Aerocapture is similar to aerobraking, but distinct in that it is used to reduce the velocity of a spacecraft flying by a planet so as to place the spacecraft in orbit around the planet with a single atmospheric pass. Aerocapture could be very useful for planetary orbiters because it would allow a spacecraft to be launched from Earth at high speed, resulting in a short trip time, and then decelerated purely by aerodynamic drag at the target. Without aerocapture, a large propulsion system is needed to bring about the same reduction of velocity, thus reducing the amount of deliverable payload. However, aerocapture is a more extreme maneuver than aerobraking because it occurs at higher speeds and digs deeper into a planet's atmosphere.
An aerocapture maneuver would begin with a shallow approach to the planet, followed by a descent to relatively dense layers of the atmosphere. Once most of the needed deceleration has been achieved, the spacecraft would maneuver to leave the atmosphere. To allow for inaccuracy of the entry conditions and for atmospheric uncertainties, the vehicle would need to have its own guidance and control system as well as maneuvering capabilities. Most of the maneuvering would be done using the lift that the vehicle's aerodynamic shape provides. Upon exit, the heat-shield would be jettisoned and a short propellant burn carried out to raise the periapsis (lowest point of the orbit). The entire operation would require the vehicle to operate autonomously while in the planet's atmosphere.
Whereas aerobraking has been used on several missions to Mars and Venus, aerocapture has not so far been attempted. One of the proposals for a Neptune mission, envisages aerocapture as a possible way of entering orbit around the gas giant.