Woggles":k30vjf6k said:
A little off topic. I was thinking about the "fuel depot" concept. I believe it takes 4 pounds of fuel for every lb lifted. That is pretty expensive fuel!! I was wonder will the price of the fuel fluctuate, like at gas station here on earth? This will be a private enterprise endeavor, so obvious there will be a mark up.
Point of the concept is, that you use cheap, not so very safe or tested rockets to ferry fuel, which is rather common around here, to the depot (anyone who can do it can sell it, in the orbit), and use different, safer, much more reliable and costly spacecraft to carry people.
It gives a market to almost anyone, gives them money for development from their profits if any, and makes out-of-LEO travel cheaper, because launch vehicle lifts only what is needed to get to orbit, with empty tanks for further travel.
Example:
Zenit rocket has a price to LEO about 3000 $/kg,
Ariane around 15-20 000 $/kg, Shuttle with a rather optimistic view around 30-50 000 $/kg, depending.
Exact numbers are probably known only to the one writing check ..
There are concepts in the works, for which such a chance would mean they can get investment for their project, like Spacegun above, and many others, which promise price to LEO under 1000 $/kg, but not safe enough presently, or not even designed for human travel.