An Analogy – The International Space Station

Building a habitable structure on the Moon presents us with the greatest technological challenge to date. Two factors aid us. One; we have visited the Moon, walked through its dust and driven across its plains. Two, we have completed the International Space Station, a habited structure well above the surface of the Earth though still somewhat within the Earth’s protective atmosphere. The first gives us confidence that we can complete this task successfully. The second demonstrates to us a process for completing this project as well as enabling us to estimate its cost and schedule. With this we can show that a habitable structure on the Moon is doable today.Let our design driver be the human requirements. A person’s productivity directly relates to their basic needs; air, water and food. As well they need adequate space to move, to walk, to work. None of these are simple metrics as they each relate to many parameters. Nevertheless we have enough for an estimate.Humans on Earth breathe in air and exhale much the same but with an elevation of the carbon dioxide molecule and a decrease in the oxygen gas molecule. For this one could simply remove the carbon dioxide and add oxygen much as was well shown during Apollo 13s flight. As well we will include the amount of air that is lost through purges, airlocks and joints. Remember that our structure will be a shirt sleeve environment for people so its internal air pressure must be similar to that at sea level on Earth. However outside of the structure is the emptiness of space. The pressure differential is immense and will cause a perpetual loss of air.

Water is equally precious to humans. About 70% of each of our bodies is water. It is the conduit through which we transport in energy and nutrients as well excrete waster. It regulates our body temperature. However after we use water then we can clean it. So on the road to self-sufficiency in space then this possibility may present the greatest opportunity. Current estimates put human usage in space at 11 litres a day per person.

We eat. Most of us really enjoy eating which presents its own problems. People in space will likely never have this concern as they will never have an excess of food. Or at least they won’t until they start producing their own food. Also note that food often includes a lot of liquid so it presents a slight source of water. Current estimates put human consumption at 0.83kg per day per person.

People are used to a certain ability to move. Some in crowded cities are used to and even enjoy continual close contact with thousands of strangers. Others prefer a certain amount of distance, even isolation. While the Moon has a vast surface to wander, it is barren. People will need to stay within a habitable chamber. While the need to move varies for different activities let’s assume that we need a habitable volume 25 cubic metres per person.

Given these requirements then we see the following necessities for our habitat.

TimeNumber of PeopleWater (l)Air (kg)Food (kg)Habitable Volume (m3)
1st year453571671213100
2nd to 5th63214210007276150
6th to 10th1080355250018188250
10th to 20th253348121041775789625

This table shows that our habitat will need significant mass of supplies if its residents remain reliant upon the Earth for all its needs. This confirms our need for the residents to be self-sufficient as soon as possible.