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Aeroshell
An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spaceraft 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 drag during a spacecraft's 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 process of a spacecraft's mission, or the Entry, Descent, and Landing process. First, the aeroshell decelerates the spacecraft as it penetrates the planet’s atmosphere. The heat shield absorbs the resulting friction. During decent, the parachute is deployed and the heat shield is detached. Rockets located at the back shell are initiated to assist in the decrease of the spacecraft's descent. Airbags are also inflated to cushion the impact. The spacecraft bounces on the planet’s surface directly after the first impact. The spacecraft's lander petals are deployed after the airbags are deflated and retracted. Communication throughout this entire process is relayed back and forth from mission control and the actual spacecraft through low-gain antennas that are attached to the back shell and on itself. Throughout the entry, descent, and landing stages, tones are sent back to earth in order to communicate the success or failure of each of these critical steps.
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.
==Components==
The aeroshell consists of two main components: the heat shield, or forebody, which is located at the front of the aeroshell, and the back shell, which is located at the back of the aeroshell. The heat shield of the aeroshell faces flow during a spacecraft's atmospheric penetration, allowing it to absorb the high aerodynamic heat caused from the entry. The backshell acts as a finalizer for the encapsulation of the payload. The backshell contains the parachute, electronics and batteries that control pyrotechnic devices, a Litton LN-200 Inertial Measurement Unit, Rocket Assisted Descent rockets, and the Transverse Impulse Rocket System. The parachute is located at the apex of the back shell and slows the spacecraft during entry, descent, and landing. The pyrotechnic control system releases devices such as nuts, rockets, and the parachute mortor. The Inertial Measurement Unit reports the orientation of the back shell while it is swaying underneath the parachute. Rocket Assisted Descent rockets provide approximately one ton of force within 2 seconds, assisting in the descent of the spacecraft vehicle. The Transverse Impulse Rocket System provides horizontal force to the back shell which helps orient it to a more vertical position during the main Rocket Assisted Descent rocket burn.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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