II,” said Shinaka. “What happens afterward?"

     So,” said (Admiral) Kogo, puffing smoke. “Has any decision been reached about building the large lasers in our own habitats?"
     "We have reached an informal consensus,” replied (poltician) Seto. “If it were possible to return the engineering details to Rosinante and withdraw diplomatic recognition, we would do so."
     "That is unfortunately impossible,” said Kogo. “Have you decided yes or no?"
     "No,” said Seto. “That is, we have made no decision at this time."
     "Ah, so,” said Kogo, letting the smoke flow from his nose. “Once again our politicians temporize and waver. Does it not strike you as advantageous that if we fitted our habitats with the big laser, our navy would not be tied to their defense?"
     "That point has been discussed at length,” said Seto. “The admirals and the younger generals felt it was exciting and useful, and were outspokenly in favor. The civilians and the older generals felt it would encourage military adventurism."
     "Oh, come now,” protested Kogo. “This is the twenty-first century, after all."
     "You are in favor of producing the big lasers?” asked (Japanese intelligence service) Sumidawa. “Then please tell us against whom you would concentrate the might of the Japanese Navy."
     "We wouldn't have to concentrate it."
     "So sorry, Admiral Kogo,” replied Sumidawa. “We would at one stroke have achieved a significant but temporary military superiority in space. Which the admirals would urgently wish to exploit. Against whom? Against the North American Union (NAU), our major trading partner, here on Tellus?"
     "It is increasingly difficult to retain control of events in space,” said Seto. “The admirals, in particular, have shown a disturbing independence. You say this is the twenty-first century. How is it then that the Navy is seeking to capture the NAU base on Ceres against the wishes of the Diet?"
     "We have done far less than we might,” replied Kogo, flicking cigar ash into a sculptured bronze ashtray. “Indeed, Mr. Seto, the Navy has shown admirable restraint in the face of the NAU's provocations."
     "What provocations!” barked Seto.
     "The (NAU fleet) mutiny and the profound weakness which it revealed,” said Kogo. “We could reach out our hand and take Ceres. Instead, we piddle around with commerce raiding—piracy, if you like—because the Diet does not want us to upset the trading partners of our bloated merchants!"
     Seto flushed angrily. The House of Seto was one of the largest grain importers in Japan.
     "Stop trading and see children bloated with hunger, instead,” he said. “We depend for our life on the grain the NAU sells!"
     "They would not stop trading if we took Ceres,” Kogo commented mildly. “They need to sell the grain as much as we need to buy it."
     "You seem very willing to contemplate war with the NAU,” said Colonel Sumidawa. “What could we gain in space that would match our losses on Tellus?" (Terra)
     "We would not be starting a war,” said Kogo, “the NAU would merely have to accept our military superiority as a fact of life. On Tellus, it might lower the price of grain by ... oh, six or seven percent."
     "We can not win a war with the NAU!” said Seto. “Do you think we can win such a war?"
     Admiral Hideoshi Kogo sat back in his chair and blew a perfect smoke ring.
     "I am very sorry, Mr. Seto,” he said, “but as it happens I do think we can win such a war."

     "Right now I am concerned that the Japanese are building big laser prototypes at (Japanese asteroid colonies) Eije-Ito and Tanaka-Masada."
     "Defensive weapons, pure and simple,” Lady Dark said. “How can you worry about them?"
     "Up till now it was the Japanese Navy that provided the de facto protection,”
said Corporate Susan. “Being released from that detail, they are now free to roll around the Solar System like loose cannon. I wouldn't be surprised to find (our home) Rosinante in their path."

     "Perhaps you do not know, Captain. Please do not take offense, but Premier Ito felt that civilian control of the Imperial Japanese Navy would be weakened by building the big lasers. So in pursuit of this policy, what was done? The hijacking of the Foxy Lady was arranged, to prevent the completion of the Dragon Scale Mirror at NAU-Ceres I. Why? The NAU might build a big laser there, and then Japan would also have to build big lasers.” The image of Corporate Hulvey smoothed its slate-blue kimono. “Perfectly logical. If we did, then you must. You might call it prophylactic piracy. Why do you suppose that the NAU might want the big lasers at NAU-Ceres I?"
     "To protect their gold shipments against piracy,” Norigawa said, sipping his tea. “I, myself, have taken over two million ounces. In time, we would have taken the mines."
     "Quite so,” the computer said. “Premier Ito was already unable to control his navy. And to execute his policy, a policy designed to avoid losing still more control, on whom must he rely? That same navy, of course. It has taken time, but I have learned that the order to hijack the Foxy Lady came from the office of Admiral Hideoshi Kogo. Would it surprise you to learn that Admiral Kogo is the leading proponent of building big lasers on Japanese space stations?"

From LONG SHOT FOR ROSINANTE by Alexis Gilliland
SOLAR SYSTEM DEFENSE

STARGUARD (brev'tal bir, against the cold) The opposite of a Starcruiser (monolithic gargantuan dreadnought. Three were a match for an enemy solar system), since the diffusion of thousands of discrete members initially lacks any significant target. A Starcruiser might cut for hours through this jungle of tiny ships, mines, etc., until suddenly there were more targets than fire control could handle. Once such a ship began to take damage, the Starguard units quickly stung it to death. Total spherical complement about 4 million; mass 40 million tons; length about 100 km.

From Metagaming microgame HOLY WAR by Lynn Willis (1979)
ANTARES DAWN

The record began with a close up of one of the foldpoint fortresses. This was obviously library footage tacked on by the Sandarians for Altan benefit. The screen showed a great sphere that bristled with weapons and sensors. The dark snouts of several hundred laser ports dotted the surface of the sphere, as did a like number of missile launchers. Other features included thick layers of ablative shielding, power plant exhaust ports, and vast radiators to rid the fortresses of internal heat. A destroyer cruised past the fortress in the foreground of the picture, giving a sense of scale to the scene. The battle station was as large as a small asteroid, and brimming with destructive power.

“My God, what a behemoth!” Bethany said.

Drake nodded. “It’s even more impressive when you realize how much ship volume is normally taken up by photon engines and foldspace generators. That monster was designed to deliver its punch to the target without worrying about maneuvering. I’d estimate its power at about five blast ships, maybe more!”

From ANTARES DAWN by Michael McCollum (1986)

Space Superiority Platform

A variant on the orbital fortress is the Space Superiority Platform. Instead of defending the planet from invading spacefleets, this is an armed military station keeping an eye on the planet it is orbiting.

If a planet is balkanized, the platform will watch military ground units belonging to hostile nations, and bombard them if required. Militarily they have the high ground.

If the planet is a conquered one, or the government is oppressing the inhabitants, the platform will try to maintain government control and deal with revolts. By bombarding them if required.

Many early SF stories fret about the military advantage an armed space station confer upon the owning nation. Heinlein says trying to fight a space station (or orbiting spacecraft) from the ground is akin to a man at the bottom of a well conducting a rock-throwing fight with somebody at the top. One power-crazed dictator with a nuclear bomb armed station could rule the world! Space faring nations would need space scouts for defense.

But most experts nowadays say that turns out not to be the case. A nation can threaten another with nuclear annihilation far more cheaply with a few ICBMs, no station is required. And while ground launching sites can hide in rugged terrain, a space station can hide nowhere. Pretty much the entire facing hemisphere can attack the station with missiles, laser weapons, and propaganda.

In the real world, such platforms are currently limited to spy satellites. Orbiting nuclear bombing satellites are frowned upon. Or even things like the Strategic Defense Initiative.

Phil Shanton points out that you don't need a huge missile to destroy an orbiting space station, either. In 1979, the U.S. Air Force awarded a contract to the Vought company to develop an anti-satellite missile. It was not a huge missile from a large launch site. It was a relatively small missile launched by an F-15 Eagle interceptor in a zoom-climb. Vought developed the ASM-135 Anti-Satellite Missile (ASAT), and on 13 September 1985 it successfully destroyed the solar observatory satellite "P78-1". This means that an evil-dictator world-dominator nuke-station not only has to worry about every ground launch site, but also every single fighter aircraft.

It has also been modeled that the U.S. Navy could take out a satellite with a Standard Missile 3.

Things are different, of course if the situation is an extraplanetary fleet that remotely bombs the planet to destroy all the infrastructure. The fleet can construct a space superiority platform while the planet is struggling to rebuild its industrial base. Then the platform can bomb any planetary site that is getting too advanced in rebuilding. This is known as "not letting the weeds grow too tall.

PEACE CONTROL SATELLITE

      "It‘s getting bad, isn‘t it?" he asked.
     Heinemann sighed. "Worse than you might think, Hauptmann. Even the ranks of the Peace Enforcers are not immune to these internecine squabbles that have broken out all over the face of the Earth. If it is not the North Americans against the South, then it is the Australians versus Indonesia, or Japan against China and West Russia. I tell you the whole world is going to Satan in a hand trolley."…

     …Wing Commander Livingston was on detached service from the RAF. His powder blue uniform looked out of place next to Stassel‘s silver and black. Stassel sat in an aluminum chair and took notes as Livingston reeled off figures in his clipped, Oxford accent.
     " … Your area of responsibility will include Longitudes 100 West to 120 West, Captain. Your satellite will be in an alternating synchronous orbit with Beta-Nine, of course, and you will have prime responsibility in the Northern Hemisphere during even watch periods and Southern Hemisphere during the odd. Luckily, south of the equator there is only empty ocean between 100 and 120 West, so you‘ll be able to get some rest.
     "You are hereby directed to pay especially close attention to the situation around the US-Mexican border..." Livingston looked up, the podium light casting shadows on his face. "Watch your a** on that one, Fred. It is a tinderbox. The Mexicans are bound to try a raid between now and the Security Council vote on Friday."…

     …The second development was the formation of the UN Peace Enforcers following the twenty-day scare of the Misfire War. The Peace Enforcers were a multinational force with a single mission: To stop any aggressor who struck against any UN member state. Their unofficial motto was, "You start the war and we‘ll finish it!"
     In theory, any act of aggression by one nation against another would be met instantly by the orbital lasers and Peace Enforcer fusion rockets. However, in practice there was a threshold level of violence, a tripwire effect, below which the cumbersome Security Council machinery would fail to respond.…

     …The lift whooshed him upward toward the station axis. The familiar, ever changing Coriolus force as he approached the axis clamped his stomach muscles in a familiar vise. At the zero gravity axis, Stassel kicked off and floated to the docking port at the north pole of the station and through a flexible tube to the shuttle.
     The shuttle was a standard orbit-to-orbit supply bus — three spherical sections assembled as though they had been skewered onto a shish-kabob sword with a hydrogen-fueled rocket at one end and the personnel cabin at the other. The shuttle was used to transfer personnel and consumables from the mid-Atlantic Space Station (and her mid-Pacific counterpart) to the orbiting Peace Control Satellites.
     The station was in synchronous orbit 37,000 kilometers above the equator so that it hung perpetually over thirty degrees west longitude. The Peace Control Satellites also orbited 37,000 kilometers out, but in two separate orbits, each inclined sixty degrees from the plane of the equator and from each other. Each satellite thus described a figure eight over a stationary strip of land, taking one day for the full traverse across the face of the planet. The satellites climbed to the latitude of Hudson‘s Bay in the north and dropped to the northern tip of Antarctica in the south. Spaced every ten degrees of longitude — or 7500 kilometers apart — in their orbits, the satellites passed over every industrialized and developing nation on Earth four times daily. The seventy satellites and two space stations in orbit gave the UN‘s hundred gigawatt lasers overlapping fields of fire against any conceivable opponent. War was impossible.
     At least, that was the theory.…

     …The pilot cleared his throat. "Uh, get your things ready for transfer. We‘ll be coming up on Alpha-Nine in about twenty minutes."
     Peace Control Satellite Alpha-Nine floated into view fifteen minutes later. Like all such, it was constructed in two pieces. The thirty-meter long cylinder that housed the hydrogen-fluorine gas dynamic laser and its fuel tanks was attached by a hundred meter long umbilical to a sphere painted in a haphazard pattern of light and dark checks. The ten-meter sphere was festooned with antennas, telescopes, and the more arcane paraphernalia of a dozen different kinds of information sensors and communications devices. The doghouse, as the sphere was called, was crammed solid with hardware that acted as the satellite‘s eyes and ears and brains. The umbilical — floating limply in space as the shuttle moved in slowly for a hard dock — connected the two halves of the satellite together and isolated the laser module with its sensitive aiming mechanisms from extraneous perturbations. For instance, the force of a hundred-ton shuttle coming to rest in the doghouse‘s docking collar, or the effect of the satellite commander doing his morning calisthenics.
     The satellite living quarters were located at the end of the doghouse arbitrarily labeled 'top'. They were tiny, consisting of a control center, shower bath, and combination galley and recreation-bunk room. The crew quarters of a PCS did not have to be large. The satellite commander was the only crewmember. Even so, the UN had a perennial problem keeping seventy satellites manned with reliable people on a one-week rotation schedule. What the satellite commander lacked in numbers, he more than made up for in firepower. At his fingertips were the controls to a hundred-gigawatt laser, powerful enough to strike down any opponent. Moreover, if needed, he would be backed up by the power of the space fleet.

Interdiction Platform

This is a sort of combination of Space Superiority Platform and Planetary Defense. The idea is that the station is to prevent anything unauthorized from entering or leaving the planet it is orbiting.

  • A planet might be invested, meaning that the planet is under siege from whoever owns the space station. The station does not want planetary inhabitants escaping, nor does it want blockade runners entering.
  • A planet might be interdicted because they contain something very dangerous (Xenomorphs, thionite, the City on the Edge of Forever, replicators, or 100% lethal plagues).
  • A planet might be interdicted because it has something very valuable and the station owner does not want poachers sneaking in and stealing any.

Planetary Fortress

After the invaders have neutralized the defenders orbital fortresses, the only thing left stopping the invaders from carpet-bombing the vulnerable planet are the defending planetary fortresses. Orbital fortresses do have problems with heat radiators and supply. Planetary fortresses on the other hand have practically no radiator or supply problems, since they have an entire planet for support. In the Strategic Defense Initiative, concepts looked into included "Extended Range Interceptor", "Homing Overlay Experiment ", and "Exoatmospheric Reentry-vehicle Interception System"

In space opera, "force fields" are generally spherical. So a planetary fortress (or civilian city) protected by such a field will have a circular boarder. Anything outside of the circle will also be outside of the force field, and thus vulnerable to bombardment. If the force field prevents defending weapons from firing out along with preventing attacking weapons from firing in, the fortress might have weapon emplacements outside of the boundary of the force field. In many space operas, invaders will deal with planetary fortresses under a force field by constantly using weapons on the ground around the fort. The land will eventually become a sea of lava, which will put the fort at a disadvantage.

In Larry Niven and Jerry Pournelle's classic The Mote In God's Eye, some times Imperial task forces would find the Langston Field defense over the cities on a rebel planet too difficult to crack. If the task force was under a severe time limit, they would be forced into the draconian option of using nuclear weapons to take out all the agriculture on the planet, then leaving. The rebels would then mostly starve to death, since it is impossible to ship food for millions of people over insterstellar distances. The imperials would have fullfilled their mission, since the rebels would cease to be a threat, eventually.

NEUTRALIZING A REBEL PLANET

Rod Blaine scowled at the words flowing across the screen of his pocket computer. The physical data were current, but everything else was obsolete. The rebels had changed even the name of their world, from New Chicago to Dame Liberty. Her government would have to be built all over again. Certainly she'd lose her delegates; she might even lose the right to an elected assembly.

He put the instrument away and looked down. They were over mountainous country, and he saw no signs of war. There hadn't been any area bombardments, thank God.

It happened sometimes: a city fortress would hold out with the aid of satellite-based planetary defenses. The Navy had no time for prolonged sieges. Imperial policy was to finish rebellions at the lowest possible cost in lives—but to finish them. A holdout rebel planet might be reduced to glittering lava fields, with nothing surviving but a few cities lidded by the black domes of Langston Fields; and what then? There weren't enough ships to transport food across interstellar distances. Plague and famine would follow.

From THE MOTE IN GOD'S EYE by Larry Niven and Jerry Pournelle (1974)

And Alistair Young points out that if the spaceports of the planet use laser launchers they are also planetary fortresses.

IMPROVISATION KILLS

It is a truism of celestial warfare that among the most valuable targets to seize in the course of a major planetary assault operation is the primary planetary starport or local starports close to the intended target(s) of the operation. Starports, for all the obvious reasons, make perfect orbitheads, offering existing facilities eminently suitable for the landing and disembarkation of troops and materiel in quantity. (Orbital elevators, by contrast, are usually considered too fragile and susceptible to sabotage for this purpose, if the enemy are willing to absorb the ensuing damage to their own planet, until the orbitals and the continental area surrounding the elevator have been entirely secured.)

Why, then, are combat drops rarely, if ever, targeted at the vicinity of starports?

Again, it is important to remember that which is unseen. The popular image of starports is heavily biased towards the facilities for ground-landing starships — understandably, since the giant launch/landing pads built to handle nucleonic-thermal ships, with their blast-deflecting berms, “hot” shafts, and motile structures are some of the most impressive structures ever built — and towards the shuttleport terminals used by commuters and starship passengers alike. Nonetheless, the majority of cargo in the developed Worlds is carried by dedicated spacecraft incapable of atmospheric landing, to and from which cargo is transported in high volumes using suitably cheap methods: either laser-launch/deceleration facilities, mass drivers, or both, in which case the former handles light or delicate cargo and the latter hardbulk.

What this means in military terms is that, any other defense grid aside, the majority of starports in the developed Worlds have at their disposal a multi-gigawatt-range phased-array laser system, and/or a pair of mass drivers capable of accelerating a solid slug the size of a shipping container (or, equally effective, a shipping container packed with rubble or cheap heavy-metal ingots) to orbital velocities — both, admittedly, equipped with safety systems designed to prevent them from being used in exactly the manner which is desirable for military purposes, but that is something usually corrected readily enough by a software change — along with all the high-resolution traffic-control sensor equipment needed to target them effectively.

It is also a truism of warfare in general that one shouldn’t stab a heavily-armed man in the front. That is doubly relevant when the things they’re using as weapons are also the value that you want to capture.

— Elementary Principles of Orbit-to-Ground Maneuver Plans, pub. INI Press

SECTION 13: ORIGINS

However, it should not be assumed that any space colony will be totally defenseless.  Depending on the configuration and environment of the colony, it is possible that the colony will have some form of anti-meteor system in place, which could easily be repurposed to serve as a ground-based defense laser.  The problem with the idea of such a system is that it’s relatively easy to put a colony underground, and being underground also provides protection from radiation.  Meteors large enough to be a threat to the buried colony are likely to be too large for a practical laser system to deal with, but should also give enough warning to be deflected by other methods.

