Remember the fundamental rule of rocket design: Every Gram Counts.

The spacecraft will have to lug along inconveniently large masses of air, food, and water ("consumables") so that the astronauts can live. And if the ship runs out while in a remote location, the crew will be reduced to a castaways in a lifeboat situation drawing straws to see who dies. With the added constraint that castaways in a lifeboat at least have unlimited access to breathable air. The fact that consumables run out at all will limit the duration of any given mission.

Which explains NASA's burning interest in Closed Ecological Life Support Systems (CELSS). In theory the only input such a system needs is energy, either sunlight or some power source to run grow lights. The advantages are:

  1. The astronauts will have air, food, and water forever (or until the equipment breaks down or the energy input stops)
  2. After a certain mission duration, it will be cheaper (in terms of mass) to use a CELSS instead of transporting consumables. With a primitive CELSS this happens at about 145 days, increasing the efficiency will bring the break-even duration point lower. The mass of the CELSS is constant regardless of mission duration, the mass of consumables goes up with mission duration.

The main functions of a CELSS are:

  1. Turn astronaut's exhaled carbon dioxide into oxygen
  2. Turn astronaut poop and table scraps into food
  3. Turn astronaut pee and washing wastewater into drinkable water

The current lines of research focus on doing this the same way Terra's ecosystem does: by using plants. In order to make the CELSS hyper-efficient they have to use hyper-efficient plants. Which explains the focus on algae.

CELSS technology would be a game changer if we had it. Alas, it has proven to be a much more difficult problem to crack than they thought back in the 1960s. As I write this it is 2021 and they still haven't managed to do it. Currently the state of the art is nowhere near achieving a 100% efficient CELSS.

But an efficiency of over 75% or so would be a huge help. Sometimes a sub-100% system is called a Controlled Ecological Life Support Systems. The system might also be partial, such as a system which can 100% recycle carbon dioxide into oxygen, but cannot recycle food at all.

In NASA jargon, a closed environment life support system based on algae is called a "yoghurt box", one based on hydroponic leafy plants is called a "salad machine", and one based on a fish farm is called a "sushi maker".

Problems with creating and maintaining a balanced CELSS include carefully controlling the amount of plants consuming carbon dioxide (so they don't gobble more CO2 than the astronauts can produce, resulting in plant death from asphyxiation), and small-closed-loop-ecology buffering problems. The latter means that the smaller your CELSS system is, the more rapid and violent the results from tiny changes. With a closed-loop ecology the size of Terra, tiny changes can take months to years to show any effects, and those will be mild. With a small spacecraft CELSS, tiny changes can cause immediate and drastic effects.

Since maintaining the balance of a CELSS is so tricky, it will be a major undertaking to keep things stable if the number of crew members changes. If the number goes down (by a group on a landing mission the the Martian surface, or by crew casualties) the amount of plants will have to be cut back. Adding new crew is more of a problem. Leafy plants take time to grow to useful size when increasing square meters of cultivation. Algae is less of a problem since single celled plants multiply at a speed that puts rabbits to shame. It will probably be only a few hours to grow the biomass of algae enough to accommodate the new crew.

Another concern is the shipboard supply of phosphorus and nitrogen, since these are biological bottlenecks.

Of course there is the problem of recycling disgust, but that has to be fixed by psychologists, not engineers.


(ed note: The bussard ramjet starship Leonora Christine has suffered a little accident. As a consequence, they cannot slow down to land on a planet, only accelerate forever.)

      “Oh, we can live out our lives — reach a reasonable age, if not quite what antisenescence would normally permit,” said Pereira. “The biosystems and organocycle apparatus are intact. We could actually increase their productivity. Do not fear immediate hunger or thirst or suffocation. True, the closed ecology, the reclamations, are not 100 per cent efficient. They will suffer slow losses, slow degrading. A spaceship is not a world. Man is not quite the clever designer and large-scale builder that God is.” His smile was ghastly. “I do not advise that we have children. They would be trying to breathe things like acetone, while getting along without things like phosphorus and smothering in things like earwax and belly-button lint. But I imagine we can get fifty years out of our gadgets. Under the circumstances, that seems ample to me.”

From TAU ZERO by Poul Anderson (1970)

Growing Plants

Terra's ecosystem fundamentally works by plants feeding animals while the animals feed the plants. Pretty much all spacecraft CELSS system try to utilize plants to feed the astronauts. Replacing plants with something else seems like a silly attempt to re-invent the wheel. Why do all that work when Mother Nature has already done it for you, for free?

The plants ingest water, carbon dioxide, sunlight, and some trace elements. Using Mother Nature's photosynthesis process, the plants output carbohydrates and oxygen. The astronauts consume plant carbohydrates and oxygen. Using human digestion, the human body is nourished, while producing water, carbon dioxide, and some trace elements. If you can balance the system, it will keep spinning as long as there is sunlight available.

Photosynthesis essentially splits water into hydrogen and oxygen, spits out the oxygen, and fuses hydrogen and carbon dioxide to form carbohydrates.

According to Chris Wolfe, NASA's best estimate is that the amount of leafy plants needed to handle one astronaut's carbon dioxide exhalation will produce only half of that astronaut's food. This is a problem. If the CELSS is producing all of the crew's food, it will have twice as many plants as needed, which will rapidly deplete the atmosphere of carbon dioxide, which will suffocate all the plants. It will also overproduce oxygen, but that can be extracted from the air and put into tanks for latter breathing, for rocket oxidizer, or exported and sold.

The solution is to recover the carbon trapped in the non-edible parts of the plants harvested for food.

The easiest way is to burn those parts and feed the generated carbon dioxide to hydroponics. The ash will contain other nutrients. Another solution is to feed the leftovers to a supercritical water oxidation unit and let it generate the carbon dioxide.

For CELSS uses, plants are generally grown by using some species of soil-less cultivation. Using actual soil to grow plants, with all of its active cultures and other messy ingredients, is far to unreliable to use in a life-or-death system.

Plants require light in order to perform photosynthesis, but using direct sunlight is a problem. First off you'll have to filter out ultraviolet and other frequencies harmful to plants. A transparent window allowing direct sunlight to illuminate the plants will also allow deadly solar storm radiation to fry them to a crisp. Granted plants tolerate up to 1 Sievert per year, but lets be reasonable here. There ain't no such thing as transparent radiation shielding (as yet).

In theory a shielded shutter will protect the plants from solar storms, but it is yet another possible point of failure. This is unacceptable if you are relying upon your plants to allow the crew to keep on breathing. If the storm detector fails, if the shutter actuators fail, if the crew forget to close manual shutters, all of these mean death by asphyxiation.

A fiber optic pipe fed with filtered sunlight and containing numerous bends to defeat radiation might work. But then if the spacecraft moves further away from Sol than Terra's orbit, the intensity of sunlight drops off rather alarmingly due to the inverse square law. That moron Freeman Lowell took far too long to figure this out in the movie Silent Running.

When you figure in that plants can only use certain wavelengths of sunlight, you might as well give up and use artificial grow-lights. LEDs are best, due to their relatively low waste heat. Feed the LEDs with electricity from the power generator of your choice.

The wavelengths used by photosynthesis are called photosynthetically-active radiation (PAR). They lie in a band from 400 to 700 nanometers, more or less the visible-light spectrum. Chlorophyll, the most abundant plant pigment, is most efficient in capturing red and blue light. This is why plant leaves appear yellowish-green to our eyesight, the chlorophyll doesn't eat those wavelengths so they spit them out. PAR is usually measured in bizarre units of "µmol photons m−2s−1" because photosynthesis is a quantum mechanical process (i.e., a bizarre process).

According to Chris Wolfe, most plants flourish under 26 mol PAR per square meter per day (26,000,000 µmol PAR/m2/d). Assuming that 12 hours (43,200 seconds) of the day are daylight and 12 hours are nightime, this means the plants are enjoying about 601 µmol PAR per square meter per second (µmol m−2s−1, the negative exponents are a cute way of saying "per" or "divided by").

LEDs can produce about 1.7 µmol PAR per watt-second or 6,120 µmol PAR per watt-hour. Supplying 601 µmol m−2s−1 will require about 354 watts (601/1.7 = 354) per square meter.

In other words, your hydroponics LED lights are going to need about 354 watts of electricity per square meter of hydroponic plants, for 12 hours out of every day. Certain plants require different amounts of mols PAR per square meter, and different numbers of illumated hours per day, but this is a good back-of-the-envelope value. Lettuce and spinach want about 250 µmol m−2s−1 (not 601), while tomatoes and cucumbers can get by on only 100 µmol m−2s−1

If I am reading the reports properly, algaculture requires a wee bit more. Chlorella algae wants 450 µmol PAR/m2, and Spirulina's optimal value is about 120 µmol PAR/m2.

So doing the math, Chlorella's 450 µmol PAR/m2 will need about 265 watts/m2 of LED electricity, while Spirulina needs 71 watts/m2. Since algae is typically cultivated in tubes or tanks, I am unsure how to translate the square meters of illumination into volumes of algae culture. The thickness will not be much, because algae is so good at harvesting photons that is is practically opaque.

In terms of area, I've seen values ranging from 10 to 40 square meters and perhaps 40-160 cubic meters per person. My own spreadsheet based on densely stacked racks comes to 11.5 m² floor space, 22.14 m² growing area and 46.2 m³ volume for one person (2.5 kg per day), but we want to allow for safety and variety. People don't want to eat tomato and potato for three meals a day simply because they are excellent producers. I also want to leave volume for animal production and associated equipment, so let's start with 30 m² floor space and 120 m³ per person. About 75% of that will be lit, or 43.3 m² of grow area. We need half of 354 watts per m² or 7,667 watts per person for lighting. Additional power will be needed for pumps and fans.

The extra area provides reserve supplies of storable food like rice and beans, indulgence crops like coffee (1.62g/day*m²), tea (1.92g/day*m²) or cocoa (0.42g/day*m²) {all require several years to establish}, animal feed, plastic feedstock and extra O2 for export. One cup of coffee requires about 10 grams of grounds; a cup a day would use 6.17m² of floor space.

Life Support

Feeding a person requires about 40m³ of hydroponics volume (including row spacing, aisles, nutrient storage, equipment, seeding areas, etc., etc.). The exact amount varies and can be pushed lower (below 20m³ is my guess) but this is a reasonable number to start with. Plants need light (from LEDs), and hydroponic grow systems need pumps, fans and sensors. This gear collectively eats about 5 kW of electricity per person, nearly all of which ends up as low-grade heat.

That same volume will convert two people's CO2 back into oxygen. This is because most of a plant's dry mass is carbon compounds but only about half of that is food; the rest is waste. That carbon comes from CO2, so crops to feed one person trap a second person's worth of carbon as waste. Fortunately we can simply burn the waste to recover that carbon on demand. This would be done in a pyrolysis unit to form neat little carbon blocks for storage and controlled release; these may even be used as filters before ultimately getting burned to keep the CO2 levels high enough for growth. Since plants and humans have very different 'ideal' atmospheres, CO2 scrubbers (zeolite sorbent beds) will be used to actively move CO2 out of human spaces and into plant spaces.

Nitrogen is a buffer gas; it is inert and allows the oxygen percentage in the atmosphere to be low enough to avoid fires. It's also an important part of amino acids (and thus proteins), and is actively cycled in humans and in plants. Nitrogen gas is very stable, meaning it is hard to convert into active forms like urea or nitrate. Nitrogen fixers like legumes and many bacteria can do the job, plus there are methods of making ammonia and other nitrogen-containing chemicals directly (given enough energy). The active nitrogen compounds in the system are assembled in plants to form proteins, eaten by humans, excreted as waste, separated in a waste processor and converted into hydroponic nutrients to be fed to the plants. Some of it is bound up in plant wastes and is either recovered from there or burned back to nitrogen gas depending on how fancy the recovery system is. Quantities of nitrogen are stored in liquid form to replenish atmosphere (everything leaks). That handles the nitrogen cycle, but note that some of it is unavoidably lost over time and resupply is eventually necessary even with perfect recycling. The same applies to all other volatiles (liquids and gases).

Argon will probably be used as a buffer gas and ion engine propellant since it is readily available on Mars. It doesn't get used in biological processes but otherwise would be used in place of nitrogen for maintaining atmosphere.

The waste processing systems will recover other important nutrients like phosphorus, potassium, calcium, iron, etc., usually as salts that can be used directly as fertilizer after purification. Inputs are wastes, water and energy. Outputs are these salts, clean water, heat and CO2 (for the most part). Water circulates through most of these systems; it is taken up by plant roots and evaporated from leaves, bound up in sugars, eaten, drank and excreted, condensed on cold surfaces, etc. Power consumption is minimal for the baseline (relying heavily on bioremediation and SCWO) but could be higher for more advanced systems.

Humidity and temperature is maintained by the CO2 system, since the air must be dried before it can be filtered properly. Incoming warm, wet 'used' air is cooled and dried, passed through the filter, then heated and moistened to the desired level. The filter regenerates by pumping warm, very dry and very high CO2 air through to the plant sections. Any excess water is sent to waste processing for filtration. This means that the atmosphere system needs active refrigeration and is the primary load on the craft's radiators; it needs to be able to handle the entire heat load of the habitat since only a small amount is lost through the solid metal connections to the rest of the craft. Power consumption is roughly 1 kW per person.

