Aeroshell

An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry (see blunt body theory). Its main components consist of a heat shield (the forebody) and a back shell. The heat shield absorbs heat caused by air compression in front of the spacecraft during its atmospheric entry. The back shell carries the load being delivered, along with important components such as a parachute, rocket engines, and monitoring electronics like an inertial measurement unit that monitors the orientation of the shell during parachute-slowed descent. Its purpose is used during the EDL, or Entry, Descent, and Landing, process of a spacecraft's flight. First, the aeroshell decelerates the spacecraft as it penetrates the planet's atmosphere and must necessarily dissipate the kinetic energy of the very high orbital speed. The heat shield absorbs some of this energy while much is also dissipated into the atmospheric gasses, mostly by radiation. During the latter stages of descent, a parachute is typically deployed and any heat shield is detached. Rockets may be located at the back shell to assist in control or to retropropulsively slow descent. Airbags may also be inflated to cushion impact with the ground, in which case the spacecraft could bounce on the planet's surface after the first impact. In many cases, communication throughout the process is relayed or recorded for subsequent transfer. Aeroshells are a key component of space probes that must land intact on the surface of any object with an atmosphere. They have been used on all missions returning payloads to the Earth (if one counts the Space Shuttle thermal protection system as an aeroshell). They are also used for all landing missions to Mars, Venus, Titan and (in the most extreme case) the Galileo probe to Jupiter. The size and geometry of an aeroshell is driven by the requirements of the EDL phase of its mission, as these parameters heavily influence its performance.