A much more plausible source for some sort of fixed ground-based defense is a laser propulsion system.  This would either be used to boost spacecraft into orbit, or to propel them between planets.  In either case, the biggest issue is likely to be setting up the system to target non-cooperative spacecraft.  On the other hand, the fact that such a system is fixed removes its value as an offensive weapon, and such capability might be standard.  In either case, the existence of such a system will make the possibility of a direct attack even more remote, limiting warfare to skirmishing between the colonies involved.  A ground invasion is remotely plausible, but the defender must either be taken totally by surprise or be faced with overwhelming force, both of which are unlikely in the sort of conflict described here.  Farther problems are the requirement for overland movement, and the difficulty posed by the defender’s orbital bombardment.

by Byron Coffey (2016)
PLANETARY DEFENSE CENTER

“We’ve had time to map the planet rather extensively over the last thirty hours. In the process, we have spotted numerous large installations built on the polar ice caps. Our experts have tentatively identified them as a network of planetary defense centers. To judge by their number, this may well be the best defended planet in human space!”


Sandarian Military Headquarters was a truncated pyramid that had been built on an island of bare rock in the middle of an ocean of ice. At first, the structure was a tiny patch of brown on the horizon amid an endless panorama of white. Then, as the aircar carrying Duke Bardak, Richard Drake, and Argos Cristobal closed the distance, the true size of the building became increasingly apparent with each passing second.

“Big building,” Drake said to Bardak.

“Big enough,” the Sandarian nobleman replied. “It measures one kilometer to a side and rises half-a-kilometer above bedrock. The sides are armor plated to a depth of two meters, and screened by anti-rad fields.”

“Wouldn’t it have been more convenient to build it near Capital?” Drake asked. It had taken the aircar some three hours to fly from Capital to Military Headquarters, and for virtually the whole of that time, the car had droned above a seemingly endless expanse of ice.

“More convenient, yes. Safer, no. Military Headquarters doubles as a planetary defense center. You no doubt saw many of our PDCs from orbit.”

Drake nodded.

“An operational planetary defense center requires a lot of power and generates a considerable quantity of waste heat. In a prolonged engagement, the waste heat from a single fixed mount laser can raise the temperature of even a medium size river by several degrees. Were we to build our PDCs in the temperate zone, we would trigger a massive fish kill every time we tested the weapons. The polar ice cap, on the other hand, has a heat carrying capacity that is virtually infinite. You cannot see it, but the ice fields around Military Headquarters are honeycombed with heat rejection piping. Theoretically, we could fire every fixed mount laser in the battery continuously for days before we would have to worry about overheating problems.

“Then, of course, there are the strategic considerations. By spreading our installations evenly over Sandar’s surface, we avoid blind spots while also dispersing our military assets. Lastly, should the Ryall ever get this far — highly unlikely considering the power of our foldpoint fortresses — we hope to draw their fire to the PDCs and away from the cities.”

As Bardak talked, the aircar circled Military Headquarters to give the Altans a good look at the manmade mountain below. The sides of the pyramid were studded with phased array radar elements, as well as a variety of less identifiable sensors. Around the base, the business ends of several dozen fixed mount lasers poked skyward.

From ANTARES DAWN by Michael McCollum (1986)
LUNAR FORTRESS

(ed note: this was written before the invention of the laser. The fortress is called Project Thor, no relation to Rods From God, and is located on the Moon near Pico crater. It is about to be attacked by three spacecraft. Dr. Steffanson has invented a technobabble "ray screen" that reflects electromagnetic radiation. Jamieson and Wheeler are hiding in a crevasse several miles away near their crippled tractor. The description is so cinematic that it is just begging for an SF artist to depict it.)

EVEN TODAY, little has ever been revealed concerning the weapons used in the Battle of Pico. It is known that missiles played only a minor part in the engagement. In space warfare, anything short of a direct hit is almost useless, since there is nothing to transmit the energy of a shock wave. An atom bomb exploding a few hundred meters away can cause no blast damage and even its radiation can do little harm to well-protected structures. Moreover, both Earth and the Federation had effective means of diverting ordinary projectiles.

Purely non-material weapons would have to play the greatest role. The simplest of these were the ion-beams, developed directly from the drive-units of spaceships. Since the invention of the first radio tubes, almost three centuries before, men had been learning how to produce and focus ever more concentrated streams of charged particles. The climax had been reached in spaceship propulsion with the so-called "ion rocket," generating its thrust from the emission of intense beams of electrically charged particles. The deadliness of these beams had caused many accidents in space, even though they were deliberately defocused to limit their effective range.

There was, of course, an obvious answer to such weapons. The electric and magnetic fields which produced them could also be used for their dispersion, converting them from annihilating beams into a harmless, scattered spray.

More effective, but more difficult to build, were the weapons using pure radiation. Yet even here, both Earth and the Federation had succeeded. It remained to be seen which had done the better job—the superior science of the Federation, or the greater productive capacity of Earth.


Less than a million kilometers away, Carl Steffanson sat at a control desk and watched the image of the sun, picked up by one of the many cameras that were the eyes of Project Thor. The group of tired technicians standing around him had almost completed the equipment before his arrival; now the discriminating units he had brought from Earth in such desperate haste had been wired into the circuit.

Steffanson turned a knob, and the sun went out. He flicked from one camera position to another, but all the eyes of the fortress were equally blind. The coverage was complete.

Too weary to feel any exhilaration, he leaned back in his seat and gestured toward the controls.

"It's up to you now. Set it to pass enough light for vision, but to give total rejection from the ultra-violet upward. We're sure none of their beams carry any effective power much beyond a thousand Ångström. They'll be very surprised when all their stuff bounces off. I only wish we could send it back the way it came."

"Wonder what we look like from outside when the screen's on?" said one of the engineers.

"Just like a perfectly reflecting mirror. As long as it keeps reflecting, we're safe against pure radiation. That's all I can promise you."

(ed note: 1000 Ångströms = 100 nanometers = extreme ultraviolet)


There was no warning of any kind. Suddenly the gray, dusty rocks of the Sea of Rains were scorched by a light they had never known before in all their history. Wheeler's first impression was that someone had turned a giant searchlight full upon the tractor; then he realized that this sun-eclipsing explosion was many kilometers away. High above the horizon was a ball of violet flame, perfectly spherical, and rapidly losing brilliance as it expanded. Within seconds, it had faded to a great cloud of luminous gas. It was dropping down toward the edge of the Moon, and almost at once had sunk below the skyline like some fantastic sun.

"We were fools," said Jamieson gravely. "That was an atomic warhead—we may be dead men already."

"Nonsense," retorted Wheeler, though without much confidence. "That was fifty kilometers away. The gammas would be pretty weak by the time they reached us—and these walls aren't bad shielding."


"I can just see the dome," he said with some satisfaction. "It's quite unchanged, as far as I can tell."

"It would be," Jamieson replied. "They must have managed to explode that bomb somehow while it was miles away."

"Perhaps it was only a warning shot."

"Not likely! No one wastes plutonium for firework displays. That meant business. I wonder when the next move is going to be?"

It did not come for another five minutes. Then, almost simultaneously, three more of the dazzling atomic suns burst against the sky. They were all moving on trajectories that took them toward the dome, but long before they reached it they had dispersed into tenuous clouds of vapor.


From somewhere beyond Pico, six sheaves of flame shot up into the sky at an enormous acceleration. The dome was launching its first missiles, straight into the face of the sun. The Lethe and the Eridanus were using a trick as old as warfare itself; they were approaching from a direction in which their opponent would be partly blinded. Even radar could be distracted by the background of solar interference, and Commodore Brennan had enlisted two large sunspots as minor allies.


Then he saw that something was happening to the dome. It was no longer a gleaming spherical mirror reflecting only the single image of the sun. Light was splashing from it in all directions, and its brilliance was increasing second by second. From somewhere out in space, power was being poured into the fortress. That could only mean that the ships of the Federation were floating up there against the stars, beaming countless millions of kilowatts down upon the Moon. But there was still no sign of them, for there was nothing to reveal the track of the river of energy pouring invisibly through space.

The dome was now far too bright to look upon directly, and Wheeler readjusted his filters. He wondered when it was going to reply to the attack, or indeed if it could do so while it was under this bombardment. Then he saw that the hemisphere was surrounded by a wavering corona, like some kind of brush discharge. Almost at the same moment, Jamieson's voice rang in his ears.

"Look, Con—right overhead!"

He glanced away from the mirror and looked directly into the sky. For the first time, he saw one of the Federation ships. Though he did not know it, he was seeing the Acheron, the only spaceship ever to be built specifically for war. It was clearly visible, and seemed remarkably close. Between it and the fortress, like an impalpable shield, flared a disk of light which as he watched turned cherry-red, then blue-white, then the deadly searing violet seen only in the hottest of the stars. The shield wavered back and forth, giving the impression of being balanced by tremendous and opposing energies. As Wheeler stared, oblivious to his peril, he saw that the whole ship was surrounded by a faint halo of light, brought to incandescence only where the weapons of the fortress tore against it.

It was some time before he realized that there were two other ships in the sky, each shielded by its own flaming nimbus. Now the battle was beginning to take shape; each side had cautiously tested its defenses and its weapons, and only now had the real trial of strength begun.

The two astronomers stared in wonder at the moving fireballs of the ships. Here was something totally new—something far more important than any mere weapon. These vessels possessed a means of propulsion which must make the rocket obsolete. They could hover motionless at will, then move off in any direction at a high acceleration. They needed this mobility; the fortress, with all its fixed equipment, far out-powered them and much of their defense lay in their speed.

In utter silence, the battle was rising to its climax. Millions of years ago the molten rock had frozen to form the Sea of Rains, and now the weapons of the ships were turning it once more to lava. Out by the fortress, clouds of incandescent vapor were being blasted into the sky as the beams of the attackers spent their fury against the unprotected rocks. It was impossible to tell which side was inflicting the greater damage. Now and again a screen would flare up, as a flicker of heat passes over white-hot steel. When that happened to one of the battleships, it would move away with that incredible acceleration, and it would be several seconds before the focusing devices of the fort had located it again.

Both Wheeler and Jamieson were surprised that the battle was being fought at such short ranges. There was probably never more than a hundred kilometers between the antagonists, and usually it was much less than this. When one fought with weapons that traveled at the speed of light—indeed, when one fought with light itself—such distances were trivial.

The explanation did not occur to them until the end of the engagement. All radiation weapons have one limitation: they must obey the law of inverse squares. Only explosive missiles are equally effective from whatever range they have been projected: if one is hit by an atomic bomb, it makes no difference whether it has traveled ten kilometers or a thousand.

But double the distance of any kind of radiation weapon, and you divide its power by four owing to the spreading of the beam. No wonder, therefore, that the Federal commander was coming as close to his objective as he dared.

The fort, lacking mobility, had to accept any punishment the ships could give it. After the battle had been on for a few minutes, it was impossible for the unshielded eye to look anywhere toward the south. Ever and again the clouds of rock vapor would go sailing up into the sky, falling back on the ground like luminous steam. And presently, as he peered through his darkened goggles and maneuvered his clumsy periscope, Wheeler saw something he could scarcely believe. Around the base of the fortress was a slowly spreading circle of lava, melting down ridges and even small hillocks like lumps of wax.

That awe-inspiring sight brought home to him, as nothing else had done, the frightful power of the weapons that were being wielded only a few kilometers away. If even the merest stray reflection of those energies reached them here, they would be snuffed out of existence as swiftly as moths in an oxy-hydrogen flame.

The three ships appeared to be moving in some complex tactical pattern, so that they could maintain the maximum bombardment of the fort while reducing its opportunity of striking back. Several times one of the ships passed vertically overhead, and Wheeler retreated as far into the crack as he could in case any of the radiation scattered from the screens splashed down upon them. Jamieson, who had given up trying to persuade his colleague to take fewer risks, had now crawled some distance along the crevasse, looking for a deeper part, preferably with a good overhang. He was not so far away, however, that the rock was shielding the suit-radios, and Wheeler gave him a continuous commentary on the battle.

It was hard to believe that the entire engagement had not yet lasted ten minutes. As Wheeler cautiously surveyed the inferno to the south, he noticed that the hemisphere seemed to have lost some of its symmetry. At first he thought that one of the generators might have failed, so that the protective field could no longer be maintained. Then he saw that the lake of lava was at least a kilometer across, and he guessed that the whole fort had floated off its foundations. Probably the defenders were not even aware of the fact. Their insulation must be taking care of solar heats, and would hardly notice the modest warmth of molten rock.

And now a strange thing was beginning to happen. The rays with which the battle was being fought were no longer quite invisible, for the fortress was no longer in a vacuum. Around it the boiling rock was releasing enormous volumes of gas, through which the paths of the rays were as clearly visible as searchlights in a misty night on Earth. At the same time Wheeler began to notice a continual hail of tiny particles around him. For a moment he was puzzled; then he realized that the rock vapor was condensing after it had been blasted up into the sky. It seemed too light to be dangerous, and he did not mention it to Jamieson—it would only give him something else to worry about. As long as the dust fall was not too heavy, the normal insulation of the suits could deal with it. In any case, it would probably be quite cold by the time it got back to the surface.

The tenuous and temporary atmosphere round the dome was producing another unexpected effect. Occasional flashes of lightning darted between ground and sky, draining off the enormous static charges that must be accumulating around the fort. Some those flashes would have been spectacular by themselves—but they were scarcely visible against the incandescent clouds that generated them.


Wheeler never knew why the fortress waited so long before it used its main weapon. Perhaps Steffanson—or whoever was in charge—was waiting for the attack to slacken so that he could risk lowering the defenses of the dome for the millisecond that he needed to launch his stiletto.

Wheeler saw it strike upward, a solid bar of light stabbing it the stars. He remembered the rumors that had gone round tie Observatory. So this was what had been seen, flashing above the mountains. He did not have time to reflect on the staggering violation of the laws of optics which this phenomenon implied, for he was staring at the ruined ship above his head. The beam had gone through the Lethe as if she did not exist; the fortress had speared her as an entomologist pierces a butterfly with a pin.

Whatever one's loyalties, it was a terrible thing to see ho the screens of that great ship suddenly vanished as her generators dies, leaving her helpless and unprotected in the sky. The secondary weapons of the fort were at her instantly, tearing out great gashes of metal and boiling away her armor layer by layer. Then, quite slowly, she began to settle toward the Moon, still on an even keel. No one will ever know what stopped her, probably some short-circuit in her controls, since none of her crew could have been left alive. For suddenly she went off to the east in a long, flat trajectory. By that time most of her hull had been boiled away and the skeleton of her framework was almost completely exposed. The crash came, minutes later, as she plunged out of sight beyond the Teneriffe Mountains. A blue-white aurora flickered for a moment below the horizon, and Wheeler waited for the shock to reach him.

And then, as he stared into the east, he saw a line of dust rising from the plain, sweeping toward him as if driven by a mighty wind. The concussion was racing through the rock, hurling the surface dust high into the sky as it passed. The swift, inexorable approach of that silently moving wall, advancing at the rate of several kilometers a second, was enough to strike terror into anyone who did not know its cause. But it was quite harmless; when the wave-front reached him, it was as if a minor earthquake had passed. The veil of dust reduced visibility to zero for a few seconds, then subsided as swiftly as it had come. When Wheeler looked again for the remaining ships, they were so far away that their screens had shrunk to little balls of fire against the zenith. At first he thought they were retreating; then, abruptly, the screens began to expand as they came down into the attack under a terrific vertical acceleration. Over by the fortress the lava, like some tortured living creature, was throwing itself madly into the sky as the beams tore into it.

The Acheron and Eridanus came out of their dives about a kilometer above the fort. For an instant, they were motionless; then they went back into the sky together. But the Eridanus had been mortally wounded, though Wheeler knew only that one of the screens was shrinking much more slowly than the other.

With a feeling of helpless fascination, he watched the stricken ship fall back toward the Moon. He wondered if the fort would use its enigmatic weapon again, or whether the defenders realized that it was unnecessary.

About ten kilometers up, the screens of the Eridanus seemed to explode and she hung unprotected, a blunt torpedo of black metal, almost invisible against the sky. Instantly her light-absorbing paint, and the armor beneath, were torn off by the beams of the fortress. The great ship turned cherry-red, then white. She swung over so that her prow turned toward the Moon, and began her last dive. At first it seemed to Wheeler that she was heading straight toward him; then he saw that she was aimed at the fort. She was obeying her captain's last command.

It was almost a direct hit. The dying ship smashed into the lake of lava and exploded instantly, engulfing the fortress in an expanding hemisphere of flame. This, thought Wheeler, must surely be the end. He waited for the shock wave to reach him, and again watched the wall of dust sweep by—this time into the north. The concussion was so violent that it jerked him off his feet, and he did not see how anyone in the fort could have survived. Cautiously, he put down the mirror which had given him almost all his view of the battle, and peered over the edge of his trench. He did not know that the final paroxysm was yet to come.

Incredibly, the dome was still there, though now it seemed that part of it had been sheared away. And it was inert and lifeless: its screens were down, its energies exhausted, its garrison, surely, already dead. If so, they had done their work. Of the remaining Federal ship, there was no sign. She was already retreating toward Mars, her main armament completely useless and her drive units on the point of failure. She would never fight again


"What puzzles me most of all," Wheeler concluded, "is the weapon the fort used to destroy the battleship. It looked like a beam of some kind, but of course that's impossible. No beam can be visible in a vacuum. And I wonder why they only used it once? Do you know anything about it?"

"I'm afraid not," replied Sadler, which was quite untrue. He still knew very little about the weapons in the fort, but this was the only one he now fully understood. He could well appreciate why a jet of molten metal, hurled through space at several hundred kilometers a second by the most powerful electromagnets ever built, might have looked like a beam of light flashing a for an instant. And he knew that it was a short-range weapon designed to pierce the fields which would deflect ordinary projectiles. It could he used only under ideal conditions, and it took many minutes to recharge the gigantic condensers which powered the magnets.


(ed note: there is no reason for the metal to be molten. It is better to be solid, which would make the weapon a species of mass-driver)

From EARTHLIGHT by Arthur C. Clarke (1955)
OSNOMIAN PLANETARY FORTRESS

(ed note: This is pure space opera with zero scientific accuracy. This is probably where Sir Arthur C. Clarke got the idea of the sea of lava around Project Thor. In the following, they use a handwaving method to turn copper into pure energy with all the might of e=mc2, for electricity and explosives. The transparent material is pure handwavium that is several thousand times as strong as steel.)


"There, we can see what they're doing now," and DuQuesne anchored the vessel with an attractor. "I want to see if they've got many of those space-ships in action, and you will want to see what war is like, when it is fought by people, who have been making war steadily for ten thousand years."

Poised at the limit of clear visibility, the two men studied the incessant battle being waged beneath them. They saw not one, but fully a thousand of the globular craft high in the air and grouped in a great circle around an immense fortification upon the ground below. They saw no airships in the line of battle, but noticed that many such vessels were flying to and from the front, apparently carrying supplies. The fortress was an immense dome of some glassy, transparent material, partially covered with slag, through which they saw that the central space was occupied by orderly groups of barracks, and that round the circumference were arranged gigantic generators, projectors, and other machinery at whose purposes they could not even guess. From the base of the dome a twenty-mile-wide apron of the same glassy substance spread over the ground, and above this apron and around the dome were thrown the mighty defensive ray-screens, visible now and then in scintillating violet splendor as one of the copper-driven Kondalian projectors sought in vain for an opening. But the Earth-men saw with surprise that the main attack was not being directed at the dome; that only an occasional ray was thrown against it in order to make the defenders keep their screens up continuously. The edge of the apron was bearing the brunt of that vicious and never-ceasing attack, and most concerned the desperate defense.