A better use of plant waste would be to make animal feed with it and raise fish and chickens. Food fish have a short enough lifespan that they can be raised inside the radiation shielding water, though breeding pairs would be kept inside the storm shelter. Chicken eggs greatly expand the kinds of foods you can create and would be a big benefit to morale. This kind of microfarming can be done even for a very small population; certainly a ship carrying more than a hundred people would be able to sustain populations of both.



As previously mentioned, plants will probably be grown by using soil-less methods.

There are lots of different types of soil-less cultivation, all based around using water (Hydroponics). Some are suitable for CELSS.

  • Hydroponics: growing plants without live bacterial-infested soil ("salad machine")
    • Solution Culture: no substrate, just nutrient water
      • Static solution culture: plants in jars of still nutrient water
      • Continuous-flow solution culture: flows of nutrient water passing over plant roots
      • Aeroponics: plant roots are in the air, misted with a fog of nutrient water
      • Algaculture: microalgae cells cultivated in either static or continuous flow solutions cultures ("yoghurt box")
    • Medium Culture: using a sterile solid substrate bathed in nutrient water
    • Aquaponics: solution or medium cultures in association with tanks of fish and other sea food ("sushi maker")

Growing leafy plants for food is not as efficient as growing algae or other single-cell plant. But it is quite a bit easier. The basic idea is to grow food plants not in soil, but instead in nutrient filled water or in an inert material bathed in nutrient filled water.

Medium cultures can use all sorts of substrates: rock wool, baked clay pellets, glass waste growstones, coco peat, parboiled rice husks, Perlite, Vermiculite, pumice, sand, gravel, wood fibre, sheep wool, brick shards, and polystyrene packing peanuts have all been used.


The Executive Officer assigned other tasks not directly concerned with formal training. Matt was appointed the ship’s “farmer.” As the hydroponics tanks supply both fresh air and green vegetables to a ship he was responsible for the ship’s air-conditioning and shared with Lieutenant Brunn the tasks of the ship’s mess.

Theoretically every ration taken aboard a Patrol vessel is pre-cooked and ready for eating as soon as it is taken out of freeze and subjected to the number of seconds, plainly marked on the package, of high-frequency heating required. Actually many Patrol officers fancy themselves chefs. Mr. Brunn was one and his results justified his conceit—the Aes Triplex set a good table.

(ed note: microwave ovens had been invented about one year before Heinlein wrote this novel. That is what "high-frequency heading" is referring to.)

Matt found that Mr. Brunn expected more of the “farm” than that the green plants should scavenge carbon dioxide from the air and replace it with oxygen; the mess officer wanted tiny green scallions, fragrant fresh mint, cherry tomatoes, Brussels sprouts, new potatoes. Matt began to wonder whether it wouldn’t have been simpler to have stayed in Iowa and grown tall corn.

When he started in as air-conditioning officer Matt was not even sure how to take a carbon-dioxide count, but shortly he was testing his growing solutions and adding capsules of salts with the confidence and speed of a veteran, thanks to Brann and to spool #62A8134 from the ship’s files—“Simplified Hydroponics for Spaceships, with Growth Charts and Additives Formulae.” He began to enjoy tending his “farm.”

Until human beings give up the habit of eating, spaceships on long cruises must carry about seven hundred pounds of food per man per year. The green plants grown in a ship’s air-conditioner enable the stores officer to get around this limitation to some extent, as the growing plants will cycle the same raw materials—air, carbon dioxide, and water—over and over again with only the addition of quite small quantities of such salts as potassium nitrate, iron sulphate, and calcium phosphate.

The balanced economy of a spaceship is much like that of a planet; energy is used to make the cycles work but the same raw materials are used over and over again. Since beefsteak and many other foods can’t be grown conveniently aboard ship some foods have to be carried and the ship tends to collect garbage, waste paper, and other trash. Theoretically this could be processed back into the cycles of balanced biological economy, but in practice this is too complicated.

Even though turnip greens and such can be used in the jet, the primary purpose of the “farm” is to take the carbon dioxide out of the air. For this purpose each man in the ship must be balanced by about ten square feet of green plant leaf. Lieutenant Brunn, with his steady demands for variety in fresh foods, usually caused Matt to have too much growing at one time; the air in the ship would get too fresh and the plants would start to fail for lack of carbon dioxide to feed on. Matt had to watch his CO2 count and sometimes build it up by burning waste paper or plant cuttings.

Brunn kept a file of seeds in his room; Matt went there one “day” (ship’s time) to draw out Persian melon seeds and set a crop. Bran told him to help himself. Matt rummaged away, then said, “For the love of Pete! Look at this, Mr. Brunn.”

“Huh?” The officer looked at the package Matt held. The outside was marked, “Seeds, melon, Persian jumbo fancy, stock #12-Q4728-a”; the envelope inside read Seed, pansies, giant variegated.”

Brunn shook his head. “Let that be a lesson, Dodson—never trust a stock clerk—or you’ll wind up half way to Pluto with a gross of brass spittoons when you ordered blank spacecharts.”

“What’ll I substitute? Cantaloupe?”

“Let’s grow some watermelon—the Old Man likes watermelon.”

Matt left with watermelon seeds, but he took along the truant pansy seeds.

Eight weeks later he devised a vase of sorts by covering a bowl from the galley with the same sponge-cellulose sheet which was used to restrain the solutions used in his farming, thereby to keep said solutions from floating around the “farm” compartment during free fall. He filled his vase with water, arranged his latest crop therein, and clipped the whole to the mess table as a centerpiece.

Captain Yancey smiled broadly when he appeared for dinner and saw the gay display of pansies. “Well, gentlemen,” he applauded, “this is most delightful. All the comforts of home!” He looked along the table at Matt. “I suppose we have you to thank for this, Mr. Dodson?”

“Yes, sir.” Matt’s ears turned pink.

“A lovely idea. Gentlemen, I move that we divest Mr. Dodson of the plebeian title of ‘farmer’ and designate him Horticulturalist extraordinary.’ Do I hear a second?” There were nine “ayes” and a loud “no” from Commander Miller. A second ballot, proposed by the Chief Engineer, required the Executive Officer to finish his meal in the galley.

Lieutenant Brunn explained the mishap that resulted in the flower garden. Captain Yancey frowned. “You’ve checked the rest of your supply of seeds, of course, Mr. Brunn?”

“Uh, no, sir.”

“Then do so.” Lieutenant Brunn immediately started to leave the table, “—after dinner,” added the Captain. Brunn resumed his place.

“That puts me in mind of something that happened to me when I was ‘farmer’ in the old Percival Lowell—the one before the present one,” Yancey went on. “We had touched at Venus South Pole and had managed somehow to get a virus infection, a sort of rust, into the ‘farm’—don’t look so superior, Mr. Jensen; someday you'll come a cropper with a planet that is new to you!”

“Me, sir? I wasn’t looking superior.”

“No? Smiling at the pansies, no doubt?”

“Yes, sir.”

“Hmmph! As I was saying, we got this rust infection and about ten days out I didn’t have any more farm than an Eskimo. I cleaned the place out, sterilized, and reseeded. Same story. The infection was all through the ship and I couldn’t chase it down. We finished that trip on preserved foods and short rations and I wasn’t allowed to eat at the table the rest of the trip.”

From SPACE CADET by Robert Heinlein (1948)

(ed note: intergalactic con-artist Terence Lao-T’se Macduff has snuck into the starship passenger-liner Sutter, but has not purchased a ticket. When caught, the captain decrees that Macduff must work off the price of a ticket by doing manual labor below-decks. Macduff is suspiciously inept at all the jobs.)

      As Macduff cautiously made his way toward the lounge his memory dwelt all too vividly on his recent progress from riches to rags. His meteoric descent from job to worse job had been little short of phenomenal.
     “Would you set a cinematome to digging ditches?” he had inquired. “Would you weigh elephants on a torquemeter?” (both are delicate precision instruments that would be ruined by rugged use)
     He was told to stop gabbling and pick up that shovel. Instantly he began to work out the most efficient application of the law of leverages. There was some delay while he extended his decimals to include the influencing factor of low-threshold radioactivity upon the alpha waves of the brain.
     “Otherwise, anything can happen,” he explained, demonstrating. There was a crash.

     Macduff was then, by request, taken off the Hot Gang and put to work elsewhere. But, as he took pains to point out, his frame of reference did not include special skills in the block-processing of garbage for fuel, oiling of the symbiotic hemostatic adjustment mechanisms provided for the comfort of the passengers or testing refractive indices of liquid-coated bimetallic thermostats. He proved this empirically.

     So he was—by request—removed to Hydroponics, where the incident of the radioactive carbon tracer occurred. He said it wasn’t the carbon, it was the gammexene, and besides it wasn’t really the gammexene so much as his inadvertent neglect to supplement the insecticide with meso-inositol.
     But when thirty square feet of rhubarb plants began breathing out carbon monoxide as a result of sudden heredity changes brought on by the gammexene Macduff was promptly sent down to the kitchens, where he introduced a growth hormone into the soup, with nearly catastrophic results.
     At present he was an unvalued member of the staff of Atmospheric Controls, where he did the jobs nobody else wanted to do.

From THE VOICE OF THE LOBSTER by Henry Kuttner (1950)


Algaculture in a spacecraft CELSS is always in the form of growing microalgae, not gigantic macroalgae aka seaweed. Popular food microalgae types include Chlorella and Spirulina.

Algae is cultivated in photobioreactors. These try to hold the algae cultures in thin layers because the little greenies are so good at absorbing the light that any algae that is too deep will get no light at all. The concentration of algae is typically something like 5×108 algae cells per mililiter of water.

In 1965, the Russian CELSS experiment BIOS-3 determined that 8 m2 of exposed Chlorella could remove carbon dioxide and replace oxygen within the sealed environment for a single human (I am assuming this is in a very shallow tray). The official figure for Chlorella oxygen production is 25 to 400 femtoMol O2/cell/hour. If am I doing the math correctly, at a concentration of 5×108 cells/ml, this translates into about 0.0032 kg of O2 produced per hour per liter, and 0.768 kg of O2 produced per day per liter. Since astronauts require 0.835 kg of O2 per day, this implies they would need 1.09 liters of chlorella culture.

Algaculture Dangers

There are a few hazards associated with relying upon algae for food.


[Spirulina algae is] [h]igh in nucleic acid, which means you can only eat about fifty grams per day or you're at risk of gout. And it's going to be really, really, really embarassing if you have to list "gout" as the cause of failure for a space mission.

Dr. John Schilling

Various forms of blue-green algae can be naturally contaminated with highly toxic substances called microcystins.

Some states, such as Oregon, require producers to strictly limit the concentration of microcystins in blue-green algae products, but the same protections cannot be assumed to have been applied to all products on the market. Furthermore, the maximum safe intake of microcystins is not clear, and it is possible that when blue-green algae is used for a long time, toxic effects might build up...

...Blue-green algae can also contain a different kind of highly toxic substance, called anatoxin (ed note: AKA "Very Fast Death Factor").

In addition, when spirulina is grown with the use of fermented animal waste fertilizers, contamination with dangerous bacteria could occur. There are also concerns that spirulina might concentrate radioactive ions found in its environment. Probably of most concern is spirulina's ability to absorb and concentrate heavy metals such as lead and mercury if they are present in its environment. One study of spirulinas grown in a number of locations found them to contain an unacceptably high content of these toxic metals. However, a second study on this topic claims that the first used an unreliable method of analyzing heavy metal content, and concludes that a person would have to eat more than 77 g daily of the most heavily contaminated spirulina to reach unsafe mercury and lead consumption levels.

These researchers, however, go on to suggest that it is not prudent to eat more than 50 g of spirulina daily. The reason they give is that the plant contains a high concentration of nucleic acids, substances related to DNA. When these are metabolized, they create uric acid, which could cause gout or kidney stones. This is of special concern to those who have already had uric acid stones or attacks of gout.

The threat of contamination of the algaeculture with algae producing microcyctines, anatoxin, or other deadly substances means the life support officer had better monitor the algae closely, since the crew is going to eat that crap. If it pops up, all the algae gets thrown into the supercritical Water Oxidation to be disintegrated into oxides, the algaculture system gets flushed and sterilized, and restarted with a fresh packet of algae spores. The crew has to live on emergency rations while the algaculture grows.

This might be a good reason for some redundancy, like two separate and independent algaeculture systems. Hopefully only one would go bad at a time.

A person who goes by the internet handle of Tom I. Bystanderson noted that apparently the synthetic pathway for various algae toxins are well understood, so with a little genetic engineering some strains of toxin-safe algae could be produced (scientists are not quite why algae produce such toxins, they might be needed for algae metabolism).

SF writers with an evil turn of mind will see some interesting plot possibilites in these facts. The ship's food supply could become contaminated by an incompetent repair of the algae system utilizing lead pipes, an algae culture supplier with poor quality control, or deliberate sabotage.

Genetically engineered algae guaranteed to be anatoxin-free is of course going to be quite a bit more expensive that garden-variety common blue-green algae. A tramp freighter spaceship captain might decided to economize by using cheap algae, and live to regret it. One would think that it would be easy for one ship-captain to ask another if they could borrow a cup of engineered algae, but that would expose them to a patent infringement lawsuit on the part of the algae company. In the real world the company Monsanto has pursued about a hundred lawsuits for seed patent violations and/or breach of contract when they caught farmers who didn't purchase any of Monsanto's genetically engineered seeds but had some growing in the farmer's field. A science fiction writer can imagine agents of NoAnatox Algae Inc. doing suprise spot-checks of spacecraft algaecultures at spaceports, trying to catch violators.

