...true, but isn't a lot of the research in the US at the moment focused on burning hydrocarbon based fuels (such as the X-51) rather than liquid hydrogen?
Admittedly the X-51 looks more like a prototype hypersonic missile than a passenger carrier.
I thought that burning LH2 meant you needed a massive tank - meaning there's a whole cascade of consequential structural issues if you need to carry passengers at hypersonic speeds.