For miles beyond that edge, and as deep under it as frightful rays and enormous charges of explosive copper could penetrate, the ground was one seething, flaming volcano of molten and incandescent lava; lava constantly being volatilized by the unimaginable heat of those rays and being hurled for miles in all directions by the inconceivable power of those explosive copper projectiles—the heaviest projectiles that could be used without endangering the planet itself—being directed under the exposed edge of that unbreakable apron, which was in actuality anchored to the solid core of the planet itself; lava flowing into and filling up the vast craters caused by the explosions. The attack seemed fiercest at certain points, perhaps a quarter of a mile apart around the circle, and after a time the watchers perceived that at those points, under the edge of the apron, in that indescribable inferno of boiling lava, destructive rays, and disintegrating copper, there were enemy machines at work. These machines were strengthening the protecting apron and extending it, very slowly, but ever wider and ever deeper as the ground under it and before it was volatilized or hurled away by the awful forces of the Kondalian attack. So much destruction had already been wrought that the edge of the apron and its molten moat were already fully a mile below the normal level of that cratered, torn, and tortured plain.

Now and then one of the mechanical moles would cease its labors, overcome by the concentrated fury of destruction centered upon it. Its shattered remnants would be withdrawn and shortly, repaired or replaced, it would be back at work. But it was not the defenders who had suffered most heavily. The fortress was literally ringed about with the shattered remnants of airships, and the riddled hulls of more than a few of those mighty globular cruisers of the void bore mute testimony to the deadliness and efficiency of the warfare of the invaders.

From SKYLARK THREE by E. E. "Doc" Smith (1930)
VALERONIAN PLANETARY FORTRESS

(ed note: again, pure space opera. Again lava is a factor)

To such good purpose did every Valeronian do his part that at dawn of The Day everything was in readiness for the Chloran visitation. The immense fortress was complete and had been tested in every part, from the ranked batteries of gigantic converters and generators down to the most distant outlying visiray viewpoint. It was powered, armed, equipped, provisioned, garrisoned. Every once-populated city was devoid of life, its inhabitants having dispersed over the face of the globe, to live in isolated groups until it had been decided whether the proud civilization of Valeron was to triumph or to perish.

Promptly as that sunrise the Chloran explorer appeared at the lifeless mine, and when he found the loading hoppers empty he calmly proceeded to the nearest city and began to beam it down. Finding it deserted he cut off, and felt a powerful spy ray, upon which he set a tracer. This time the ray held up and he saw the immense fortress which had been erected during his absence; a fortress which he forthwith attacked viciously, carelessly, and with the loftily arrogant contempt which seemed to characterize his breed.

But was that innate contemptuousness the real reason for that suicidal attempt? Or had that vessel's commander been ordered by the Great Ones to sacrifice himself and his command so that they could measure Valeron's defensive power? If so, why did he visit the mine at all and why did he not know beforehand the location of the fortress? Camouflage? In view of what the Great Ones of Chlora must have known, why that commander did what he did that morning no one of Valeron ever knew.

The explorer launched a beam—just one. Then Quedrin Radnor pressed a contact and out against the invader there flamed a beam of such violence that the amoebus had no time to touch his controls, that even the automatic trips of his zone of force—if he had such trips—did not have time in which to react. The defensive screens scarcely flashed, so rapidly did that terrific beam drive through them, and the vessel itself disappeared almost instantly—molten, vaporized, consumed utterly. But there was no exultation beneath Valeron's mighty dome. From the Bardyle down, the defenders of their planet knew full well that the real attack was yet to come, and knew that it would not be long delayed.

Nor was it. Nor did those which came to reduce Valeron's far-flung stronghold in any way resemble any form of space ship with which humanity was familiar. Two stupendous structures of metal appeared, plunging stolidly along, veritable flying fortresses, of such enormous bulk and mass that it seemed scarcely conceivable for them actually to support themselves in air.

Simultaneously the two floating castles launched against the towering dome of defense the heaviest beams they could generate and project. Under that awful thrust Valeron's mighty generators shrieked a mad crescendo and her imponderable shield radiated a fierce, eye-tearing violet, but it held. Not for nothing had the mightiest minds of Valeron wrought to convert their mechanisms and forces of peace into engines of war; not for nothing had her people labored with all their mental and physical might for almost twoscore days and nights, smoothly and efficiently as one mind in one body. Not easily did even Valeron's Titanic defensive installation carry that frightful load, but they carried it.

Then, like mythical Jove hurling his bolt—like, that is, save that beside that Valeronian beam any possible bolt of lightning would have been as sweetly innocuous a caress as young love's first kiss—Radnor drove against the nearer structure a beam of concentrated fury; a beam behind which was every volt and every ampere that his stupendous offensive generators could yield.

The Chloran defenses in turn were loaded grievously, but in turn they also held; and for hours then there raged a furiously spectacular struggle. Beams, rods, planes, and needles of every known kind and of every usable frequency of vibratory energy were driven against impenetrable neutralizing screens. Monstrous cannon, hurling shells with a velocity and of an explosive violence far beyond anything known to us of Earth, radio-beam-dirigible torpedoes, robot manned drill planes, and many other lethal agencies of ultrascientific war—all these were put to use by both sides in those first few frantic hours, but neither side was able to make any impression upon the other. Then, each realizing the other's defenses had been designed to withstand his every force, the intensive combat settled down to a war of sheer attrition.

Radnor and his scientists devoted themselves exclusively to the development of new and ever more powerful weapons of offense; the Chlorans ceased their fruitless attacks upon the central dome and concentrated all their offensive power into two semicircular arcs, which they directed vertically downward upon the outer ring of the Valeronian works in an incessant and methodical flood of energy.

They could not pierce the defensive shields against Valeron's massed power, but they could and did bring into being a vast annular lake of furiously boiling lava, into which the outer ring of fortresses began slowly to crumble and dissolve. This method of destruction, while slow, was certain; and grimly, pertinaciously, implacably, the Chlorans went about the business of reducing Valeron's only citadel.

The Bardyle wondered audibly how the enemy could possibly maintain indefinitely an attack so profligate of energy, but he soon learned that there were at least four of the floating fortresses engaged in the undertaking. Occasionally the two creations then attacking were replaced by two precisely similar structures, presumably to return to Chlora in order to renew their supplies of the substance, whatever it was, from the atomic disintegration of which they derived their incomprehensible power.

And slowly, contesting stubbornly and bitterly every foot of ground lost, the forces of Valeron were beaten back under the relentless, never-ceasing attack of the Chloran monstrosities—back and ever back toward their central dome as ring after ring of the outlying fortifications slagged down into that turbulently seething, that incandescently flaming lake of boiling lava.


Valeron was making her last stand. Her back was against the wall. The steadily contracting ring of Chloran force had been driven inward until only one thin line of fortified works lay between it and the great dome covering the city itself. Within a week at most, perhaps within days, that voracious flood of lava would lick into and would dissolve that last line of defense. The what of Valeron?

All the scientists of the planet had toiled and had studied, day and night, but to no avail. Each new device developed to halt the march of the encroaching constricting band of destruction had been nullified in the instant of its first trial.

"They must know every move we make, to block us so promptly," Quedrin Radnor had mused one day. "Since they certainly have no visiray viewpoints of material substance within our dome, they must be able to operate a spy ray using only the narrow gravity band, a thing we have never been able to accomplish. If they can project such viewpoints of pure force through such a narrow band, may they not be able to project a full materialization and thus destroy us? But, no, that band is—must be—altogether too narrow for that."

Stirred by these thoughts he had built detectors to announce the appearance of any nongravitational forces in the gravity band and had learned that his fears were only too well founded. While the enemy could not project through the open band any forces sufficiently powerful to do any material damage, they were thus in position to forestall any move which the men of Valeron made to ward off their inexorably approaching doom.

Far beneath the surface of the ground, in a room which was not only sealed but was surrounded with every possible safeguard, nine men sat at a long table, the Bardyle at its head.

" ... and nothing can be done?" the coordinator was asking. "There is no possible way of protecting the edges of the screens?"

"None." Radnor's voice was flat, his face and body alike were eloquent of utter fatigue. He had driven himself to the point of collapse, and all his labor had proved useless. "Without solid anchorages we cannot hold them—as the ground is fused they give way. When the fused area reaches the dome the end will come. The outlets of our absorbers will also be fused, and with no possible method of dissipating the energy being continuously radiated into the dome we shall all die, practically instantaneously."

From SKYLARK OF VALERON by E. E. "Doc" Smith (1934)
HEXAN PLANETARY FORTRESS

(ed. note: still more space opera)

A WAILING signal interrupted the conversation and every Vorkul in the vast fleet coiled even more tightly about his bars, for the real battle was about to begin. The city of the hexans lay before them, all her gigantic forces mustered to repel the first real invasion of her long and warlike history. Mile after mile it extended, an orderly labyrinth of spherical buildings arranged in vast interlocking series of concentric circles—a city of such size that only a small part of it was visible, even to the infra-red vision of the Vorkulians. Apparently the city was unprotected, having not even a wall. Outward from the low, rounded houses of the city's edge there reached a wide and verdant plain, which was separated from the jungle by a narrow moat of shimmering liquid—a liquid of such dire potency that across it, even those frightful growths could neither leap nor creep.

But as the Vorkulian phalanx approached—now shooting forward and upward with maximum acceleration, screaming bolts of energy flaming out for miles behind each heptagon as the full power of its generators was unleashed—it was made clear that the homeland of the hexans was far from unprotected. The verdant plain disappeared in a blast of radiance, revealing a transparent surface, through which could be seen masses of machinery filling level below level, deep into the ground as far as the eye could reach; and from the bright liquid of the girdling moat there shot vertically upward a coruscantly refulgent band of intense yellow luminescence. These were the hexan defences, heretofore invulnerable and invincible. Against them any ordinary warcraft, equipped with ordinary weapons of offense, would have been as pitifully impotent as a naked baby attacking a battleship. But now those defenses were being challenged by no ordinary craft; it had taken the mightiest intellects of Vorkulia two long lifetimes to evolve the awful engine of destruction which was hurling itself forward and upward with an already terrific and constantly increasing speed.

Onward and upward flashed the gigantic duplex cone, its entire whirling mass laced and latticed together—into one mammoth unit by green tractor beams and red pressors. These tension and compression members, of unheard-of power, made of the whole fleet of three hundred forty-three fortresses a single stupendous structure—a structure with all the strength and symmetry of a cantilever truss! Straight through that wall of yellow vibrations the vast truss drove, green walls flaming blue defiance as the absorbers overloaded; its doubly braced tip rearing upward, into and beyond the vertical as it shot through that searing yellow wall. Simultaneously from each heptagon there flamed downward a green shaft of radiance, so that the whole immense circle of the cone's mouth was one solid tractor beam, fastening upon and holding in an unbreakable grip mile upon mile of the hexan earthworks.

Practically irresistible force and supposedly immovable object! Every loose article in every heptagon had long since been stored in its individual shockproof compartment, and now every Vorkul coiled his entire body in fierce clasp about mighty horizontal bars: for the entire kinetic energy of the untold millions of tons of mass comprising the cone, at the terrific measure of its highest possible velocity, was to be hurled upon those unbreakable linkages of force which bound the trussed aggregation of Vorkulian fortresses to the deeply buried intrenchments of the hexans. The gigantic composite tractor beam snapped on and held. Inconceivably powerful as that beam was, it stretched a trifle under the incomprehensible momentum of those prodigious masses of metal, almost halted in their terrific flight. But the war-cone was not quite halted; the calculations of the Vorkulian scientists had been accurate. No possible artificial structure, and but few natural ones—in practice maneuvers entire mountains had been lifted and hurled for miles through the air—could have withstood the incredible violence of that lunging, twisting, upheaving impact. Lifted bodily by that impalpable hawser of force and cruelly wrenched and twisted by its enormous couple of angular momentum, the hexan works came up out of the ground as a waterpipe comes up in the teeth of a power shovel. The ground trembled and rocked and boulders, fragments of concrete masonry, and masses of metal flew in all directions as that city-encircling conduit of diabolical machinery was torn from its bed.

A PORTION of that conduit fully thirty miles in length was in the air, a twisted, flaming inferno of wrecked generators, exploding ammunition, and broken and short-circuited high-tension leads before the hexans could themselves cut it and thus save the remainder of their fortifications. With resounding crashes, the structure parted at the weakened points, the furious upheaval stopped and, the tractor beams shut off, the shattered, smoking, erupting mass of wreckage fell in clashing, grinding ruin upon the city.

The enormous duplex cone of the Vorkuls did not attempt to repeat the maneuver, but divided into two single cones, one of which darted toward each point of rupture. There, upon the broken and unprotected ends of the hexan cordon, their points of attack lay: theirs the task to eat along that annular fortress, no matter what the opposition might bring to bear—to channel in its place a furrow of devastation until the two cones, their work complete, should meet at the opposite edge of the city. Then what was left of the cones would separate into individual heptagons, which would so systematically blast every hexan thing into nothingness as to make certain that never again would they resume their insensate attacks upon the Vorkuls. Having counted the cost and being grimly ready to pay it, the implacable attackers hurled themselves upon their objectives.

Here were no feeble spheres of space, commanding only the limited energies transmitted to their small receptors through the ether. Instead there were all the offensive and defensive weapons developed by hundreds of generations of warrior-scientists; wielding all the incalculable power capable of being produced by the massed generators of a mighty nation. But for the breach opened in the circle by the irresistible surprise attack, they would have been invulnerable, and, hampered as they were by the defenseless ends of what should have been an endless ring, the hexans took heavy toll.

The heptagons, massive and solidly braced as they were, and anchored by tractor rays as well, shuddered and trembled throughout their mighty frames under the impact of fiercely driven pressor beams. Sullenly radiant green wall-screens flared brighter and brighter as the Vorkulian absorbers and dissipators, mighty as they were, continued more and more to overload; for there were being directed against them beams from the entire remaining circumference of the stronghold. Every deadly frequency and emanation known to the fiendish hexan intellect, backed by the full power of the city, was poured out against the invaders in sizzling shrieking bars, bands, and planes of frenzied incandescence. Nor was vibratory destruction alone. Armor-piercing projectiles of enormous size and weight were hurled—diamond-hard, drill-headed projectiles which clung and bored upon impact. High-explosive shells, canisters of gas, and the frightful aerial bombs and radio-dirigible torpedoes of highly scientific war—all were thrown with lavish hand, as fast as the projectors could be served. But thrust for thrust, ray for ray, projectile for massive projectile, the Brobdingnagian creations of the Vorkuls gave back to the hexans.

The material lining of the ghastly moat was the only substance capable of resisting the action of its contents, and now, that lining destroyed by the uprooting of the fortress, that corrosive, brilliantly mobile liquid cascaded down in to the trough and added its hellish contribution to the furious scene. For whatever that devouring fluid touched flared into yellow flame, gave off clouds of lurid, strangling vapor, and disappeared. But through yellow haze, through blasting frequencies, through clouds of poisonous gas, through rain of metal and through storm of explosive the two cones ground implacably onward, their every offensive weapon centered upon the fast-receding exposed ends of the hexan fortress. Their bombs and torpedoes ripped and tore into the structure beneath the invulnerable shield and exploded, demolishing and hurling aside like straws, the walls, projectors, hexads and vast mountains of earth. Their terrible rays bored in, softening, fusing, volatilizing metal, short-circuiting connections, destroying life far ahead of the point of attack; and, drawn along by the relentlessly creeping composite tractor beam, there progressed around the circumference of the hexan city two veritable Saturnalia of destruction—uninterrupted, cataclysmic detonations of sound and sizzling, shrieking, multi-colored displays of pyrotechnic incandescence combining to form a spectacle of violence incredible.

But the heptagons could not absorb nor radiate indefinitely those torrents of energy, and soon one greenishly incandescent screen went down. Giant shells pierced the green metal walls, giant beams of force fused and consumed them. Faster and faster the huge heptagon became a shapeless, flowing mass, its metal dripping away in flaming gouts of brilliance; then it disappeared utterly in one terrific blast as some probing enemy ray reached a vital part. The cone did not pause nor waver. Many of its component units would go down, but it would go on—and on and on until every hexan trace had disappeared or until the last Vorkulian heptagon had been annihilated.

From SPACEHOUNDS OF IPC by E. E. "Doc" Smith (1931)
MARINE PLANETARY FORTRESS

      Major General Eunan Charles Gorman looked up as another incoming gravitic round struck the perimeter shields with piercing thunder. The deck of the headquarters dome rocked with the impact, and both lights and display monitors dimmed and flickered as the screens strained to dissipate the surge of energy grounding out of the sky. It wouldn’t be long before the screens overloaded; when that happened, the defense of Mike-Red would come to an abrupt and pyrotechnic end.
     The large three-view in the center of the HQ dome currently showed the Marine beachhead—a slender oval five kilometers long and perhaps two wide, sheltered beneath the shimmering hemisphere of an energy shield array six kilometers across. They were well-situated on high, rocky ground, but the terrain offered few advantages at the moment. The enemy was attempting to burn them out, pounding at the shield with nukes and heavy artillery, some fired from space, some fired from emplacements surrounding the beachhead and as far as a hundred kilometers away. All of the ground immediately around the Marine position was charred and lifeless, the sand fused into black, steaming glass. Incoming fire was so heavy the Marines could not lower the screen even for the instant required for a counter-battery reply.
     That was the worst of it—having to sit here day after day taking this hammering, unable to shoot back.

     Commander Marissa Allyn brought her gravfighter into a flat, high-speed trajectory, hurtling low above the surface. The orange ground cover gave way in a flash of speed-blurred motion to bare rock. The surface for fifty kilometers around the Marine perimeter was charred black or, in places, transformed into vast patches of fused glass. Over the past weeks, since the Turusch had brought the Marine base under attack, hundreds of nuclear warheads had detonated against the Marine shields, along with thousands of charged particle beams. The equivalent of miniature suns had burned against that landscape, charring it, in places turning sand to molten glass.

     Energy screens and shields were three-dimensional projections of spacial distortion, an effect based on the projection of gravitational distortion used in space drives. Shields reflected incoming traffic, while screens absorbed and stored the released energy.
     While screens were useful in relatively low-energy combat zones, they could be overloaded by nukes, and they weren’t good at stopping solid projectiles like missiles or high-energy KK rounds. With shields, incoming beams, missiles, and radiation were twisted through 180 degrees by the sharp and extremely tight curvature of space. Warheads and incoming projectiles were vaporized when they folded back into themselves, beams redirected outward in a spray of defocused energy. Warheads detonating just outside the area of warped space had both radiation and shock wave redirected outward.
     As the ground around the outside of the perimeter became molten, however, some heat began leaking through at the shield’s base faster than heat-sink dissipaters could cool the ground. When the projectors laid out on the ground along the perimeter began sinking into patches of liquid rock, they failed. The enemy’s strategy in a bombardment like the one hammering Mike-Red was to overload the dissipaters and destroy the projectors.
     The Marines were using shields and screens in an attempt to stay ahead of the bombardment, with banks of portable dissipater units running nonstop in the ongoing fight to keep the ground solid.