Tom I. Bystanderson observed that suppliers might try to enforce their intellectual property rights by making their custom algae dependent on a slowly-consumed, hard-to-synthesize licensing molecule.

And you'd better keep the algae tanks far from the atomic drive. The last thing you want is for the little green darlings to mutate into something you can't eat. Or worse: something that is really inefficient at producing oxygen.

Christopher Huff begs to differ:


Actually, the algae tanks would make pretty good radiation shielding. "Clean" cultures of the original strain of algae would be easy to carry along to replenish the main tanks if an inedible form did take hold...just stick some packets of dry spores in the radiation shelter. As for the last possibility, a strain that was poor at conversion of CO2 would quickly be out-bred by the better strains. With algae constantly being removed for food, it would quickly be eliminated from the system.

Christopher Huff


In THE MILLENNIAL PROJECT, Marshall Savage sings the praises of Spirulina algae. However, you'd best take the following with a grain of salt. There is often a long distance between the ideal and the real.

Anyway, Spirulina is apparently almost the perfect food, nutritional wise. A pity it tastes like green slime (though Savage maintains that genetic engineering can change the flavor). Spirulina is highly digestible since it contains no cellulose. It is 65% protein by weight and contains all eight essential amino acids in quantities equivalent to meat and milk. It also has almost all the vitamins, with the glaring exception of vitamin C (I guess rocketmen will become "limeys" again). It is also a little sparse on carbohydrates. Savage calculates that it will be possible to achieve production rates of 100 grams (dry weight) of algae per liter of water per day. It breaks down 6 liters of algae water per person, supplying both food and oxygen, while consuming sunlight (or grow-lights), CO2 and sewage. 6 liters of algae water will produce 600 grams of "food" (540 grams is 2500 calories, an average daily food requirement), 600 liters of oxygen, and consume 720 liters of CO2 and an unspecified amount of nutrient salts extracted from sewage. Since food is generally 75% water, 600 grams of dry food will convert into about 2.4 kg of moist food, which compares favorably with the 2.3 kg on the USS Wyoming.

600 liters of oxygen is about 0.8574 kg of oxygen, which is above the NASA requirement of 0.835 kg of oxygen per astronaut per day.

NASA commissioned a study back in 1988 to determine how difficult it would be to cultivate Spirulina as part of a closed ecological life support system.

Algae Tankage

The advantage of algae is that it can theoretically form a closed ecological cycle. This means that 6 liters of algae water, one human, some equipment, and sunlight can keep the human supplied with food and oxygen forever. Theoretically, of course. 0.006 m3 per person compared to 90 m3 per person is a strong argument for lots of green slime dinners for enlisted Solar Guard rocketmen. Of course the Biosphere II fiasco shows how far we are from actually achieving a closed ecological cycle. Don't forget the 0.25 liters of water per person per day to make up for reclamation losses.

“All right, you two!” broke in Tom good-naturedly. “Enough’s enough! Come on. We’ve got just enough time to run up to the mess hall and grab a good meal before we check the ship.”

“That's for me," said Astro. “I've been eating those concentrates so long my stomach thinks I've turned into a test tube."

Astro referred to the food taken along on space missions. It was dehydrated and packed in plastic containers to save weight and space. The concentrates never made a satisfactory meal, even though they supplied everything necessary for a healthful diet.

From DANGER IN DEEP SPACE by Carey Rockwell (1953)

There were some figures in a report on a cruder life-support set up written in 1953. This used Chlorella algae, which isn't quite as good as Spirulina since it has an indigestible cellulose cell wall. The figures assume a Chlorella culture density of 55 grams per liter of water and a daily yield of 2.5 grams per liter. Savage's 100 grams per liter sounds a little optimistic, and 2.5 sounds a little pessimistic. The truth is probably somewhere in between.

At a yield of 2.5 g/l, to provide one rocketeer with 500 grams of food (instead of Savage's 600 grams) will require 200 liters of algae culture.

Urine is passed through an absorption tube to remove excess salt (which would kill the algae) but retaining urea and other nitrogen compounds the algae needs. Faeces are irradiated with ultraviolet to kill all bacteria and added to the urine. This is fed to the main algae tank along with pressurized carbon dioxide (previously removed from the air with calcium oxide). A pump sends a flow of algae culture to the growth trays under filtered sunlight. The culture then passes through a centrifugal separator on its way back to the main tank. The separator performs two functions: [1] removing excess gas to maintain a pressure equilibrium with the carbon dioxide injection and [2] periodically harvesting algae for food. Harvest will occur once a day, extracting 500 grams of algae from nine liters of culture per person. The pump will be controlled such that the algae on the average will experience two minutes of sunlight then three minutes in the darkness of the main tank before it starts the cycle anew.

A fresh batch of urine and faeces is added immediately after algae harvest, to give the algae twenty four hours to consume it. So by next harvest there is no human excretions contaminating the food (you hope).

Now for the answer you've been waiting for. Dr. Bowman estimates that the equipment will mass approximately 50 kg, plus 200 kg per man for algae culture. Since the equipment is such a small fraction of the total, mass savings depend upon getting the algae yield higher than 2.5 g/l. Such as Savage's 100 g/l Spirulina with 6 kg per man of algae culture.

Dr. Bowman points out that when one compares an algae system with merely stocking crates of food, the break-even point occurs at a mission of 145 days (about five months). Below this time it takes less mass to bring crates of food, as the mission duration rises above 145 days the algae tanks get more and more attractive.

Water Wall

This is from Water Walls Life Support Architecture: 2012 NIAC Phase I Final Report (2012)

The idea here is to make a environmental control life support system (ECLSS) with a higher redundancy and reliability by making it passive, instead of active. Meaning instead of needing a blasted electrically-powered water-pump moving vital fluids around, use special membranes so that the vital fluids automatically seep in the proper direction. Fewer points of failure, fewer moving parts, no electricity needed, much more reliable.

The system harnesses the power of Forward Osmosis (FO), which mother nature has been using for the last 3.5 billion years since the first single-celled organism. Each unit has two compartments A and B, which share a wall made out of what they call a "semi-permeable membrane".

Compartment A contains contaminated water. Compartment B contains a solution (the "draw solution") which attracts water like a magnet using osmotic pressure. The contaminated water gets sucked through the semi-permeable membrane but leaves the contaminants behind (because the membrane won't let them through). The pure water (or purer water) winds up in compartment B with the draw solution and the contaminants remain in compartment A.

Since osmotic pressure is used there is no need for an electrical-powered water pump. It happens naturally just like a ball rolling downhill.

The research team noted that there already exists a commercial example of this: the X-Pack Water Filter System by Hydration Technology Innovations. You put nasty river water full of toxins and pathogens in compartment A and add a special sports-drink syrup into compartment B as draw solution. In about 12 hours compartment B will be filled with a refreshing sterile non-toxic sports-drink and all the horrible crap will be left behind in A.

So the research team realized that they could make a full ECLSS if they could develop some different types of forward osmosis bags and connect them together. They need bags that can do CO2 removal and O2 production (via algae), waste treatment for urine, waste treatment for wash water (graywater), waste treatment for solid wastes (blackwater), climate control, and contaminant control.

As a bonus cherry on top of the sundae, since all these will basically be bags of water, they can do double duty as habitat module radiation shielding.

The reliability comes from using lots of independent inexpensive disposable bags. The current system depends on driving an electromechanical water pump until it fails, then frantically trying to repair the blasted thing before all the toilets back up. Because the FO bags are cheap and low mass, they can be considered disposable, the spacecraft brings along crates of them with the other life support consumables. Because each bag uses forward osmosis as a built-in pump, there is no single point of failure. When one bag or cluster of bags, or integrated module of bags uses up their capacity, you switch the water line to the next units in sequence. The used bags can be cleaned, filled, and reused. Alternatively they can be stuffed somewhere in the habitat module to augment the radiation shielding.

This might work well as an affordable life support system for a cheap Maw and Paw TransHab habitat module. May or may not be useful in a SpaceCoach.

Growing Meat


Other SF novels have suggested vats of yeast or tissue cultures of meat ( in vitro meat ) to supplement food supplies. H. Beam Piper's Terro-Human series had spaceships equipped with "carniculture" tanks. A. Bertram Chandler's Rim World stories featured spaceships with all sorts of food vats. Tissue-culture for meat, hydroponics for vegetables, algae and yeast for single-celled food.

But unless they can re-cycle wastes from the crew, it seems more efficient to just carry more boxed food.

Currently scientist can only grow tissue cultures as a single sheet of cells, making them thicker will require figuring out how to make them grow blood vessels to nourish all the cells ("vascularization"). But some technicians figure that they can grow lots of meat cell sheets, then laminate the sheet layers together to approximate a slab of meat.

There are researchers exploring several different strategies to make full-blown vascularization. But it ain't easy. Strategies include material functionalization, scaffold design, microfabrication, bioreactor development, endothelial cell seeding, modular assembly, and in vivo systems. See link for details.

The joke name for this process is "In Meatro"

If you are trying a closed cycle with tissue cultures, you will have to deal with the problem of the Food Chain. Typically each higher level of the pyramid has one-tenth the biomass of the one below, for reasons you can read about in the link. What this means is that you will have to feed ten meals worth of algae to the meat tissue culture in order to produce one meal worth of meat. Even on Terra, this is the reason why meat is more expensive than vegetables.

Obviously the food chain effect also applies to diverting some of the algae to fatten up some fish as a special meal.

At least the tissue culture helps increase the meat ratio. For instance, an entire cow is about 40% edible meat. The rest is bones, hooves, hide, and other inedible parts. Tissue cultures would theoretically turn that up to 100% edible meat. Granted the inedible parts can be recycled via supercritical Water Oxidation, but the inefficiency of wasting all that algae food energy on growing inedible bones kills this idea dead. Not that it would have been practical to bring a cow along on your spaceship in the first place.

As a side note, the idea of lab grown in vitro meat has caused some controversy among the vegetarian community. Any person who is vegetarian on the basis of avoiding animal cruelty, should have no objection to eating in vitro meat. But some vegetarians still maintain that one should not eat meat because of Reasons.

Of course things can become a real moral quagmire, as Sir Arthur C. Clarke points out in his disturbing short story The Food of the Gods.


Feeling suddenly both helpless and useless, Calver left her there in the little pantry, went to his cabin and turned in.

He was surprised at the speed with which he was able to adjust himself to the rather slovenly routine of Lorn Lady. She was pitifully shorthanded by the standards to which he was accustomed; there was no Third Officer, there were no junior engineers for either the Interstellar Drive or the Reaction Drive, and the Surgeon was also the Biochemist and, as such, was in charge of hydroponics, tissue culture and the yeast and algae vats. There were no cadets to do all the odd jobs that were beneath the dignity of the officers. Such jobs were done, if they were essential; otherwise they remained undone.

Safety first, Maclean had said. Safety First. Efficiency second. Spit and polish this year, next year, some time, never. Yet the gleaming, ever-precessing gyroscopes of the Mannschenn Drive Unit (FTL drive) sang softly and smoothly, with never a stammer; and the pumps that drove the fluid propellant into the furnace of the Pile (obsolete term for nuclear reactor) functioned with a reliability that could have been the envy of many a better found vessel. Old Doc Malone was an efficient farmer, and there was never a shortage of green salads or fresh meat in the mess; the algae served only as air and water purifiers, never as article of diet.

From THE RIM OF SPACE by A. Bertram Chandler (1961)

      Sunday dinner we always ate in the wheel, where we had real pseudo-gravity and Ganny could cook the old-fashioned way. Usually we had chicken roast, because that was the tradition, but not always. Chicken was just the fastest-growing protein. And most cost-effective. Ganny was a budget-n*zi. But we also had goose, duck, swan, ostrich, dodo, pigeon, rabbit, beaver, beef, horse, pork, goat, venison, elk, antelope, moose, mutton, lamb, buffalo, tuna, swordfish, salmon, shark, lobster, shrimp, sea turtle, clam, squid, snake, alligator, rhinoceros, dinosaur, or any of the hundred different hybrid-proteins Ganny was growing in the meat tanks. We also had synthetic sasquatch, bandersnatch, yeti, and tribble. If you can imagine it, someone has probably already gene-tailored it.

     The thing about protein farming, you don’t have to worry about flavor too much, because you can add whatever flavor you want long before you start slicing, but you do want to pay attention to muscling, fat content, marbling, and digestibility. All the pieces of the viability equations. And of course, how you exercise the collagen web determines the texture and chewability, which is even more important than flavor. When you get all that balanced, then you either leave it alone, because some people prefer the natural flavor of the meat, or you start adding flavor components, genes, enzymes, hormones, whatever, because other people like their meat pre-spiced—but to Ganny it’s all about cost-effective protein design. So even before the tissue-starters go into the growth tanks, she’s doing targeted gene-splicing and chromosome-braiding and designer-musculature. Starsiders are always looking for better ways to turn CHON into stuff that tastes good, so you have to keep a big library of resources on hand, because you never know when someone is going to invent another new culinary fad, like rhinoceros green burrito or fried buffalo sushi or mango horse fish. On the gig (the momentum-transfer whirligig, their home) there’s always something that needs harvesting and even though most of it was grown to order, it always worked out that there was enough left over for dinner, sandwiches, stews, and snacks. Ganny said it was quality control. She wouldn’t sell anything she wouldn’t eat herself. Mostly.

