reentries

Reentries refer to the phase of a spacecraft’s mission when it returns from space into a planetary atmosphere, most commonly Earth. During reentry, vehicles transition from orbital velocities to subsonic speeds, experiencing intense heating and aerodynamic loads as they decelerate due to atmospheric drag. The design of the entry sequence and the thermal protection system is critical to safe recovery of crew and payload.

Reentries can be ballistic or guided. Ballistic reentry follows a steep, largely unpowered trajectory with high peak temperatures and rapid deceleration, while guided or powered reentry uses attitude control and lift to moderate the flight path and reduce peak loads. The entry interface is typically reached at roughly 120 kilometers altitude depending on vehicle.

Thermal protection is central to surviving reentry. Spacecraft employ heat shields made from ablative materials, reinforced carbon-carbon, or high-temperature ceramics. Ablative shields absorb heat by gradually charring and eroding, while tiles and other insulators protect areas of structural importance. Materials are tested to withstand peak heating rates and dynamic pressure.

Flight dynamics include a deorbit burn to lower orbital velocity, a hypersonic entry phase with intense heating, a radio blackout caused by ionized plasma, and a final deceleration stage using parachutes, retrorockets, or a controlled flight path to a landing site or splashdown.

Historically notable reentries include the Apollo command module from lunar return, the Space Shuttle with its extensive thermal protection system, Soyuz capsule descents, and recent missions such as SpaceX Dragon and NASA’s Orion. Reentry research has driven advances in materials science, thermal analysis, and guidance and control, and continues to influence safety standards and mission planning.