reentry

Reentry is the phase of flight during which a spacecraft returns from space into a planetary atmosphere, culminating in landing or splashdown. For Earth missions it begins when the vehicle enters the upper atmosphere and ends when it reaches subsonic speeds near the surface.

During reentry, speeds remain hypersonic and air is compressed, forming a shock layer and extreme heating. A plasma sheath can surround the vehicle, causing a temporary communications blackout. Heating and dynamic pressure are mitigated by the vehicle’s thermal protection system, which is designed to keep the structure and crew safe.

Thermal protection systems use ablative shields, ceramic or carbon-based tiles, or other insulating structures. The TPS absorbs or sheds heat while the vehicle decelerates. Materials chosen depend on the mission profile, heat flux, and whether reuse is intended.

Trajectory and attitude control influence heat load and deceleration. A blunt-body, ballistic reentry often provides stability; some vehicles use lift to steer toward a specific landing zone. A deorbit burn from orbit sets the entry corridor and timing for a controlled descent.

Peak deceleration varies by design, typically a few g’s for crewed capsules. After entry, the vehicle transitions to subsonic flight, deploys landing systems such as parachutes or retrorockets, and lands. Debris that survives reentry can pose risks if it lands in populated areas, though most large fragments are expected to disintegrate.

Reentry has been demonstrated across programs from early capsule designs to modern spacecraft. It remains a critical, carefully engineered phase for returning humans and in discussions of space debris and atmospheric reentries.