reentry

Reentry is the phase of spaceflight when a spacecraft returns to Earth's atmosphere. This process uses atmospheric drag for braking, but also generates intense heat due to air compression in front of the fast-moving vehicle. Early spacecraft used ablative heat shields that burned away, while newer designs employ refractory materials, active cooling, or metallic alloys.12

Precise control of the reentry angle is critical. Too shallow an angle can cause the spacecraft to skip off the atmosphere, while too steep an angle can overwhelm the heat shield and deceleration capabilities. Spacecraft like the Apollo command modules approached Earth at speeds near 40,000 km/hour, experiencing temperatures up to 3,000 °C (5,400 °F). Parachutes are often deployed for a soft landing, either in the ocean (splashdown) or on land, as seen with Soyuz spacecraft. The space shuttle, however, glided to a runway landing. Reentry is a dangerous phase, as tragically demonstrated by the Columbia disaster in 2003.123