     Being born on Earth, Ganny and Gampy still had a few dirtside prejudices. Ganny was adamant that she would never grow chimpanzee or any other kind of ape, whale, or dolphin. Also on the list were rat, mouse, squirrel, possum, bat, cat, dog, wolf, hyena, lion, tiger, eagle, vulture, and most other scavengers and predators. No monkeys or elephants either. She did keep all those stem-cells in vitro, in case someone else wanted to buy starters for their own farms, but she wouldn’t grow them for our own consumption. She did give in once on whale and dolphin, just to see, but she wasn’t happy with the amount of water it took to produce a kilo of flesh, even though the water really didn’t go anywhere and we always reclaimed it, but she said the recycling overhead had to be figured in and she felt it was prohibitive. That was what she said anyway. But while she allowed some wiggle room there, she was an absolute wall when it came to chimpanzees and other major primates. “I’m not a cannibal,” she said. “I won’t eat my cousins. Not even metaphorically. Maybe some people will, I won’t.”

From GANNY KNITS A SPACESHIP by David Gerrold (2009)

(ed note: "Chicken Little" is a chicken breast meat tissue culture.)

Arielle went to bed, too, but first she stopped off at the sick bay to get patches for her cracked fingernails, then at the galley to get a bite to eat. She had a double helping of protocheese with real garlic from Nels's hydroponic gardens, two algae shakes with energy sticks mixed in for crunch, then, still hungry, she finished with a desert consisting of a half-pound of white-meat sticks from "Chicken Little" — her real-meat ration for a week — sliced into thin strips and hot-cooked with James's secret recipe of herbs and spices.

From ROCHEWORLD by Robert L. Forward. (1990)

You know I admire classical artists like Rembrandt and Bonestell, and don’t care for abstractions or chromodynamics. I’m not very musical. I have a barrack-room sense of humor. My politics are conservative. I prefer tournedos to filet mignon but wish the culture tanks could supply us with either more often. I play a wicked game of poker, or would if there were any point in it aboard this ship.

From TAU ZERO by Poul Anderson (1970)

“What’s it going to be tonight?” Grevan asked, reaching up to guide them in to an even landing.

“Albert II in mushroom sauce,” said Klim. She was a tall, slender blond with huge blue eyes and a deceptively wistful expression. As he grounded the cooker, she put a hand on his shoulder and stepped down. “Not a very original menu, I’ll admit! But there’s a nice dessert anyway. How about sampling some local vegetables to go with Albert?”

“Klim thinks Albert is beginning to look puny again,” Cusat announced. “Probably nothing much to it, but how about coming along and helping us diagnose?”

The Group’s three top biologists adjourned to the ship, with Muscles, whose preferred field was almost-pure mathematics, trailing along just for company. They found Albert II quiescent in vitro—as close a thing to a self-restoring six-foot sirloin steak as ever had been developed.

“He’s quit assimilating, and he’s even a shade off-color,” Klim pointed out, a little anxiously.

They debated his requirements at some length. As a menu staple, Albert was hard to beat, but unfortunately he was rather dainty in his demands. Chemical balances, temperatures, radiations, flows of stimulant, and nutritive currents—all had to be just so; and his notions of what was just so were subject to change without notice. If they weren’t catered to regardless, he languished and within the week perversely died. At least, the particular section of him that was here would die. As an institution, of course, he might go on growing and nourishing his Central Government clients immortally.

They reset the currents finally and, at Cusat’s suggestion, trimmed Albert around the edges. Finding himself growing lighter, he suddenly began to absorb nourishment again at a very satisfactory rate.

“That did it, I guess,” Cusat said, pleased. He glanced at the small pile of filets they’d sliced off. “Might as well have a barbecue now.”

“Run along and get it started,” Grevan suggested. “I’ll be with you as soon as I get Albert buttoned up.”

From THE END OF THE LINE by James H. Schmitz (1951)

Several calves were born, and seemed to be doing well; the biochemistry of Tanith and Khepera were safely alike. Trask had hopes for them. Every Viking ship had its own carniculture vats, but men tired of carniculture meat, and fresh meat was always in demand. Some day, he hoped, kregg-beef would be an item of sale to ships putting in on Tanith, and the long-haired hides might even find a market in the Sword-Worlds.

From SPACE VIKING by H. Beam Piper (1962)


There is an alternative between eating algae and the daunting task of growing vascularized meat tissue cultures, but you ain't gonna like it.

There are quite a few edible insects that will happily eat algae. Since they are live, they make their own vascularization. They are very efficient at converting algae into insect meat. And a much higher percentage of insect body mass is edible meat.

Yes, most people from western cultures find the thought of eating bugs to be incredibly disgusting. However the astronauts are already drinking recycled urine so it just takes some training. Processing will help, a compressed-protein bar composed of finely ground insects will be easier to eat than a plate full of microwaved bugs with too many legs.

In the following table, the "Algae for 1 kg of animal" is how much algae an entire animal will need to eat in order to increase its weight by one kilogram. "Edible meat" is the percentage of the animal's mass that is edible. "Algae for 1 kg of meat" is how much algae the entire animal will need to eat in order to increase its edible meat mass by one kilogram (i.e., reciprocal of edible meat percent times algae for 1 kg of animal).

You can probably use the "Algae for 1 kg of animal" figure as a ballpark figure for a tissue culture.

Algae to Meat Conversion
AnimalAlgae for
1 kg of animal
Edible meatAlgae for
1 kg of meat
Cow10 kg40%25.0 kg
Pig5 kg55%9.1 kg
Chicken2.5 kg55%4.6 kg
Cricket1.7 kg80%2.1 kg

Data from Edible insects: Future prospects for food and feed security.

If you figure a beef tissue culture requires 10 kg of algae for each new kilogram of beef, the freaking live crickets are still more efficient.

At harvest time, insects are killed by freeze-drying, sun-drying or boiling (in space, exposing them to vacuum probably counts as freeze-drying). They can be processed and consumed in three ways: as whole insects; in ground or paste form; and as an extract of protein, fat or chitin for fortifying food and feed products. Insects are also fried live and consumed, but a deep-fat fryer in microgravity is insanely dangerous. Some species need to have their legs and wings removed before eating.

In practice, extracting insect protein is probably not worth the effort. Needs lots of exotic chemicals and equipment, and reduces the percentage of edible mass. It is easier just to grind them into powder or paste and make bug-burgers.

For more details than you really want to know, read the report.

Science fiction authors could use this as an interesting bit of historical detail. Old-timer spacers can tell tales about back in olden days when they had to eat bugs. You young whipper-snapper spacers have it easy nowadays, what with your vascularized filet mignon tissue cultures.


I was reading the article in Atomic Rockets about growing meat in space where you suggested growing insects as an alternate to lab-grown meat cultures. You use crickets as your example insect. As someone who has raised crickets in captivity I can tell you that there is no way you're going to get a cricket farm in a closed system like a spacecraft. Even a well maintained cricket colony smells like a just-opened bag of chicken feces that has been sitting in the sun.

Go down to a pet store and ask to sniff their crickets if you don't believe me. Those things are absolutely pungent.

Also, crickets are annoying to culture because they eat each other if you're not careful and there's a lot of work that goes into making sure that doesn't happen too much. Plus, they're fast and they jump (and fly!) which makes them hard to keep contained even on earth.

Know what insect is slow moving and has a very mild odor? Cockroaches.

It would thrill me to no end to crack open a paperback one of these days to read about astronauts eating processed cockroach bars. I'm a big fan of cockroaches.

I no longer have a colony of roaches but thinking back to the smell of the colony I'm 95% certain that the only odors were that of decaying paper from the egg cartons and toilet paper rolls I raised the creatures in and the smell of any food I gave them. I raised Blaptica dubia roaches, by the way, because of their inability to climb glass and their lack of sexual behavior at normal room temperature. In case my tank ever broke I would be assured that the subsequent roach infestation would last only a single generation. Also, I could easily throttle the rate that they bred by switching on and off the tank's heater. Male B. dubia roaches have wings, however, and while they do not typically fly they will, apparently, flutter if you pick one up and drop it. I'm not sure how that would work in microgravity. Probably better to choose a species that has no wings at all.

I'll need to think about an ideal roach species for breeding in space, but B dubya is at the top of my list so long as the males don't start flying about in microgravity. A couple factors I would consider is whether or not the roach can cling to glass (so you can open their container without having roach stuck to the lid), whether or not they deposit or carry their egg sacks while they gestate, and whether or not they fly or stink.

From Samantha Davis (2015)


A shmoo is a fictional cartoon creature created by Al Capp, they first appeared in his classic comic strip Li'l Abner in 1948. Shmoos were prolific, required no food (only air), are delicious and nutritious, have no bones or other waste, and are eager to be eaten. (Ironically, they are the greatest menance to humanity ever known. Not because they are bad, but because they are good.)

Oddly enough, shmoos share many common traits with one-celled yeast. Yeast even looks a little like a shmoo. When a yeast cell senses the mating pheromone, it initiate polarized growth towards the mating partner, creating the characteristic outline of a shmoo. The process is called "shmooing", which shows that biologists have a sense of humor. As to the matter of the deliciousness of yeast, see the exerpt from Lucky Starr and the Oceans of Venus below.

The science fiction version of a shmoo is a Frumious Bandersnatch, from Larry Niven's "Known Space" series.

In the real world, left-over brewers' yeast is used to create such foods as Marmite and Vegemite. Even in 1902 people realized that it was a criminal waste to just throw away the huge quantities of perfectly edible yeast protein that was a by-product of making beer. Marmite and Vegemite are still being sold today. Actually in Australia, Vegemite is more or less a food staple.

In science fiction, one occasionally encounters the term "dole yeast". In future societies that have some form of social welfare system for unemployed people, the food given is generally a portion of unpalatable raw yeast, since that is usually the cheapest food available. Single-cell protein is very inexpensive, especially if you grow it on minimally processed sewage.


      He glanced at the menu on a waiter’s chest, and recoiled. “Ye gods. The prices!”
     “This is as expensive as it gets. At the other end is dole yeast, which is free—”
     “—and barely worth it. If you’re down and out it’ll keep you fed, and it practically grows itself."

From PROTECTOR by Larry Niven (1973)

      Bigman turned his attention reluctantly to his dessert. The waiter had called it "jelly seeds," and at first the little fellow had regarded the dish suspiciously. The jelly seeds were soft orange ovals, which clung together just a bit but came up readily enough in the spoon. For a moment they felt dry and tasteless to the tongue, but then, suddenly, they melted into a thick, syrupy liquid that was sheer delight.
     "Space!" said the astonished Bigman. "Have you tried the dessert?"
     "What?" asked Lucky absently.
     "Taste the dessert, will you? It's like thick pineapple juice, only a million times better.

     Lucky smiled and went on, "Venus is a fairly developed planet. I think there are about fifty cities on it and a total population of six million. Your exports are dried seaweed, which I am told is excellent fertilizer, and dehydrated yeast bricks for animal food."
     "Still fairly good," said Morriss. "How was your dinner at the Green Room, gentlemen?"
     Lucky paused at the sudden change of topic, then said, "Very good. Why do you ask?"
     "You'll see in a moment. What did you have?"
     Lucky said, "I couldn't say, exactly. It was the house meal. I should guess we had a kind of beef goulash with a rather interesting sauce and a vegetable I didn't recognize. There was a fruit salad, I believe, before that and a spicy variety of tomato soup."
     Bigman broke in. "And jelly seeds for dessert."
     Morriss laughed hootingly. "You're all wrong, you know," he said. "You had no beef, no fruit, no tomatoes. Not even coffee. You had only one thing to eat. Only one thing. Yeast!"
     "What?" shrieked Bigman.
     For a moment Lucky was startled also. His eyes narrowed and he said, "Are you serious?"
     "Of course. It's the Green Room's specialty. They never speak of it, or Earthmen would refuse to eat it. Later on, though, you would have been questioned thoroughly as to how you liked this dish or that, how you thought it might have been improved, and so on. The Green Room is Venus's most valuable experimental station."
     "I am guessing," said Lucky, "that yeast has some connection with the crime wave on Venus."
     "Guessing, are you?" said Morriss, dryly. "Then you haven't read our official reports. I'm not surprised. Earth thinks we are exaggerating here. I assure you, however, we are not. And it isn't merely a crime wave. Yeast, Lucky, yeast! That is the nub and core of everything on this planet."
     For a moment they sipped in silence; then Morriss said, "Venus, Lucky, is an expensive world to keep up. Our cities must make oxygen out of water, and that takes huge electrolytic stations. Each city requires tremendous power beams to help support the domes against billions of tons of water. The city of Aphrodite uses as much energy in a year as the entire continent of South America, yet it has only a thousandth the population.
     "We've got to earn that energy, naturally. We've got to export to Earth in order to obtain power plants, specialized machinery, atomic fuel, and so on. Venus's only product is seaweed, inexhaustible quantities of it. Some we export as fertilizer, but that is scarcely the answer to the problem. Most of our seaweed, however, we use as culture media for yeast, ten thousand and one varieties of yeast."
     Morriss looked soberly at the small Martian and said, "If you wish. Bigman is quite correct in his low opinion of yeast in general. Our most important strains are suitable only for animal food. But even so, it's highly useful. Yeast-fed pork is cheaper and better than any other kind. The yeast is high in calories, proteins, minerals, and vitamins.
     "We have other strains of higher quality, which are used in cases where food must be stored over long periods and with little available space. On long space journeys, for instance, so-called Y-rations are frequently taken.
     "Finally, we have our top-quality strains, extremely expensive and fragile growths that go into the menus of the Green Room and with which we can imitate or improve upon ordinary food. None of these are in quantity production, but they will be someday. I imagine you see the whole point of all this, Lucky."
     "I think I do."
     "I don't," said Bigman belligerently.
     Morriss was quick to explain. "Venus will have a monopoly on these luxury strains. No other world will possess them. Without Venus's experience in zymoculture.
     "In what?" asked Bigman.
     "In yeast culture. Without Venus's experience in that, no other world could develop such yeasts or maintain them once they did obtain them. So you see that Venus could build a tremendously profitable trade in yeast strains as luxury items with all the galaxy. That would be important not only to Venus, but to Earth as well- to the entire Solar Confederation. We are the most over-populated system in the Galaxy, being the oldest. If we could exchange a pound of yeast for a ton of grain, things would be well for us."

