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.

NASA technologists are developing ways to place robotic space vehicles into long-duration scientific orbits around distant Solar System destinations without the need for the heavy fuel loads that have historically limited vehicle performance, mission duration, and mass available for science payloads.

A study showed that using aerocapture over the next best method (propellant burn and aerobraking) would allow for a significant increase in scientific payload for missions ranging from Venus (79% increase) to Titan (280% increase) and Neptune (832% increase). Additionally, the study showed that using aerocapture technology could enable scientifically useful missions to Jupiter and Saturn.

Aerocapture technology has also been evaluated for use in manned Mars missions and found to offer significant mass benefits. For this application, however, the trajectory must be constrained to avoid excessive deceleration loads on the crew. Although there are similar constraints on trajectories for robotic missions, the human limits are typically more stringent, especially in light of the effects of prolonged microgravity on acceleration tolerances.

The aerocapture maneuver can be accomplished with three basic types of systems. The spacecraft can be enclosed by a structure covered with thermal protection material also known as the rigid aeroshell design. Similarly another option is for the vehicle to deploy an aerocapture device, such as an inflatable heat shield, known as the inflatable aeroshell design. The third major design option is of an inflatable, trailing ballute—a combination balloon and parachute made of thin, durable material towed behind the vehicle after deployment in the vacuum of space.

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Wikipedia