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I'm trying to figure out how big a martian greenhouse would need to be to feed one person or supplement a significant portion of their diet.

Question: What is the maximum amount of Calories one cubic meter greenhouse in optimal conditions can produce per day?

Assumptions:

  • Volume does not include environmental regulation systems and we assume the greenhouse, no matter the size, is at the ideal temperature, pressure, and atmospheric conditions.

  • Advanced farming techniques are used (aeroponics + vertical farming probably)

  • Genetically engineered plants may be used as long as they exist today (even if they're still in labs)

  • We've got a nuclear reactor/ large solar panel farm ensuring energy for lighting is available 24/7 should it be needed

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  • $\begingroup$ The sunlight is 1/3 compared to an equivalent location on Earth. The greenhouse will need three times the area of one on Earth. $\endgroup$ Apr 28, 2018 at 4:38
  • $\begingroup$ This question is related. If the plants make enough oxygen for someone to breathe, they also make enough food for them to eat, more or less space.stackexchange.com/questions/26668/… $\endgroup$ May 1, 2018 at 20:44
  • $\begingroup$ @C.TowneSpringer My experience with most plants I have grown is that they will adjust the amount of chlorophyl in their leaves to match the available light. If I take a plant and put it in partial shade its leaves will darken, and if I put it in direct sunlight its leaves will lighten. So, a larger greenhouse might be necessary, but maybe less than 3X in size. $\endgroup$
    – user4574
    Nov 29, 2022 at 21:54

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This research I was involved in may help answer your question. The project outlined below used algae, which is sort of a plant, in a bioreactor. The research was concerned with producing oxygen, not food. The design objective was to recycle one person's CO2 into O2, with the C being converted back into carbohydrates and other biomolecules.

The study used Chlorella vulgaris algae for generating medical oxygen using solar energy in off-grid medical facilities.

Bottom line: it requires one cubic meter (one metric ton) of nutrient medium per person. The mass of the algae itself is trivial compared with the growth medium.

Light is toxic to the photosynthetic enzymes in algae. Sunlight needs to either be attenuated or intermittent. Light intensity decreases as it passes through the medium. If you are attempting to minimize the mass of the medium, you will need to use LED light source (and the attendant solar panels) rather than direct sunlight.

The algae themselves attenuate light so either algae density needs to be low (lots of medium) or LEDs must be close together (lots of LEDs).

Algae are not very efficient at converting light to O2. That’s not what evolution selected them for. Overall, they are 12% energy efficient at separating CO2 into O2 and carbohydrates. The bioreactor process is power intensive, so it becomes a major power load on a spacecraft or on a Mars-based installation.

The bioreactor needs to be mixed, but very gently since the algae are fragile. On Earth this is usually done with bubbles rising through the medium, but the bubble size needs to be controlled to prevent shear forces on the algae. In microgravity, bubble mixing is not available. Mixing the cubic meter of medium in small passages is a non-trivial problem. On Mars, bubbles would work fine. Not so on a space vehicle.

Separating O2 bubbles from the medium is easy if gravity is present as it is on Mars. Once again, not on a space vehicle.

High O2 productivity is dependent on keeping the algae on a particular point of their growth curve by regulating density, light intensity and nutrient levels. The bioreactor will need attention, maintenance and problem solving. The Martian astronaut becomes a farmer.

The bioreactor produces a large amount of green goo and consumes significant amounts of electrolyte nutrients. In theory a closed loop could be engineered where Mars astronauts could poop in the bioreactor and eat the goo. You might want to run that past them first.

Bottom line:

  • Mass of algae and medium: 1 metric ton per person

  • Size of container: 1 cubic meter (within Mars colony's temperature
    controlled pressure hull).

  • Mass of containment, solar panels, lights, pressure hull volume and
    control systems: 1 metric ton per person

So (in very round numbers) you are looking at 2 metric tons per person for the bioreactor.

According to NASA each person aboard the ISS consumes 0.84 kg O2 per day. 2 tons of O2 per person would last 6.5 years at that rate. From a mass budget perspective it makes more sense to use O2 boil-off from propellant tanks than to carry a bioreactor for interplanetary voyages or Mars colonies. Boil-off would also be much more reliable.

So bioreactors don't make sense for producing O2 on Mars. Maybe they do make sense for making edible green goo.

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  • $\begingroup$ “Edible green goo” reminds me of the mysterious goo from Kerbal space program. $\endgroup$ Nov 29, 2022 at 5:54

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