A human or alien civilization could be at the same technology level as our human protagonists from the Terran empire. But tech levels are the clunky one-dimensional way of measuring the relative technological advancement of a given culture. All the cool science fiction writers are using Tech Trees in their novels.
Tech trees give far more flavor to various cultures. Culture Alfa may have advanced relatively far down the subatomic physics branch of the tree, but be relatively ignorant of the organic chemistry branch. For Culture Bravo the situation may be the reverse. Compare this to the dull situation where according to tech levels, both Alfa and Bravo are exactly the same at Tech Level Six.
In other words, different cultures emphasize different branches of the tech tree. In contemporary culture here on Terra the current state of nuclear physics and computer science is pretty darn advanced, but the state of sociology and psychology is woefully primitive.
In fact, some cultures might be altogether unaware of the existance of certain branches.
A popular trend in science fiction (and sometimes in the real world) are underlying philosophies and ideologies setting the direction of technological advance. For example, from the real world we have the debate over fossil-fuel energy as opposed to renewable energy.
Since science fiction is literature, and commonly has a theme of conflict, there are often two major ideologies. And they don't like each other very much.
Bruce Sterling (perhaps inspired by Freeman Dyson's essay "The Greening of the Galaxy" found in his book Disturbing the Universe) created his Shaper/Mechanist universe. Both factions are posthuman civilizations. The Shapers direction of technology is advancement by manipulating the human body: genentic engineering and psychological training. Mechanists on the other hand direct their technology along the lines of cybernetic implants, computer software, drugs, and permanently implanted space suits. The third faction is the traditionalists who like human bodies the way they are right now, thank you very much, and do not like either the Shapers nor the Mechanists.
In Alastair Reynolds' Revelation Space universe most of the factions are reasonably human, except for the Conjoiners. They use technology to augmenting human consciousness, creating group minds and amplyfing intelligence. They actually created a mini-Singularity called the Transenlightenment. Of course this triggered a war with the other more conventional-human factions. The Conjoiners eventually lost the war, fled the solar system, and colonized other systems.
Science fiction writers tend to equip their aliens with organic technology just to make them unique and different, not because it makes any sense. Unfortunately this has been used so often that it has its own entry in TV Tropes. So much for "unique and different"
About the only use case where organic technology makes sense is for use by an alien species that lives underwater. It is real hard to smelt iron when fire doesn't burn underwater, and equally hard to use electronics when the blasted seawater keeps short-circuiting everything. But existing aquatic creatures can be genetically engineered to be tools or electronics, and work just fine underwater.
The other advantage associated with organic tech is that broken machines can try to heal themselves. This generally appears in science fiction in the form of a organic living starship recovering from damage inflicted by meteors or hostile weapons fire.
Thirdly, instead of manufacturing tools and machines, with organic tech you might be able to breed them.
RocketCat points out some of the draw-backs.
- The Greening of the Galaxy
- Pentapods from 2300AD RPG: "an amphibious species with a preference for aquatic environments, with a biotechnological technical infrastructure (including starships that are massive living beings)". Their equipment works very well, but is usually damp and has to be regularly given food and water.
- Tyranids from the Warhammer 40,000 universe. Imagine if the Xenomorphs from the Alien movies had genetically engineered themselves to produce living starships, combat creatures, and weapons. Tyranid organic technology has the classic "warm, moist, skooshy and drips goo everywhere" along with a side order of "far too many sharp pointy bits."
- Z'ensam from Rogue Powers by Roger MacBride Allen. Though the Z'ensam aliens appear to have only a medieval level of technology, that is only with conventional technology. Their covert organic technology is terrifyingly powerful. You see, the species somehow actually has the innate power of Lamarckism. Changes in an individual Z'ensam will be passed on genetically to its offspring. Including surgical changes. In other words they discovered genetic engineering before they discovered how to use fire or chip flint. The bad guys think that the Z'ensam are just lizard cave-men who are good at biological warfare, so they contract them to make some combat germs. The bad guys find out too late that they are at the Z'ensam's mercy.
- Tnuctip from Larry Niven's Known Space series. These were an alien species, enslaved by the Thrints. Covertly they used genetic engineering to create things that were apparently of value to their masters, but turned out to be harmful. Items included Stage Trees (trees that created a core of rocket fuel as they grew, to make cheap rocket boosters), Sunflowers (tall plants whose silver parabolic flowers can focus sunlight into deadly beams, used to protect Thrint households), and Bandersnatchi (thought to be non-sentient food beasts, they were actually both sentient and immune to the Thrint telepathic slavery)
- Living Spaceships. Another well-used troup
- The Crucible of Time by John Brunner. The pneumatic aliens of the saga use bio-engineered animals for most of their technological history. But they are not above using metal-based tech when they start building rocket ships.
- Lords of the Psychon by Daniel Galouye. Aliens who are energy creatures conquer Terra. Their technology is based on a weird energy called "psychon plasma", which can only be controlled by thought. The aliens periodically hunt and kill humans in order to harvest bits of their brain. So if the aliens want a support truss for a machine, they take a bit of still-living human brain tissue, force it to constantantly think of being a support truss, and link it to a measure of psychon plasma. Instant support truss.
- Gaean series by John Varley. The titanic ring-like structures around Saturn appear to be space habitats. They are, but they are made from organic-tech, not metal-tech. And they are intelligent too.
- Amnion from The Gap Cycle by Stephen Donaldson. All their tools and artifacts are manufactured by genetically engineered organisms. This is one of the few science fiction stories where it is made clear that organic tech is inferior to human technology.
