> It's a hypersonic thruster, i.e. 5 or more times the speed of sound. Far too fast for civil aviation. It's probably even too fast for "safe" manned flight. Th

> It's a hypersonic thruster, i.e. 5 or more times the speed of sound. Far too fast for civil aviation. It's probably even too fast for "safe" manned flight. This is the speed at which the air ionizes around the vehicle. It's like flying inside a fireball. Ionization occurs at considerably higher temperature. The hypersonic regime is described as when vibrational excitations of air molecules begin to significantly affect the specific heat. After that, dissociation sets in, and only after that does ionization become significant. Temperature ranges, as I understand it, are (for air at 1 bar): Vibrational excitations: > 800 K Dissociation of oxygen: > 2500 K (nearly complete ~4000 K) Dissociation of nitrogen: > 4000 K (nearly complete ~9000 K) Ionization: > 9000 K Lower pressure will reduce the temperatures at which dissociation and ionization become significant.