From LUCKY STARR AND THE OCEANS OF VENUS by Paul French (Isaac Asimov)(1954)

This near the center of Ceres' spin, that wasn't from gravity so much as mass in motion. The air smelled beery with old protein yeast and mushrooms. Local food, so whoever had bounced the girl hard enough to break her bed hadn't paid enough for dinner.

He poured a glass of moss whiskey, a native Ceres liquor made from engineered yeast, then took off his shoes and settled onto the foam bed.

An hour later, his blood warm with drink, he heated up a bowl of real rice and fake beans—yeast and fungus could mimic anything if you had enough whiskey first—opened the door of his hole, and ate dinner looking out at the traffic gently curving by.

Miller took another forkful of fungal beans and vat-grown rice and debated whether to accept connection.

Kate Liu returned to the table with a local beer and a glass of whiskey on her tray. Miller was glad for the distraction. The beer was his. Light and rich and just the faintest bit bitter. An ecology based on yeasts and fermentation meant subtle brews.

From LEVIATHAN WAKES by "James S.A. Corey" 2011.
First novel of The Expanse

Growing Both

William Seney points out that as a luxury, some of the algae can be diverted to feed fish such as carp, catfish or tilapia for an occasional treat.

"Aquaponics" is a way of raising both plants and meat in one tank. You use an over-sized deep hydroponic tank to grow the plants. Below the plants you raise fish. The fish are fed food pellets. The hydroponic nutrient media is supplemented by the waste the fish excrete. The plants consume the nutrients, purifying the water and keeping the fish healthy ("rhizofiltration"). The system is more stable than a standard hydroponic rig, since the larger tank will buffer and moderate any changes. The larger volume of water also means you can get away with a more dilute solution of nutrients.

Not just standard fish can be cultivated, the system can also be used for shellfish such as lobsters, shrimp, clams and oysters.

In NASA jargon an aquaculture system is called a "sushi maker".


Also, in addition to fish, a small colony of shrimp or crabs could be fed off the algae, providing a bit more variety in the food supply. Clams could also have a place, providing a useful sink for calcium, carbon, and oxygen in their shells as well as helping to process water. A combination of fresh and salt water systems might work out best.

Christopher Huff

Synthetic Food

If you really want to get back to basics, you can try to synthesize food in a laboratory, with no plants or animals involved. It is probably harder and less efficient than growing food, but might be the only thing left if there is an utter disaster in the CELSS. The crew will call this the horror of Food Pills, and they will be right.

NASA looked into this between the 1960s and 1970s.


LILITH DAWN I'm not fully convinced that synthetic amino acids can replace protein foodstocks. Mainly, I'm concerned about micronutrients which might not be available in plants — although right now I admit I'm not sure what that might look like. Either way, while simplifying food supply is crucial for space exploration, we can't over-simplify it without potential health risks.

WINCHELL CHUNG I suspect that micronutrients will be quite difficult to get correctly. By which I mean human colonization of space will take an ugly toll on the pioneers, as they learn the hard way what is a nutritional luxury and what will cause hideous deficiency diseases if omitted.

In a world building sense, space folk can probably look at an elderly person and peg what year they emigrated into space by observing the physical symptoms of which disease they suffer from.

"Oooh, look at that poor guy's bowed legs. Rickets. He must have moved out in 2215, before they got the calcium level right in the compressed food bars."

From a thread on Google+ (2016)

Between the 1960s and 1970s, the NASA Ames Research Center embarked on a project (check out that link!) to produce food without using traditionally eaten living organisms, such as crops or livestock. The basic premise of the project was that astronauts would continue to explore space on longer and longer missions. The space and weight available for stored foods aboard spacecraft would be limited, and other processes would be needed to feed the human crew. While growing food was considered a viable option, the speed and area in which food could be grown would limit the amount of food available at any point in time. Instead, the program investigated simple chemical methods that could regenerate food using waste products and rocket fuel.

Several publications were published on processes developed to generate edible carbohydrates from water, carbon dioxide, and electricity. These processes relied on the electrochemical splitting of water into hydrogen and oxygen gas. The hydrogen gas would be reacted with carbon dioxide, captured from the exhalation of aerospace crew, to form methane. Methane would then be converted into formaldehyde by a careful partial oxidation with oxygen and led into a series of catalyzed reactions that formed formose sugars or glycerol from the formaldehyde. Formose sugars are similar to the typical sugars we eat, such as glucose, sucrose, or fructose, and so can be readily digested by humans for energy. Glycerol is a common intermediate formed in the human body on the way to metabolizing sugars, and so is also an edible product. These pure carbohydrate products can be further reacted together to form long polymers similar to starch or used directly as sweeteners.

The overall food-generating system would only be limited by the amount of electricity available to run the electrolysis reaction to form hydrogen and could provide the bulk of carbohydrate calories needed by humans. Lipids and proteins are also required for a balanced diet, but the chemical processes needed to produce these food compounds are complicated and laborious. To bypass these challenges, the investigators suggested using a bacterium, Hydrogenomonas eutropha, which feeds on hydrogen gas, carbon dioxide, and minerals, and converts these into a protein-rich supplement that also contains lipids, vitamins, and other essential nutrients needed by the human body. Although a living organism would be used in this process here, the bacteria could produce biomass quickly and without extensive maintenance. That way, an entire diet could be produced using only simple chemical and biological technologies that could be placed in a space craft. However, the technology was never implemented in any practical form for space missions.


(ed note: In the novel, the first trip to the moon is not a two-man Apollo mission. It is more like the Collier's "Man Will Conquer Space Soon!" lunar mission. A huge rocket transports 15 astonauts who build a lunar base. After about two years a relief ship will arrive and ferry everybody back to Terra.

Calamity and woe! The relief ship crashes and is utterly destroyed, along with its crew. And since the lunar base has been thoughtfully located on the far side of Luna, there is no radio contact with Terra. They won't even know that anything was wrong until the relief ship is overdue at Terra.

There is plenty of mineral resources, the explorers have been manufacturing solar power cells, they have all they need &helllip; except food. The genius chemist Moore desperately tries to figure out how to synthesize food from available chemical elements. As a side issue it turns out one of the crew is a self-centered bastard who starts stealing food from the stockroom.)

      July 6: I was surprised today, and seriously sorry, to see Moore secretly swallowing something. I can scarcely believe that he has been our thief, yet the stores were tampered with last night most ingeniously, despite a trip-wire I had strung.
     July 7: I have been watching Moore, and today again he drew a tremendous amount of power to run a small furnace. While it was running he went off and again swallowed something. Tonight he pleaded sick, and did not eat. It attracted some attention, as he did not look sick, and when food is scarce, it is seldom refused.
     August 21: Sixty photo-cells today. Miners overjoyed with new conditions, and report rapid progress. A new bulkhead has been erected. A cableway has been installed in the mine, hauling the loaded trucks back and forth, from the working level, to the lock, out to the roadway. The bulkhead doors are plates taken from the ship. There are but five left now.
     Moore extremely, but not dangerously ill. His stomach was terribly upset, and he vomited for several hours intermittently. I feel sure I know what he is doing, and the man is a hero. Unfortunately the moon supplies no guinea-pigs.

     September 6: My theory was right! At last Moore has talked. He presented Whisler with a 500 c.c. beaker of a peculiar smelling liquid, rather thick, and tarry in appearance, and told him to put it, with one can of peas or some similar vegetable, into a pan with sufficient water to make soup for all, and season it heavily. Whisler did as ordered. The odor was rather awful, the taste nothing to boast of. But within ten minutes of eating we seemed to feel new strength coming back. Moore explained that the stuff was a synthetic protein and fat mixture, exceedingly nutritious, mixed with some of the stimulant stuff he compounded before by accident. However, it requires tremendous power to make the stuff, and needs cells. He will be unable to make any at night, for we cannot supply enough power then. (lunar night is about 2 weeks long, and photocells give no power during night. They burn hydrogen and oxygen for heat, electrolyzed from water)
     He is working on flavor now. Admittedly the flavor is very bad. It has no vitamin content, and our vitamin concentrate is almost exhausted.
     He requires enormous power, since he must use acetylene as the base of his synthesis. This he makes from his natural carbides, but there are a number of complex reactions, all taking power, after that. To get sufficient to make his product for thirteen men, two meals a day, will require far more power than we can readily supply at once, and we have an immediate need for the food. Fortunately we can reduce on the production of water and oxygen temporarily, and turn Reed's power over to Moore and Tolman.
     September 7: Again today the food supply was generously helped out by a portion of the sticky, tarry liquid Moore is producing. We are all helping Moore set up the complicated apparatus he needs—and also mining our food supplies! Food and air from the rocks! Man has conquered this frozen hell, and is living off the most inhospitable territory ever touched. I believe that with men like these we could have wrested a living from cold, frozen Pluto itself!
     Already we feel new strength. The almost pre-digested protein material that Moore made up flows into the blood stream almost as quickly as water, and the small portion of stimulant added raised our spirits.
     The flavor is still vile. Whisler is cloaking it as best he can with tremendous quantities of clove, onion-flavor extract, pepper and celery-seed. But we who have so recently felt our limbs bloating and aching horribly from over-exertion and under-eating can forgive the flavor as we feel the new strength!
     September 8: Last of Moore's already-prepared supply of food-stuff gone, but the new apparatus has begun functioning, and by the day after tomorrow a plentiful, steady supply will be coming in. Moore has three distinct chains of apparatus: one synthesizes carbohydrates, simple sugars, the second modifies part of this product to proteins, and the third makes fats.
     I have not stated that the food-making apparatus — since the tiny battery-house was too small, and the Dome already crowded — has been set up in the great lounging room, as Long calls his upper cavern. It will be moved later to a deeper level.

     September 9: Moore brought up some carbohydrate material, already made. Glucose. We had sweetened coffee again, and the glucose was clear, clean, and crystalline. It had no flavor save sweetness. Protein and fat processes are slower; they will be ready tomorrow, however. Our natural food supplies are down to a few pounds of flour, a little bacon, a keg of cottonseed oil, and six tubes of vitamin concentrate. One small can of dried egg, half used, and a third of a can of dried milk also left.
     September 10: Soup tonight, rich, and highly spiced. Whisler found a can of sage, and that stuff would drown any flavor. This food is certainly highly nourishing. We are all gaining weight again, with astounding rapidity. Dr. Hughey says that is because of the extreme digestibility of the foods.
     Moore has made an astounding proposal. He wants all our old, worn-out clothes! He says he will make them into bread. As they are nearly all cotton or linen, cellulose products, starch will be easy. That is an original use for old clothes. I have heard of men who were forced to eat their clothes, shoes, sleeping bags etc., but not in the form of bread!
     September 11: The food-liquid has been vastly improved. It is a milky fluid now, and almost odorless and tasteless, only a slight acrid taste, something like lemon. The first of our old clothes are back, in the form of a starch that made the soup thicker, and less watery looking. Whisler produced a "vegetable" dye, and colored it red. The menu announced it as puree of tomato. It didn't taste like it, but it was good, we all agreed.
     Plenty to eat again, and we all feel better. The knowledge that we have an inexhaustible supply of food, water and air is tremendously heartening. If it takes a year to build the relief ship, we will be comfortable.
     Moore reports that he will have enough food to carry us over the night.
     September 18: Moore has been adding various things to his food-syrup. It has acquired a flavor today. Like his chocolate-smelling stimulant, but it tastes of chocolate, with some vanilla. Not at all unpleasant. He has also added calcium-and-iron containing compounds, and one with some iodine. Magnesium also. And every day we are growing stronger, and eating more of our old clothes as a fairly tasty bread. These will give out soon.
     September 21: Moore is asking for further platinum supplies for catalysts, as he is making his apparatus 100% automatic. He is working on other elements now. We will need phosphorus and potassium, sodium, other elements than the carbon, hydrogen, oxygen sulphur and nitrogen of his simple food-syrups. He is still working hard at making vitamin concentrates. Hughey is helping him now.
     September 23: Moore gathered up several reams of old paper, some old books we no longer need, and from the Dome some wooden furnishings. Promises other foods. Hughey says we may be afflicted with serious bowel trouble since our synthetic foods contain no bulk whatsoever. One hundred percent digestible.
     September 24: Moore wants a larger laboratory, or another one, really, and a separate power board. Rice is aiding him in making his apparatus purely automatic. It is constructed of gleaming silver and quartz; some tubes, handling particularly violent acids or bases, he has made of the osmiridium alloy. Now he need only put his acetylene in one end, and get sugar automatically.
     September 29: Moore has moved in, and is much pleased. The room has been decorated with a very clever symbolic picture of the chemist with test-tube in one hand, and a loaf of bread in the other, and some more conventional lunar scenes on the other walls (they have moved into the gypsum mine tunnels. They roast gypsum to obtain water).
     October 2: Moore announced making of vitamin A concentrate, an important step. More coming, he says.
     October 8: The very last scrap of natural food, save spices, and a can of tomato catsup, has been used now. They have been put in with the artificial foods occasionally, and now the last has gone. But barren, alternately baked and frozen Luna is supplying us bountifully from her rocks themselves.
     Moore made vitamin C today, and that has been added. Also, he has made a curious, greyish cake, which he asked us all to try. It was rather tasteless, sweetened, and not unlike an ordinary cake. Evidently some form of baking powder has been used. He advised against chewing it too vigorously, and gave us each but a little.
     Tasteless as it was, it was a welcome relief, as the continual soups, though nourishing, pall. They leave your stomach empty quickly. This stayed with me an amazing, almost annoying length of time. We learned it was made with ground pumice stone, a starch-flour made from paper, wood, and cotton, and his food-syrups. I don't know that I want any more. Reed calls them "stoneage cakes."
     October 10: Vitamin B! announced tonight, in considerable quantity. We will have the entire group soon, Moore promises.
     October 21: The night is half gone. Moore has introduced Vitamin G and F into the diet, and has at last succeeded in making a solid organic compound, impregnating it with food-syrup and serving it. It was far better than his solid rock cakes of a few days ago. He says it is pure wood soaked with pre-digested meat and sugar. Anyway, it's good, and it's filling.
     October 31: Moore introduced another vitamin today, so that now our diet is practically complete. The last of the woodwork of the Dome and the last spare paper used up, so in the future all our food will be wholly artificial.
     November 9: Five tons of iron ore brought in. Very heavy labor for all of us. We have been working very hard, and seem to have been losing weight slightly. Moore is increasing the food allowance.

