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.