An aerogravity assist, or AGA, is a theoretical spacecraft maneuver designed to change velocity when arriving at a body with an
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
. A pure
gravity assist
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the p ...
uses only the gravity of a body to change the direction of the spacecraft trajectory. The change in direction is limited by the mass of the body, and how closely it can be approached. An aerogravity assist uses a closer approach to the planet, dipping into the atmosphere, so the spacecraft can also use
aerodynamic lift with upside-down wings to augment gravity and further curve the trajectory. This enables the spacecraft to deflect through a larger angle, resulting in a higher
delta-v
Delta-''v'' (more known as " change in velocity"), symbolized as ∆''v'' and pronounced ''delta-vee'', as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such a ...
(change in velocity). This in turn allows a shorter travel time, a larger payload fraction of the spacecraft, or a smaller spacecraft for a given payload.
The related techniques of
aerocapture
Aerocapture is an orbital transfer maneuver in which a spacecraft uses
aerodynamic drag force from a single pass through a planetary
atmosphere to decelerate and achieve orbit insertion.
Aerocapture uses a planet's or moon's atmosphere to accom ...
,
aerobraking
Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit (periapsis). The resulting drag slows the spacecraft. Aerobraking is ...
, and
atmospheric entry
Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the ent ...
also attempt to use the body's atmosphere to help reduce propulsion requirements. In an aerogravity assist, however, the goal is not to use the atmosphere to slow the spacecraft down, but instead use it to achieve a larger change in direction.
While the use of an aerogravity assist has been proposed for a variety of missions, including the capture of a spacecraft into orbit about Saturn,
[James Lyne and Philip Ramsey (2006), Investigation of Titan Aerogravity Assist for Capture into Orbit about Saturn, Journal of Spacecraft and Rockets, Vol. 43, No. 1, pp. 231-233. DOI:10.2514/1.9274. https://www.researchgate.net/publication/245438177] the technique has not yet been used in practice.
See also
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Planetary flyby
A planetary flyby is the act of sending a space probe past a planet or a dwarf planet close enough to record scientific data. This is a subset of the overall concept of a flyby in spaceflight.
The first flyby of another planet with a functioni ...
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Flyby (spaceflight)
A flyby () is a spaceflight operation in which a spacecraft passes in proximity to another body, usually a target of its space exploration mission and/or a source of a gravity assist to impel it towards another target. Spacecraft which are specif ...
References
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Spacecraft propulsion
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