problem with useing the moon as a base, is that you still have gravity to contend with. Even though its considerably lighter, you still have to get the entire thing off the surface. Considering the size, the most likely event would be that it would have to be assembled in space. so why bother going to the moon for material in the first place. Every week there are asteroids of small but useable size that strick the earth or pass it nearby. Im not talking about things miles long, im talking about ones that are 10 to 50 meters in size. most of those break up and are burned up in the atmosphere, with a small number actually hitting somewhere. Most of them hit water (the earth is 70 percent water after all), and the ones that dont often hit unnoticed. If we were to send up a system to spot these and the ones that by pass the earth without hitting. and send out solar sails ships (largely remote controlled), we could begin to assemple the material for the ship for little money. solar sails would use the energy of the light of the sun to manuver. The largest cost would be to send it out and to manufacture it.