     It was a fight they were losing.

     One reason the beachhead had been set up on a rocky ridgetop was that molten rock tended to flow downhill, not up into the perimeter and the shield projectors. Repeated shocks against the lower slopes of the ridge, however, were threatening to undermine the perimeter. Gorman had already given orders to set out two replacement projectors, for number five and number six, placing them back a hundred meters as the ground sagged and crumbled beneath the originals.

     Eventually, enemy fire would eat away the entire hill.

From EARTH STRIKE by William H. Keith, Jr. (under pseudonym Ian Douglas) (2010)
STELLAR CONQUEST

7.0 PLANETARY ATTACK AND CONQUEST

Planetary Attack may occur when one player has warships in a star hex which contains another player's colonized planet and that colony possesses Planetary Missile Bases (MB) and/or Advanced Missile Bases (AMB). Planetary Attack may occur only after all Ship/Ship Combat in a player's turn has ended. A colony is conquered when all of its defenses (missile bases) cease to exist and the attacker has a warship occupying that star hex. Warship barrage fire and missile base fire is considered to occur simultaneously. All warships and missile bases existing at the beginning of a Fire Turn may fire in that Fire Turn. A colony with a PFS is unconquerable. Any ship attacking a Planetary Force Screen (PFS) is automatically destroyed.


7.14 The colonist player may now announce the destruction of Industrial Units and/or Robotic Industrial Units (RIU) that are in excess of the Population/Industry ratio of one million population to one IU. The colonist player does this to prevent industrial capacity from falling into enemy hands. It is a last resort if the colonist player does not expect to re-conquer the colony in a reasonable amount of time. The colonist player may declare excess industrial capacity destroyed only if some colony missile bases still exist at this point in the Fire Turn sequence. If the colony has been conquered during this Fire Turn, as defined next, he may not exercise this option.


7.1.5 Planetary Attack on the contested colony is over for this Fire Turn if all the attacking players' warships are destroyed, or if all colony missile bases have been destroyed, and the colony conquered, or the attacking player declares the attack ended. The colony is not conquered if all remaining warships and missile bases were destroyed during the same Fire Turn. If there is more than one colonized planet in the con tested star hex, the attacking player may attack them separately or together or alternate his attacks at will. Planetary Attack is ended in the contested star hex if the above stated conditions apply to all colonies and warships in that star hex.


7.2.8 The Conqueror may destroy the population and Industrial Units of a conquered colony on a one to one basis. The population and industry destruction occurs during the Planetary Attack step of a Player Turn. Each type of warship the conquering player has in the conquered planet's star hex may destroy on the following basis:

  • For each Escort warship (ESC), 1 million population and 1 IU.
  • For each Attack warship (ATK), 3 million population and 3 IU.
  • For each Dreadnought warship (DN), 5 million population and 5 IU.

Each warship may destroy the above amounts only once during the Planetary Attack step of a Player Turn.


7.2.9 If a colonized planet's population consisting of 10 million or more colonists has been destroyed by an opponent's warships, that planet is rendered uninhabitable by any means for the rest of the game and is so marked on the Player Record Sheet. This uninhabitable Planet does not count any points toward winning, regardless of its original habitability type.

From game STELLAR CONQUEST by Howard Thompson (1975)

Deep Down Defenses

If the inhabitants of the planet lack handwavium force fields, and the besiegers have no shortage of bombardment weapons, sooner or later the planet people are going to have to resort to living underground. The more frightful the bombardment, the deeper they will have to dig.

This is why in the real world the US NORAD Cheyenne Mountain Complex is built under six hundred meters of solid granite. Proof against EMP, and the blast doors are rated to withstand a 30 megaton thermonuclear explosion as close as two kilometers.

In the 1955 movie This Island Earth, the planets Metaluna and Zagon are at war. Metaluna's surface has been laid to waste by Zagonian asteroid bombardment. The Metaluna's cities are now all underground, but even then they are planning to seize and relocate to Planet Terra before Metaluna becomes totally uninhabitable.

In the 1974 anime series Space Battleship Yamato the warlike Gamilas have devastated Terra by a continual asteroid bombardment. But these asteroids are radioactive. Even though the people of Terra have retreated underground, the radiation is slowly seeping downward. The people of Terra have about one year left to live before the radiation kills them. Lucky for them they receive help from a certain Queen Starsha of the planet Iscandar in the Greater Magellanic Cloud.

The queen offers a wonderful machine that will cleanse Terra of all the radiation. The catch is that the Terrans have to travel to the GMC go fetch it. Starsha hopefully gives them blueprints for a faster-than-light-drive/unreasonably-powerful-Kzinti-Lesson, but the Terrans have to build the drive and the ship to house it.

Lucky for them, the asteroid bombardment has conveniently evaporated the seven seas, exposing all the historical shipwrecks in general, and the wreck of the 1940 battleship Yamato in particular. There is not enough underground space to build a huge spacecraft, but the Yamato is reasonably large and strong enough to be converted. The Terran secretly tunnel underneath it and covertly rebuilt it, so as to not tip off the Gamilas.

TRIPLANETARY

While any Eddorian-could, if it chose, assume the form of a man, they were in no sense manlike. Nor, since the term implies a softness and a lack of organization, can they be described as being amoeboid. They were both versatile and variant. Each Eddorian changed, not only its shape, but also its texture, in accordance with the requirements of the moment. Each produced extruded members whenever and wherever it needed them; members uniquely appropriate to the task then in work. If hardness was indicated, the members were hard; if softness, they were soft. Small or large, rigid or flexible; joined or tentacular — all one. Filaments or cables; fingers or feet; needles or mauls — equally simple. One thought and the body fitted the job.

They were asexual: sexless to a degree unapproached by any form of Tellurian life higher than the yeasts. They were not merely hermaphroditic, nor androgynous, nor parthenogenetic. They were completely without sex. They were also, to all intents and purposes and except for death by violence, immortal. For each Eddorian, as its mind approached the stagnation of saturation after a lifetime of millions of years, simply divided into two new-old beings. New in capacity and in zest; old in ability and in, power, since each of the two “children” possessed in toto the knowledge and the memories of their one “parent”.

And if it is difficult to describe in words the physical aspects of the Eddorians, it is virtually impossible to write or to draw, in any symbology of Civilization, a true picture of an Eddorian’s — any Eddorian’s mind. They were intolerant, domineering, rapacious, insatiable, cold, callous, and brutal. They were keen, capable, persevering, analytical, and efficient. They had no trace of any of the softer emotions or sensibilities possessed by races adherent to Civilization. No Eddorian ever had anything even remotely resembling a sense of humor.

While not essentially bloodthirsty—that is, not loving bloodshed for its own sweet sake—they were no more averse to blood-letting than they were in favor of it. Any amount of killing which would or which might advance an Eddorian toward his goal was commendable; useless slaughter was frowned upon, not because it was slaughter, but because it was useless and hence inefficient.

And, instead of the multiplicity of goals sought by the various entities of any race of Civilization, each and every Eddorian had only one. The same one: power. Power! P-O-W-E-R!!

Since Eddore was peopled originally by various races, perhaps as similar to each other as are the various human races of Earth, it is understandable that the early history of the planet while it was still in its own space, that is, was one of continuous and ages-long war. And, since war always was and probably always will be linked solidly to technological advancement, the race now known simply as “The Eddorians” became technologists supreme. All other races disappeared. So did all other forms of life, however lowly, which interfered in any way with the Masters of the Planet.

Then, all racial opposition liquidated and overmastering lust as unquenched as ever, the surviving Eddorians fought among themselves: “push-button” wars employing engines of destruction against which the only possible defense was a fantastic thickness of planetary bedrock.

From TRIPLANETARY by E. E. "Doc" Smith (1948)

      Now they had reached the border of a great sea, where a huge mountain range seemed to run off into the water in a series of islands. Their escort had taken the lead, and was hovering over one of the islands now.
     Suddenly Aarn gasped, for the tiny blazing sun and the deep violet sky was obscured by a mist that grew more and more dense, a rapidly rising, vapory cloud that swept up from the sea. In a minute the entire district was veiled in an impenetrable fog. Even the television was badly hampered, so badly it could show but a few hundred feet ahead as they followed the leading ship closely. Auto Rayl was silent, intently watching the screen.
     The destroyer ahead was making straight for the largest of the near-by islands. And, as they neared it, a peninsula a quarter of a mile long slid silently out to sea and sank beneath the waves. A great metal-lined bore was revealed, and instantly the destroyer dropped into it. The Sunbeam was directly behind. That bore was an oval cylinder, five hundred feet wide, and two hundred long, and extending down beyond sight, curving into the bowels of the planet.
     The lighted bore was suddenly darkened by the settling of the great rocky lid back in place.
     The tunnel had straightened out. Now, suddenly, they came upon a great factory, a huge, brightly lighted under ground workshop. Gigantic forms were in construction off across the big, pillared cavern.

From THE MIGHTIEST MACHINE by John W. Campbell jr. (1934)

      “That big sea,” said Warren briefly. “There’s a city under it!” exclaimed Putney. “That’s the place for a city! No heat rays would ever reach them there, no bombs even. Why aren’t all the cities under water?”
     “Not enough room probably. Also not all their eggs in one basket. This is probably the capital.”
     The planes were slowing now, and as they neared a low range of mountains that ran down to the lake, they stopped. They hovered in tight circles above the mountains for a few moments, then suddenly one entire hill, nearly a half-thousand feet in height, and fully 1000 long, slid serenely out into the lake, seemingly floating on the water. Beneath it was a vast cavern opening. The giant ships sank into it three abreast, while the smaller ships sank down whole fleets side by side.
     Warren was already in the cavern. It led straight down for half a mile, turned back toward the lake for a mile, then straight down for another mile. At the bottom were titanic lock gates of solid metal at least fifty feet thick set in great grooves cut in the living rock. The surface toward the city did not, at present, touch the surface of the grooves. Both were lined with thick layers of some dark substance, evidently similar to rubber. A quarter of a mile further on was a similar titanic set of gates. And with the first gates the lighting began. Heretofore great searchlights on the ships had illuminated the passages, for scarcely had they passed the mouth of the cavern when the mountain began moving back into place.
     “There’s one sure thing — these fellows have some source of power that beats anything earth had two years ago. Earth could never have dug this channel, they could never have moved that mountain around, and they’d have been plumb out of luck if anything like those ships came after them. Wonder what it is?”
     The ships ahead began slowing to an even lower rate, turned an abrupt corner, and the Terrestrians suddenly came into a blaze of brilliant. lights. A huge cavern widened out from the tunnel, a gigantic place with a dozen levels of metal floors on which, one by one, the planes began to settle. Thaen touched Warren’s shoulder and pointed to the topmost one. “Yuarn,” he said.
     Warren nodded. “I don’t see why this doesn’t fall in on them.”
     “I’m beginning to. Don’t go near those columns of light. I think the light just marks out the beam of force — yes, look at that magnetometer. A powerful beam. Probably they have projectors on the cavern floor, and on the various floors, and on the roof, that distribute the pressure. Look — see how that beam there widens at the middle — I’ll be willing to bet anything that’s how they drive their ships. Nasty weapon it would make too, if you didn’t have any magnetic defense field. Just touch one of those beams with a weak field and see what happens.”
     Warren set some controls, and pulled a lever back gently. The surrounding columns of light swayed gently away from the ship, then gently toward him, bending at the joints. “Magnetic,” he nodded.

     A picture of an arid, dry plain swam into being on the screen of mist (movie projector screen). Unlike an earthly moving picture it grew swiftly from a spiral till it filled the entire screen with a round picture with a peculiar suggestion of depth.
     There was nothing but the level plain, and the clear violet sky with occasional clouds floating high in it. But somewhere a faint, heavy hum began to come into being; it grew till it was a majestic, full-throated roar echoing through all space.
     As they watched, a fleet of giant battle planes swam into view from somewhere behind, moving onward and upward at an unbelievable speed. They climbed at an angle of forty-five degrees, yet their wings tilted back no more than thirty degrees. Some force other than pure air-lift was raising them. So swiftly they mounted that in moments they were out of sight.
     Suddenly the ground cracked, broke, and a ring of squat, hemispherical metal domes pushed their way up through the sand. Several seconds passed, then from one, then another, broke a great flare of electric-blue fire that reached fanshaped to the sky, bent, and intermingled in a dome of solid fire above all. It fluctuated, wavered, twisted, and then steadied after a moment to a solid, motionless sheet. A constant, steady hum echoed through the great cavern.
     Something materialized on the screen, a black dot high, high in the violet sky. It grew with accelerating speed, expanding rapidly to a torpedo-shaped body ten feet long, three in diameter, ending in a finned tail that kept it whirling with terrific speed, a gyroscopic missile that would maintain its orientation against any deflecting force. Half a mile from the ground a stream of fire issued from it, and the giant bomb leapt forward with speed that must have reached miles a second.
     At the last instant it swerved violently, landing finally in the exact center of the dome of blue fire. A single stupendous flash of light, a titanic explosion sharp as the crack of a rifle, and it was gone.
     It was merely a sighting shot. A hundred black dots appeared magically, and as they came into being, and grew from somewhere in the far reaches of that violet sky, blue-glowing cones of dim radiance reached up to them. They staggered, twisted in their paths as the beams touched them. Some jerked violently aside. All slowed visibly, and became red, many released their explosive energies harmlessly on the air, but a majority rained down on the protecting dome of fire.
     Strangely, none seemed directed at the center of the dome, the force beams seemed engaged in directing them there. Most fell toward the edge of the protecting ring.
     Other dots were appearing far above now. The planes were descending again, and now accompanied with long, slim ships, shaped like pencils pointed at each end. Lashing beams smashed out between them. The faintly glowing force-beams from the ships, long tubes of hazy light, some other beam, twin pipes of brilliant light that started from each other, and curved inward to meet at their object in a constant, terrific display of lightning. A dozen planes attacked each ship, the ships seemed content to sink slowly downward, dropping their gigantic bombs, and firing tiny, explosive shells toward the dodging planes.
     The planes were not dodging successfully apparently, for a constant and growing rain of broken metal began to fall. From each of the hundred pencil-ships a ray reached out presently, something dim and half seen that exploded into a point of incredible incandescence if it touched a plane.
     As at a signal, the giant attacking planes winged over suddenly, pointed their noses toward the planet, and descended in a terrific, shrieking power drive that must have raised their speed to nearly a mile a second. Their wings were folded into the ships in some manner, till only a knife edge projected from the fuselage. The great planes twisted and weaved as they shot downward, avoiding rays that sliced after them. They turned, leveled off, and streaked across the plain in a dodging course at a rate that carried them beyond the horizon in seconds.
     The pencil-ships were not left to come on unhindered, for each great plane ship had spewed forth a great fleet of tiny midges that swarmed in darting, flitting motion about the ships, discharging brief bursts of that twin explosive electric ray. But somehow the ray always seemed to explode just short of the ships, leaving them unscathed.
     Some signal was given. The hundreds of tiny ships all darted suddenly toward one of the pencil-ships, every ray burst forth simultaneously in a single blinding sheet of flame — and the pencil-ship was falling, white-hot wreckage. The midges scattered themselves as though fragments of an exploding bomb. Vengeful heat-rays lashed across the sky where they had been seconds before. The score must have been half a hundred — but by far the greater number escaped.
     The battle was progressing on a level now, nearly fifty miles above the city evidently, for some telescopic device had been attached to the camera. Ships and midges circled steadily for the advantage.
     Again the concerted rush — again white-hot wreckage descended streaming from the pencil-ship, and two score more of the midges followed it.
     “The ships have some sort of screen — if the planes can get enough power over, the screen fails — when the ships don’t have to use power for their screen, they can work those heat-rays,” said Warren hastily. “The ships will win — too many.”
     There was a sudden shift in the position of the pencil-ships. One rose half a mile above the rest, while the others set up a barrage of their heat rays about it, protecting it. The midges seemed suddenly to concentrate on attacking that ship, for fully a third of them rose to it, and poured their weapons against it — most of them to fall mangled wreckage.
     For an instant the ship seemed unguarded. Then, from bow and stern, broke two new rays. They moved in a curve if the ship spun rapidly, their range was less than a quarter of a mile, but they seemed to stretch a web of force between them and around them that swept the midges from the sky like some gigantic broom. Only near the enemy ships were the planes safe, from this weapon, and there the heat-rays reached them.
     The midges folded their wings and, like the giant planes, shot planet-ward with terrific speed. Not a full hundred reached the surface. The pencil-ships descended in massed, close-packed formation, majestically and slowly, toward the glowing dome of fire. At ten miles the forts went into action. For a single second, every one of the fan beams snapped out, to snap on as concentrated pipes of radiance smashing their way to the massed enemy ships. A wave of fire washed over the formation, it flowed like some squirted liquid, striking a solid glass plate. But it was like an acid, for it began eating holes that showed red against the blue flame, holes that expanded as some half dozen beams concentrated instantly on it — and a ship disappeared in flaming destruction beyond.
     But presently this eating of holes stopped, the holes grew fewer, and smaller, ships avoided them in the meantime, and they hung motionless over the city.
     Hours must have passed. The scene was at night, suddenly, and the ships showed brilliantly outlined by the wash of electric fire, the heavens were illuminated by the great, bright stars of this world, but they were overcast now, clouds were gathering.
     The ships were no longer massed, their formation was a circle with a hub and spokes. But only half the ships were so engaged. The rest seemed moving about freely behind this shield. They began to concentrate above the hub, and the ships of the hub rose to join them. Blue beams began to reach from one to another, till all the ships were linked in a single network of power beams.
     The center ship hovered over the center of the shield. A mistiness grew suddenly before it, a spinning misty globe of blue light. It attained size, then suddenly broke free, and went spinning erratically downward. It ate a hole through the shield. It drank up the blue electric flame on the other side, and grew fat on it. It jerked its way down and to one side. It acted like a light ball suspended in a jet of air. Suddenly a particularly violent jerk led it into one of the great beams. Instantly, with the speed of light, it followed that beam back to its source, puffed softly as it struck the dome-fort, and bounced aloft. The fort was a heap of powdery ash.
     Frantic magnetic beams were jerking at it; they could deflect it when it moved, but only served to make its erratic motion more so. And another sphere was falling, jerking about like the first.
     In minutes the last of the forts were gone. The enemy ships came slowly downward, cautiously. The spheres seemed repelled by them, and rolled swiftly away, out across the plane, moving erratically as ever, and every touch left a great, powdery scar, but every touch made them smaller.
     The ships were pouring their heat beams into the rock. It was day once more, and a cauldron of molten rock half a mile across bubbled gently. It was night again — the cauldron of rock was three miles across. Day found it fully four, and bubbling gently.
     The scene on the screen of mist vanished. It was replaced by a scene in a great subterranean city. Men, women, and children were hurrying about on moving ways, suspended on spidery bridges that spanned the great lighted tunnels. Each wall of the tunnel here was a great apartment house, and the great tunnels must have been a hundred and fifty feet tall, and fifty wide. The scene was at a “cube” — the three-dimensional equivalent of a city square, where four great tunnels intersected. Everyone seemed to be leaving. The reason was obvious. Above the spider-work bridges, above the glowing magnetic columns that supported the rock pressure above, a slow smoke was originating, and falling downward. The rock became dull red while they watched. The last hurrying people looked back over their shoulders with frightened faces.
     Suddenly one of the great magnetic columns began to wobble erratically. It twisted, the upper section broadened, and seemed to be trying to slide off the lower. It did, its beam a cone that sharply deflected the four surrounding beams till they too began to wobble. The dull red rock was brightening. The beams were all spreading now; the first to fail suddenly went out as an explosion wrecked the projector. A great crack appeared in the rock, and with a terrific roar of sound the whole roof split wide. A river of molten rock came pouring through. The spider-work bridges and ways vanished in a puff of smoke and a brief sparkle of fire. A wall of white-hot rock moved rapidly toward the screen. The camera swayed, the picture went out of focus, and suddenly a plume obscured the screen.
     An instant later the camera was looking down the tunnel from a distant station. The wave of rock was moving more slowly, cooled by surrounding rock, and by the great refrigerating plants that must have been cooling the city. A huge line of pipe had been hastily laid, and was spouting a sparkling blue liquid that hissed instantly into invisibility as it struck the rock — which cooled it. A dike was being built, a dike of frozen rock.
     It was useless. The roof of the tunnel itself began to glow, and the pipes were turned on it. The Niagara of lava still flowing in from the original break overflowed the dike, and rolled on.
     The city was doomed.
     The screen went blank in a burst of flame at that moment, and stayed blank.

