Space Habitat

Baring a breakthrough in physics, sending human beings anywhere in space beyond the moon is going to take a very long time. Even a trip to mars will take a year just to get there. Given this situation I think it would be a good idea if we got started with building a space habitat where we could learn how to live in space, not just survive. All the ideas I have seen about building a ship to go to Mars all look like they come from cheapskates. The bare minimum of equipment, the bare minimum of shielding, just enough that the crew, if they are lucky, will survive. It looks like a recipe for disaster. We should take a page from the Victorians and building something that could survive most anything the universe can dish out. Building a habitat at Lagrange point L4 (never mind L5, everyone else has already talked L5 to death) would give us a chance to see what it is really like to operate in space.

Lagrange Point Habitat

I am thinking we would want a sphere about one mile in diameter. Spin it at a rate of one revolution per minute and you would have one gravity of acceleration at the largest radius. I like the idea of making the surface of the sphere out of foot thick steel, but this may not be the right choice. The skin of the sphere will have several functions:

• Keep air and water vapor inside
• Keep dangerous radiation outside
• Absorb and/or deflect meteors and other debris
• Hold itself together, i.e. have some structural integrity

To do all this may require several layers of various materials and in fact may be a hundred feet thick and honeycombed with access passages. One thing to remember is that we probably are not going to want much on the outside of the skin near the equator. The skin at the equator will be traveling at about 200 miles per hour. Anything that is attached there that loses its grip is going to leave very quickly.

A large diameter cylinder would be fitted to the inside of the sphere and concentric with axis of spin. It would take up one third to one half of its' length. This would give us a large surface of even gravity on which which to house our people. A cylinder a third of a mile long and one mile in diameter would give us about one square mile of "land": 640 acres. We should be able to do something with this, perhaps farm, or even raise cows. The area between the cylinder and the skin of the sphere could be used for water tanks. In case of a breech of the hull, large valves could be opened into these tanks and quickly drain any surface water into the tanks before it all evaporated into space. Water in these tanks could also be transferred around the diameter of the sphere to compensate for any imbalance.

The large diameter offers several advantages:

• Low gravity gradient. There would little difference in the apparent force of "gravity" as you changed elevation. For instance there would a negligible difference between your head and your feet, and the difference would still be small for an elevation change of 100 feet.
• Slow spin rate. I would hope that an angular velocity of one revolution per minute would minimize any problems with vertigo either for permanent residents or visitors. As far as I know there is no way to tell. Research and testing will be necessary.
• High linear velocity. The high linear speed of 200 MPH means that any motion in the vessel, like walking, will have a minimal effect on your perceived weight. Running, either with or against the rotation, will no doubt have a noticeable effect, though it should be something most people should be able to deal with.
• Wide open spaces. Having a "ceiling" a thousand feet in the air would give people a feeling of wide open spaces like they have on the Earth's surface. It might help prevent attacks of agoraphobia in people returning to Earth, and attacks of claustrophobia in people arriving at the habitat.
• Large volume of air. This means that we can survive small leaks until they are found and a small amount of anything unpleasant or noxious would be diluted to the point where it is harmless.

A smaller diameter cylinder would also be fitted into the sphere, also concentric with axis of spin. This cylinder would be much smaller in diameter, perhaps a couple of hundred feet. This cylinder would be used for docking of cargo and passenger vehicles. This ends of the cylinder would be doors. Since the entire cylinder would be exposed to vacuum, the surface of this cylinder would need to have many of the same attribute as the surface of the sphere. The doors at the end of the cylinder would span perhaps a quarter of the diameter of the cylinder. Vessel docking would be accomplished by:

• contact with a long probe which would stabilise the vessel's position and relative velocity.
• with the aid of the probe the vessel would be maneuvered into position directly outside the sphere and in-line with its' axis of rotation
• a cage-like frame would close about the vessel and be secured
• the cage would be drawn into the sphere
• the cage, and the contained vessel, would be spun up to match the sphere's rotation
• the cage would be moved sideways, relative to the axis to a docking berth

We could have two kinds of berths. One would just hold the cage, and could provide an airlock for crew and passengers. The other could be enclosed so that it could be pressurized. A vessel a mile in diameter can expect to have a fair amount of traffic coming and going. Having this central cylinder devoted to docking would allow incoming vessels to enter at one end, be docked along the walls, and exit through the other end. A continuous stream of traffic could beaccommodated this way.

In most cases docking could be carried out in vacuum, but there will be cases where bringing the vessel into a pressurized chamber would make things easier. Emergency would be one case, and external repairs would be another. It is easier to build and seal a small door rather than a large door. If vessels where constructed as long cylinders, then they could enter a pressurized chamber through a relatively small door. So pressurized docking chambers would be cylinders perhaps three times the diameter of a vessel and slightly longer.

We would probably not need to accommodate winged vessels like the space shuttle. We would be a long ways from anyplace where wings would be useful. The expense of boosting them this far out would be very hard to justify. However, if this structure is going to be a mile in diameter, just how big are the ships going to be? Right now I find it difficult to imagine anything larger than about 30 feet, but I have seen numerous engineering projects that had to be revised to accommodate the bigger, larger and more powerful.

At one point I was thinking that sand would be the perfect material to use for shielding the outer skin of the sphere. Easy to transfer, simply pour from one container to another. Good for absorbing impacts from micrometeorites and cosmic rays. And it could be used as a raw material. Apply enough heat and you get oxygen and silicon. Oxygen is always handy for air breathing mammals. Problem is any small holes in the "underside" of the containing vessel would let the sand drain out and be lost. There are ways to compensate, like putting a chamber below the sand to catch any that leaks out, and allow maintenance to plug whatever holes show up in the floor of the sand chamber.