- Yilanè from West of Eden by Harry Harrison. Everything they use on a daily basis is a genetically modified creature.
- Davey Jones' Ambassador by Raymond Gallun. The squid-people who live on the ocean floor are forced to use organic aquatic tech for the usual reasons. They bio-engineer organisms to serve as everything from transportation to weapons to architectural elements, and produce whatever substances they need as secretions from these creatures.
- Early Bird by Theodore R. Cogswell and Theodore L. Thomas.
On a very weird planet, the local apex predator has internal organic weapons: lasers, missiles, particle beams, that sort of thing. Momma creature lays an egg (about the size of an aircraft hangar) then broadcasts on the mating frequency. All male creatures in range elevate their artillery and fire off a volley of sub-orbital spermatozoon missles, targeting the egg. Momma creature sets up an anti-missile barrage, because she only wants the missile with the highest combat skill to survive and fertilize her egg.
Our hero is in a fighter spacecraft, at war with some hostile aliens. He passes nearby the egg. Momma creature is astonished at the combat power of the space fighter. She uses a tractor-beam to grab the fighter and causes it to crash into her egg and fertilize it.
The egg hatchs, and our hero wakes to find that his space fighter has been hybridized into the ultimate war machine, using organic tech. He finds the rest of his fighter wing and has them fertilize other eggs. The hybrid fighters then fly off and proceed to kick the living snot out of the entire hostile alien armada.
- The Flintstones. Any machine not made out of rock is made out of a re-purposed dinosaur
Spacecraft that are partially or totally composed of a living creature are a neat-oh, keen-oh, golly-gee-whiz science fiction idea that apparently was invented by Robert Sheckley in 1953. The concept turns up occasionally when the author wants to throw in something weird to remind their readers that they ain't in Kansas any more. Justifications include:
- The organic ship can be "spawned" as a tiny sprat and automatically grown to full size by feeding it, instead of requiring a spacecraft graving dock in a shipyard and large numbers of skilled workers to build the blasted thing
- Component breakage and combat damage can be "healed" instead of requiring the ship to be towed to a repair yard
- The author insists for handwaving reasons that organic ships are somehow much better than conventional dead metal ships, even though that does not make logical sense.
RocketCat says if you want something organic you can go look in his litter box.
Another common type of organic spacecraft is a Space Tree equipped with an engine. Those are listed here because most space tree are stationary.
Most science fiction authors and many real scientists are of the opinion that any alien race that live underwater are going to have a real problem trying to advance out of the stone age and develop science. All that water is a problem. For one thing the water is most counter-productive if one is trying to discover fire and all the technology it enables.
The standard science fiction dodge is to postulate the aquatic aliens using organic technology. Aquatic aliens do not need to figure out how to make fire burn underwater in order to smelt steel, not if they can genetically engineer the local equivalent of whales into living submarines. Living things can be created without fire, and water is their natural element.
In lieu of aquatic aliens using organic technology, the fallback science fiction dodge is that some air-breathing aliens (like humans) visit the aquatic aliens and give (or sell) them enough air-based tech so that they can bootstrap themselves. Tech like remote control robot drones that can be use to mine metals and build factories on islands, while the aquatic aliens can control the drones from the comfort of adjacent lagoons. This same dodge is often used to give high technology to aliens living in the atmospheres of gas giant planets. Such aliens are not handicapped by living in water, but they do have a problem with a lack of land area to lay their tools and equipment on.
The other major drawback that science fiction authors love to harp on is that aquatic spacecraft life-support systems are difficult. You see, with gas breathing mix like we humans use, the gas can be compressed into tanks so it takes up less room. Sadly, water is almost totally uncompressible. The aquatic breathing mix tanks are going to be huge.
For computers and digital devices, slebetman and Journeyman Geek are of the opinion that the logical thing for an aquatic race to do is use Fluidics aka "fluid logic". This uses pneumatics and hydraulics instead of electronics to do analog and digital operations. Note that such devices are more or less immune to electromagnetic interference, ionizing radiation, and EMP; unlike electronic devices. Fluidics also will not suffer catastrophic electrical short circuits if immersed in sea water, also unlike electronic devices.
One of the main draw-backs of fluidic computers is the maximum clock frequency is only a tens of kilohertz, as compared to the gigahertz typical to computers such as the one you are using to read this website. This means an aquatic race using fluidics would try the parallel, multi-core approach much sooner than we did.
The second-most serious drawback is fluidics cannot be miniaturized anywhere near the scale of electronics. At a rough guess a halfway powerful computer will fill a room, much like old vacuum tube computers.
After the limits of fluidic computing were reached, it would be relatively easy to make the conceptual leap to optical computing.
Basically this is technology that uses no electricity or electronics (digital or otherwise). There are some applications where this is an advantage. And I am not really talking about SteamPunk, though they do bear a superficial resemblance to each other.
(ed note: understand that it can be a full-blown self-replicating machine, with all that implies)
Many interesting ideas have been conceived for building space-based infrastructure in cislunar space. From O’Neill’s space colonies, to solar power satellite farms, and even prospecting retrieved near earth asteroids. In all the scenarios, one thing remained fixed — the need for space resources at the outpost. To satisfy this need, O’Neill suggested an electromagnetic railgun to deliver resources from the lunar surface, while NASA’s Asteroid Redirect Mission called for a solar electric tug to deliver asteroid materials from interplanetary space. At Made In Space, we propose an entirely new concept. One which is scalable, cost effective, and ensures that the abundant material wealth of the inner solar system becomes readily available to humankind in a nearly automated fashion. We propose the RAMA architecture, which turns asteroids into self-contained spacecraft capable of moving themselves back to cislunar space. The RAMA architecture is just as capable of transporting conventional sized asteroids on the 10m length scale as transporting asteroids 100m or larger, making it the most versatile asteroid retrieval architecture in terms of retrieved-mass capability.
