Electrically Charged Plasma - Product of Re-Entry

During re-entry, astronauts see a "light show" outside the shuttle's port holes.  What causes that?

"As a spacecraft re-enters the earth's atmosphere, it is traveling very much faster than the speed of sound. The aircraft is said to be hypersonic.

"Typical low earth orbit re-entry speeds are near 17,500 mph and the Mach number M is nearly twenty five,  M < 25.

"The chief characteristic of re-entry aerodynamics is that the temperature of the flow is so great that the chemical bonds of the diatomic molecules of the air are broken.

"The molecules break apart, producing an electrically charged plasma around the aircraft.

"The air density is very low because re-entry occurs many miles above the earth's surface. Strong shock waves are generated on the lower surface of the spacecraft."

Credits

Information and quoted passage, NASA's Glenn Research Center.