From THE SPACE BEYOND by John W. Campbell, Jr. (1976)
ALAKARS

(ed note: Alakars are Warbots, soldiers wearing ultra-high-tech powered armor mostly made out of forcefields and nanotechnology. Steel pimples are free flying auxiliary units of the armor, about the size of a golf ball. Amorphoid is what we now call "programmable matter", smart materials constructed out of nanotechnology which can alter its forms and functions on command. Most machines and tools are made out of amorphoid.)

Antares, who had always seemed to have the last thing to say insofar as weapons advances were concerned, finally sent a squad of Ultimate Alakars onto the field of war.

The Alakar himself wore no weapons, though he carried a few hand weapons of negligible presence (mostly fashioned from Link), wore no helmet and had six steel pimples, which performed all the functions of the helmet, as well as being able to operate as battlecrafts. The Alakar, upon landing on a planet, which had not been invaded, would immediately alert the civilians to go to the public shelters hundreds of miles beneath the planetary crust and take all personal valuables with them. They were given twenty-four hours, but during this time, since the Alakar was almost sure to be under attack, he would certainly be occupied. His steel pimples would head for the nearest masses of amorphoid, often automobiles and private spacecraft, and perform virus-function. Whatever the amorphoid had been previously would be erased; the pimples would realign and combine all available amorphoid into great robot fortresses, fleets of battlecrafts and orbiting platforms, and would infect normal metals with amorphic domain, causing entire communications networks to start converting into amorphoid weapons. If it went on mainly unchecked, within fifty hours of commence-attack, the military command centers buried in the centers of the planets could expect their control panels to swim like quicksilver and turn into atomic bombs.

The planetary defenses would initiate their own amorphic conversions, trying to fight back, and would cause the comm networks to fight back at ground level. Flotillas of planetary steel pimples would commandeer as much amorphoid as possible, until the entire war began to resemble the attack of a viral disease upon a protoplasmic organism. If the planetary defense won, the Alakar was killed or forced to retreat, and the mass-computer would return every bit of registered amorphoid on the surface to its original state (unregistered amorphoid, such as kitchen appliances, generally kept firing away until told to desist. Registered amorphoid, which had a certain key-pattern built in, instantly reverted).

If the Alakar won, the same thing would be done, except that he would now control the planet and invite his forces into orbit. Since the governments of Antares and the TOSS were very similar, in basic policies, the civilians rarely cared too much who held the upper hand, so long as they were not too often changed.

Naturally, this being a war, damage was done. A wrecked city stayed quite wrecked, though there was rarely any loss of life. But recovery from an attack took several years, and when Antares finally bested the TOSS, they found that they had a tremendous financial responsibility to rebuild what they had undone.

From THE WARBOTS by Larry Todd (1968)
Note that the GALAXY magazine and the Bodyarmor 2000 articles have totally different artwork

Surface Defenses

In addition to large planetary forts, there may be scattered anti-spacecraft weapons sited all over the planet. The main difference is these have no real protection except being very good at hiding. Instead of armor or magic force fields, they are either one-shot sacrificial weapons or capable of frantically scuttling away after they give away their position. Or they are weaponized spacecraft launching facilities that the enemy wants or needs to capture intact so they are loath to damage it.

Because as soon as a ground (or sea) based gun opens fire on an enemy ship in orbit, the enemy is going to plaster the entire area with ortillery.

If you have sufficient stealth technology, it might be a good idea to put some planetary defensive weapons inside submarines. This made good sense back in the days of Mutual Assured Destruction, but nowadays orbital observation satellites have made it much harder for submarines to hide. Be aware though that their stealth is destroyed the instant they fire their weapons, and the attackers in orbit will lob a nuclear depth-charge that will crush the submarine like an eggshell. US Navy Ohio-class submarines carry 24 missiles, a planetary defense submarine would probably be carrying a similar amount. The PD sub would be well-advised to launch all of its missiles at once, and preferably the sub should be a remotely controlled drone.

In the 1955 Operation Wigwam test, the US military discovered that a 30 kiloton nuclear depth charge could kill a modern submarine with a radius of a bit more than a mile.


Like planetary fortresses, surface defences are at a disadvantage with respect to hostile spacecraft in orbit due to the gravity gauge.

Rick Robinson is of the opinion that the gravity gauge is not quite as one-sided as it appears. In an essay entitled Space Warfare I - The Gravity Well he makes his case. The main point is that the orbiting invading spacecraft have nowhere to hide, while the defending ground units can hide in the underbrush.

Of course it is a bit easier to inflict damage on orbital person now that lasers have been invented. Keep in mind that if the planet in question has an atmosphere similar to Terra some laser wavelengths should be avoided.

And keep in mind that the defender's anti-orbit rocket also does not need a warhead, a bursting charge surrounded by nails and other shrapnel will do. The relative velocity between the more or less stationary cloud of shrapnel and the orbital speed of orbital person will do the rest. Orbit person will be riddled by shrapnel traveling at about 27,500 kilometers per hour (7,640 m/s) relative.

SWORD AND SCEPTER

Twenty-three hundred kilometers to the west at Allansport, Sergeant Sherman White slapped the keys to launch three small solid rockets. They weren't very powerful birds, but they could be set up quickly, and they had the ability to loft a hundred kilos of tiny steel cubes to a hundred and forty kilometers. White had very good information on the Confederate satellite's ephemeris; he'd observed it for its past twenty orbits.

The target was invisible over the horizon when Sergeant White launched his interceptors. As it came overhead the small rockets had climbed to meet it. Their radar fuses sought the precise moment, then they exploded in a cloud of shot that rose as it spread. It continued to climb, halted, and began to fall back toward the ground. The satellite detected the attack and beeped alarms to its masters. Then it passed through the cloud at fourteen hundred meters per second relative to the shot.

Four of the steel cubes were in its path.

From SWORD AND SCEPTER by Jerry Pournelle (1973)
SECTION 4: SURFACE DEFENSE

Traditionally, spacecraft attacking targets on a planetary surface are assumed to have a high-ground advantage, referred to by Heinlein as the “gravity gauge”.  This assumption, like many about space warfare is wrong for several reasons.  Firstly, a spacecraft in orbit is very vulnerable to ground-launched kinetics, which only need to intercept it to do lethal damage, as described in Section 8.  Second, the ground-based defenders are able to use the clutter of the planetary surface to hide their actions, while the attackers are clearly visible.  Lastly, the planet itself offers advantages in the construction of defenses that serve as a very powerful force multiplier for the defender.

The thought experiment that underlies the gravity gauge is two men, one at the bottom of a well, the other at the top, having a fight with rocks.  The man at the top has an obvious advantage.  However, like many analogies, this one has deep flaws.  The largest is a misunderstanding of orbital mechanics.  Because of the motion of the orbital craft, any projectiles that it launches must slow down before they can leave orbit, and in low orbit, the delta-V requirement can be significantly higher than is required for a defender’s projectile to reach the attacker.  The requirement depends heavily on the geometry of the situation, but it is outside the scope of this section.  For more details, see Section 12 and Space Weapons, Earth Wars.  A warhead is unnecessary for the defender’s weapons, as the target’s orbital velocity provides all the kinetic energy required for the job.  Another issue is that the rocket necessary for this type of mission is quite small.  An R-17 Scud-B can reach a maximum altitude of approximately 150 km with a warhead of 985 kg and a launch weight of 5,900 kg, providing a marginal capability against targets in very low orbit.  Another version, the Scud-C, is capable of reaching about 275 km, with a warhead of 600 kg, and a total launch weight of 6,400 kg.  The MGM-31A Pershing has an apogee of about 370 km, a warhead of 190 kg, and a launch weight of 4,655 kg.  All of these missiles date back to the 1960s or before, but, with the proper seeker systems, should be capable of engaging targets in low orbit.  Their warheads are rather heavier than would be optimal for engaging orbiting vessels, and lighter warheads could result in somewhat higher altitudes.  For higher-orbit engagements, something like the Pershing II (altitude ~885 km, warhead 400 kg, launch weight 7,490 kg) is probably called for.  Above that, the various ICBM-type systems would take over, with apogees in the range of 5,000 km.  

Note that all of these missiles have warheads which are far heavier than are required for direct-hit kill on any practical spacecraft.  There are two ways this fact can be exploited.  First, the warhead could be replaced by another stage carrying a smaller warhead and achieving a greater altitude.  This should be good for another few hundred kilometers altitude, depending on the size of the warhead available and the previous burnout velocity.  Second, the unitary warhead could be replaced by a bursting warhead, as described in Section 8.  A detailed treatment of this concept with regards to planetary defense can be found in the Appendix to Section 12 of Physics of Space Security.

The two extant missiles that most closely approximate what would be required of a low-altitude surface-to-orbit missile (SOM) are the THAAD (Terminal High-Altitude Area Defense) and the SM-3.  The current model of THAAD, the block 4, has a launch weight of 640 kg, a warhead of approximately 40 kg, and a maximum altitude between 150 and 200 km.  Later (and presumably heavier) models could improve the maximum altitude to as much as 500 km.  The SM-3, which is currently ship-launched, has a launch weight of 1500 kg, a warhead of 23 kg, and a maximum altitude of as much as 500 km.  Later versions are reported to be capable of 1000 km, and have launch weights of approximately 2600 kg.  Both missiles use the same sensor system, which is reportedly able to acquire targets (presumably ballistic missile warheads) at ranges above 300 km.

 The above missiles are listed to demonstrate that the basic physical requirements for an SOM are quite simple, and well within the grasp of current technology.  All of the listed missiles are fired off of trucks of some sort or another (with the exception of the SM-3, which does have a fixed land-based version).  THAAD itself is launched from a vehicle the size of a semi.  If a system was designed explicitly for the SOM role, it should be very easy to conceal the missiles in trucks until the time of launch, preventing the attackers from detecting and destroying them.  Even if the attackers can see everything clearly, if the trailer is self-contained and built to look like an ordinary semi-trailer, the attacker won’t be able to tell it apart from the millions of others in use.  

Extensive tracking and control stations will be unnecessary, as the ship in question will be moving in a more-or-less predictable orbit, and the missile will have enough homing capability to compensate for the imprecision.  Orbit determination is a well-established science.  All that is needed are a few measurements of time, observer’s position, and target bearing.  These sensors are even easier to hide then the missiles themselves, as they could be as simple as a sextant at dusk or dawn.  At night, it should be possible to detect the vessel, probably through radiator glow.  During the day, it is somewhat more difficult.  This suggests that a sun-synchronous orbit might be ideal for an attacking spacecraft, as dawn and dusk occur over the poles which are (presumably) largely uninhabited.  However, the same could be said of any polar orbit, and other conditions are likely to play a large part in attack orbit selection. The advantage of a sun-synchronous orbit is that the illumination angle beneath the spacecraft is nearly constant, but for a long-period orbit, the inclination is likely to be fairly low, potentially placing dawn over an inhabited area.  Geographical conditions are as likely to dictate the orbit as astrodynamical conditions, although the astrodynamic effects of attacking a non-Earth planet should not be discounted.  In some cases a sun-synchronous orbit will place the attacker over territory that he would rather avoid.  For example, a 24-hour sun-synchronous attack orbit aimed at a target in North America will spend a large amount of time over South America, a situation that is hardly idea.  For optimal results, attacks would be made in daylight, which gives the best conditions for the attacker’s sensors and the worst for those of the defender.

The obvious counter to the visibility of spacecraft is for the spacecraft to maneuver regularly, hopefully spoiling any shots the defender may take.  A burn of approximately 3 m/s in the prograde or retrograde direction in a 150 km Earth orbit will change the period of the orbit by 2 seconds and the semi-major axis by about 5 km.  What this means is that the spacecraft will arrive on the opposite side of the orbit either a second late or early respectively, and will be either 10 km above or 10 km below where it was supposed to be depending on which direction the burn was made in.  However, this is unlikely to be enough to spoil the attack.  If the missile seeker locks on 30 seconds out, a 330 m/s delta-V would be sufficient to compensate for the divergence, and it is quite likely that SOMs will be designed to frustrate such tactics.  So long as the change remains relatively small, the results above can be linearized, with a 12 m/s delta-V producing a 4-second change in arrival time, and a 40 km change in altitude.  Note that the divergence in position only occurs in the orbital plane.  The plane itself can be changed by a burn half an orbit away, but the spacecraft will still pass through a point opposite the location of the burn.  For out-of-plane dodging, it is best to burn a quarter-orbit away (three-quarters of an orbit will produce identical results).  Moving the ground-track 10 km in our 150 km Earth reference orbit will require 12.25 m/s of delta-V, significantly more than an equivalent amount of in-plane dodging.  To a first approximation, the dodge delta-V for a quarter-orbit burn will be approximately twice that required for a half-orbit burn.  All of this assumes the initial orbit is circular, and the delta-V is fairly small.  Finding values for larger burns will require elaborate computations, which are beyond the scope of available data.  The requirements for a given amount of miss distance will be somewhat lower at higher altitudes, but this must be balanced against the fact that at higher altitudes, the missile will probably have significantly more time between lock-on and impact, reducing the delta-V required to compensate.

Of course, this does not address the practicality of using regular maneuvers to frustrate missile attacks.  For a ship with a high-thrust drive, the limiting factor is delta-V, and this dodging scheme will require something like 0.4 m/s/km/hr. for half-orbit burns, or 0.8 m/s/km/hr. for quarter-orbit burns.  Over the long term, this would add up, needing 10 to 20 m/s/km/day.  This is vaguely practical for small miss generation, but small miss generation is easily compensated for by the missile.  Even a minimal estimate of a required miss distance of 10 km would need 100 to 200 m/s/day, which will get expensive if the siege drags on more than a few days. Low-thrust systems might be more effective, although the achievable miss distance will be limited by the acceleration of the spacecraft.

The exact altitude requirements for an SOM are actually quite difficult to figure out.  A missile will only be able to attack a target at its maximum altitude if the target in question passes directly over the launch site.  All of the numbers posted above are estimated maximum altitudes, and in practice the maximum altitudes will be some fraction of those listed.  The one use of the SM-3 for ASAT purposes was at an intercept altitude of about 250 km, and used an early model, putting the interception at about half of the theoretical maximum.  The missile used in the Chinese ASAT test has a theoretical altitude of somewhere between 1350 km and 1500 km, and was used against a target at an altitude of approximately 860 km.  All of these indicate that the maximum practical altitude for a missile is probably not much more than half of the maximum theoretically achievable, though 75% might be possible for a battery positioned close to an important target, where the enemy will pass almost directly overhead.  Air-launched ASAT systems, such as the ASM-135, are theoretically capable of achieving much more nearly 100% due to better positioning of the launching platform, although the only known air-launched ASAT test, the ASM-135 shot at the Solwind P78-1, occurred at an altitude of 555 km out of an apogee altitude of 1000 km.  The question then becomes what sort of altitudes will be required of an SOM system.  The ISS orbits at approximately 400 km, while most recon satellites orbit between 250 and 600 km.  These put the requirements clearly into the SM-3 category.  Seapower and Space contained an interesting note on ASAT envelopes.  The Thor of Program 437 was apparently capable of engaging targets at 200 nm (370 km) at slant rages of up to 1,500 nm (2,778 km) (and higher targets at shorter ranges), while the Nike-Zeus was demonstrated up to 150 nm (278 km).  Encyclopedia Astronautica credits the Thor in question with an apogee of 500 km, and the Nike-Zeus with somewhere between 200 and 280 km, depending on the variant.  It therefore seems prudent to assume that the altitude given for Nike-Zeus was in fact the maximum altitude the weapon could reach.

Another factor controlling the altitude requirements of missiles is the necessity to hold down flight time.  Table 2 gives values for times of flight and view times for missiles fired at spacecraft at various altitudes, with the missiles having an apogee equal to the spacecraft altitude.  The missiles were assumed to be ballistic throughout, which is not a good assumption, but one that must be accepted for purposes of analysis.  Clear view was assumed to begin at 75 km, to account for the fact that defensive fire and sensors may not be fully effective through the atmosphere.  In this case, view time and rise time are very similar, and neither is likely to be strictly dominant.  The fact that view time is normally very close to rise time actually means that given the slowing a missile would experience during passage through the atmosphere, the target might not be able to see it during its burn, or would only be able to see it through a great deal of atmosphere.  If the missile is relatively stealthy during the unpowered portion of the ascent, the spacecraft might not have a good track until it is quite close.

Table 2
Altitude (km)1001502002503005007501000
Rise Time (sec)142.8174.9201.9225.8247.3319.3391.0451.5
View Range (km)1,122.11,369.91,576.81,757.31,919.02,447.02,952.13,359.4
View Time (sec)145.3179.4208.9235.5260.1346.6441.2528.7
Clear Rise Time (sec)71.4123.7159.6188.9214.2294.4371.0434.3
Clear View Range (km)567.1979.11,260.01,486.21,679.92,280.42,831.03,266.1
Clear View Time (sec)72.6126.8165.0196.8225.0319.3418.2508.1

It is obvious that even at the lowest altitudes, the missiles are vulnerable for a considerable period before impact. The obvious solution is to fire a missile that has an apogee considerably above the altitude of the target, minimizing this vulnerability. Table 3 shows the effects of apogee above that of the target.

