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Viking 1 aeroshell

An aeroshell is a rigid heat-shielded shell that protects a vehicle from pressure and heat created by drag during atmospheric entry (see blunt body theory), slows it down during entry, and may protect it from debris during spaceflight. 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.

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.

NASA's Planetary Entry Parachute Program[edit]

USAF Aeroshell "Flying Saucer" on public display in Missile Park at White Sands Missile Range.

NASA's Planetary Entry Parachute Program (PEPP) aeroshell, tested in 1966, was created to test parachutes for the Voyager Mars landing program. To simulate the thin Martian atmosphere, the parachute needed to be used at an altitude more than 160,000 feet above the Earth. A balloon launched from Roswell, New Mexico was used to initially lift the aeroshell. The balloon then drifted west to the White Sands Missile Range, where the vehicle was dropped and the engines beneath the vehicle boosted it to the required altitude, where the parachute was deployed.

The Voyager program was later canceled, replaced by the much smaller Viking program several years later. NASA reused the Voyager name for the Voyager 1 and Voyager 2 probes to the outer planets, which had nothing to do with the Mars Voyager program.

There is one PEPP Aeroshell left, at White Sands Missile Range in New Mexico.