Building a large permanent colony on Mars presents significant challenges for whomever is responsible for administering it.
Humanity has some experience with (relatively) closed, space-based systems that reuse air. For a detailed discussion of how the International Space Station maintains its air supply, see here.
There are several component factors involved in supplying a Mars colony with air: the initial supply, which is likely imported in one or more forms which we’ll discuss in more detail below; new and ongoing resupply; filtration methods; and locally produced air.
Since there is very little margin for error with regards to air supply, the colony will likely use a mix of different methods in order to maintain a breathable atmosphere.
Also, some of the same issues of scale apply to air, as they do to water. Tens of thousands of colonists have a significant daily requirement for breathable air. Demonstrating the scale is harder though, because (unlike with water) we’re used to not having to think about the issue in a terrestrial environment. One example is that it takes on average 5 to 7 three liter bottles of compressed air to climb Mount Everest. You can see some images of the enormous garbage pile at the top here. Now multiply that by tens of thousands – per day.
Air can be transported to the colony in several forms, including compressing it (which could pose safety issues), or transporting one of various chemicals which can easily be turned back into some combination of oxygen and other byproducts. Many of these types of systems have extensive history of usage on a variety of space-based platforms. None of them are entirely reliable, so are typically used in combination with various backups. One implication is that these systems will need to be designed for local servicing – i.e. spare parts should be easily made with 3D printers, and the architecture should allow for simple maintenance.
Mechanical filtration typically consists of two different systems: one to remove carbon dioxide from the air, and the other to remove various types of odors. The CO2 filtration system will need to be designed with some of the same constraints as O2 production, so that it can be easily repaired. In addition, it will be backed up by natural systems as described below. Odor removal is a significant issue in closed-cycle environments. Anyone who has worked in an office building understands the issue viscerally. Some odorous gases can be physically harmful at certain levels of concentration at well (i.e. methane). For both the physical and mental well being of the colony, this subsystem will need to work reliably!
The colony will likely have very substantial plant growth, and not just in defined agricultural zones. In some ways, the plant biomass will help regulate the atmosphere, although it may cause complications as well, since plants have a regular “breathing” cycle. Plants should therefore be considered a valuable backup to mechanical systems, rather than the primary.
It will likely be necessary to produce at least some oxygen locally. No environment can ever be entirely closed (one example: airlocks tend to outgas somewhat on each cycle), and losses will have to be replaced. The results of baking a sample of Mars’ soil in Curiosity’s oven produced oxygen vapor, along with other chemicals (see chart, partway down the page here). Some analysis will no doubt need to be done to determine the economic feasibility of largely producing the necessary atmosphere locally. One potential hitch is that some of the other gases produced will need to be filtered out (i.e. chlorine). Aside from health issues, it would be very unpleasant it the colony continually smelled like an indoor swimming pool.
We have somewhat less practical experience with growing food in enclosed environments. While many space-based experiments have involved growing plants, actual attempts to grow food for eating by astronauts are still in planning stages, and wouldn’t come close to producing enough food to supplant the regular supply visits.
On Earth, the most famous (or possibly infamous) experiment of this nature was Biosphere 2. While at least one crew managed to feed itself with their own efforts, others didn’t. Its worthwhile reading the linked Wikipedia article for some of the other issues that they encountered, many of which are relevant for a Mars colony. In addition to these, there are two further points worth mentioning: the variety of food was necessarily somewhat limited (which is possibly ok for a small team of dedicated researchers over a defined period of time, and less so for a small city), and the experiments don’t reveal whether the methods can be adequately scaled up.
Ensuring that the food supply is safe, and protected from disease or disaster will be high on the administrator’s priority list. Variety and multiple redundancy, as well as a hefty margin of error, will all need to be factored into the plan.
As with everything else, the food supply for the colony will consist of a mixture of expensive imports, and cheaper (but less various) locally produced foods. There will need to be a significant effort to produce as wide of a variety of foods as possible locally; variation in diet is tremendously important for adequate nutrition. In addition to basic staple crops and fruits, there are a number of animals that aren’t too ecologically taxing, and that would provide some (somewhat expensive) protein, in addition to leather and other materials.
There is a lot of argument over how much space is required to grow crops for a given number of people. Although there will be no shortage of physical room on Mars, remember that food will be produced in closed environments with their own air supply, and that somebody needs to physically build them in the first place, and then maintain them – quite aside from the labor involved in farming. Consider the volume of farmland that surrounds a typical Western city. Even with high yield techniques, such as multiple layers of hydroponic systems, feeding that many people will require an industrial-scale effort.
Who will do the farming? This question will be dealt with in a future post about demographics. Even with significant automation, providing food for the colony will require significant numbers of people. If the average one-way ticket to Mars costs hundreds of thousands, or millions of dollars, there will need to be some way to ensure that sufficient numbers of farmers (never mind agricultural researchers) make that trip.
Some final quick points – who will get to decide which foods are available? Will different cultures have access to favored foods? Will unhealthy snacks be produced? What about alcohol? These decisions, and also how they will be made, are going to be vital for the ongoing health of the colony. Substantial effort will need to be made in order to ensure that the process works.
Continued in part 4, here.
Mars Colony Administrator’s Handbook – Navigation:
- Part 1 – Introduction
- Part 2 – Resources, Water
- Part 3 – Air, Food
- Part 4 – Energy, Raw Materials, People
- Part 5 – Supply Chain Management, Urban Planning
- Brief Intermission
- Part 6 – Jurisdiction and Law, Economics
- Bonus Post
- Part 7 – Manufacturing, Communications
- Part 8 – Emergency Services, Failure Modes