User:Aarchiba/starship design

This page is a speculative design for a generation ship, taking advantage of the information in the article "spacecraft propulsion" and many others in Wikipedia. It's meant partly as a lark, and partly as a test of Wikipedia as a resource on this sort of issue - I'm intending to try to make sure any general-purpose information I need is in Wikipedia and easy to find.

General Design

Two asteroids. One is for habitation, and is spun to provide roughly an Earth gravity near the surface. The other is for heavy industry, nuclear power plants, and for use as reaction mass.

The inhabited asteroid is approximately 10 km in diameter. It is honeycombed with bubbles, up to perhaps 1 km in diameter, which serve as habitats. Homes and other buildings may be carved out of the surrounding rock, opening into bubbles, or they may be freestanding within the bubbles. Many bubbles serve as parks full of wildlife.

The uninhabited asteroid is also approximately 10 km in diameter. It has several mass drivers which serve as the main propulsion system; as reaction mass, they throw pieces of the asteroid itself. It is also the location of those industries which might otherwise pose ecological problems. Since it is not spun for gravity, it is also the place to put industries that work better in free fall, as well as external service ports, telescopes and most other sensors.

Propulsion

The main propulsion system is several mass drivers. These are large linear motors. It is probably most efficient to base them on a coilgun design which accelerates a reusable bucket.

For safety, the bucket can be loaded with finely-divided dust; the dust could even be given an electrostatic charge so that it would disperse rapidly. Of course, by loading the engines with solids, they could be made into weapons, although they probably couldn't be pointed rapidly.

Assume that the muzzle velocity is around 100 km/s, giving a specfic impulse of 10000 s. The launcher would be 10 km long, and loads would undergo 50000 gravities for 0.2 seconds before being launched. If loads mass 1 kg, the energy required is 5×10⁹ Joules, which is 1.4 MWh. To throw loads continuously, 25 GW are needed. This would be provided by several large nuclear reactors, possibly pebble bed reactors modified to work in free fall. These could, of course, also power the habitat.

Nuclear fuel (in large quantities - how large?) would obviously be needed. Possibly asteroid material could be used (how much uranium is found in asteroids?). Waste disposal, on the other hand, is easy; just put it in with the reaction mass and it's gone.

The vehicle as a whole masses about 4×10¹⁶ kg. If half of that is consumed as fuel, then the maximum delta-v is about 50 km/s.