Aerocapture

Aerocapture is an orbital transfer maneuver used to reduce the velocity of a spacecraft from a hyperbolic trajectory to an elliptical orbit around the targeted celestial body.

Aerocapture uses a planet’s or moon’s atmosphere to accomplish a quick, near-propellantless orbit capture to place a space vehicle in its science orbit (most science orbits require a near circular orbit around the celestial body). The aerocapture maneuver starts as the spacecraft enters the atmosphere of the target body from an approach trajectory. The aerodynamic drag generated by the dense atmosphere slows the craft. After the spacecraft slows enough to capture into orbit, it exits the atmosphere and executes a small motor firing to circularize the orbit. This nearly fuel-free method of deceleration could significantly reduce the mass of an interplanetary spacecraft. Less spacecraft mass allows for more science instrumentation to be added to the mission or allows for a smaller and less-expensive spacecraft, and potentially a smaller, less-expensive launch vehicle. However, this approach requires significant thermal protection and precision closed-loop guidance during the maneuver. This level of control authority requires either the production of significant lift, or relatively large attitude control thrusters.