Table 3
Altitude (km)100100100150150150200200
Missile Apogee (km)150200250200300500400800
Rise Time (sec)73.959.150.9101.072.452.283.654.1
View Range (km)1,122.11,122.11,122.11,369.91,369.91,369.91,576.81,576.8
View Time (sec)145.3145.3145.3179.4179.4179.4208.9208.9
Clear Rise Time (sec)22.716.914.058.739.327.255.534.7
Clear View Range (km)567.1567.1567.1979.1979.1979.11,260.01,260.0
Clear View Time (sec)72.372.372.3125.3125.3125.3161.9161.9
Vertical Velocity (km/s)0.9901.4011.7160.9901.7162.6201.9813.431
Impact Energy Factor1.021.031.051.021.051.111.061.19
Altitude (km)30030050050075075010001000
Missile Apogee (km)40060075010001000150015002500
Rise Time (sec)142.8102.4165.3132.2225.8162.0233.7160.9
View Range (km)1,919.01,919.02,447.02,447.02,952.12,952.13,359.43,359.4
View Time (sec)260.1260.1346.6346.6441.2441.2528.7528.7
Clear Rise Time (sec)114.679.9145.2115.0208.5148.0219.7150.1
Clear View Range (km)1,679.91,679.92,280.42,280.42,831.02,831.03,266.13,266.1
Clear View Time (sec)217.4217.4299.6299.6378.6378.6444.4444.4
Vertical Velocity (km/s)1.4012.4262.2153.1322.2153.8363.1325.425
Impact Energy Factor1.031.101.081.171.091.261.181.54

In most cases, the rise times and particularly clear rise times have been dramatically reduced, meaning shorter engagement times for the target.  The vertical velocity at impact will also increase the damage the warhead does (although the impact energy is not increased significantly unless the excess apogee is very large).  The impact energy factor is the KE of the warhead with the vertical velocity divided by the KE the warhead would have if it were stationary in front of the target.  The biggest drawback is that it is likely to make the missile and launch site easier for the target to locate.  This may not be a major concern if the attacker has a large number of deployed sensors, which could accurately locate the launch site and ascending missile no matter when it is fired.  Another potential problem is that it obviously requires a significantly larger missile to engage a given target with a given warhead.

ICBM-class weapons are less likely to be useful, due to the longer flight times involved.  This gives the target significantly more time to dodge the missile or shoot it down, moving the warhead into the realms described in Section 8.  The size of the weapon is also a serious hindrance to its operational use.  Even the Midgetman mobile ICBM’s launcher was an incredibly large vehicle, which would make it difficult to camouflage as a civilian vehicle.  Even if it could be successfully camouflaged, the number of vehicles of such size is relatively small, and it might be possible to simply destroy all of them.  A more plausible alternative would be to use immobile camouflaged silos.

Other launch platforms are possible as well.  THAAD is somewhat smaller than a BGM-109 Tomahawk cruise missile, which is launched from a variety of platforms, including submarines.  Early SM-3s are of a very similar size and shape to the Tomahawk.  Submarines have the advantage of being able to hide and maneuver in the sea, and are quite difficult to attack from orbit, even if an initial location is known.  The Ohio-class ballistic/guided missile submarines make excellent candidates for this analysis.  Originally built with 24 tubes for the Trident missile, four of them have been modified since the end of the Cold War to carry 7 Tomahawks each in 22 of those tubes, the other 2 being reserved for special operations equipment.  With a dedicated SOM submarine, it would likely be possible to switch out THAAD-class missiles, SM-3-class missiles, and ICBM-class missiles at the dock, giving the vessel capability against various types of targets.  

The single largest issue with submarine-based missiles is targeting.  A submerged submarine obviously cannot use most sensors, and it is unlikely that it will be capable of independently targeting, launching, submerging, and escaping, all before it is destroyed, either by nuclear depth charge or homing torpedo.  Transmissions to submerged submarines are usually made on the ELF (Extremely Low Frequency) and VLF (Very Low Frequency) bands.  The practical issues are the large size of the antennas required to transmit the signals, and the low bandwidth (a few minutes per character to a few characters per second).  The low bandwidth renders it virtually impossible to transmit the targeting data to a submerged submarine, while the size of the antenna sites makes them very vulnerable to attack from orbit.  It might be possible to harden one of these sites, as the US Navy proposed to do with Project Sanguine, or to use an airborne transmitter, such as the E-6B Mercury.  Both present practical difficulties.  The E-6 must orbit such that the trailing antenna is near vertical, while the expense of hardening is considerable, and can be defeated with a sufficiently large number of hits.  In both cases, the problems of bandwidth still remain.  The VLF/ELF systems are usually used to order the submarine to the surface for further orders.  That remains the most likely solution, but hardly the only one.  VLF communication might be able to provide rough orbit parameters, and a sufficiently advanced guidance/sensor system would be able to take that information and home in independently.  Another option is to make a burst transmission to the missiles as they clear the water.  This has the advantage of not requiring the submarine to come close to the surface. Coming to the surface (which is not the same thing as surfacing) is quite likely anyway, given that most submarine-launched missiles are fired at periscope depth, around 18 m (depth of keel).  The Tridents on the Ohio, however, can be fired from at least 40 m.

The effectiveness of the entire submarine-based system assumes that, as is the current situation, it is very difficult to detect submarines from orbit unless they are very close to or on the surface.  This may be changing, most likely due to blue-green lidar, which has been reported to have depth capabilities of 200 m.  The US has used similar systems to detect mines, starting with the Kaman Magic Lantern of the mid-90s, and continuing to the current AN/AES-1 Airborne Laser Mine Detection System (ALMDS).  A system of that type would significantly hinder if not defeat the operation of SOM-carrying submarines.  However, recent blue-green lidar systems have proven ineffective at finding submarines, due to the required dwell time.  They are excellent for searching a confined area for targets that do not move, but less effective as a wide-area search sensor.  

Nor is lidar the only option for orbital detection of submarines.  There have been rumors about programs involving the use of orbital radar platforms to detect submarines since the early demise of Seasat, which many allege was because it was detecting US submarines.  In theory, submarines produce several distinct features on the surface, including a Bernoulli Hump (a bulge in the sea surface) and a Kelvin Wake with a characteristic angle that distinguishes it from that of surface ships.  It also changes the surface wave spectrum, an effect the Soviets attempted to detect with a laser shortly before the end of the Cold War, along with other attempts involving detecting changes in the ocean structure as a result of the submarine’s passage.

A submarine should produce a detectable thermal wake, both because of the onboard heat and because of the disturbance in the ocean’s structure.  The Soviets attempted energetically to exploit this effect, but their IR detectors proved best suited to distinguishing between land and water.  Another possibility is the detection of the chemical wake, either the chemicals that come from the submarine’s hull or possible transmutation products produced by the radiation from the submarine’s reactor.  Attempts were even made to detect the electromagnetic effects caused by the submarine and its wake.  This involved using a laser to detect certain changes in atomic structure that should be caused by the submarine.  Bioluminescence was also investigated, but absorption of light by water appears to have frustrated this in most places.  There are, however, a few places where it is reportedly an effective means of submarine detection.

Unclassified accounts indicate that all of the concepts have been difficult to put into practice, because the signals are very weak unless the submarine is moving very fast very close to the surface, and because there are lots of objects that tend to produce signatures similar to submarines.  In theory, increased computational power and improved sensors should make detecting these features easier, but improved knowledge of the oceans will also be required.  This might be a problem when working with different planets.  The author is not an oceanographer, and does not know how much of the knowledge will be generalizable to other planets, and thus available to an invader, and how much will not. 1

If nonacoustic methods are infeasible, then the attacker must fall back on the old standby, sonar.  This would probably involve the use of what are essentially very large passive sonobuoys, which listen for submarines, and report back to the ships in orbit.  It might be wise to give them some mobility and the ability to submerge temporarily as well.  They would obviously have to run the gauntlet of the existing defenses to make it down, but once down, they would be extraordinarily difficult for the defender to deal with.  Provided that they landed a reasonable distance away from any defenders, they would have to be hunted like mines, and minesweeping in the open ocean is nearly impossible.  (Minelaying in the open ocean is nearly futile, so this is not something the Navy spends a lot of time worrying about).  How effective such a system would be is a matter of conjecture, made worse by the fact that anything to do with sonar performance is highly classified.

As depth increases, launching missiles becomes more difficult, and the communications problems increase.  A towed buoy would solve the communications problem, but it also runs the risk of revealing the submarine’s position.  There are several systems currently in service that use this principle, but all of them impose serious limitations on the depth and speed of the submarine, and most are intended to communicate with satellites, a possibility not available to the defender in this scenario.

In fact, the lack of satellite communications for the defender raises a serious problem.  Direction-finding on radio traffic was and is a major concern for military forces the world over, particularly navies.  One of the solutions to this has been the use of satellite communications, because the uplink from the ground to the satellite is very difficult to direction-find unless a satellite is directly in the uplink beam.  The downlink can be intercepted, but the satellite can be detected by other means as well, and a sufficiently wide beam means that the intercept gives no information on the location of the recipient.  With this capability denied, the defender would be forced to return to older means of communication, which are less reliable, slower, and vulnerable to direction-finding.  Obviously, the use of wired communications would eliminate this vulnerability, but that imposes restrictions on the location of the units, and is totally unsuitable for submarines.

One solution to the communications issues proposed today is a blue-green laser on a satellite.  The problem with that solution is twofold.  First, the defender can be assumed to no longer have any satellites.  Secondly, the defender must be tracking the submarine to a fair degree of accuracy, which is very difficult by definition, and any steps taken to make it easier would probably also make it easier for the attacker to detect the submarine.  It might be possible to avoid this problem by limiting the amount of information transmitted by the laser, and sweeping it over a vast area of the sea instead, to ensure that the target submarine receives it.  While the laser could be mounted on an airplane, communicating with a submarine by that method could give away the submarine’s general location.

Another option is the perennial darling of submarine communications, sonar.  There have been dozens of attempts over the years to use sonar to allow submarines to talk like surface ships.  All have failed for a variety of reasons, including limited range or bandwidth, and multipath scrambling, although the biggest problem has always been that a submarine is inherently stealthy, and announcing its presence to communicate defeats this.  It has been suggested that computers can deal with the multipath problem, and careful system design might allow adequate bandwidth.  The link can probably be made one-way, removing the problem of the submarine announcing its presence.  For that matter, if the attacker has not constructed a sonar net on the planet (as described above), the submarine could talk back without fear of being detected.  This alone might be a reason to deploy some form of sonar system, even if it is not capable of locating the submarines passively.

Attacking a submarine from orbit is likely to be just as difficult as finding it.  Proposed options for this task include homing torpedoes, nuclear depth charges, and dropping minisubmarines.  All of these weapons have issues.  Homing torpedoes suffer from short ranges, somewhere under 15 km for modern air-launched torpedoes.  At a submarine speed of 30 knots, from detection, it will take the vessel a little over 15 minutes to clear that radius.  The minimum time for a kinetic weapon drop, per Space Weapons, Earth Wars, is 12 minutes, although this requires between 40 and 150 satellites for constant worldwide coverage.  This is not as big of a problem as it seems at first.  Submarines are only likely to be detected when a ship is overhead, and the 12-minute time is for a projectile dropped straight down (which does require a large amount of delta-V).  The actual practical range of the homing torpedo is likely to be considerably shorter, as it has to acquire the target and chase it down.  This might also be less of a problem than it appears on the surface, as the projectile would probably be able to be steered after it is dropped.  While the projectile will be blinded by plasma for long periods during the drop (see Section 12), it must slow down to enter the water, giving a window during which it can receive commands.  The logical extension of this idea is fitting the torpedo into a miniature UAV, remotely steered onto the target in a manner similar to the Australian Ikara system.  This assumes, of course, that the target is still in sight, which depends on the altitude of the launching spacecraft and the technology used to detect the submarine.  While the physical range of the torpedo might be improved by advances in technology, the difficulty of the torpedo’s own seeker acquiring a target is unlikely to decrease by a significant amount.  Nuclear depth charges have radii that are likely to be on the order of 10 km, which means that the attacking spacecraft has to be in low orbit for them to reach the target in time to be effective, or the above-mentioned mini-UAV must be used.  Dropping a manned minisubmarine requires a fairly large gap in the defenses, and once it is in the water, it must deal with defensive submarines.  UUVs commanded by blue-green lasers are a better option, although they would likely suffer from limited armament and the possibility of being killed by the defender.  Both of these can be dealt with by making the UUV expendable, which would also eliminate the need for a nuclear power plant.  At the extreme, an expendable UUV would look quite similar to a long-range torpedo taking command guidance from orbit.  Some combination of those and orbital weapons would be the best way to deal with the submarine problem.

One practical issue with submarines is deployment time.  Modern US SSBNs patrol for 90 days at a time, and this seems to be a fairly hard limit based on human factors.  It might be stretched slightly in wartime, but submarine bases would be a priority target for any attacker.  On the other hand, it is also possible that the human factors issues will have been solved due to the demands of long-term spaceflight, which has many similarities to submarine operations.  Other operational issues would then limit the deployment time, such as food (although this could probably be resupplied by boat when there is cloud cover) and maintenance (which is the ultimate limiter in any case).

Another major option for planetary defense is lasers.  These lasers differ from those for deep-space use, both in the fact that they do not have to deal with the weight and heat restrictions of space-based systems, but they (and any bombardment lasers) must be of wavelengths that can penetrate the atmosphere.  This limits the range that said lasers can achieve due to diffraction.  Adaptive optics and other techniques can compensate for most of the various phenomena that occur when a high-powered laser is fired through an atmosphere, as can siting the laser at high altitude.  The largest weakness of ground-based lasers is that they are immobile, and thus can be targeted by high-velocity kinetics.  This is compounded by the fact that when a laser is fired it immediately reveals its position to the target.  The attacker can then pull back to an orbit out of reach of the laser and bombard it at his leisure.  

There are numerous factors involved in determining the viability of such an installation, including the vulnerability of such installations to bombardment, the effectiveness of the laser, the cost of the laser, and the difficulty of intercepting the bombardment projectiles.  The first is a difficult question to answer.  How effective is a deep bunker against kinetic bombardment?  While the projectile is unlikely to penetrate deep enough to be a threat to a Cheyenne Mountain-type installation (unless the projectile is very large), the shock wave from the impact could damage the laser machinery.  Shock mounting might mitigate this, although a full treatment of such matters is outside the scope of this discussion.  However, the main mirrors themselves must be located near the surface, and would be the points attacked anyway.  It would be entirely feasible to have one generator feeding multiple mirrors, but that tactic is unlikely to be used unless the mirror in question costs significantly less than the generator.  Such a ratio is significantly below the theoretically optimum ratio for mirrors and generators, as shown in Section 7.  The effectiveness of the laser is another question.  It has been suggested that a ground-based laser might be capable of attacking targets as far out as geosynchronous orbit, and could also be used to detect incoming kinetics, giving the laser as much as 12 hours to attack them.  If this is the case (which assumes a 10 meter mirror) the laser system might be intended for use in the defense of the higher orbits, the lower orbits being defended by missiles.

There is also the potential for submarine-based lasers.  It is theoretically possible to create a laser that can be mounted and fired from a submarine, probably using some combination of superhydrophobic surfaces and high-strength windows in front of the mirror that can take the shock of water on them being vaporized.  The problem is that the submarine itself does not make a good laser platform.  Modern submarines are optimized for underwater operation, which tends to mean poor stability on the surface, and mounting the mirror is not a trivial task when one remembers that the submarine as a whole has to be waterproof.  However, such a submarine is not entirely unprecedented.  The USS Triton (SSRN-586) was designed as a radar picket, and built to perform well on the surface.  This had significant drawbacks, most notably in making the submarine very noisy underwater.  On one hand, Triton was designed before the beginning of serious emphasis on submarine silencing.  On the other, a large portion of the noise problem is likely to be inherent in the hull form required for surfaced performance.  On the gripping hand, sonar detection is likely to be somewhat less important in planetary defense.

A laser launch system would also serve as an effective planetary defense station, provided with the proper targeting systems.  The drawback is that the laser itself is in a known location, denying it the element of surprise even for its first shot. Depending on the geometry of a planetary invasion (discussed in section 12) it might or might not be capable of firing on incoming enemies before it is destroyed.

Other means of intercepting the bombardment projectiles have been proposed, as well.  Most of these rely on the fact that a kinetic projectile is vulnerable to disruption during its entry into the atmosphere.  These proposals have ranged from nearby explosions to barrage balloons to some form of hit-to-kill CIWS.  All would disrupt the projectile enough for it to disintegrate, dumping almost all of its kinetic energy into the atmosphere.  The presence of effective defenses of some sort would greatly reduce the vulnerability of ground targets, particularly dug-in ones.  A similar concept was the ‘Dust Defense’ proposed during SDI, which involved using buried nuclear weapons to throw dust high into the atmosphere to destroy incoming warheads.  However, only limited information on the concept is available, precluding further analysis.  

A potential use for smaller, portable lasers is a dazzle system.  Smaller, lower-powered lasers are used to blind the attackers, allowing the defender to escape observation for a short time.  However, this is easily defeated by the use of multiple networked sensors, some of them on small, unmanned satellites that are essentially impossible to detect passively from the ground.  In some ways the best use of such lasers might be as a distraction from something important going on elsewhere.  Both optics and processing power make it impossible to monitor an entire hemisphere in high detail and in real time.

The last option the defender has is cannon of some kind.  When first proposed, this solution was questioned, as firing a cannon up a couple hundred kilometers runs into the problem of firing through the atmosphere.  It was later realized that Project HARP had done exactly that in the early 1960s.  Using a modified 16-inch gun, sub-caliber projectiles were fired to altitudes of up to 180 kilometers.  Obviously the HARP launcher would be unsuited to planetary defense roles, but it has been proved possible to fire ballistic projectiles from sea level (the HARP test site was on a beach in Bermuda) to significant altitudes.  However, these altitudes alone are insufficient to reach a target in most orbits.  The muzzle velocity for the high-altitude tests was approximately 2100 m/s.  This can be compared to 2500 m/s for the Navy’s railgun project.  For comparison, the early models of the SM-3 had a delta-V of about 4 km/s, while the later models are about 6 km/s.  If increases in velocity due to a switch to electromagnetic launching prove insufficient, then there is the option of using a rocket-boosted projectile.  This would require significantly less delta-V than a conventional rocket, preserving many of the advantages of the purely ballistic system.

Ballistic defense shares advantages and disadvantages with both lasers and missiles.  Any installation will almost certainly be fixed, as it requires a long barrel, though advanced coil/railguns might not have to be.  However, unlike lasers, a ballistic system does not by definition give away its position with each shot.  It is likely that the enemy could spot the muzzle flash if a chemical cannon is used, but railguns and coilguns do not have this problem.  The projectile would have to be guided, but it is possible to acceleration-harden a projectile, and aerodynamic effects could be used for minor course changes while low in the atmosphere, reducing required delta-V and preventing backtracking to the launch site.  At the same time, intense surveillance and intelligence efforts could probably locate the launch site eventually, and unlike lasers, all of the machinery must be close to the surface.

