Ram jet engines

[Ravenger]

The SR-71 (which should have been called the RS-71, but the President announced the name wrong, and rather than embarass him by correcting the mistake they spent missions altering all the plans, documentation and other items to reflect the mispronounced name) used a fuel that was inert without its starter chemical, at least at normal temperatures because at Mach 3 air resistance makes the aircraft really, really hot. So hot that the nose (made out of titanium like the rest of the aircraft) partially melted out of shape during each flight and they had to get a blowtorch out to reshape it every time it landed.

 

The biggest problem with ramjet powered aircraft is the heat shielding. The space shuttle uses ceramic tiles for heat shielding, but those are very fragile, as was shown during the tragic loss of the shuttle Columbia.