Gravity assist

A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby which makes use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.

For powered flybys, see Oberth effect.

Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed or redirect its path. The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft.^[1] Any gain or loss of kinetic energy and linear momentum by a passing spacecraft is correspondingly lost or gained by the gravitational body, in accordance with Newton's Third Law. The gravity assist maneuver was first used in 1959 when the Soviet probe Luna 3 photographed the far side of Earth's Moon, and it was used by interplanetary probes from Mariner 10 onward, including the two Voyager probes' notable flybys of Jupiter and Saturn.

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Historical origins[edit]

In his paper "To Those Who Will Be Reading in Order to Build" ("Тем, кто будет читать, чтобы строить"),^[6] published in 1938 but dated 1918–1919,^[a] Yuri Kondratyuk suggested that a spacecraft traveling between two planets could be accelerated at the beginning and end of its trajectory by using the gravity of the two planets' moons. The portion of his manuscript considering gravity-assists received no later development and was not published until the 1960s.^[7] In his 1925 paper "Problems of Flight by Jet Propulsion: Interplanetary Flights" ("Проблема полета при помощи реактивных аппаратов: межпланетные полеты"),^[8] Friedrich Zander showed a deep understanding of the physics behind the concept of gravity assist and its potential for the interplanetary exploration of the solar system.^[7]

Italian engineer Gaetano Crocco was first to calculate an interplanetary journey considering multiple gravity-assists.^[7]

The gravity assist maneuver was first used in 1959 when the Soviet probe Luna 3 photographed the far side of the Moon. The maneuver relied on research performed under the direction of Mstislav Keldysh at the Keldysh Institute of Applied Mathematics.^[9]^[10]^[11]^[12]

In 1961, Michael Minovitch, UCLA graduate student who worked at NASA's Jet Propulsion Laboratory (JPL), developed a gravity assist technique, that would later be used for the Gary Flandro's Planetary Grand Tour idea.^[13]^[14]

During the summer of 1964 at the NASA JPL, Gary Flandro was assigned the task of studying techniques for exploring the outer planets of the solar system. In this study he discovered the rare alignment of the outer planets (Jupiter, Saturn, Uranus, and Neptune) and conceived the Planetary Grand Tour multi-planet mission utilizing gravity assist to reduce mission duration from forty years to less than ten.^[15]

an asteroid which periodically has gravitational slingshot encounters with Earth

3753 Cruithne

Delta-v budget

a type of gravitational assist where a spacecraft is gravitationally snagged into orbit by a celestial body. This method is usually executed in the Earth-Moon system.

Low-energy transfer

Dynamical friction

an anomalous delta-v increase during gravity assists

Flyby anomaly

Gravitational keyhole

Interplanetary Transport Network

n-body problem

applying thrust near closest approach in a gravity well

Oberth effect

, first Out-Of-The-Ecliptic mission (OOE) proposed, for Jupiter and solar (Sun) observations

Pioneer H

a gravity-assisted mission which used Earth's Moon to eject two spacecraft from Earth's orbit into heliocentric orbit

STEREO

at NASA.gov

Basics of Space Flight: A Gravity Assist Primer

discussion at Phy6.org

Spaceflight and Spacecraft: Gravity Assist

. MathPages.com.

"Gravitational Slingshot"

Double-ball drop experiment

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