Bootstrapping the On-Orbit Fuel Depot
Ok, so Griffin says he wants the private sector to set up an on-orbit fuel depot. He has even said that this could make some lucky entrepreneur very wealthy. Since most new space entrepreneurs are currently tied up with trying to reach orbit in a somewhat economical manner, it may be a while before anyone attempts to take him up on his challenge. This need not be the case.
My first thought was that the cost for developing the hardware and techniques for launching, storing, and transferring propellant on-orbit would be prohibitively expensive for any startup company to manage. For one thing, I'm pretty sure the Russians are the only ones who regularly do propellant transfer on orbit (from the Progress resupply vehicles to the Zvezda service module). As far as I'm aware, the US does not have very much experience with these kinds of operations, and so far NASA has not been able to find room in the budget to squeeze in this kind R&D into the ESAS.
But then it occured to me that we can use the ISS core complete as a testbed for developing the technology for an eventual stand-alone fuel depot. This can be accomplished using the existing (and soon to be flown) infrastructure on the station with the addition of maybe a couple of extra off-the-shelf components.
Currently, the ISS generates oxygen for the astronauts by electrolyzing water using the Russian Elektron unit. The hydrogen released from this process is vented into space as waste. In addition, carbon-dioxide must also be scrubbed from the air and vented. This always struck me as a rather wasteful way to handle life support.
Then, while looking for more information about life support on the ISS, I came across this article at the Science@NASA website. The article describes the Environmental Control and Life Support Systems (ECLSS) that is to be integrated into Node 3. It mentions that the engineers left space on the ECLSS rack for a Sebatier reactor. This is a device which would combine the hydrogen from electrolysis with the excess carbon dioxide in the atmosphere to produce methane and water. (4H2 + CO2 -> CH4 + 2H2O). The water could be cycled back into the electrolyzer to reclaim the oxygen that otherwise would have been vented as CO2 and the methane is a perfectly good rocket fuel which can be safely stored for long periods of time.
So, just using these components, it should be easy for NASA (or some other company interested in providing a fuel depot) to begin getting experience handling fuel on-orbit. In my mind, this would be a very prudent course of action to follow. The potential to begin a real off world economy will begin with fuel and energy production. Just to get things started, imagine how much the presence of this fuel depot would improve the business case for developing reusable space tugs. At the end of each mission, they could return to the ISS and top off their tanks, thereby becoming the first fully reusable spacecraft.