One advantage of cannons over missiles is that the projectile is much harder to detect during the climb.  The projectile lacks the exhaust signature of the missile, and is also smaller, both contributing to lower detection ranges and engagement times.  Also, it can be presumed that shells are cheaper than missiles. There have been some real-world investigations of electromagnetic suborbital launch systems, most notably by the ESA 2. Their investigation concluded that it would indeed be possible to use a railgun to replace sounding rockets, firing a 3 kg payload through a 22 m barrel at a velocity of 2,158 m/s.  The maximum altitude of the system was expected to be 120 km.  While this is a bit lower than would be necessary in a planetary-defense system, it does show the feasibility of such a system, and there is even the potential that it could be truck-mounted.  The largest problem with such a mounting would probably be power, although ultracapacitors could be used to store and transport power generated by deeply-buried reactors to the launch trucks.

In the absence of effective laser bombardment capability, aircraft become a viable defensive platform.  They are nearly impossible to target with kinetics, although some form of autonomous antiaircraft missile might be effective. The use of aircraft for planetary defense has some precedent.  The US ASM-135 ASAT missile was air launched, and had a ceiling of approximately 560 km.  The greatest advantage of air launch is that the launch platform can rapidly move to cover a vulnerable area.  The greatest disadvantage is the facilities required to base a conventional aircraft, which are immobile and vulnerable to bombardment.  VTOL aircraft would make this more practical, but the support facilities (and landed aircraft) would still be capable of being targeted.  However, it might be possible to use point defenses to secure an aircraft base, and deploy the aircraft as mobile missile platforms at need.

Lasers could also be mounted on aircraft, much like the YAL-1.  Aerodynamic limitations on the size of the mirror make it doubtful that an aircraft could successfully duel a spacecraft, and it is hard to see a set of technical assumptions under which aircraft-mounted lasers are practical but spacecraft-mounted ones are not.  Among other things, the physical environment of an aircraft is rather less well-suited to precise control of a laser than is a properly-designed spacecraft.  The aerodynamic forces on the aircraft will tend to produce vibration, which is undesirable when using lasers, and absent in spacecraft.  Crew, fluids, and thrust will also contribute, and are likely to be larger in magnitude than those found on spacecraft.  The atmosphere does provide a slight advantage in terms of cooling, and the fact that an aircraft can be presumed to be operating near a base increases the practicality of chemical lasers.  On the other hand, aircraft can successfully use clouds to protect themselves against lasers, which require gigawatt levels of power to burn through fast enough to track an aircraft.  

        While not technically surface defenses in the conventional sense, fortifications on moons could be vital for planetary defense.  Luna is a bit far out from earth for it to make a really effective fortress, but Phobos and Deimos would make excellent bases for large lasers.  The mass of the moon gives lots of places to dump vibration and heat to, and Phobos orbits in 7 hours 40 minutes, while Deimos takes 30.3 hours.  Even Luna could be strategically important, depending on the scenario.  Ignoring possible infrastructure present on Luna that would make it worth defending in its own right, there are several reasons that a defender would desire to deny it to an attacker.

        The most likely reason to land on Luna would be remass, although the practicality of that depends on the remass used by the fleet.  That in turn depends on the type of thruster used.  The standard cases used throughout this paper are chemfuel, nuclear-thermal, and electric of some kind.  Availability of remass for chemfuel and nuclear-thermal engines obviously depends upon the type of remass.  Some chemful mixtures, like aluminum-oxygen, are readily available anywhere on the lunar surface.  Others require much scarcer and more valuable elements, particularly hydrogen.  While the LCROSS mission did confirm the presence of large amounts of water at the poles, this water is likely to be too valuable for life-support purposes to be used as remass feedstock during normal times.  A potential attacker, however, might not care.  An NTR can theoretically use just about anything as remass, with exhaust velocity varying based on temperature, it is incredibly difficult to build one that will run with both oxidizing remass, such as oxygen, carbon dioxide and water, and reducing remass, such as hydrogen, ammonia, and methane (See Section 14 for more details on this).  Of these, only oxygen is truly readily available from lunar sources.  While there is water, the quantity is limited enough that using it for remass is questionable.  Also, the high molecular mass of the water makes it a less-than-ideal candidate for NTR usage.

        Electric thrusters are less likely to be able to get remass from Lunar sources (due to lack of information about both thruster propellants and body composition, the author refuses to speculate about other celestial bodies).  On the other hand, electric thrusters have much higher exhaust velocities, so less remass in total is required for a campaign.  In fact, the availability of a given remass is likely to play a significant factor in its selection for use on a vessel.  Most modern Hall Thrusters and other ion thrusters use Xenon for remass.  While Xenon is basically ideal for use as remass, it is far too rare to support the level of interplanetary trade that would be a prerequisite for any sort of serious war.  Krypton is the next best choice, but it is also too rare.  Argon is less effective, but probably the best among the noble gasses from an operational and engineering standpoint.  Some early ion thrusters were tested with Cadmium and Mercury, but both of these have had serious operational issues during tests, and are not notably abundant on or off Earth.  Possibly the best option is colloidal thrusters.  These use some form of hydrocarbon fuel, which has the advantage of being no less abundant than the other options throughout the solar system, and significantly more abundant on Earth.  However, the technical advantages of one of the other designs might well outweigh the logistical ones of the colloidal thruster, and the author does not know enough about the issue to be sure one way or the other.


1 Seapower and Space by Norman Friedman provided most of the information on attempts to detect submarines from space, along with information on the importance of satellite communications. It also pointed out that some stories of US nonacoustic detection might have been the result of deceptions intended to trick the Soviets into spending money in an attempt to match them."

2 Electromagnetic Railgun Technology for the Deployment of Small Sub-Orbital Payloads.

by Byron Coffey (2016)
ANTI-ORBIT LASER SUBMARINES

Laser-equipped nuclear-powered submarines are the perfect last line of defense against an attacking force in orbit.

The situation

You don't win every fight. Eventually, there will come a time in space warfare where a fleet of space warships has defeated all your mobile forces and your immobile defenses. They will bear down on you from above with lasers, missiles and kinetic projectiles and you will have to find a way to prevent their forcing of an unconditional surrender.

We will refer to the opponents as the 'attackers' and to you as the 'defenders'. The first step to devising an effective defense is to understand the situation.

So what is the situation?

An attacking warship will start out in high orbit. This is an altitude of 2000km or above. Whether it has just arrived from an interplanetary voyage or has recently destroyed your remaining warships, it will go to high orbit to maximize the effectiveness of its space superiority. Space superiority, borrowing from the term 'air superiority', is when a force has complete dominance over all the orbits around a planet. No space-borne forces can oppose this superiority and no reserve forces can challenge them without being quickly destroyed.

What does losing space superiority mean for defenders?

The most important consequence is that enemy warships have free reign to change orbits, maneuver into favorable positions and receive re-supplies. Their mobility is unconstrained.

Attackers in high orbit can make optimal use of their laser weaponry. They can get clear lines of sight onto any spot on the surface, and the long distances between objects forces travel times to length with the secondary effect of giving lasers plenty of time to shoot down targets. Laser effectiveness is generally dependent on how far they are from a target and how much 'dwell time' a beam can spend on a target.

De-orbiting objects from high altitude is inexpensive in terms of deltaV. This works in favour of missiles sent down from orbit by allowing them to use very little propellant to strike ground targets, which makes them lightweight and cheap to send by the hundreds. Additionally, falling towards Earth gives them a big boost to the velocities they achieve before impact.

The same applies to kinetic projectiles, a fact applied in the Rods From God concept of orbital bombardment.

Retaliating

So you want to shoot back at the attackers.

Missiles can do the job. They are currently our only method of delivering weapons into orbital space. Something like an ICBM with an additional stage can reach LEO. Reaching higher orbits will require either a very large rocket, a high Isp engine for the upper stage or a launch system such a laser launch or ram accelerator.

However, each of these solutions have major issues when trying to shoot down an opponent in high orbit.

Large rockets are easy to target and shoot down. A chemical-propellant rocket that needs to minimize its dry mass to achieve the necessary deltaV capacity will have very good acceleration but will end up being very fragile. Nuclear-thermal or nuclear-powered rockets can be much smaller and more durable, but getting sufficient acceleration out of them implies a very high power requirement, which might make them very expensive to throw at the enemy.

Regular launches take tens of minutes and cannot be disguised from the attackers. Shortening this window of vulnerability can be done by using a launch system that powers the rocket or accelerates it externally. However, the infrastructure for the launch systems will in turn become a priority target for the attackers. Massive, hard to hide and immobile, they will receive a lot of firepower. Some launch systems are practically impossible to shield from damage, such as a laser launch system that needs thousands of exposed laser optics, and others reveal their positions as soon as they fire a rocket. Building underground is also a very expensive endeavour when considering that all the work can be undone by a single 'bunker buster'-type weapon.

The logistics of launching missiles against attackers sitting in orbit works against the defenders. The attackers can de-orbit a missile by expending only a few tens to hundreds of meters per second of deltaV. A defender must equip each missile with tens of thousands of meters per second of deltaV. It might be easier to build more missiles and create rocket fuels on the ground at the start of the war, but after an orbital bombardment campaign by attackers with space superiority, it is unlikely to be the case.

Kinetics that can be shot all the way to high orbit need to handle hundreds to thousands of Gs of acceleration, traverse the lower atmosphere at dozens of kilometers per second, survive laser fire for several minutes with minimal capacity to dodge and take out a target with a very short window of interception. This is a tall order!

So, what are the defender's options?

They need to retaliate with something that cannot be shot down, from a platform that can avoid counter-fire and can maintain functionality after infrastructure and services have been disabled world-wide.

One option that fits the bill is laser submarines.

Lasers cannot be shot down and hit their target instantly. They can be used so long as electrical power is supplied. Submarines operate underwater, an environment that can hide them until they surface and protects them from high-velocity projectiles and lasers while submerged. The can protect themselves this way for months on end, and if they employ the same life support systems as on spaceships, then it can add up to years.

For the same reason that today's submarine fleets are considered an unbeatable means of retaliating against a foe after nuclear armageddon has wiped out the homeland, laser submarines will be able to operate and remain dangerous even after orbital attacks destroy all support infrastructure.

Let us now look at how a submarine can be used to retaliate against attackers in orbit.

The Challenges

Submarines are already equipped with a high electrical power generation. Large modern nuclear submarines are already able to produce over 100MW for years on end. In a futuristic setting with common space travel and space wars, power generation technology developed for interplanetary travel will allow submarines to produce gigawatts or more.

The most likely generators for space travel will be nuclear due to their high power density. The biggest limitation to generating power from nuclear reactors is waste heat capacity: It is easy to heat up the reactor core but much harder to remove the heat. Submarines will have an entire ocean as a heatsink so will be able to produce more watts compared to a spacecraft with a reactor of the same mass and volume.

All of this electrical power can be used to power a laser generator.

Three elements determine a laser's effectiveness: wavelength, radius of focusing optics and beam power.

We have already determined that laser submarines will likely be able to produce more electrical power than a similar laser space warship, so laser submarines will also have the advantage in beam power.

The radius of the focusing optics will depend on the specific arrangement of the laser weapon's components and how they are deployed. We will look into the possible designs down below.

The wavelength however is not a variable laser designs have much control over. Submarines operate in an aquatic environment, on top of which is a hundred kilometers of Earth's atmosphere. At the interface of the ocean's surface is sea mist and suspended droplets of water in fog or clouds. The ocean's surface is not flat either, with waves of a few centimeters to a few hundred meters rolling over it endlessly. A beam emitted by a submarine will have to penetrate all of this environment and still travel the hundreds of thousands of kilometers' distance separating it from a target in high orbit.

The optical properties of water are therefore the determinant factor for which wavelengths the laser should produce.

Here is the absorption spectrum of water:

The lower the 'Relative Absorption value', the less the wavelength's energy is absorbed. We can clearly see that the lowest values are for the 'optical window' that corresponds to the 400-700nm visual spectrum. The highest absorption is for 100nm ultraviolet wavelengths and 3000nm infrared wavelengths.

Here is the absorption spectrum for our atmosphere:

The atmospheric attenuation of electromagnetic radiation has similar features to that of water: short wavelengths such as X-rays cannot go through while long wavelengths such as radio penetrate easily.

It might be easier to consider the laser beam as being fired from space and coming down to the surface.

A 100nm ultraviolet laser beam will traverse the vacuum of space with ease, but will stop short of reaching the upper atmosphere. A 400nm blue laser will go through the atmosphere and through 460 meters of water before being reduced to less than 1% of its initial power. A 1000nm infrared laser will lose 20% of its power to the atmosphere and be completely absorbed by half a meter of water. A 100m radio wavelength just bounces off the ionosphere.

While shorter wavelengths are preferred for laser weapons, as they allow a beam to be focused to destructive intensities over longer distances, a laser submarine should use 400nm wavelength lasers to penetrate water and the atmosphere without losing a lot of beam power.

The equation for how much of a beam's energy is retained after traversing a medium is given by:

Percentage transmitted: e^( -1 * Attenuation coefficient * Depth) * 100

The attenuation coefficient is usually given in cm^-1, so the depth should be converted into cm units.

For example, near-infrared light at 800nm wavelength has an attenuation coefficient of 0.01cm^-1. We want to know what percent of a near-infrared laser's energy remains after passing through one meter of water.

One meter equals 100 cm. Per our equation, we find the percentage to be approximately e^(-0.01*100)*100: 36.8%. Just over a third of the beam gets through.

Here is a table of values for how much beam power is lost if the blue wavelength laser submarine fires its weapon at different depths, using an attenuation coefficient of 0.0001cm^-1:

We see that to maintain a good percentage of laser power getting through the water, a laser submarine would have to fire at rather low depths. According the the table above, a 10 meters depth using blue laser light looks like a good compromise: deep enough to escape orbital surveys and strikes, with at least 90% of the laser power going through.

So is a laser being fired at 10 meters depth a good idea?

The table gives an incomplete picture. While laser power being absorbed is an important factor to consider, there is a large number of other elements that affect how effective a laser is. One such element is thermal blooming. That 90% power transmission rate implies that 10% of the laser power is absorbed and goes into heating the water. If the laser power is rated in megawatts, the heat absorbed by the water becomes significant. Hot water has different optical properties compared to colder water - it will work as a lens in reverse, effectively de-focusing the laser.

Another significant issue is the water/gas interface. When light travels between two mediums of significantly different density, like seawater and atmospheric gasses, it is bent by refraction. Even worse, the sea's surface is constantly disturbed by waves, tides and other movements. Instead of a smooth surface, which angling the laser can compensate for, it is continuously changing and bending light in different and hard to predict direction. Here is a familiar example of the effect:

This effect is familiar to astronomers trying to gaze at stars through the moving atmosphere, and adaptive optics are used to compensate for the deviations in light traversing the atmosphere.

Adaptive optics cannot be employed as effectively when used underwater. While the atmosphere's movements are already difficult to detect and correct, trying to effectively measure how light moves through two mediums with a complex and moving interface is much harder. Guide lasers are used for measurement, with the light reflecting off the ionosphere creating an artificial 'guide star' for astronomers to calibrate their instruments. A guide laser placed underwater would submit to the same chaotic disturbances as the weapon laser and would be unusable. They would also have to work much harder. Refraction means that inaccuracies are multiplied once they pass through the water/air interface.

Finally, there's the problem of reflection. While water is decently able to let higher wavelength visible light penetrate, the massive difference in density between the water and the air (x1000) above it means that it is a good reflector. Laser light would travel from the submarine to the water/air interface, and just be bounced back below the surface. For sea water, less than 6% of the laser light would be reflected at angles below 30 degrees.

While the above table might not give any large figures, remember that the angle is measured against the rippling, swelling and rolling waves. A nominal angle of 10 degrees against the water's surface might transition between -20 and 100 degrees as a wave moves over a laser. This is the difference between 3% and 45% of the laser not going through the ocean's surface.

The principal advantage of staying underwater is that the submarine will be protected from high velocity strikes and retaliatory laser fire. However, if it cannot return fire from this position, then it cannot serve as a perfect last line of defense.

The Solutions

So, based on the previous section, we can affirm that attempting to shoot a laser while underwater provides unequalled benefits but also significant challenges.

We can either tackle the problems a laser submarine faces directly or attempt to circumvent them.

-Long wavelengths

Previously, we considered that blue wavelengths were optimal for shooting while underwater as they were absorbed the least. The reduced absorption would have allowed a submarine to transmit over 90% of the laser power to the ocean's surface from a depth of 10 meters. However, the distortion at the water/air interface rendered this option impractical.

How about using a wavelength that is less efficient at penetrating water, but is less affected by distortion?

Looking at the absorption spectrum of water, we notice that wavelengths longer than 100 micrometers are absorbed less and less as the wavelength increases. At 1m wavelength, the laser would traverse water as easily as blue light. This corresponds to a frequency of 300MHz. This is the radio band.

Not coincidentally, frequencies of lower than 300MHz are used to communicate with submarines. At 3 to 30kHz, which is wavelengths of 10 to 100km, can penetrate the seas to a depth of several hundred meters. Using even lower frequencies further increases penetration depth, but would require impractically large lens to focus onto a target in high orbit. Another factor working against longer wavelength radio is that the ionosphere can reflect signals back down to the surface at frequencies below 30MHz.

A 1m wavelength radio laser will be able to traverse the atmosphere mostly undisturbed and go through the ionosphere without refraction. The features of waves are too small to cause it to wobble chaotically at the sea/air interface. The beam would bend coming out of the sea, but it is a single predictable deviation that can be corrected.

A radio-wavelength coherent beam or 'raser' can be generated by a Free Electron laser or inductive output tubes with an efficiency exceeding 70%.

The advantages of a radio-based anti-orbital system is that it allows a submarine to fire upon targets while deep underwater. Even at 20 meters depth, the radio beam would transmit 82% of its power through water and lose less than 1% going through the atmosphere. It is much less affected by small waves and other turbulence in the water, and mostly immune to above-surface weather effects.

There are several downsides however. Such a large wavelength makes it impossible to focus the beam down to destructive intensities without a very large radio dish - this might get impractical when you also want the submarine to move quickly while underwater. Another issue is that the beam won't interact with the target in a consistent manner.

Lasers, for example, are absorbed by the outermost layers of the materials the target's surface is made of. The heating is concentrated in the 'skin' of the target. Sufficiently intense laser beams heat this skin layer to very high temperatures, causing the material to boil away or even explode.

Radio beams would use wavelengths a million times longer that do not interact with the target's materials at an atomic level. They are much more sensitive to the conductivity of the materials they are striking. Good conductors such as steel or aluminium efficiently reflect radio waves and are not heated. Good insulators such as ceramics or glass are mostly transparent to radio waves and do no absorb the beam's energy as it passes through them. Radio absorbing materials have to be neither good conductors or insulators, such as (sic)

This is bad news if the targets are space warships with an external metallic hull and an internal structure based on advanced carbon-composite and ceramic materials. Large propellant tanks will let the radio waves pass straight through. Small features of 10cm or smaller are completely invisible to the radio waves too.

However, there will still be ways to deal damage.

