Re: Let's replace "1970s-era hydrogen technology"...
Liquid hydrogen is a fantastic fuel but its density is less than a tenth of that of kerosene, so you need comparatively huge fuel tanks to store it. Huge fuel tanks generate lots of atmospheric drag, so to get through the lower parts of the atmosphere, hydrocarbons or solid boosters are typically used. The propellant used in modern solid rocket motors is about 25 times the density of liquid hydrogen, which is partly responsible for their popularity as boosters.
I should also point out that LH2 powered engines are the most efficient, but they're not the most powerful, not by a long shot. Of engines that have actually been used, the most powerful kerosene engine produces just over twice as much thrust as the most powerful hydrogen engine, while the most powerful solid rocket motor produces four times as much.
Are you suggesting that Europe and Russia don't have the ability to send hydrogen fuelled rockets? Because they certainly do. Ariane 5 for example is LH2 all the way, with solid boosters to help it out of the atmosphere.
Biting the hand that feeds IT