This report describes the results of the Phase I study funded by the NASA NIAC program for Made In Space to establish the concept feasibility of using space manufacturing to convert asteroids into autonomous, mechanical spacecraft. Project RAMA, Reconstituting Asteroids into Mechanical Automata, is designed to leverage the future advances of additive manufacturing (AM), in-situ resource utilization (ISRU) and in-situ manufacturing (ISM) to realize enormous efficiencies in repeated asteroid redirect missions. A team of engineers at Made In Space performed the study work with consultation from the asteroid mining industry, academia, and NASA.
Previous studies for asteroid retrieval have been constrained to studying only asteroids that are both large enough to be discovered, and small enough to be captured and transported using Earth-launched propulsion technology. Project RAMA is not forced into this constraint. The mission concept studied involved transporting a much larger ~50m asteroid to cislunar space. Demonstration of transport of a 50mclass asteroid has several groundbreaking advantages. First, the returned material is of an industrial, rather than just scientific, quantity (>10,000 tonnes vs ~10s of tonnes). Second, the “useless” material in the asteroid is gathered and expended as part of the asteroid’s propulsion system, allowing the returned asteroid to be considerably “purer” than a conventional asteroid retrieval mission. Third, the infrastructure used to convert and return the asteroid is reusable, and capable of continually returning asteroids to cislunar space.
The RAMA architecture, as described in this report, was shown to be cross cutting through the NASA technology roadmap as well as the future goals of the greater aerospace industry. During the course of the study it was found that the RAMA technology path aligns with over twelve NASA roadmap missions across seven NASA technology areas, and has the opportunity to substantially improve the affordability and scalability of both the Human Exploration and Operations Mission Directorate (HEOMD) and the Science Mission Directorate (SMD) stated goals.
ACRONYM LIST ABS Acrylonitrile Butadiene Styrene ADCS Attitude Determination and Control System AGI Artificial General Intelligence AM Additive Manufacturing AMF Additive Manufacturing Facility AREE Automation Rover for Extreme Environments ARM Asteroid Redirect Mission AU Astronomical Unit (Earth-Sun Distance) C&DH Command and Data Handling DMLS Direct Metal Laser Sintering DRM Design Reference Mission EBM Electron Beam Welding FBD Functional Block Diagram FSW Friction Stir Welding GMAT General Mission Analysis Tool GMAW Gas Metal Arc Welding GNC Guidance Navigation and Control GTAW Gas Tungsten Arc Welding IOT Internet of Things ISM In-Situ Manufacturing ISS International Space Station Isp Specific Impulse ISRU In-Situ Resource Utilization JPL Jet Propulsion Laboratory JSC Johnson Space Center KSC Kennedy Space Center LBM Laser Beam Welding LD Lunar Distance LENS Laser Engineered Net Shaping LIDAR Laser Imaging Detection And Ranging LOX-H2 Liquid Oxygen + Liquid Hydrogen MT Metric Tonne NEO Near Earth Object NEA Near Earth Asteroid NHATS Near Earth Object Human Spaceflight Accessible Targets Study NIAC NASA Innovative Advanced Concepts PMF Propellant Mass Fraction RAMA Reconstituting Asteroids into Mechanical Automata ROI Return on Investment RTG Radioisotope Thermoelectric Generator SBDB Small Body Database SEP Solar Electric Propulsion SOA State of the Art TCS Thermal Control System TRL Technology Readiness Level TTL Transistor-Transistor Logic μg Microgravity ΔV Change in Velocity
1.3 THE RAMA SOLUTION
Made In Space developed RAMA to solve the problem of transporting large supplies of asteroid resources from their natural orbits to orbits of greater use in cislunar space. RAMA is a revolutionary, mass-minimalist approach to explore and exploit space resources. The concept is based on a “Seed Craft”; a spacecraft which contains technically sophisticated ISRU, Additive Manufacturing and robotic capabilities. The Seed Craft uses these capabilities to convert the available materials of an asteroids into spacecraft subsystems including propulsion, energy storage and guidance systems. The asteroid (now a spacecraft in its own right) is able to autonomously carry out a basic mission; such as relocation for easier future rendezvous, or to divert to a more useful location empty space. Meanwhile, the Seed Craft which initiated the transformation is free to plot a course to the next asteroid, repeating the RAMA process indefinitely.
Designing RAMA and the Seed Craft is a project of advanced automation. To accomplish a task as difficult as converting an asteroid into a spacecraft, the Seed Craft must be outfitted with sophisticated robotic manufacturing and material processing technologies. Such technologies do not yet exist, but we anticipate ten to twenty years from now they will be developed to a technology readiness level high enough for the initial RAMA missions. With computation capabilities that rival todays super computers, the Seed Craft would be able to plan an entire mission on its own, adapting and building new equipment to accommodate the unique conditions it encounters on each asteroid.
We can be hopeful for the future of these technologies because many are currently in active development in other industries, with large growth potential here on Earth. Alphabet, the parent company of Google, has a fleet of self-driving automobiles on the roads of Silicon Valley where Made In Space is head quartered. These vehicles adopt low cost LIDAR and radar sensors married with sophisticated feedback, machine learning, and other software tools to provide a level of driverless autonomy that meets the high standards of our nation’s roadways. Made In Space is currently working on the space manufacturing technologies that, among other capabilities, will enable the RAMA mission. Vacuum based additive manufacturing of polymers, metals, and composites in microgravity; large-scale structure manufacturing/assembly in space, and advanced robotics are all under currently funded programs at Made In Space.