Openings in the metallic hull would allow radio waves to enter and then bounce around on the internal surface. Like a microwave oven, the trapped radiation will pass through radio transparent materials thousands to millions of times before being fully absorbed. A human is mostly composed of salted water. He or she would absorb about between 0.1 and 1% of a radio beam going through their body. If the radio beam stays inside a 10m diameter hull for just 76 microseconds, 2300 bounces are possible and the percentage of beam energy absorbed rises to 90%. When the beam power is measured in tens to hundreds of megawatts, this has dire consequences for a human crew.

Another effect is induced current. If even a few watts manage to circulate in microcircuitry, it is enough to short-circuit or even melt down computers, avionics and delicate sensors. RF Shock and Burn is a serious issue for electricians and engineers working on conductive structures near a high frequency radio source. At the power levels radio-laser submarines will pump into targets, induced current is enough to melt steel.

Modern submarines are not powerful enough to compensate for the diffraction of a 1m wavelength radio beam. With 100MW of available electrical power, 30% of which is lost in an inductive output tube and another 10% to seawater and atmospheric absorption, less than 63MW will reach space. Even the largest submarines, such as the Ohio-class SSBN, have a hull diameter (beam) of 13m. Mounting an internal dish to focus a radio beam up to this diameter will create a very low performance laser.

Targets at 10km distance will receive about 22W/m^2 - a great radio signal, but a terrible weapon. Targets in low orbit and high orbit will receive milliwatts of power.

What is needed is much more power and an externally mounted radio dish. Thankfully, a 300MHz beam can be focused by a dish with holes up to a tenth of the wavelength in size. A radio dish for this wavelength can is very lightweight and easily collapsible, with conductive spars spaced by 10cm lengths. The spars can be made hollow to have neutral bouyancy, allowing them to support themselves without many structural elements. At 10m depth and below, there are few disturbances in the surrounding water.

Dish diameters of 100 meters or more are envisageable, massing less than 1kg per m^2. Tension wires hold the shape and serve as the mechanisms for adaptive optics to act on the dish.

A group of submarines using space-grade nuclear reactors might be able to put together 500GW of power with a combined reactor mass of only 2500 tons. Between them, they can hold up a dish 1km in diameter, as follows:

This arrangement allows the submarines to focus a 315GW beam to an intensity of 67kW/m^2 at an altitude of 1000km. For low orbit targets, the intensity is 1.67MW/m^2. These intensities are far from enough to melt or physically damage the structure of a spaceship. However, the beam is large and entirely envelops the target. Any hole through a metallic exterior or any cavity lined by a radar reflector will turn the spaceship into a microwave oven receiving megawatts of heating over time. At high altitudes, the intensity is lower by the targets orbit much slower, giving the Rasar beam time to boil crews to death and melt components directly or indirectly.

-Interface lens

The biggest trouble with optical wavelengths is the chaotic distortions and reflections created by the sea/air interface. They would allow submarines to physically damage targets with relatively small lens and shoot on the move, but aiming though the interface seems impossible...

... unless an interface lens is used.

It is an optical array that floats on the ocean's surface, serving to handle the beam's transition from underwater to atmospheric mediums. Glass can be made to have a refractive index similar to that of water. A laser beam traversing a sea/glass interface would not suffer any distortion. This is the reason why some transparent objects disappear completely while underwater - our eyes cannot make out any distortions that reveal their presence.

The interface lens can also serve to focus the laser. It can be made much larger than whatever the submarine can carry, as it is not confined by hull dimensions or hydrodynamics.

One primary advantage of these floating structures is that they can be deployed before firing commences, and each is much cheaper than a submarine. When a target passes overhead in orbit, a laser submarine can rise to firing depth and start shooting. It only needs to equipment to focus the beam from the laser generator to the interface lens, a distance of ten meters or so. The floating lens receives the beam, corrects the angle and aims at the target overhead. If the target is not destroyed, it can trace the laser back to its origin and initiate a retaliatory strike.

An interface lens is not very mobile and needs to stay on the surface, so it cannot protect itself by diving. There is a good chance it will be destroyed... at which point the laser submarine switches to firing through another interface lens and so on.

Although the lens will have to be rather large and heavy to receive a laser beam from a wide variety of angles underwater, and re-focus it in a moving target hundreds of kilometers above, which makes it expensive, it must be considered as an expendable asset when compared to cost and size of a nuclear submarine. Also, the lens can be covered by an isothermal sheet and made out of materials transparent to radar, making it hard to detect from orbit until it starts firing.

Using a 10m diameter interface lens, even a modern submarine with 100MW of available output will be able to deal serious damage to targets in low orbit. About 40MW of the submarine's power will reach the target using a diode laser generator at 400nm wavelength, but at an intensity of 133GW/m^2 at 200km altitude. This is enough to rip through 14.8 meters (!) of aluminium per second, or even 6.5m/s of carbon armor. Any target caught by this beam for even a second will be cut in half. At 1000km, its performance is still a respectable 52mm/s through carbon.

More advanced submarines can get away with smaller lens that are harder to counter-attack and still deal devastating damage to high orbit targets. A 10GW laser beam focused through a 4m wide interface lens can blast away targets at a rate of 837mm/s at 1000km.

Disadvantages of this system is the cost of 'expendable' large adaptive mirrors and possibly the inability to use floating structures in severe storms with large waves rocking the optics.

-Towed Lens

This fixes the problem with floating optical arrays. The laser is focused by towed apparatus that can be held underwater until firing starts, and then moved around after an initial volley to avoid counter-fire.

The towed lens can be lighter and cheaper than a fully independent floating lens. Electrical power, computing operations and other functions can be provided by the submarine towing the lens, with only the actuators and suspension retained.

Lasers have been carried through optical fibres with nearly zero losses of beam energy over distance. This is because internal reflection of the beam is done at grazing angles within the optic fibre. In other words, laser beams of megawatts to gigawatts power levels can be transported by optic fibres without any significant losses and no special provisions against heating.

Optical fibres can carry a laser generated by a submarine to the towed lens, and they can run parallel to the load bearing cables attaching the lens to the submarine. This method of delivering the beam to the lens bypasses the losses and complications of having the beam penetrate several meters of water to reach the surface.

To these advantages come some downsides. The submarine becomes more vulnerable that if it relies upon fully independent floating lens. If an enemy target locates a floating lens, it might correctly assume that the much more valuable submarine is very close to the lens. When a target spaceship in orbit sends down counter-fire before the submarine is ready, the latter would be forced to cut loose the lens and dive... this breaks the optical fibre cable and renders the lens useless.

Tactics using towed lens might involve dragging along a fleet of lenses and rotating them to the surface and back. Longer fibre optic cables gives the submarine more freedom to move, while a mix of decoys and intermittent and random firing patterns reduces the disadvantages of the design.

-Optical phased array floater.

Do away with the submarine!

A specialized vehicle can be built solely for the purpose of hiding a laser weapon underwater and surfacing for short bursts of fire. Since this weapon only attacks from above the water and does not have to worry about hydrodynamics, nifty solutions such as an optical phased array can be used. The laser generator's size is equal to the lens diameter and if it received damage, it will only suffer reduced output.

The more delicate components such as the power generator can remain submerged, only transporting electricity to the phased array on the surface through cables. A reactor embedded in the sea floor can be a very difficult target to locate and destroy.

-Supercavitating platform.

If submarines have access to gigawatts of power, they can also use it for propulsion.

This level of power output can enable submarines to reach supersonic speeds through supercavitation through water. If they can rise to the surface, fire, dive and relocate in a matter of seconds, then they can evade counter-fire through sheer agility.

It might be best in this case to mount a set of optical phased array lasers tailored to trans-atmospheric wavelengths to be used once a submarine surfaces. Gigawatts of power means gigawatts of heating: the local atmosphere can be cleared of moisture and mist that distorts the beam most heavily.

A 1GW laser at 400nm focused by even a relatively small 4m diameter lens can blast past 23.7m/s of aluminium or 10.4m/s of carbon at 200km, and remains deadly at 1000km with 83mm/s of carbon penetration. This allows for short bursts of laser fire to take down any target.

Advanced techniques such as thermal lensing using the Kerr effect is being developed in programs such as the Laser Developed Atmospheric Lens (LDALs) by DARPA. LDALs can allow high-power submarines to extend their effective range to tens of thousands of kilometers while reducing the effectiveness of laser counter-fire.

Conclusion.

Lasers and underwater environments don't mix well, but there are many solutions to gain the protection a submarine enjoys while attacking instantly and repeatedly with direct energy weapons.

Once these solutions are applied, a defending planet with deep oceans can hope to maintain an effective last line of defense against invading spaceships.

From ANTI-ORBIT LASER SUBMARINES by Matter Beam (2017)
THROUGH STRUGGLE, THE STARS

One of Rand’s soldiers addressed him.

“I’m getting a yellow on Miss B*tch, Mirror 6,” said Private Tim Yancey. Miss B*tch was the affectionate name for one of Rand’s three cannons. (Alpha Dawg and California Girl were the others.) “Think it’s stuck, or at least moving slowly. Might be some gunk in the way.”

Some officers didn’t like to swear in front of their people. Rand was not one of those officers. When he was finished, he said, “All right, I’ll go look at it. Get Smith and Ekkers to meet me down there.”

Rand walked half a klick through an extinct underground lava tube to reach Miss B*tch, buried beneath 20 meters of earth to protect it from bombardment.

His laser cannon looked nothing like the compact guns mounted on warships; with the earth stripped away, the entire contraption would appear as a giant, overturned spider. The beams were generated in the spider’s head, powered by batteries that drew energy from a fission plant buried underneath Fort Patton. A rotating emitter fired the beam down the spider’s “legs,” eight long, hollow corridors that angled toward the surface. When the cannon was fired, the beam would be directed down a random tube.

Mirrors directed the beams at each turn; a final mirror, mounted on an armored cupola that rose above the surface, directed the beam toward any target in Sequoia’s sky. This last mirror was “deformable;” with every shot, thousands of tiny actuators inside the mirror would subtly alter its shape, preventing distortion from Kuan Yin’s atmosphere from defocusing Rand’s beam. (The level of distortion was gleaned from a second, low-power laser that fired from atop the cupola a fraction of a second before the primary blast.)

After a shot, the cupola would drop beneath the surface, and a camouflaged hatch would close above it, more or less concealing it, at least to a spaceship hundreds or thousands of klicks away.

The whack-a-mole rig was a design of necessity; ground-based laser cannon were too large and heavy to safely operate on a planet’s surface or in its atmosphere. A 480-megawatt laser capable of drilling a hole in a starship 5,000 klicks distant needed a lot of batteries, it was simply too big a target to mount on wheels or turbofans.


     One of the nice things about the artillery was you got the best telescopes. Rand had a terrific view of the battle, and early on, it seemed to be going well, despite China’s superior numbers. The Chinese ships had formed a two-dimensional diamond, with one flat face to the main body of the American squadron. The American commander had elected to split his fleet and was coming at the Chinese from two directions, about 90 degrees off from one another. He was gunning for the Han assault carriers, which were hanging well back from the battle. The Chinese responded by concentrating their fire on only one group of American ships, leaving a flank exposed.
     At least two small Han vessels had suffered catastrophic failures in their fusion candles; their explosions were visible to anyone looking up from Kuan Yin’s surface. At least one American destroyer was badly damaged, drifting away on a vector that would take it out of the battle.
     Then, all at once – it was impossible from Rand’s vantage to tell what exactly happened – the battle came apart for the Americans. The senior captain’s flagship, the Puerto Rico, vanished in a fusion-fueled fireball. The light cruiser Norfolk died moments later. The surviving American ships – two frigates and an escort – turned and fled for the only American keyhole (stargate) in the system. A final barrage of missiles aimed at the Han troopships was shot down, their destruction showing up as pinpoint flickers on Rand’s monitor. The Han fleet then quickly disposed of the American surveillance and communications satellites in all but the lowest orbits over the planet.
     Major Montaño was on the comms a few minutes later. “Space Force did what they could. We’re up next. The Han formation will be in range in four-zero minutes. Out.”
     Rand’s platoon was in four separate locations in the underground complex, one crew at each gun in addition to his command center staff. Rand could control all three lasers from here, but the teams were stationed near each cannon in case communications were cut, and to perform any repairs that might be needed during a battle.
     He switched over to his platoon’s network. Time to say something inspiring.
     “Space Force had its shot,” he said. “They made sure the battle was over our heads rather than the other side of the planet, so we owe them one for that. It will be our turn in a little more than half an hour. They’ll shoot at our guns first, so everybody get in your armor. Primary target is their assault carriers, secondary is their bombardment ships. And for god’s sake, protect your mirrors! Good luck. Time for the artillery to shine. Castillo out.”
     It actually took an hour; the Hans were careful in forming up for their bombardment runs on Sequoia. They could either bunch up their fleet and do a massive strike on the surface every three hours, or spread out and keep up continuous fire, never giving the Americans on the surface a breather.
     They chose to concentrate their force.
     “Han ships moving in range,” said the battalion sensor officer over the comms net.
     Half the Chinese ships, including the assault carriers, hung back above 10,000 kilometers. The rest moved to a 6,000-klick orbit and kept descending. At that range, the artillery’s firepower far exceeded that of the Hans; the Chinese needed to get closer to use their bombardment lasers effectively.
     “All guns, target Bandit-3 and fire at will,” Montaño transmitted. “Two second duration.” Bandit-3 was the Wuhan, a battlecruiser, likely the Chinese flagship. Rand relayed the command to his gun crews, heard acknowledgements from all four.
     Sixteen of the battalion’s 18 cannon fired (two had been down for service when the battle started); their invisible, infrared beams were joined by shots from the other laser cannon buried across the continent. Several had to burn through overhead clouds, and the thunder of scorched air rolled across the surface of Sequoia.
     Almost all of the beams struck the Wuhan in the nose; a few, betrayed by faults in their targeting software or mirror-control machinery, simply missed. The Wuhan was well-armored, but the beams drilled multiple holes in her. Giant sparks of plasma exploded outward from the point of impact; at the same time, a second set of sparks exploded on the ship’s starboard rear quarter – at least one laser had burned all the way through.
     Cheers resounded. One of Rand’s operators shouted over them.
     “Counterbattery fire coming in!” A nervous pause as weak beams played across the Sequoia, aiming for mirrors even as they descended beneath the surface. “All guns reporting nominal. No damage.”
     More cheers. Rand watched his screen as his guns cooled for the next shot. Ten seconds, and a second barrage punished the Wuhan again. One laser touched part of her cooling system; an explosion of superheated lithium punched outward through the hull. The ship’s nose looked like Swiss cheese. The ship tumbled end over end.
     A kill! We might actually win this, Rand thought. Somebody called out over the comms net that the ship was burning out of control and would likely break up in Kuan Yin’s atmosphere.
     Then, “Vampire! (military brevity code for "Hostile antiship missile") Radar shows multiple kinetics inbound to our position from orbit!”
     Montaño’s voice: “Target on the kinetics.”
     That’s their plan, Rand thought. They must have launched missiles from high up, and timed their assault so we’d have to deal with them. Their timing wasn’t perfect, or else we wouldn’t have nailed that battlecruiser as well as we did.
     Scores of missiles entered the atmosphere above Sequoia. Battle computers analyzed their trajectories and noted their likely targets: the spaceports, government offices, and the bases of the 33rd Brigade.
     The artillery made a good accounting of itself, wiping out most of the missiles high above the surface. Some debris rained to the planet below, crashing into houses and lighting vast fires. Three missiles got through and destroyed the remote railway junction connecting Cottonwood to the other cities on the continent.
     But the weapons had also provided the necessary cover for the Han fleet; its orbit took it to the far side of the planet, where the few surviving U.S. satellites spotted it lowering its altitude preparing for a bombardment pass.
     During the respite, Rand let his crews take breaks in turns, allowing them to stretch, go to the bathroom and score some food, but he did not rise from his seat, even as the Vampire call came yet again.
     The Hans had timed their second bombardment pass with another wave of descending missiles. The ships and missiles “rose” over the far side of Sequoia first, leaving Rand and his guns to wait until they were higher in his sky.
     Reports came in from the other side of the continent, and the news wasn’t good. The Hans now had a good track on the locations of the American artillery stations, and bombarded them relentlessly. Lasers pounded mirrors as soon as they rose from the ground; missiles with penetrators burrowed into surface, seeking and finding the cannons emitters and batteries. The fire from the surface of Sequoia slackened …
     … and suddenly Rand’s unit was targeted. The lasers came first, burning across the landscape, aiming at known points where mirrors had surfaced thus far in the battle. Several bombardment beams found their targets, digging through the cupola armor and wrecking the mirrors below. The battalion’s radar also took a hit; computer-run telescopes would have to manage targeting going forward. Miss B*tch lost three mirrors; California Girl lost two.
     Rand, angry, tapped his handheld, called Alpha Dawg’s commander. “I’m taking your gun off defensive fire,” he told the junior sergeant. “I want to kill some Hans.” He looked over the list of ships in his sky and targeted a vulnerable-looking frigate that was contributing to the fire above him.
     The gun got two one-second shots off in thirty seconds. Laser fire from the frigate stopped, but two other ships targeted Alpha Dawg. The gun lost half its mirrors in a minute.
     Rand’s boss, Captain Groves, was in another underground control center 20 klicks away, but her shout came through crystal clear over the comms system.
     “Castillo, put your guns back on the designated target matrix, now! And don’t deviate from it again!”
     Rand knew better than to argue. He’d gotten his lick in …
     A corner of his screen started flashing. A moment later, the battery targeting officer called him.
     “Rand, several inbound kinetics are changing course toward your location. I think you p*ssed them off.”
     Groves’ voice, low with frustration: “Updating target priority matrix.”
     The battery’s remaining lasers targeted the inbound missiles, but it was clear that the defenses were wearing down. Several missiles dropped decoys, further complicating the defenders’ efforts. Chinese lasers took out more and more mirrors; missiles were still dying, but they were getting closer to the surface before being shot down. After a few minutes, California Girl was completely offline, her octet of mirrors shattered. Alpha Dawg had three mirrors left; Miss B*tch had two – Rand was bizarrely pleased to note that the mirror at the just-repaired hatch was among them. Most of the other gun platoons were in the same shape or worse.
     Rand hoped the guns would hold on until the Han fleet set over the planet; then his crews would have time to replace some of the damaged mirrors.
     Then the call came in: “More missiles inbound!”
     There weren’t enough lasers to stop them all.
     A penetrator warhead slammed into the ground just above Alpha Dawg, which was about 50 meters from Rand’s control room. It dug into the earth below. The earth collapsed into the cannon’s emitter, burying it under tons of dirt and rock.
     A roar filled Rand’s ears. In the control room, computer screens died, and everything went dark, save for the small blue glow from self-powered handhelds. A cloud of dust washed over him.

From THROUGH STRUGGLE, THE STARS by John J. Lumpkin

Atomic Rockets notices

This week's featured addition is BDM EXPLORATION CARRIER

This week's featured addition is METASTABLE SUPER-EXPLOSIVES

This week's featured addition is ASAPH-1 MISSION TO PHOBOS

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