Martian farming

Mars is famously a barren planet of dust and rocks, having nothing that could qualify as soil. Earth soil consists of 45% minerals and a varying composition of organic material, water and bacteria. Mars however is covered in a layer of oxidized iron dust, which gives the planet its' famous red hue. This dust also contains other nutrients like sodium, magnesium and potassium, but not enough to support growing plants. No wonder mars has no vegetation!

But there are ways to make our own soil that is able to sustain plant life. The most important elements for plant nutrition is nitrogen, phosphorus and potassium, with sulfur, magnesium and calcium being secondary in importance. Martian "soil" already contains magnesium and potassium, and there exists water frozen on Mars which could help hydrate the soil. But we would need at least 2 of the 3 important elements to support plant life, where do we find those elements?

That's right. Human feces contain our remaining elements phosphorus and nitrogen, and have been used in agriculture for centuries. While there can be health risks to using untreated human feces as fertilizer, the process of drying it out removes the risk of parasitic or bacterial infections while still preserving the necessary elements for fertilizing soil. A toilet system on the Mars colony could be made to reclaim as much water as possible from human waste, and to process the remains into usable fertilizer. The ISS orbiting earth already recycles water with a 98% water reclamation rate, so the technology does exist. And with careful use of water in the greenhouses, the whole system should stay sustainable, with additional water gathering available in martian permafrost.

A martian colony would require as much reuse as possible to stay sustainable by itself. Sending supplies from Earth is too costly and take too long to arrive, which is why the colonists would have to live by 'Waste not, want not' to survive.

So we've already talked about the water reclamation system used on the ISS, but this only reuses the water already found within the system. What can be done to get enough water to get the colony and farm up and running, without having to resort to expensive cargo transports of water from earth? Well, we just dig it up.

During unmanned missions on Mars, there has been discovered permafrost 1-3km thick all over the planet. During a study  conducted by NASA, they concluded that using microwave technology it was very simple to melt the permafrost and make water for any potential colonies. Using small unmanned crafts, we can collect bits of permafrost and bring it into another facility which melts the ice, filters it and introduces the water into the system.

Mars is a harsh environment to grow in, even when supplemented with our state of the art fertilizer. So the crops we elect to grow have to be robust generalists that can survive without specialized growing conditions. They also have to provide nutrition to our colonists and have to provide adequete oxygen production through photosynthesis.

Undergraduate students have, in collaboration with NASA, attempted growing various crops in simulated Mars like soil, and found that various crops grow surprisingly well and taste almost no different than their terrestrial counterparts. As long as the soil is kept hydrated, maintaining a consistant 50%-60% humidity rate, crops like potatoes, carrots, onions, kale and garlic could grow like regular. And while sunlight is only 43% as strong on Mars as it is on Earth, it is still strong enough to support photosynthesis in leafy crops.

Photosynthesis only requires sunlight, water and carbon dioxide, and works optimally when the plants get some hours of dark to rest. Optimally, crops in the greenhouses would produce oxygen for 16 hours, supplementing sunlight with growth lamps when needed. Plants would then get the remainder of the martian 24,5 hour day off in the dark to rest. 

So we've solved the questions of plant growth, fertilizer, air, food and water. But all of this requires power! How would such an operation stay powered on?

In most martian colony models, the use of solar power is very common. Relatively cheap when set up properly, and infinitely available. Though as we stated earlier, sunlight is only 43% as strong on Mars as on Earth, so the power generated from solar power would be very lacking compared to the yield on Earth. Additionally, Mars' surface is very prone to dust storms, so the panels wouldn't produce any power during a storm or even at night.

Nuclear power would provide a constant flow of power during any part of the day. Radioisotope Thermoelectric Generators, or RTGs, have been used for unmanned missions to mars to power rovers, but would have issues providing enough power to en entire colony. Though they would still be useful for small unmanned crafts performing tasks on the martian surface. Such as small diggers that can dig up martian permafrost, and bring it back to be used in the colony.

Kilopower Heat Pipe reactors however, using fissile uranium, produce a lot of power and a lot of heat. As such, using one would greatly benefit the colonies since the power it would provide is sufficient, and the heat it gives off can be used in addition to the colony heating system to keep the colony's temperature at a comfortable level. The downside to these generators however is that the fuel they require isn't readily available on Mars. Though it might be possible to find fuel through mining, there is no guarantee. As such, fuel for the generators would have to be shipped to mars when required. But nuclear fuel lasts a very very long time, so refuel runs like that would not be required often enough to be an issue.

Therefore, we propose a combination of solar power and nuclear power to keep the colony running. Solar power, while weaker on Mars, is still a semi permanent energy source, and nuclear power is a long lasting energy source which works around the clock. Together they could make up for eachothers differences and would be safer in case one experienced a problem.