Word
Gravitational assist
A planetary flyby that changes a spacecraft's path and speed relative to the Sun
Examples
Mariner 10 used a gravitational assist at Venus to reach Mercury.
A mission planner may accept a longer route to gain a useful gravitational assist.
Origin
The term belongs to orbital mechanics and is also shortened to gravity assist or called a planetary swingby. Assist describes the encounter's usefulness, not an exception to conservation laws. The planet is moving too, so the encounter can change the spacecraft's motion relative to the Sun.
How it connects
The word names an encounter that changes the route without a large propulsive burn.
This word appeared in Borrowing motion from a planet, the Involves connection for September 9, 2026, which asked: How can a spacecraft change course without carrying all the fuel for the turn?
Check yourself
Which mission maneuver is a gravitational assist?
An unpowered planetary flyby changes the craft's solar-relative trajectory. Exactly. A gravity assist uses a close encounter with a moving body to alter a trajectory.
What the sources establish
Gravity assists alter a spacecraft's trajectory and solar-frame energy through encounters with moving planets.
Sources
What are gravity assists? (European Space Agency), Explanation of momentum exchange and reference frames