08-24-2015, 07:25 AM

High Frontier is about orbital colonies, but there's been a lot of talk lately about planetary colonies, especially on Mars (even though the Moon would make far more sense). So I've been thinking about what would be required to make a decent colony on (or below) a planetary surface.

The big problem with living in caves or buried tunnels on the Mars or Moon is the gravity. We don't know that 1/6 or 1/3 G is enough for kids to grow up healthy. The only substitute for gravity is acceleration, and in practical terms, that means spinning. In an orbital colony, that's no big deal; but on a planetary colony, you're spinning something surrounded by a large (planet-sized), non-spinning mass of dirt and rock. So how fast that interface is going by matters. It's very much like a train on Earth: the potential for disaster goes up with the speed.

So, what kinds of speeds are we talking about? I did some quick back-of-the-envelope calculations to find out:

The big problem with living in caves or buried tunnels on the Mars or Moon is the gravity. We don't know that 1/6 or 1/3 G is enough for kids to grow up healthy. The only substitute for gravity is acceleration, and in practical terms, that means spinning. In an orbital colony, that's no big deal; but on a planetary colony, you're spinning something surrounded by a large (planet-sized), non-spinning mass of dirt and rock. So how fast that interface is going by matters. It's very much like a train on Earth: the potential for disaster goes up with the speed.

So, what kinds of speeds are we talking about? I did some quick back-of-the-envelope calculations to find out:

So, presumably you would have your outer hull on some sort of track, very much like a train (in fact your colony could actually be a train, which offers an interesting way to start small-scale!). The columns on the right above show how fast this train would be going, relative to the tracks.

These are not outrageous speeds; high-speed trains on Earth routinely go 200 km/hr, and records over 400 km/hr have been set. The engineering challenges in a perfectly circular track running in a near-vacuum (such as the atmosphere of Mars or the Moon) are somewhat easier than what these trains face. On the other hand, the potential disaster is much greater if something goes sideways.

Still, it's not unreasonable. I'm sure we will have some people living on Mars and the Moon: research bases, tourist towns, etc., and these will probably take the form of underground rings or discs less than 1 km in radius, spinning along a track.

Joe Strout

Lead Developer, High Frontier