Monday, March 25, 2013

A Trip Into Space - Geostationary Orbit

Today, I am continuing a series that I am writing mostly for enjoyment on the value of developing space.

I mentioned one important reason why a space station should be on an equatorial orbit - and why anybody intending on building a useful space station would focus on one in such an orbit. It is because one does not want to turn in space. Without an atmosphere, turning takes a lot of energy.

This is important because, above our low-earth-orbit space station, at an altitude of 35,786 kilometers, is Geostationary Orbit.

At this altitude, an object in orbit stays constantly above a fixed point on the Earth's equator. A satellite here orbits the earth as fast as the earth spins.

These satellites are in an equatorial orbit. The station in low earth orbit is a way point. Consequently, it is best to have the station in low earth orbit be in an equatorial orbit (or very close to it). This is the gateway to space.

You have left the rocket that brought you here from Earth a few days ago. You have spent that time getting used to space, perhaps being trained in some of the skills that are useful in space. Some people have trouble adapting . . . and may get sent home. However, we will assume that you have adapted well and you are ready to start work.

On your day of departure, you will board a space ship.

This space ship is not of a type often seen in science fiction (modeled too much after ocean-going ships). It will likely be a sphere - having the greatest ratio of volume to surface area, and no corners that the inside air pressure would want to push apart. Once on board, a rocket will fire, and you will be on your way to high earth orbit.

This resource is already being used for communication satellites and for some weather and earth monitoring satellites. It will be important for solar power satellites that beam their energy down to fixed fields on the Earth.

One of the businesses of space development will be the construction and maintenance of these satellites. In fact, the space habitat itself may become a communication hub (where the habitat picks up and rebroadcasts information).

These stations are above the Van Allen belts, which means that occupants will be exposed to cosmic rays. Protection from this and other forms of radiation can be accomplished with about 1 meter of solid mass. Any mass will do - though with mass having a greater density the shield can be thinner.

We can get this mass from asteroids - bringing them (or parts of them) into a high Earth orbit. The asteroid material would be pulverized and refined - with the useful material extracted, leaving behind large lump of tailings. These otherwise useless tailings can be used to make the shell within which our space inhabitants would live - perhaps being formed into a cylinder 3 kilometers in diameter and 20 kilometers long. The cylinder does not rotate; however, the community built inside would. That community would have three counter-rotating sections; 5 kilometers roasting one way, 10 kilometers rotating the other way, and the final 5 kilometers turning the same direction as the first five. This way, angular momentum transferred from the station to the shell will be cancelled out.

The metric for travel in space is called "delay-v" or "change in velocity". It determines how much energy is required to change something from its one orbit to another - from an asteroid's orbit to earth's orbit. On this metric, there are hundreds of known and thousands of unknown asteroids "closer" than the moon.

Nature itself is constantly making small adjustments to the orbits of these asteroids. Over time, these random changes bring some of them into a violent confrontation with Earth. Even ignoring everything said with respect to the usefulness of space development, we have many and strong reason to seek some influence over their orbits.

One option is to move them into a safe earth orbit where we can do something constructive with them.

One of the implications of this is that geostationary orbit will not only be the location for communication and power generation, but also for mining and manufacturing.

Communication, a source of energy to last billions of years, mining, manufacturing, earth defense, and "because it's there" - these are some of the high-value goods to be acquired in high-earth orbit.

No comments: