Hypersonic missiles in service are characterized by what speeds?

• A. Subsonic speeds
• B. Mach 3 speeds
• C. Speeds exceeding Mach 5
• D. Mach 1 speeds

Answer: (C)

Hypersonic means moving at five times the speed of sound or faster. The speed of sound depends on the surrounding air, but the Mach number is a simple way to compare speeds: subsonic is slower than sound, transonic hovers around the sound barrier, and supersonic is faster than sound but typically below about Mach 5. Once you reach Mach 5 and above, you’re in the hypersonic regime, which comes with very different aerodynamics and heating than the lower regimes.

So when describing missiles that are currently in service, the characteristic speed that defines hypersonic missiles is speeds exceeding Mach 5. Mach 3 is fast but still in the supersonic range, and Mach 1 is the speed of sound, not hypersonic.