Compared to the state-of-the-art (SOA) Asteroid Redirect Mission architecture, RAMA simply does more for less. Because RAMA makes use of materials found at the asteroid for mass intensive tasks (like providing reaction mass for the propulsion systems), a greater mass can be returned for equivalent mass launched. This is even more true if the RAMA Seed Craft can redirect multiple asteroids in a single mission, either by using the asteroid’s propulsive capabilities to redirect itself towards another target before returning, or using the asteroid’s resources to replenish the Seed Craft’s propellant reserves. The asteroid-spacecraft itself also has several advantages over transporting resources with conventional spacecraft. An asteroid spacecraft can be 100% radiation hardened due to the abundance of shield material, and its interior can be completely shielded from micrometeorite debris, making it ideal for long-term missions on the order of 5-50 years. Due to the composition of these ISRU-derived (largely mechanical) systems, the “useless” materials on the asteroid (that would be separated and disposed of once the asteroid had returned to cislunar space) is put to good use in the RAMA concept as structural support and propellant reaction mass.
Taken to the extreme, the RAMA architecture enables a continuous train of resources to be redirected from interplanetary to cislunar space: A train of mechanically driven, asteroid spacecraft, “mine carts,” stretching from the depths of the asteroid belt to within 1 Lunar Distance (LD) of the Earth-Moon system. A symphony of endless revolving resources working in concert that, once in place, humans could hitch aboard and use as “free rides” to interplanetary space and back. Over time, such a system could convert these rudimentary spacecraft into sophisticated vehicles fit for human habitation; or fit them with sensors as research platforms to map other asteroids. Ultimately RAMA will create a system that will give humanity access to safer, faster and cheaper options for accessing the wealth of resources in our solar system.
2 RAMA ARCHITECTURE CONCEPT
2.1 THE ASTEROID SPACECRAFT
The purpose of the RAMA spacecraft is to leverage a small amount of mass and equipment delivered to the asteroid by a Seed Craft, and use it to return a larger mass of asteroid raw materials to cislunar space. To accomplish this, the RAMA craft requires all the functions of a conventional interplanetary spacecraft, subject to the constraints that they be 1) Manufactured from materials available on the asteroid, 2) Manufactured on/by equipment available on the Seed Craft. The specific solution will depend on the asteroid, but in general, the RAMA craft must have the capabilities shown in Figure 2-1.
2.2 MECHANICAL SYSTEMS CAPABILITIES & LIMITS
2.2.1 CREATING SPACECRAFT FROM MECHANICAL SYSTEMS
Mechanical and analog devices have been in existence for centuries. Examples of mechanical computing devices date back to 200 BC and were used as navigational instruments in the early days of spaceflight before being superseded by electrical computers. Figure 2-2 outlines eight different mechanical machine examples. The combination of these examples establishes a level of feasibility for constructing spacecraft from mechanical systems. Additionally, research and development in this field has led to analog based 3D printers that require no power or electronics to manufacture a pre-designed object.
Creating spacecraft from mechanical systems is entirely possible, and given the right mission, is even desirable. NASA NIAC has funded work to JPL under the AREE project (Automaton Rover for Extreme Environments) to develop a Venus rover made entirely of mechanical subsystem capable of surviving the harsh environment on the Venus surface. The RAMA mission class also represents a desirable case for mechanical subsystems. Propulsion systems to move 100-meter asteroids are too large to launch, but can be built in-situ as mechanical mass drivers; flywheels for attitude control are too heavy to launch, but could be constructed within an asteroid to control its spin rate and store energy. It is also possible to create mechanical computation devices for spacecraft that could perform basic avionics-style routines. For missions that require independence from Earth, with no supply of Earth made electronics, the creation of basic mechanical computers may serve as an alternative.
2.2.2 SUBSYSTEM REQUIREMENTS
The performance requirements for each subsystem will depend on the size, mass and type of asteroid they are being built for. A rough estimate of their requirements is provided Table 2-1 for a “typical” asteroid that RAMA might be expected to operate on.
Table 2-1: The general capabilities and performance requirements of each of the asteroids sub-systems. Values reported are for a baseline 100m, 1.5 million tonne asteroid in a near earth orbit.
Table 2-1: The general capabilities and performance requirements of each of the asteroids sub-systems.
Values reported are for a baseline 100m, 1.5 million tonne asteroid in a near earth orbit.
Subsystem Capability Performance Requirement Propulsion Earth intercept maneuver, plus lunar flyby and breaking into cislunar orbit if tug is not available. High enough performance for sufficient asteroid mass to remain after the maneuver is complete Total ΔV: 100-1000 m/s
Isp: 10-100 sec
Vejection: >100 m/s
Structure Maintain the asteroid’s cohesion while accelerating under propulsive loads, possibly with reinforcement from structural asteroid materials. 10-100 μg’s propulsive acceleration
0.5-1 g centrifugal acceleration.
Power and Energy Storage Store all the mechanical energy of the propulsion system, and dispense it at the appropriate time. 1-10 MJ Attitude Control Maintain asteroid orientation during maneuver, manage spin rate for artificial gravity control. 5-50% inertial moment of the asteroid Thermal Control Maintain adequate temperature range of all hardware on the asteroid, and reject heat due to manufacturing process. 50-500K
~1 MJ, or ~10% of power production
Communications Position and status reporting to Seed Craft or Earth receiver. Receive and activate flight termination if off course. Transponder providing range and rate information at ~1AU.