(ed note: they manage to make a little moon hopper, with a LH2/LOX rocket engine. They have plenty of fuel from the gypsum. They make trips to the lunar nearside and send radio messages to Terra)

     November 16: Dr. Hughey and Moore are both worried. All of us have continued to lose weight gradually but steadily, despite the large quantities of energy we have absorbed in our foods. Though eating over five thousand calories per man per day now, far more than necessary, we continue to lose. All known vitamins have been made, and are being included in the diet. Also we are getting plenty of calcium, magnesium, iron, iodine, aluminum and other metals and non-metals. Moore is really worried. This has not been publicly announced. I have sacrificed one of my few remaining shirts, and Garner, Hughey and Moore as well to make some more of the natural-base starch, as Moore calls it. We will watch results.
     November 18: The converted shirts were served tonight. We will watch for results. I, and the other men felt unusually lazy after the meal. Going to sleep now.
     November 19: I have been immensely surprised, and so have Hughey and Moore, to notice that with a startling rapidity, in a single twenty-four hour period, the men have visibly gained pounds! We are convinced that there is some subtle vitamin-like thing in natural substances, that is, organic substances, that makes it possible for accretion to take place. While it is evident our foods supply fuel for our bodies it is also apparent they can't supply repairing materials without the aid of that mysterious something in organic foods. Even organic foods that have been changed from cotton to starch. Then, like vitamins, this something can force the inorganic foods into the body (this is science fiction, but the danger is not. ).
     November 20: The effect of the starch has worn off, and the men are rapidly losing that gain. Unless a constant supply is kept up they will starve with plenty of food! It has been announced publically, and shirts, trousers, everything have been contributed. We now have one suit of clothes apiece.
     November 21: We left in the rocket early this morning, taking off easily, and landed without trouble at our previous position, as determined by Long. The Atlantic coast of North America was in view, and we commenced simultaneous signals with the spotlight and radio. Soon we were in communication again.
     We sent several straight messages, and finally sent a code message Garner had prepared, directed to his backers. This was repeated to us from Earth, and found correct after some trouble. In English it read: "Artificial food lacks ability to support life. No natural food left. Slow starvation. Appears unknown vitamin-like substance missing. We are using cotton, converted chemically to starch. Supply nearly exhausted. Advise doctor with rescue ship."
     More cotton starch tonight.
     November 28: Moore has been giving us nearly 7000 calories of food per day, and with the life-vitamin of the converted cotton, we have been putting on weight at a prodigious rate. It does not seem to strain the digestive system, probably because the food is practically all pre-digested. But now the last of the converted clothing has given out. We can spare no more. We have but one blanket apiece, shoes, one pair of socks, one shirt, one pair of heavy trousers, and whatever woolen material we may have had, which was little, most of it being very heavy duck, or broadcloth shirting. Wool, Moore says, does not adapt itself to his processes.
     November 29: Moore and Hughey devoting most of their time to the work on the few scraps of life-materials they have. Attempts were made to ferment or mold some of our artificial food, on the basis that the molds would be life, even though unpleasant. Our Castle is absolutely hygenic, so much so that no trace of any mold has been found! All our food was brought canned, or treated to make it proof against molds and bacteria. None now to be found, save a few disease germs that can be depended on to be present. Apparently these are too high a form of life, for they will not live in our purely artificial mediums. Even a disease might mean life!
     November 30: Hughey and Moore are preparing a statement of our artificial food supply, and the results observed. This will be sent to Earth when we next go to the message relay point, and fourteen days later we will return, for a statement from the scientists on Earth. Perhaps they will be able to suggest or discover something. Our present situation is rather less pleasant than we had thought. It was hoped that we could live here indefinitely, but unless we can discover the new life-vitamin, it will be impossible. Hughey says that two months is the absolute limit for us now. That allows of only simple starvation, but as many other deficiency diseases, beriberi, scurvy, pellagra and such, do not act as simple starvation, there may be more serious complications. No one knows. Hughey is asking that it be tried on laboratory animals, of which we have none, such as white mice and guinea pigs, which live more rapidly than men.
     December 1: Some of my books on Physics, and Melvilles on astrophysics are being sacrificed. A curious dinner! We are becoming bookworms and moths! Moore has promised us some unusual flavours, at any rate.
     December 4: We gained nearly two pounds apiece on the books. Moore took advantage of the natural starches the sacrificed books provided, to give our weight another boost.
     December 7: The little rocket functioned perfectly. We landed at the relay point in time to be visible from Eastern Europe this time, and gradually all of Europe and the Atlantic came into view. We left again when California was well visible, and part of the Pacific.
     All signalling done by the new spotlight, much more powerful than our other, but radio was worked in conjunction with it. The long articles were sent twice through, and repeated back for corrections. The greatest difficulty was encountered with some of Moore's complex chemical formulas, particularly as they were necessarily structural formulas, and the empirical formula was useless. My chemical learning was slight, but it helped.
     Williamson, in charge of the relief rocket, reports a minimum of six weeks for repairs and equipment, and the pilots will absolutely have to have a month's training before setting out on their trip. That is two weeks longer than Hughey allows us of life. We will have to live an extra two weeks despite medical knowledge. It would be foolish to leave Earth before the rocket pilots knew the handling of their ship, for it, like the first relief, might be wrecked, and the further wait would certainly be fatal. I have taken the responsibility of assuring them we will be able to survive. Garner approves, though Hughey does not, claiming that it will be impossible. There are four other lives on the rocket to consider, however.
     December 17: We are losing weight again, and it has been decided that the last books must go, save the treatises on metallurgy that are left us, since our metallurgists are gone. A last attempt at "weight lifting," as Hughey calls it, will be made.
     December 18: The converted starches today, and heavy meals. Sunrise tomorrow afternoon, and tomorrow we will again get converted starch. This will be practically the end of our supplies of convertible materials. The sheets even, and towels have been taken, and locked in the food lockers! It reminds me again of the thief who stole such considerable supplies of food last fall. I believed, and still believe he hid them. I wonder where they are, and who he was?
     December 19: We have returned (from the Terra radio point) with rather discouraging news. The scientists of Earth have tried and failed. They said that Moore was a genius — which we knew — and that they had had great difficulty in carrying out some of his reactions. Moore has explained (I should say apologized) that he has space to evacuate into, and can work under conditions they cannot procure.
     But their experimental animals all died.
     Very tired now. We all tire easily on these artificial foods.
     December 25.
     Our third Lunar Christmas.
     The ancient songs sound better in our Castle than they did in the Dome — and Moore achieved the near-impossible. The dessert for Christmas Dinner was a real gelatine-like substance of excellent flavor. The protein material was solid — somewhat more so than necessary or intended, perhaps, but even though it was somewhat rubbery, the presence of solid food gave a festive air to the occasion.
     January 3: We are weakening rather rapidly now; most of our fat has gone. Despite the fact that we are consuming more than enough energy, we cannot even retain our weight. Apparently it has never before been known how rapidly the human body wears out.
     January 4: My face is hollow, and cheeks sunken, as with all of us. Our limbs are all well rounded, heavily flushed. They are swollen, but give a deceptive appearance of health. We are wearing only woolen trousers and woolen socks, with our thick rubber shoes. These cannot be converted anyway. Everything that can be is gone. Cuts and abrasions are curiously slow in healing, frequently tending to grow larger instead of smaller.
     January 5: There was no help waiting us. Earth has learned only that the animals all die — and can give us no details of the death. I think they can, but our request for full accounts were answered by saying that the information was not to hand.
     (Duncan was correct in his belief. Dr. Hugh R. Monroe who did much of the hurried work was actually with the operators, but refused to send the requested information. )
     January 7: Moore says he has enough food-syrup on hand to last the rest of our stay here, but will continue work for a while next lunar day.
     We are starving now, but curiously we don't feel hungry, only very tired, and arms and legs and backs ache. And thanks to Moore's stimulants we feel happy.
     January 8: Poor Melville was lecturing on astro-physics. With least body material to use, he is, I fear, failing rapidly. His leg stump is badly swollen.
     January 17: Melville does not seem to be recovering properly, and Hughey is much afraid.
     January 18: Shortly after two o'clock this morning we were wakened by a weak cry from Melville's room. We found his bunk soaked with blood, flowing freely from his stump. Hughey did everything in his power to check it, but tourniquets would check it only temporarily, so long as they were in place. A tourniquet was maintained, but Melville had lost too much bood. He died shortly before seven o'clock. The membrane covering his wound, the new flesh, had been dissolved away during the period of starvation.
     He has been buried on the highest peak of the Cliff above the Castle.
     January 23: Only three quarters of a ton of nitride ore could be brought in, as King fell down on the way back, and seemed to hurt himself seriously. He could not walk, and ore was dumped off, while he was put on our sledge.
     Our crew cannot make the trip next time, our legs are painfully swollen, and Dr. Hughey forbids it. King he says is suffering from a torn muscle. It has, apparently torn itself in two. It is extremely painful, but the pain is rapidly diminishing. King is under an hypnotic drug now. His leg, which was injured, seems sunken, and Dr. Hughey is fearful.
     January 24: We returned safely with a half a ton of limestone, to find King awake and comfortable. On examination Dr. Hughey told us that the torn muscle had been entirely dissolved away! A most horrible form of cannibalism! The body is feeding on itself, any injured member will be removed almost at once by the starving tissues. King says he feels much better. But his leg will be practically useless, as it was the great driving muscle of walking that was torn.
     January 26: Rice has broken his bad leg once more. It suddenly gave way under him while he was going down the corridor, and he fell forward heavily. He caught himself with his hands, and scratched them slightly. Dr. Hughey says this is dangerous. Rice has been put to bed, and his leg is in a cast. It cannot knit till he gets natural food, but it is in the right position.
     Dr. Hughey is more afraid of the small scratches. He has covered them, after thoroughly washing them with antiseptic, with collodion.
     King seems to be getting along all right.
     January 27: King died early this morning. About three thirty he called to us, and we found him in agony. His injured leg was swollen horribly, and a purplish-red color, the skin distended like a bag. The leg muscle had evidently permitted a hemorrhage, and the blood had filled his leg, draining the body. He was very weak, and there was no way to revive him. A stimulant would simply increase the hemorrhage. Blood poisoning was apt to set in as it was. Dr. Hughey drained the leg, after applying a tourniquet.
     About eight o'clock King died. He has been buried beside Melville.
     We begin to understand what it was the doctors of Earth refused to send us, the information on our probable manner of death.
     February 1: Hughy has, with Moore, prepared a report on the probable best treatment for us when relief comes, with instructions as to what will be found in each of the numbered food-syrup jars. These documents will be left in the air-lock chamber. Instructions for operating the lock have been painted on the door.
     February 2: Today was Tolman's last day. He woke this morning about eleven, dazedly. He thought it was the thirtieth, and complained of pain in his abdomen. They got worse presently, and by noon he was writhing horribly. About two o'clock his abdomen collapsed on itself, and he went into a coma, and at 3:45 was dead. I have prepared a cyanide capsule for myself, and several of the others have, after seeing poor Tolman's death.
     We were too weak to transport him to Cemetary Crater, so he was carried on one of the steam cars up to the little rocket hangar, and there we left him, the air being pumped back into the Castle. In the vacuum of space his body will be preserved for burial when the Relief ship brings help.
     Our hair has been falling out for some days, and now we are all almost entirely bald, even eyebrows have gone. Our fingernails and toenails have also begun to drop out, and the quick of the finger, ordinarily protected by the nail, is exposed, and makes every motion agony.
     February 5: Our teeth have been loosening for some days, and two of mine came out today. The gums are bleeding and I cannot stop it. It is slow, but steady. Hughey says it will be fatal, but he cannot reach me as he is across the room.
     This marks the end of Duncan s diary.


