Mars, The Moon and Asteroids

Building on Mars, the Earth’s Moon, and on an Asteroid that is put into Earth orbit are all seen as possible first steps towards human's expansion into space. In addition to the challenges of space, these locations has their own pros and cons. It is undoubtedly true that if our species becomes a true space-faring race, we will settle all three locations. However, looking at the challenges and advantages of each location will help us build out intuition on when each should be settled, and in which order.

Asteroid Habitats Advantages

1) You can move your asteroid into earth orbit. This will make both communication and transportation with earth much easier. Sending resources down to earth can be done cheaply with aero-braking and a re-entry capsule with parachutes.
2) Optional Gravity. You can have low gravity areas, Earth gravity areas, and zero gravity areas in your habitat. It is easy to set the gravity to whatever strength you require.
3) No natural hazards. Everything can be built, and you don’t have to work around natural features.
4) Can sneak inside Earth’s magnetosphere to avoid some cosmic rays. In Low Earth Orbit, you can avoid some of the cosmic rays from the sun, decreasing the need for shielding

Asteroid Habitats Challenges

1) Acquiring mass to build with. It takes a fair amount of time and money to get a rock from the asteroid belt, where the most mass is. It would take even more fuel to shift the orbit into the correct position. Near earth asteroids are a possible source for asteroid capture.
2) Need for micro-gravity manufacturing techniques. While we have some techniques for building in micro-gravity, we have not perfected the art. The first few times we build out of asteroids would be untested by years of construction practices.
3) Need for constant missions to capture new asteroids for new material. Chances are, an asteroid habitat will not be 100% efficient. You would need to launch occasional new missions to get new metals, water, or materials that the asteroid is losing or exporting.

The Earth’s Moon

The Moon’s Advantages
1) Natural Resources. The moon is big enough that you can find almost any element on it.
2) Close to Earth. A journey to the moon takes less than a week, and it is only 1.3 light-seconds away, so communication is relatively fast.
3) Low Gravity and lack of atmosphere. At 16% of earth gravity, it is very easy to reach escape velocity. With no atmosphere to slow launches down, a magnetic accelerator can be built at ground level, allowing for easier entry into orbit.
4) Tidally Locked. Earth stays in a fixed position in the sky. You can build antennas pointed at earth and never have to move them. Systems that transport stuff to earth only have to be aimed when they are built. There are certain weapons that people would feel uneasy building if they could be turned towards earth. Building these weapons on the dark side of the moon means they never can hit earth.

The Earth’s Moon’s challenges

1) Month long day/night cycles. Except in very specific areas in the polar region, everywhere on the moon has two weeks of sunlight, followed by two weeks of dark. This is challenging because you cannot rely on solar power in these areas without batteries that can store massive amounts of energy. This same cycle also causes very large swings in temperature.
2) Not enough gravity for humans. You would probably have to build centrifuges in order to prevent bone loss.

Mars

Mars Advantages
1) There is gravity. At 40% of earth it would not cause short term health problems like micro-gravity does. The long term effects are unknown, but presumably wouldn’t be severe.
2) Natural Resources. Mars has an abundance of natural resources. Water, metals and other materials can be sourced locally.
3) A thin atmosphere. The atmosphere of mars is thick enough to mine for things like carbon dioxide and nitrogen. At .06% of earth’s atmosphere's thickness, breathing without a space suit is not very different from doing so in space.
4) Possible terraforming target. Mars has the potential to be terraformed in the distant future. As a futurist, this would be important for plans on the order of 500 years down the road.

Mars Challenges
1) One way trip. Long term effects of living 0.4G has not been studied. It is probable that there are no long term effects as long as colonists stay on mars, however emigrating back to Earth gravity is probably going to be a problem. Long term muscle and bone loss will make any colonization a one way trip.
2) Dust storms. Mars has periodic dust storms, effecting solar power generation and above ground transportation. Any martian colony must take this into account when designing the city.
3) Isolation. Mars is isolated from Earth. Comm lag varies from 4 minutes to 24 minutes. This means that it is impossible to have a real time conversation between planets. Additionally, sending supplies takes months.
4) Economics. Mars has nothing of value that does not exist on Earth. There is nothing on Mars that is rare enough to be worth trading with Earth. While launching from the martian gravity well would be 4-10x cheaper, as the escape velocity is 5/11ths of earth, the cost is still significant. This makes mars unattractive as a first colonization target.
5) Further from the sun. Mars gets 30% less sunlight than earth. This makes the mean temperature quite cold, and decreases solar power yield.

As we can see, both the moon and asteroids pulled into Earth orbit are the best candidates for initial human habitation. Whether you build on the moon or on asteroids depends on whether you are willing to spend the longer amount of time required to capture an asteroid, or are willing to brute force a moon base. On longer time scales, asteroids are probably a better place for habitation than the moon, but they need a significant amount of time to be captured into Earth orbit.

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