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reentry
The period of return to Earth when a spacecraft passes through the atmosphere before landing. During reentry the spacecraft decelerates and is heated intensely due to aerodynamic friction. Radio communication may be blacked out for several minutes as a plasma sheath – an envelope of ionized air – surrounds the vehicle.
As a spacecraft reenters the Earth's atmosphere, it is traveling very much faster than the speed of sound. The vehicle is is said to be hypersonic. Typical low earth orbit reentry speeds are near 20,000 kph (17,500 mph) and the >Mach number M is nearly twenty five, M < 25. The chief characteristic of reentry 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 vehicle. The air density is very low because reentry occurs many kilometers above the Earth's surface. Strong shock waves are generated on the lower surface of the spacecraft.
Related entries
Related category
• REENTRY PHYSICS AND TERMINOLOGY
Source: NASA/Goddard Space Flight Center
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