100-1000 W transmitter.
Command & Data Handling Timing and sequencing of maneuver operations after the Seed Craft departs. Unknown
2.2.3 ADVANCED MECHANICAL COMPUTERS
The previous section described the driving requirements of the asteroid spacecraft subsystems, which help indicate the constraints on making such subsystems from mechanical means. Of all the subsystems, the most challenging one to create from mechanical means alone are those that require complex computation; notably, GNC and C&DH. In order to address this challenge it is useful to explore the current state of the art of advanced mechanical computers.
By definition, a mechanical computer is a computer built entirely from mechanical components, such as gears, levers and pulleys, rather than electronic components. Early mechanical computers could do basic addition and counting exercises, while later developments saw multiplication, division, and differential analysis. By the 1960’s mechanical computers could calculate square roots.
Some notable mechanical computers are the Antikythera Mechanism, circa 200 BC, Blaise Pascal’s Pascaline machine of 1642, Charles Babbage’s Analytical Engine of 1837, and the Voskhod Spacecraft Globus Navigation Unit of the early 1960’s. All of these machines are remarkable in their own right, but the Antikythera Mechanism is uniquely so.
2.2.4 RAMA FUNCTIONAL BLOCK DIAGRAM
The fundamental concept of the RAMA architecture is in the conversion of an asteroid into a spacecraft. In order to do this, the Seed Craft creates spacecraft subsystems out of asteroid materials. For certain asteroid types, material compositions, and mission parameters the best configuration for conversion is to create mechanical subsystems. In all cases studied in this report there are at least some mechanical subsystems that can be made and make sense to make.
Figure 2-4 shows the Functional Block Diagram (FBD) for an asteroid converted into an entirely mechanical spacecraft via the RAMA process. At the heart of the mechanical spacecraft is a 3D printed analog computer that operates on a series of simple gears. The computer is powered by a store of potential energy found in 3D printed springs and flywheels. Mission objectives for the mechanical spacecraft will be fairly basic in nature requiring simple GNC. Flywheel gyros can be 3D printed and will keep the spacecraft on course by feeding momentum data into the analog computer which subsequently commands the propulsion system to propel asteroid materials and impart course corrections.
Example RAMA Process
Upon asteroid rendezvous, the RAMA Seed Craft analyzes the asteroid, and begins effectively organizing available in-situ resources. The asteroid is broken down and materials are stockpiled as manufacturing feedstocks, as well as viable “waste” mass for propellant. Mechanical energy storage systems (such as examples in Figure 2-2B and Figure 2-2E) are also fabricated on the asteroid, and charged with power from the Seed Craft. Finally, the Seed Craft assembles a unique array of mechanical linkages for the asteroid (like the examples in Figure 2-2 A, C, and F) from ISRU derived components. These will allow for timing and control of the asteroids systems after the Seed Craft has departed for the next target. Some asteroids may require a very complicated series of controls, limited only by the complexity of what the Seed Craft can manufacture before it disembarks to the next asteroid. When the Seed Crafts departs, it triggers the asteroid’s carefully preprogrammed sequence of events, which sets the asteroid on its own path to return to cislunar space without the Seed Craft. Upon arrival in cislunar space, the spacecraft has been significantly lightened by the expenditure of waste material as propellant, and is easily intercepted via the same techniques planned in the crewed portion of ARM.
2.2.5 MECHANICAL SYSTEMS LIMITS
To Build or To Bring? The fully developed RAMA vehicle would require no material input from the Seed Craft. The Seed Craft would provide power and fabrication capabilities, but every component of the finished spacecraft would be built from asteroid materials, allowing the Seed Craft to continue to convert asteroids indefinitely (or until it was rendered inoperable by equipment failure, or obsolete by new asteroid mining methods). However, this capability comes with a tradeoff. We have shown that mechanical components exist that could in theory provide any capability required by the RAMA spacecraft, but the specialized equipment to manufacture the components imposes additional complications and mass penalties onto the Seed Craft’s design.
The question should be asked: “Does the equipment required to build this capability locally impose a greater mass penalty than would bringing this component from Earth?” Undoubtedly, the Seed Craft could produce a mechanical computer from asteroid metal, and make it intricate enough to perform orbital calculations to control the Earth return maneuver. But would the complexity and mass penalty of building such a system outweigh the cost of simply bringing an advanced flight computer from Earth, and leaving it on the asteroid? A small spacecraft computer (especially 10-20 years from now) could easily weigh <100g and be the size of a postage stamp, but the equipment to manufacture the mechanical equivalent of such a computer could weigh thousands of kilograms, and impose even higher mass penalties on the power system. Does manufacturing mechanical equivalents locally for every asteroid system really make sense, when equally capable and less massive equipment can just be brought from Earth?The same can be said for communications and other systems on the low mass end of the spectrum shown in Figure 2-1. Simple radios and communication electronics can no doubt be produced from asteroid materials, but the electronics are not the mass intensive portion of any communication system, the driven elements (the antenna) and the amplifier are.
For contrast, capabilities like propulsion are inherently massive, by the simple physics of their operation. Even an extremely high performance propulsion system with an Isp of 5000 s (far higher than anything under consideration today) would have to consume 22% of the asteroid’s mass to affect a modest 1000 m/s in ΔV. The Seed Craft delivering this much mass to the asteroid from Earth would more than double the mass of the Seed craft for even a modestly sized 5m asteroid, and would be completely impossible for an asteroid in the target 50-100m range for RAMA. Clearly, propulsion is a capability that is better provided from asteroid resources than communications or computing power.
