[geoschmo]

Originally posted by JurijD:
We have the technology to construct self sustainable environments... there are about 200 of them floating uder the worlds oceans (called nuclear submarines) They surface once every 6 months only to resupply on food beause it would be too unpractical to have it produced on-board. Everything else... water, oxygen, heat etc. is produced by the nuclear reactors that turn CO2 to O2 and recycle urine and the vapour in the air to usable water....

No, you are missing my point. I wasn't talking about renewable recourse like food and water. I know we are very close to or have acchieved teh basic technology needed for these things. I am not even talking about basic energy needs. Nuclear power is a good long term option, and there is some talk about magnetic scoops to pull hydrogen molecules from the surounding space.

I am talking about the huge amount of raw materials and manufacturing capability you would need to be able to build replacment parts for all the myriad pieces of technology on board the ship. It's not simply a matter of scale, or making a larger ship. Because the bigger you build it and the more equipment you have dedicated to these support functions, the more things you have that can break. It's a curve that I am not confident you can ever get ahead of when you consider you are looking at decades long trips at least.

The submarines are not nearly as self-sufficent as you think. 6 months suberged is nothing. They can surface any time they need and head for a repair dock if something breaks. Or a helicopter can bring them a new circuit board in a matter of hours.