     ON JANUARY 30, against all advice, the Relief ship had taken off from Mojave on the long trip, after less than three weeks of training for the pilots. It shot into the heavens with all its power, striving to gather it's utmost speed before the detachable fuel-rocket tail was dropped. At a height of one thousand five hundred miles this was blown off, and hurled back. Now the main body of the rocket began to spout flame, and the ship continued on. Straight into space they bored, and five days later they were circling the Moon, in a steadily diminishing orbit, turning and moving with the utmost care as they accustomed themselves to the machine and the lesser gravity. They had located the Dome, and as they flashed around the satellite they sent back word to Earth. Then the door of the famous Castle was discovered, and radio messages sent. This was late evening of February 6,1982. They received no answer, and realized that the men were either dead, or so nearly so as to be unable to reach the apparatus. They strove desperately to reach the surface. Yet it was nearly noon, February 7, that they landed, a mile and three quarters from the Castle, on an open space, the abandoned road to the Dome, actually.
     They reached the sealed door of the airlock, hurriedly glanced at the instructions, which they had already memorized from Rice's messages sent over a month ago, and entered. The manuscripts inside were at once picked up, and glanced at before any move was made to enter further.
     They found the right one, and hurried down. In the Hall they stopped. Seven emaciated caricatures of men lay on seven pneumatic mattresses. A thin trickle of blood seeped from the mouth of each, and from each finger end. Aghast Caldwell went to the nearest, Rice it was, and listened. Living! He called out quick orders, and these men, who, when not learning to subdue the treacherous Relief rocket that had brought them, had been studying the little guinea pigs, starving on artificial foods, set to work. They knew what to do even better than Dr. Hughey had. Since the last message had been exchanged, the hitherto unguessed vitamin-like RB-X had been discovered, in every form of living matter, and now armed with this they fell to. Quickly Caldwell examined. One — two — three — seven! All living now. But would they survive.
     Hughey opened his eyes inside of three hours, Moore responded next. One by one — till only Whisler was left. He never opened his eyes again. Rice was last to revive, Kendall barely pulled through. But at last all were awake.
     Then, with the invaluable RB-X solution, the natural foods not only weren't wanted, but were not as good as those same starving artificial food syrups, for their digestive systems were ruined. In a day they were recovering, in a week they were moving about. When the next lunar noon came around, they were almost wholly recovered; enjoying once more the Castle, and mourning the friends lost.
     The Garner expedition was ended. The frozen hell of the Moon was left behind. But an enormous thing had been accomplished. Thirteen men, by the might of their brains, and the work of their hands, had wrested from Luna a living, and more, comfort. Had they but known of RB-X solution, they need never have feared. They had established an outpost! The Castle! What memories of the great and the famous that stirs in our minds today? Duncan — Rice — Johansen — Murgatroyd —
     In five years Luna was thoroughly explored, and the Castle was the base. Mines sprang up, other, and lesser, Castles appeared; and then the Lunar Government set the Castle aside as a National Monument. But before that Johansen had used it as his base for the trip to Mars, Murgatroyd had left there, never to return, but only to send back a ceaseless stream of messages from Venus, where he exiled himself, knowing he could not return.
     Today it is open to the public, with the wonderfully fine murals Kendall left as an enduring monument to the Garner Expedition, with the same crude, but staunch and dependable steam engines Rice made, the same little rocket ship, and the same generator. From the great tankrooms came the fuel that carried Johansen to Mars, and Murgatroyd to Venus.
     It is an enduring monument to the adaptability, the determined resistance of Man. On the lifeless, barren Moon, they could not find comfort, so they made it.
     And by their example, made men follow!

From THE MOON IS HELL! by John W. Campbell ()

 Plants are not a particularly efficient source of protein. They tend to be better at producing carbohydrates. As a result, vegetarian diets often focus on a few high-nitrogen plants like beans, soy and peanuts.

 I tend to explore food systems that are familiar, but let's take a minimalist approach and see where it leads. Instead of deriving protein from plant sources directly, what if we use microorganisms to produce amino acids in bioreactors using plant starch as input? This is like that sci-fi staple 'vat meat', but with neither texture nor flavor. Still, amino acids can be stored for years (possibly decades) if powdered and sealed.

As with all my posts, this article is based largely on internet research. I am not a process biologist. I've included sources where possible, but these results should be considered preliminary at best.

Short results: vat-grown amino acids can be yours for 4-6m³ per person.
That includes vats, supporting equipment, hydroponic space and waste treatment.
You will still need to provide bulk calories and other nutrients.

 Let's start with demand. The indispensable amino acids  are tryptophan, threonine, isoleucine, leucine, lysine, methionine, phenylalanine, valine and histidine. Required amounts vary; women typically need the least at about 14g, men in the middle with about 18g and children requiring the most at about 22g. Contrast with protein requirements of 110g, 140g and 90g respectively. These figures are from my menu tracker which is based on US dietary recommendations, so do not take this as specific dietary advice.

 Dietary protein serves two purposes: first as a source of food energy and second as a source of amino acids. If we eat only amino acids then the 'missing' food energy needs to be provided by additional carbohydrates and fats. That also means we only need to eat enough amino acids to satisfy the body's need for building material. The science is not settled, so let's assume we need twice the minimum amount or an average of 36 grams per person per day. Some of this will be provided by other food items but let's ignore any other protein sources for now.

 Production is varied as there are several distinct chemical structures involved in the various amino acids. Each type or family requires a specific environment, feedstocks and process. A basic overview is available on Wikipedia, while a deeper look at processes for the aromatic amino acids is available here. This is just an example; the industry has been active for decades and there is a lot of material available on this technology.
 Plant starches can be readily decomposed into glucose using microbes or enzymes. (see for example the process of making sake; rice is decomposed by a fungus to produce sugar-rich material for yeast to ferment into alcohol.) Sweet potato mash with autolyzed yeast and/or spirulina should be a reasonable starting point for producing a viable nutrient solution.
 The chosen microorganism is grown in a starter culture (1-5l) for half a day and then transferred to a large vat (100-500l) for fermentation over an additional one to three days. For industrial and medical purposes the finished broth is lysed by freezing, vibration or centrifugation and then separated by centrifugation. Further purification steps are applied including filtration and fractional crystallization. For nutritional use this high-grade purification may not be necessary. An example might be alanine as a byproduct of valine production; for an industrial process this would be a contaminant but as a food source it's beneficial. In this case a single-step centrifugation/separation can be applied with the result tested for composition and then dried without further processing.

Yields listed below are lab results, specified in units of product per unit of glucose. Nonessential amino acids are in italics. Many of these values leave significant room for improvement.
There is also a note in the book "Corynebacterium glutamicum: Biology and Biotechnology"  (edited by Nami Tatsumi, Masayuki Inui) on page 111 giving a snapshot look at yields of industrial C. Glutamicum fermentation processes. These values are weight percent, given in {} brackets below; as you can see, most products scale up well but a few do not.

Glutamate - {50%}
Glutamine -  {40%}
Proline - 36% g/g
Arginine - 35% g/g

Aromatic amino acids
Phenylalanine - 25% g/g {50%}
Tyrosine - 30% g/g
Tryptophan - 14% mol/mol {22%}

Lysine - 42% mol/mol {50%}
Asparagine - unknown
Methionine - 20% {17%}
Threonine - 60% {45%}
Isoleucine - 22% {25%}

Ribose 5-phosphate
Histidine - 5.5%

Serine - 45% g/g {32%}
Glycine - unknown
Cysteine - unknown

Alanine - 86% g/g {50%}
Valine - 88% mol/mol {35%}
Leucine - 30% mol/mol

A ballpark value for the overall average yield is perhaps 40% by weight, requiring 90 grams of glucose per person per day.

 Final concentrations average around 20g per liter, with some exceptions (histidine in particular is perhaps 5g/l while some others are over 45g/l). That works out to 8g/l/day or 4.5l per person. Let's double that volume again (for redundancy) and call it about ten liters of bioreactor volume per person. Space is required for starter cultures, nutrient processing and storage; let's assume this supporting volume (and wasted space due to packing issues) is twice that of the vats and call it 30 liters of volume per person. At a thousand liters per cubic meter, 1m³ could serve a bit over 30 people.

Let's go over the drawbacks:

 - The bioreactors have to be controlled (pH, temperature, glucose, nitrogen, oxygen, agitation), which requires energy. Information on power requirements are difficult to find, so I can't offer even a bad guess. This also means some smart tech is required for automation.
 - Product yield is less than 1% of the final broth, so assume that the entire volume has to be treated as wastewater. About 5 liters per person per day.
 - As a biological process, cleanliness is essential. Quantities of soap, alcohol or bleach and washwater will be required.
 - Population control is important. Bacteria evolve rapidly and cross-contamination is a possibility. Vats must be monitored for invasive species and unexpected byproducts. Reserve supplies
 - At least nine separate product lines are required. More may be needed to completely replace food protein needs.
 - The nutrient solution has to provide everything needed for the microbes to grow and thrive. This is on par with intensive hydroponics for complexity.
 - Centrifuges are tricky in microgravity. Angular motion needs to be carefully balanced, so vats should always be counter-spun in mass-matched pairs.
 - The system requires carbohydrates as inputs. These in turn require production of enzymes to break the starch into glucose.
 - Amino acid powders are not particularly appetizing.

These are largely the same drawbacks that apply for alcohol production and can easily be integrated into that workflow. Nutrient supply can be integrated with the hydroponics workflow. Wastewater can be handled largely by evaporation or ultrafiltration (though centrifugation should yield concentrated sludge and fairly clean water as separate outputs), with concentrated wastes blasted in the SCWO reactor and recovered by spirulina. Carbohydrate supply can be provided by either sweet potato (24.0g/m²/day) or wheat (18.5g/m³/day), requiring 3.8 to 4.9 m³ per person. These inputs would co-produce edible protein extracts amounting to 8.6g or 16.5g respectively. Not much can be done for the taste other than combining with protein extracts or other food ingredients, unfortunately; perhaps that will change with applied research.

Here are the advantages:

 - No animals.
 - Simple waste streams.
 - Extremely compact.
 - The tools and techniques can be applied to other biosynthesis products such as ethanol and other industrial feedstocks as well as a broad variety of medicinal compounds.
 - The techniques for producing the necessary inputs are largely the same as for intensive hydroponics.
 - A variety of techniques are available for continual improvement, including selective breeding, directed mutation and outright genetic engineering. Microbial gene editing (such as with CRISPR) allows earth-based developments to be applied to in-space organisms by sending only data.
 - The process can be scaled easily for populations from one to a thousand or more.
 - All of the technology can be built, tested and optimized on Earth. A round of low-gravity performance testing and some engineering sweetness to handle periods of microgravity would be a good idea before deployment but not strictly necessary for use on a spinning habitat.

I still believe it would be beneficial to use all plant wastes as feed for insects, fish and possibly chickens. This represents recapture of energy that would otherwise have gone to waste into food products for variety. Even so, a vat process could be paired with suitable hydroponics for complete nutrition with high efficiency. Sweet potato greens are edible, so a menu could be devised that minimizes plant waste. A steady diet of sweet potatoes, salad and amino acid seasoning doesn't sound very appealing to me but it might be among the earliest self-sufficient space food systems.


(ed note: this is actually creating protein by growing bacteria instead of chemically synthesizing food, but it is the closest attempt yet. It is ten times more energy efficient than growing algae)

A batch of single-cell protein has been produced by using electricity and carbon dioxide in a joint study by the Lappeenranta University of Technology (LUT) and VTT Technical Research Centre of Finland. Protein produced in this way can be further developed for use as food and animal feed. The method releases food production from restrictions related to the environment. The protein can be produced anywhere renewable energy, such as solar energy, is available.

"In practice, all the raw materials are available from the air. In the future, the technology can be transported to, for instance, deserts and other areas facing famine. One possible alternative is a home reactor, a type of domestic appliance that the consumer can use to produce the needed protein," explains Juha-Pekka Pitkänen, Principal Scientist at VTT.

Along with food, the researchers are developing the protein to be used as animal feed. The protein created with electricity can be used as a fodder replacement, thus releasing land areas for other purposes, such as forestry. It allows food to be produced where it is needed.

"Compared to traditional agriculture, the production method currently under development does not require a location with the conditions for agriculture, such as the right temperature, humidity or a certain soil type. This allows us to use a completely automatised process to produce the animal feed required in a shipping container facility built on the farm. The method requires no pest-control substances. Only the required amount of fertiliser-like nutrients is used in the closed process. This allows us to avoid any environmental impacts, such as runoffs into water systems or the formation of powerful greenhouse gases," says Professor Jero Ahola of LUT.

Tenfold energy efficiency

According to estimates by the researchers, the process of creating food from electricity can be nearly 10 times as energy-efficient as common photosynthesis, which is used for cultivation of soy and other products. For the product to be competitive, the production process must become even more efficient. Currently, the production of one gram of protein takes around two weeks, using laboratory equipment that is about the size of a coffee cup.