Where exactly this tradeoff fall will depend on technology factors we cannot anticipate at present. It will be the responsibility of the designer of future RAMA concepts to perform the Bring vs. Build tradeoff for a given asteroid, considering the expected lifetime of the Seed Craft, and the penalties paid by each extra capability added. For the remainder of this report, it will be assumed that only the four most mass intensive systems of the RAMA craft (propulsion, structures, power storage and attitude control) must be built from asteroid materials. The remaining capabilities can either be provided by the Seed Craft, or built like one of the examples shown in Figure 2-2, but the requirements they place on the Seed Craft / RAMA system are not assumed to be significant enough to change the design. An updated version of the asteroid spacecraft based on this understanding is shown in Figure 2-5.
2.3 THE SEED CRAFT
The Seed Craft shown in Figure 2-6, is a more conventional robotic interplanetary vehicle than the RAMA asteroid spacecraft. It contains a high performance low thrust ion engine, along with advanced robotic manufacturing capabilities to produce components of the RAMA vehicle from asteroid feedstocks. The extent of these manufacturing capabilities depends on the target asteroid. For example, a small 10m organic rich asteroid would likely require storage tanks for water-ice, and enough solar arrays to run a ~10 kW electrolysis plant. But a larger 100m metallic asteroid will require additional equipment for processing large quantities of metal ore, including a centrifuge for separation, and a larger solar array capable of powering a ~1 MW electric furnace. Satisfying this large range of requirements is accomplished through having a highly modular Seed Craft.
The Seed Craft is designed around a single common spacecraft bus, incorporating the bare minimum of features required for every mission (propulsion, power distribution and regulation, communication, ADCS etc.) Specific manufacturing modules are then added to the Seed Craft bus to provide the required capabilities for converting a give asteroid. With prior knowledge of the size and composition of the asteroid, the Seed Craft can be fitted with the required manufacturing modules, and fitted with a correctly sized power system before departing cislunar space.
Each module is serviced by a common robotics system, which runs along the length of the interior of the spacecraft. Robotic manipulators are free to traverse the length of the track, transferring materials from one operation to another, and performing maintenance as required. The entire interior of the spacecraft remains unpressurized, allowing the manufacturing operation to take place free of atmospheric contamination.
3.4 ISRU MANUFACTURING ASSESSMENT
3.4.1 IN-SITU RESOURCE AVAILABILITIES AND OPPORTUNITIES
While rare metals like platinum and palladium are available in the asteroids, the true value of asteroid resources does not come from the presence of valuable trace materials. The value of the asteroids comes from the availability of common materials without the need to ship them from Earth. Launching material from Earth to cislunar space costs ~$40000/kg, meaning that material, once it is delivered from Earth to cislunar space, is literally as valuable as gold.
For any major project in cislunar space (such as the construction of large habitats or radio telescopes) it is impractical to ship bulk materials from Earth at that rate. Bulk materials, if available in space, will be exploited in space, with launch capacity from Earth being reserved for complex equipment and trace materials that cannot be obtained without Earth’s complex industrial base. Even assuming futuristic advances in technology like space elevators, the energy required to ship materials from Earth’s surface to cislunar space will always be higher than the energy required to ship the same material from the asteroids, implying that the theoretical minimum cost of sourcing the materials from Earth will always be higher.
Resource Overview: Asteroid compositions mimic the composition of Earth, but without the benefits of gravity and geologic processing that have concentrated and dispersed materials throughout Earth’s interior. Asteroids thus contain abundant supplies of iron/nickel (present in Earth’s core) silicates and oxides (present in Earth’s mantle) and water-ice and other volatiles (present on Earth’s surface). These asteroid resources can be combined to produce effectively anything that a maturing space civilization requires. Examples of this are shown in Figure 3-3.
The range of processes illustrated in Figure 3-3 shows why the modular design of the Seed Craft is essential. An M-type asteroid for example is not expected to contain any significant quantities of volatiles. Any capabilities on the upper branch of the chart would represent wasted mass of the Seed Craft. By contrast, a volatile rich but metal poor C-type asteroid would be restricted by material availability to an upper branch of the tree as shown in Figure 3-4.
Even limited to these options, the C-type asteroid has the materials to produce high performance rocket propellant, which can be used to propel the RAMA spacecraft to new locations. The availability of polymers also permits composite structures to be manufactured along with the crushed rock and regolith, forming a composite material with excellent tensile and compressive strength. A prototype of composite ISRU based additive manufacturing was created during this study shown in Figure 3-5. A spring loaded propellant cannon was created using polymer based additive manufacturing methods shown in the left of the image. On the right side of the image is a JSC-1A regolith simulant combined with a polymer to create a composite structure with functioning gearbox inside.
A metal rich asteroid would be constrained to the lower left side of the chart as shown in Figure 3-6. Manufacturing techniques on the M-type asteroid would employ methods such as the carbonyl based Mond process and powder sintering methods to produce strong metallic structures. Propulsion options are much more limited, but one possibility would be the use of surplus metal to produce an electromagnetic cannon powered by locally manufactured photovoltaics.
A stony asteroid process, shown in Figure 3-7, presents a middle ground between the C and M types, permitting the use of both metals and stones as manufacturing materials. Propulsion options include the use of excess stone as projectiles in a high strength steel sling.
Additive manufacturing technologies provide unique opportunities for the S-type asteroids. For example, additive manufacturing represents an instance of the fully autonomous robotic operations required by Step 5) Excavating. For manufacturing complex metallic parts without the support of a planet scale industrial base, additive manufacturing also provides an alternative to the Mond Carbonyl process. It is for these reasons that the current study focuses on the S-type asteroid for RAMA mission design.
