Why does the Space Shuttle Orbiter make a double sonic boom when it lands?

As a simple example, consider an aircraft flying at supersonic speeds. The aircraft typically creates two shock waves: a bow wave and a tail wave. These waves continue with the aircraft the entire time it flies at supersonic speeds.


Each of the two waves actually generates a cone. The two cones intersect the ground. A region of overpressure exists between the cones.
Imagine that you are standing on the ground. The air pressure is the normal atmospheric value. Suddenly, the bow wave from a supersonic aircraft comes past you. The air pressure level rises instantaneously. You hear a sonic boom as a result.
You are now between the bow wave and the tail wave. The pressure gradually decreases and even dips below the normal atmospheric value. Suddenly, the tail wave comes past you. The air pressure jumps to the normal atmospheric value. You hear a second sonic boom as a result.
Of course, all of this may happen in a fraction of a second depending on the aircraft size, aircraft speed, wind conditions, and other variables.
The aerodynamics of a landing shuttle are more complicated, but the basic principle is the same.
The space shuttle orbits the Earth at about 17,500 miles per hour, which is about Mach 25. It is traveling at this speed as it re-enters the atmosphere. It is moving at about 224 miles per hour as it touches down. The duration from touchdown to complete stop is about 70 seconds.

Extra: Famous photo of F/A-18 Hornet with attached shock wave cones.


 Smithsonian Air & Space Magazine

Please send comments and questions to Tom Irvine at: tomirvine@aol.com
Space Index | Science Home