compressibility Capable of being compressed

hypersonic Operation at Mach number exceeding 5.

interstellar Located, taking place, traveling among the stars

Mach number Ratio of true airspeed to speed of sound in surrounding fluid (which varies as square root of absolute temperature). Mach 1 equals the speed of sound, which is 340.294 meters per second or 761.59 mph at sea level.

ramjet Air-breathing jet engine similar to a turbojet but without mechanical compressor or turbine; compression is accomplished entirely by ram and is thus sensitive to vehicle forward speed and non-existent at rest.

scramjet Supersonic combustion ramjet; one in which the flow through the combustor itself is still supersonic.

shock wave A compressional wave of high amplitude caused by a shock to the medium through which the wave travels

speed of sound See Mach number

subsonic Speed being less than that of sound in air

supersonic Speed one to five times the speed of sound

transonic Relating to speeds near that of sound in air

wind tunnel A tunnel-like structure through which air is forced at known and controllable velocities to determine the effects of wind pressure on objects held stationary in the air stream