Manufacturing Methods and Analysis
During the Phase I study the team created a list of manufacturing technologies that hold promise for applicability with the RAMA mission. The technologies selected for analysis all had to be conceivable for potential use within the Seed Craft framework within the anticipated timeframe to first mission commencement. For the most part, the manufacturing technologies studied are additive in nature. Some of which are not solely manufacturing techniques though. In many cases the methods studied are traditionally considered “welding” technologies; but with proper R&D investment could be adapted for additive construction capability with the RAMA architecture. There are other methods that are more subtractive in nature, but still lend well to being used for the desired mission needs. The full list of methods studied is shown in Table 3-13.
3.5.1 THE FAR END OF THE SPECTRUM – ASTEROID 2009 UY19
We chose to study in depth a known asteroid that exists at the far end of the “feasibility spectrum” in an effort to show the true possibility of the RAMA architecture. Asteroid 2009 UY19 is an S-type asteroid with an estimated diameter of 50-150m. Part of what makes this a far end of the spectrum asteroid to study is the conversion time needed to convert it into an asteroid spacecraft. Shown in detail within this section, UY19 will require nearly a decade of Seed Craft conversion in-situ to be ready for its mission to Earth-Moon L5. This conversion rate is based on modest assumptions of Seed Craft functionality, which in due time may improve significantly, thus decreasing conversion time. Nonetheless, the study of this large of an asteroid, and the feasibility analysis of doing so, outlines the true disruptive capability of the RAMA architecture.
The asteroid 2009 UY19 was discovered during a close flyby of Earth in October 2009, and makes periodic close passes of the Earth every 29 years. During these passes, it comes within a few million km (~10 Lunar Distances) of Earth, and the next pass in 2039 requires a ΔV of only 437 m/s to be diverted towards the Earth-Moon L5 point. This makes it an attractive target for returning to cislunar space for resource extraction. It is too massive to be recovered by any proposed ARM architecture, but it is a prime target for the RAMA concept. The orbital parameters of 2009 UY19 are shown in Table 3-15.
Table 3-15: Orbital Parameters of 2009 UY19 2009 UY19 Asteroid Orbit Semi-major axis 1.02361 AU Eccentricity 0.030796 Inclination 9.05 deg Period 1.036 years Synodic Period 29.07 years
Seed Craft Loadout
With no known sources of volatiles at UY19, the Seed Craft is customized for metal working and stone mining. No chemical processing equipment is included; instead the Seed Craft is loaded with four modules containing the following equipment:
- Optical mining rig, containing a bank of one hundred 10kW lasers and a collection inlet, capable of spalling and collecting asteroid material at a rate of ~.5 kg/s.
- 5kW furnace for smelting and electromagnetically separating iron/nickel from rock.
- 5000 kg of alloying elements and equipment for producing high strength steel.
- A die extruder for extruding high strength steel into a circular beam 16 cm in diameter.
- A 750 kg electromagnetic bearing assembly for permanent installation on the asteroid.
UY19 Mission Timeline
The Seed Craft is boosted away from its base in cislunar space on a trajectory to intercept the asteroid. It ignites its 60-kW solar electric propulsion system 4 months later, affecting a rendezvous with UY19 0.32 years after launch. After 2-4 days orbiting the asteroid and mapping details of its mass distribution and gravity, it docks with UY19 along the asteroid’s spin axis, and anchors itself to the surface. The Seed Craft is now effectively part of the asteroid, and continues with it out of cislunar space. The Seed Craft then reconfigures itself for operations on the asteroid, deploying a group of independent robots to assist with securing the Seed Craft, removing obstructions, and any precision work that is required during the process. The full capacity of the Seed Craft’s four 27x34m solar arrays is deployed, providing the full 4 MW of solar power required to convert the asteroid into the RAMA spacecraft.
With its assumed composition and size, gravity at the asteroid’s surface is only .00002 g’s (~2 um/s2). The asteroid is thus likely to be a single monolithic piece, as any loosely bound components would have escaped the asteroid long ago. The lack of gravity and the cohesive nature of the asteroid will make mechanical excavation very difficult. Optical mining methods have been previously studied as ways of overcoming both difficulties in mining C-type asteroid. With a 10kW Optical Mining system operating at a temperature of 1000K, an excavation rate of ~5 mm3/min of material per W of power was observed. By directing the full power of the Seed Craft’s solar array to the optical mining system and operating at the higher temperature required to decompose stone and metal, an excavation rate of ~200 cm3/s can be expected.
The resulting debris from the mining site are lost to space until the Seed craft has bored a hole deep enough to insert the mining module into the asteroid, forming a closed cavity to prevent the loss of more debris. The material is then directed to an inlet adjacent to the optimal mining rig, where it is collected and conveyed away from the mining site to be purified and smelted.
The melted rock is allowed to cool in measured batches (“shots”) 18 cm in diameter. By cooling them in the presence of an electromagnetic field, they are left with a remnant magnetic field that makes them cohere to each other magnetically, and to the walls of the asteroid. These 18 cm shots will be used as the propellant for the mechanical propulsive system, and are packed around the wall of the ever-growing interior of the asteroid.
The process of optically hollowing out the interior of the UY19 takes 8 years, producing a new shot every 17 seconds. Figure 3-15 shows the concept of the Seed Craft conversion of UY19 into the asteroid spacecraft, and Figure 3-14 shows a more detailed depiction of the Seed Craft operations on the asteroid. For the first decade of this process, a small fraction of the iron and nickel extracted from the material is not returned to the interior of the asteroid or embedded in the shots, but is separated and combined with the carbon and other alloying elements from the Seed craft to produce high strength steel. The steel is extruded through a die out through radial bore holes in the asteroid excavated by the robots until it extends 40 m in length.