The next step the researchers are aiming for is to begin pilot production. At the pilot stage, the material would be produced in quantities sufficient for development and testing of fodder and food products. This would also allow a commercialisation to be done.

"We are currently focusing on developing the technology: reactor concepts, technology, improving efficiency and controlling the process. Control of the process involves adjustment and modelling of renewable energy so as to enable the microbes to grow as well as possible. The idea is to develop the concept into a mass product, with a price that drops as the technology becomes more common. The schedule for commercialisation depends on the economy," Ahola states.

50 per cent protein

"In the long term, protein created with electricity is meant to be used in cooking and products as it is. The mixture is very nutritious, with more than 50 per cent protein and 25 percent carbohydrates. The rest is fats and nucleic acids. The consistency of the final product can be modified by changing the organisms used in the production," Pitkänen explains.


Chose three ingredients to make a nutritious meal and it's unlikely you'd pick carbon dioxide, water and microbes. But researchers in Finland are developing a way to zap that simple recipe with electricity inside a bioreactor to create a powder that's about 50 percent protein and 25 percent carbohydrates.

The edible powder could be mixed into a shake or turned into a tofu-like food for people. It also could be transformed into feed for animals. Because it's processed inside in a bioreactor — similar to how beer and Quorn, a British meat substitute, is made — it doesn't require the tremendous amounts of land, water or other resources necessary for large-scale agriculture and doesn't emit greenhouse gases into the atmosphere.

"We detach the whole process from the land," says Jero Ahola, a professor in the department of electrical engineering at Lappeenranta University of Technology. If solar power is used to produce the electricity, the process is about 10 times more efficient at producing food than conventional agriculture that relies on soil, says Ahola.

For this proof-of-concept endeavor, the bioreactor used was the size of a coffee cup, and the process to produce 1 gram of the protein took about two weeks. Ahola and colleague Juha-Pekka Pitkänen, a principal scientist at VTT Technical Research Centre of Finland, say they are working on plans to build a larger bioreactor, about 6 liters (1.6 gallons) in size, by early next year. After that, they'll apply for additional funding to scale up the system even more, building a 2-cubic-meter (71-cubic-foot) bioreactor that can produce 5 kilograms (11 pounds) of powder per day. Imagine one of those 10-pound bags of flour or sugar, and you get the idea.

"We think that we would be able to scale it up rather soon now that we have got it working," says Pitkänen.

At the moment, the system is running at about 26 percent efficiency, meaning that 26 percent of the electricity is going directly toward turning the mixture into food. The team says they feel confident that they can almost double that to achieve upward of 50-percent efficiency.

The Recipe

To make the powder, Ahola and Pitkänen combine carbon dioxide, water and Knallgas bacteria with ammonium, sulfate and phosphate salts, which act like fertilizers. When the ingredients are inside the bioreactor, the scientists deliver a constant electric current through the mixture. The electricity splits the water molecules, which are made of hydrogen and oxygen atoms. Once freed from its molecular bond to oxygen, the hydrogen can be used by the Knallgas bacteria as energy, which helps the bacteria take in CO2 and turn into protein.

"The first real application could be in the desert, feeding people in Africa," says Pitkänen.

Although electrifying a bacterial concoction to make food seems futuristic, it actually dates back to the 1960s, says Pitkänen, when renowned German microbiologist Hans Günter Schlegel and co-author R.M. Lafferty published a research paper in the journal Nature describing the notion. After that, Soviet and NASA scientists began experiments to see if they could use microbes to create food for astronauts.

"They were investigating how one could turn CO2 and microbes into microbial biomass," says Pitkänen.

But the technology for efficiently generating electricity in space was not well-developed. Space ships are a closed system, where everything must be used or recycled. Carrying heavy fuel onboard to make food didn't make sense, and renewable energy was still in its infancy. For years, the idea of turning microbes into food fell behind.

Today, with renewable energy on an upward trajectory, generating zero-emission electricity and using it to convert a brew of water, CO2 and microbes into a powdery protein makes more sense. With a renewed interest in human space travel, food from electricity could find its way into the cosmos.

In the meantime, it has plenty of applications on Earth. Today, 795 million people worldwide lack enough food to eat. A nutritious, high-protein powder could help address global hunger. It may also help the planet overall reduce greenhouse gases, and Finland specifically, which has set a goal to lower CO2 emissions by 80 percent by the year 2050.

"Our Earth is becoming like a kind of spaceship," says Ahola. "We realize that we are approaching limits and we have to think of similar kinds of solutions for these problems."



     Population growth and changes in dietary patterns place an evergrowing pressure on the environment. Feeding the world within sustainable boundaries therefore requires revolutionizing the way we harness natural resources. Microbial biomass can be cultivated to yield protein-rich feed and food supplements, collectively termed single-cell protein (SCP). Yet, we still lack a quantitative comparison between traditional agriculture and photovoltaic-driven SCP systems in terms of land use and energetic efficiency. Here, we analyze the energetic efficiency of harnessing solar energy to produce SCP from air and water. Ourmodel includes photovoltaic electricity generation, direct air capture of carbon dioxide, electrosynthesis of an electron donor and/or carbon source for microbial growth (hydrogen, formate, or methanol), microbial cultivation, and the processing of biomass and proteins. We show that, per unit of land, SCP production can reach an over 10-fold higher protein yield and at least twice the caloric yield compared with any staple crop. Altogether, this quantitative analysis offers an assessment of the future potential of photovoltaic-driven microbial foods to supplement conventional agricultural production and support resource-efficient protein supply on a global scale.

     Production of nutrient-rich foods derived from microbial biomass, better known as microbial protein or single-cell protein (SCP), offers a promising means to address food security without exacerbating pressure on the environment, as it utilizes water and nitrogen more efficiently than plants. Several companies are already producing SCP derived from algae, fungi, or bacteria at commercial scale destined for animal or human consumption. The feedstock used to cultivate these microbes is typically either agriculturally derived glucose or fossil-derived methane and methanol. Yet, a more sustainable alternative, which minimizes reliance on fossil carbons and agricultural land, is to use renewable energy (here, photovoltaics) to convert atmospheric carbon dioxide and water into molecules that can serve as electron donors for microbes. Previous studies have considered the land requirements for SCP production using feedstocks derived from agriculture, fossil fuels, and, more recently, also renewable energy. Nevertheless, a comprehensive assessment of land and energy efficiency of fully photovoltaic-driven microbial food production is still lacking. Focusing on solar energy allows us to compare the potential of food production using microbes against contemporary agriculture on an even playing field, since both technologies rely on the same primary resources (i.e., land, sunlight, water, and fertilizers). More specifically, this study sought to answer how productive photovoltaic-driven SCP (PV-SCP) systems can be in terms of calorie and protein production per unit time and land area in comparison to other SCP systems and to conventional crops, focusing on the effect that solar irradiance has on PV-SCP yields. This quantitative comparison can assist in planning the future allocation of limited land resources toward feed and food production.


     The cultivation of microbial biomass, which is rich in proteins as well as other nutrients, can play a vital role in achieving food security while mitigating the negative environmental footprint of agriculture. Here, we analyze the efficiency associated with using solar energy for converting atmospheric CO2 derived from direct air capture into microbial biomass that can feed humans and animals. We show that the production of microbial foods outperforms agricultural cultivation of staple crops in terms of caloric and protein yields per land area at all relevant solar irradiance levels. These results suggest that microbial foods could substantially contribute to feeding a growing population and can assist in allocating future limited land resources.


Energetic Efficiency of SCP Production. We considered a PV-SCP system that converts solar energy into energy stored in food by the following four generalized steps (Fig. 1):

Process (1) corresponds to PV solar farms capturing solar energy and converting it to electricity. Process (2) represents the electrochemical conversion of electrical energy into chemical energy stored in an electron donor and/or carbon source. Process (3) refers to microbial growth which converts the chemical energy from the previous step into chemical energy stored in biomass. Process (4) describes a filtration step whereby nucleotides, fatty acids, and carbohydrates are discarded while only the protein is retained. The removal of nucleic acids is crucial when SCP serves as a human food since in too high of concentrations, their catabolism leads to an accumulation of uric acid, which cannot be easily degraded and can form gout. Unlike humans, all farm animals possess the enzyme uricase, which precludes this effect, therefore making nucleic acid removal unnecessary for feed production. Each of these processes is associated with different energetic efficiencies—ηpv, ηec, ηbio, and ηfilter (Fig. 1)—which we calculate according to available measurements, as explained in Methods. These four steps describe the direct transfer of energy from solar to biochemical storage in food. However, operating the SCP system also requires several electricity inputs not depicted in this linear chain, and we account for all of them by introducing another efficiency term η*, which is described below. For example, η* accounts for the energetic cost of operating DAC which supplies the CO2 required at steps (2) or (3).

Fig. 1. Schematic representation of energy transfer during production of single-cell proteins from solar energy. Each conversion step is associated with an energetic efficiency, η. The effective electricity use efficiency, η*, corresponds to the fraction of electricity used for electrosynthesis of the electron donor. The rest of the electricity (dashed red arrows) is distributed among supporting processes, including DAC of CO2, provision of macronutrients, bioreactor operation, and biomass downstream processing. The entry point of CO2 in the production chain, depicted by an “exclusive or” rhombus, depends on the choice of the electron donor. When hydrogen serves as the electron donor (case A), concentrated CO2 is supplied to the bioreactor along with the H2 and O2 produced in the electrochemical cell. For the production of formate (case B) and methanol (case C) as electron donors, CO2 is supplied to the electrochemical unit, while the only input gas supplied to the bioreactor is oxygen. In each case, we assumed that the oxygen fed into the bioreactor is derived from water splitting (in the electrochemical unit) and that CO2 from the bioreactor off-gas is directly recycled with negligible energy cost. Following growth in the bioreactor, the harvested biomass enters downstream processing. Two production scenarios are depicted depending on the desired final product. For the production of animal feed, the feed downstream processing includes only the removal of water, by centrifugation and spray drying, such that all cellular components are retained in the final product. For the production of human food, the food downstream processing includes two additional steps to reject nucleic acids, beadmilling and microfiltration, which discard the nonproteinaceous components from the final product. Hence, the food downstream processing requires additional supporting energy and includes an energy loss step (in the form of discarded biomass), denoted by ηfilter.

     Following the conversion of solar energy to electricity, electrical energy is converted into chemical energy by producing simple molecules (electron donors), which support microbial growth. To provide a broad perspective on the properties of different electrochemical and biological processes, we considered three electron donors (hydrogen, methanol, and formate) and several microbial assimilation pathways. For the production of all of the three electron donors considered, water is first split and oxidized at an anode to provide electrons and oxygen (O2) to the processes. Carbon dioxide (CO2), which is the only primary source of carbon in the production process, is obtained via DAC of CO2, and, as shown in Fig. 1, there are two possible entry points for CO2.

Recycling Wastes

Wastes have to be fed to the algae, or whatever. But it would be nice to turn the astronaut poop into sterile chemicals first instead of infecting the algae tanks with E. coli bacteria. And the problem of reducing to useable form plant stalks, fish bones, chicken feathers, and other tough scraps. Not to mention all the plastic bag bits.

Enter the Supercritical water oxidation (SCWO) unit.

By placing water at temperatures and pressures above the thermodynamic critical point, it turns into a fluid that combines the worst properties of a blast furnance and sulphuric acid. You feed anything into one of these hellfire-in-a-box thingies and nothing is going to come out the other end except water, oxidized chemicals, and mineral ash. This happens at about 374.1°C and 22.12 Mpa.

The only estimates I've managed to find (Parametric Model of a Lunar Base for Mass and Cost Estimates by Peter Eckart) for a SCWO unit are:

  • Mass: 150 kg per person being supported
  • Expendibles required: 10 kg per person per year
  • Volume: 0.5 m3 per person
  • Power required: 0.36 kilowatts per person
  • Heat load: 0.09 thermal kilowatts per person
  • Liquid waste input: 27.18 kg per person per day
  • Solid waste input: 0.15 kg per person per day

Waste products from the astronaut's septic tanks and tablescraps are run through the SCWO. The appropriate output chemicals are fed to the Spirulina, which multiplies in meters of transparent tubes run under filtered sunlight. Filtered because raw sunlight in outer space is quite deadly to algae, and it isn't too healthy for humans either.


Water is pretty near the universal solvent at room temperature. Heat it to quite high temperatures, under fairly high pressure so that it doesn't boil, and it gets, uh, more so. Dissolve a bit of oxygen in it, and you have a fantastically corrosive witches' brew that will vigorously attack almost anything. Throw in just about any organic substance you care to name, and out comes water, CO2, nitrogen, and sterile ash (oxides of metals, mostly). One of the bigger practical problems, in fact, is making the equipment stand up to it. The other major problem is that it's pretty power-intensive, because of the high temperature and high pressure.

It's pretty much the preferred way to recycle organic wastes — kitchen garbage, human wastes, etc. — in designs for advanced closed-cycle life-support systems.

Henry Spencer

There is more information on SWO units here. The first reference describes a facility with a volume of just over 20 cubic metres that can process 7.5L per minute, more than enough for a crew of 300. (30L/person/day - 20 hours a day). Thanks to William Seney for these link.

General Atomics has some developed some SWO units for waste disposal.

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