Growing food on Mars is an exercise in efficiency. The facilities will not (at least initially) be available to grow every kind of fruit, vegetable, grain, nut and herb that we are used to. We may only be able to grow small amounts of a small number of crops. For a while there may be restrictions on the number of available ingredients and therefore the meal choices. The challenge is to find which crops deliver the most nutrition for the amount of volume, mass and energy required to produce them.
Top of this list would surely be spinach. Tomatoes, mushrooms, cabbages, garlic, kale, carrots would perhaps also make the list. What is the best way to grow each of these?
There are 3 primary mechanisms proposed for producing food on Mars:
- In soil
Experiments are already underway to grow food in Martian soil simulant. Because all the chemical elements necessary for life are available in Martian soil, it should be possible to grow plants in it; however, it will be necessary to analyse the crops thus produced, in order to determine if they have healthful levels of vitamins and minerals. They will not necessarily have the exact same nutrient profile as their counterparts on Earth, because of the availability of those elements in the soil.
Some chemical processing of the soil may be necessary to prepare it for plant growth; for example, it may be too acidic or salty. Therefore the addition of a specially prepared fertiliser may be necessary. It may be beneficial to introduce worms to the soil and feed them with food scraps, so they can process the dirt grains and organic material together to make fertile soil. Of course, for this to happen we would initially need food scraps, which would have to come from somewhere, so this would not be an option for the first crops.
In any case, the first crops are more likely to be grown using hydroponics or aeroponics. These are similar setups in that the plants are grown in a dirt-free environment, fed with nutrient-rich water. In the case of hydroponics, the water flows through pipes in which sit the roots of the plants, so they can access the nutrients in the water. In the case of aeroponics, the plants are suspended, with their roots exposed to the air; nutrient-rich water is provided to the roots as a mist.
The primary advantage of aeroponics over hydroponics is that the water requirement is minimal, which will be important for a Mars base where water may be scarce in the early years. The disadvantage, however, is that the mist greatly increases the relative humidity of the greenhouse atmosphere. Relative humidity of controlled environments like spacecraft atmospheres should not exceed 70% (according to NASA guidelines), as this can interfere with electronics or cause build-up of mould. This could be addressed by separating the greenhouse environment from the main habitat environment by a gate.
A double-gate, whereby a person transitioning from the habitat to the greenhouse would open one gate, step through, close that gate behind them, open a second gate, step through and close that one behind them, may be an effective method of containing humidity in the greenhouse. However, this level of control is probably unnecessary, and a single gate will work fine if people don’t leave it open. The small amount of water vapour that would travel across from the greenhouse to the habitat would be easily soaked up by the habitat’s ECLSS.
One way to mitigate the migration of water vapour from the greenhouse into the habitat would be to place intake fans near the gate, which draw air form the region around the gate into the THC (Thermal and Humidity Control) subsystem of the habitat’s ECLSS, which will remove any surplus water vapour from the atmosphere.
Aeroponics may therefore be the preferred choice. The questions remain:
- What crops would be good to commence experimentation with? (e.g. spinach and tomatoes)
- What nutrients are added to the water provided to the system, if any?
- What mass and volume of equipment is required to produce what mass, volume and nutrient value of food?
Another downside of aeroponics is that in some cases the crops will not grow as large as they would in a hydroponic system or if they were grown in soil. This is usually due to lack of available nutrients in the provided water. When using water enriched with sufficient nutrients, and with the proper equipment, aeroponic crops can grow to full size.
Therefore, if we are to experiment with an aeroponic system on Mars, it will be important to take with us a supply of nutrients optimised for aeroponic crop production.
Aquaponics combines hydroponics with fish-farming, and is another approach to food production that has been suggested for Mars. The fish can be fed food scraps, possibly supplemented with special food; the water in which the fish swim becomes nutrient-rich due to the metabolic outputs of the fish, and is then provided to the plants via the hydroponic system.
The main problem with aquaponics is the amount of water required, which is naturally much higher than for the other proposed methods. It is far more likely that Martians will be vegetarians, which is perfectly safe and healthy; many millions of people on Earth live healthfully on plants only. Producing food from plants is considerably more efficient in terms of energy and water, which will be crucial on Mars. In fact, it’s also crucial on Earth, but humanity is still learning this. Some scientists predict that by 2050 everyone (or perhaps the majority of people) on Earth will be vegetarian due to expansion of the population. In any case, if aquaponics is implemented on Mars it will probably not be for a few years, when water and energy production are much higher.