I'm not an expert on fuel cells, but it seems that they would be a likely candidate for increasing hydrogen utilization in spacecraft. Seems like one could use fuel cells to generate electricity for expansionary hydrogen gas propulsion instead of using the complex, somewhat messy engineering of external power sources. Expansionary hydrogen propulsion increases the specific impulse of hydrogen from 250 seconds to approximately 1000 seconds (not my figure, so I haven't double checked the math). Using approximate energy conversion rates and some fuzzy math that I won't go into here, it would take around 12,000 imperial tons of liquid hydrogen (plus ultra efficient fuel cell technology) to generate electrical output sufficient for obtaining Low Earth Orbit...excluding the hydrogen required for the expansionary propellant. It can get hairy lifting those kind of tonnages (not even considering airframe and payload weight), but airship technology could act at as a first stage of a multistage system. Such a system would be a concentrated use of solar energy (using renewable resources to split hydrogen from water) in a form practical for high performance flight applications. One could probably reduce the fuel load requirement by instituting a lower atmosphere air breathing stage of some sort. I'm probably way off here, but it's an interesting idea.
Payload and Airframe Weight: 2000 tons
Liquid Hydrogen for Electrical Generation: 4500 tons (based off of 7.9 KwHr per pound to reach GEO and 15.1 KwHr per pound of liquid hydrogen)
Hydrogen for Expansionary propellent: 5400 tons (based off of specific impusle of expansionary hydrogen of around 1000 seconds)
Total Craft Takeoff Weight to GEO: 12900 tons
One of the issues I see is accounting for the weight of the hydrogen for electrical generation in crunching these numbers. I used the value of 1200 tons and came up with needing 4500 tons. How do I account for the weight of hydrogen used for expendable purposes for electrical generation?
Also, is the figure quoted in the reference applicable to these type of vehicles and not just tethers? (http://www.kestsgeo.com/pages/
