Aerobraking is the action of atmospheric drag in slowing down an object that is approaching a planet or some other body with an atmosphere. Also known as atmospheric breaking, it can be deliberately used, where enough atmosphere exists, to alter the orbit of a spacecraft or decrease a vehicle's velocity prior to landing. To do this, the spacecraft in a high orbit makes a propulsive burn to an elliptical orbit whose periapsis (lowest point) is inside the atmosphere. Air drag at periapsis reduces the velocity so that the apoapsis (highest point of the orbit) is lowered. One or more passes through the atmosphere reduce the apoapsis to the desired altitude at which point a propulsive burn is made at apoapsis. This raises the periapsis out of the atmosphere and circularizes the orbit.
Generally, the flight-time in the atmosphere is kept to a minimum so that the amount of heat generated and peak temperatures are not too extreme. For high-speed aeromaneuvering that involved large orbit changes, a heat-shield would be needed. However, small orbit changes can be achieved without this, as demonstrated by the Magellan spacecraft at Venus. In Magellan's case, the aerobraking surfaces were just the body of the spacecraft and its solar arrays. Aerobraking and aerocapture are useful methods for reducing the propulsive requirements of a mission and thus the mass of propellant and tanks. This decrease in propulsion system mass can more than offset the extra mass of the aerobraking system.
In the novel 2010: Odyssey Two by Arthur C. Clarke two manned spacecraft, one Russian and one Chinese, use aerobraking in Jupiter's atmosphere to slow down and position themselves for exploring Jupiter's moons. The film version of 2010 includes a dramatic sequence in which the Russian spacecraft is shown making its aerobraking maneuver.