These “slings” are used for the main component of RAMA’s propulsion system. The base of each sling is firmly anchored to the interior of the asteroid. A series of 16 slings are extruded at equally spaced intervals around the asteroid. While the amount of material consumed in their production is large, (300 mT of materials to produce 80 mT of metal) it is small compared to the amount of material required to produce the shots. The minimal ability to extrude 29 kg (220 mm of beams) per day would take less than a year to finish. After that, metal is available to reinforce the interior of the asteroid, provide scaffolding for the robots, or reduced into a powder for joining and reinforcement via laser engineered net shaping with the mining lasers.
After 8 years, when the asteroid is ~50% hollowed out, the 750 kg electromagnetic bearing assembly is detached from the Seed Craft and transported by the robots to the opposite interior of the asteroid. The base is welded to the interior wall, with its drive axis parallel to the spin axis of the asteroid. As construction continues, surplus iron and nickel from the smelter are combined with the remaining alloying elements from the Seed Craft to produce Inconel powder. Under robotic control using the Laser Engineered Net Shaping (LENS) technology from the manufacturing trade study in section 3.4.2, the powder is additively sintered radially outward from the electromagnetic bearing system, allocating the remaining metal composition of the asteroid into a single mass of metal, mounted on the electromagnetic bearing. The RAMA craft now has a crude mechanical spin stabilization and energy storage system.
Construction of the RAMA spacecraft is now complete (Figure 3-19). During manufacturing, the Seed Craft has gradually used its own propulsion system to stabilize and orient the asteroid’s spin axis in the correct direction. The system must now wait for the Earth return window to open. The Seed Craft stows its solar panels to protect them from debris, powers down its manufacturing systems, and waits 13 years for the return window to open. During this time, it periodically reawakens to perform status checks and remote sensing operations on any other targets the asteroid may pass close to.
One month before the window opens, the Seed Craft wakes up, and redeploys its power systems. It now applies the power from the 4 MW photovoltaics (previously used to power manufacturing operations) directly to the motors in the flywheels. This power is applied for 25 days, at the conclusion of which, the two flywheel are spinning at ~4000 rpm (their approximate material limit) and have stored ~1 GJ of energy, the amount of energy required to return the asteroid to Earth. Slightly charging one flywheel over the other imparts a greater rotation to the reinforced asteroid shell, producing significant artificial gravity at the surface of the asteroid, further adhering the shots up against the interior of the asteroid and up against electromechanical exit ports bored by the robots.
Finally, the Seed Craft uses its own propulsion system to provide a series of forward “kicks” to the asteroid. These kicks impart no significant ΔV, but are properly timed to match the fundamental frequency of the 16 extended slings protruding from the asteroid. The slings begin to oscillate back and forth, and after 3 days of continuous kicks, the slings are rocking back and forth with a high enough amplitude to be bend all the way back to the asteroid’s surface. The slenderness ratio of the slings (250:1) is large enough to remain fully elastic when bent this far, allowing it to continue to oscillate like a pendulum with only thermal losses. The Seed Craft, its decades long task complete, disengages from the asteroid and departs for its next target.
The slings, once set in motion, oscillate at a period of 2.1 seconds, and at the peak of their swing, the tips are travelling at 312 m/s, achieving the theoretical maximum velocity of the material (Figure 3-20). At the extreme of each swing, the tip of the sling passes close to the exit ports near the asteroid’s equator, where extremely strong rare Earth magnets on the tip of each sling adhere to a single 10 kg shot. The strength of the permanent magnet on the tip and the remnant magnetism if the shot is calibrated such that the adhesion strength is exceeded exactly at the full extension of the swing, where the centrifugal force is maximized, hurling the shot astern of the asteroid at 312 m/s, and imparting a small but non-trivial 13 microns/sec ΔV onto the asteroid. At full “throttle”, with all slings operating, the asteroid accelerates at a constant 11 micro-gs.
This low impulse maneuver persists for 27 days. Each shot carries away a small fraction (0.55%) of the sling’s energy with it. Over time, this loss will cause the slings to oscillating through a smaller arc and the asteroid to spin at a slower rate. To compensate for this loss of energy, the flywheels, which have remained spinning since they were charged by the Seed Craft, are slightly braked each time the slings reload, imparting a slight transfer of angular momentum to the asteroid itself, and thus to the swing arms.
This low impulse maneuver persists for 27 days. Each shot carries away a small fraction (0.55%) of the sling’s energy with it. Over time, this loss will cause the slings to oscillating through a smaller arc and the asteroid to spin at a slower rate. To compensate for this loss of energy, the flywheels, which have remained spinning since they were charged by the Seed Craft, are slightly braked each time the slings reload, imparting a slight transfer of angular momentum to the asteroid itself, and thus to the swing arms.
This places the asteroid on an intercept path to Earth-Moon L5, where it is intercepted 249 days later after a lunar flyby by a cislunar tug. The asteroid at this point is considerably lighter (34,000 mT vs 230,000 mT) and the returned material is considerably “purer”, as 90% of the asteroids worthless mass (its stone) has been ejected as propellant. The remaining mass is in the form of a pure metal flywheel and a hollow reinforced shell approximating the original shape of the asteroid, with an average wall thickness of ~4 m. The 30-year RAMA mission is complete, having delivered the mass equivalent of ~85 International Space Stations to the Earth-Moon L5 location.