Gravity assist

A spacecraft maneuver that uses a body's gravity and orbital motion to change the spacecraft's velocity relative to a central body, usually the Sun.

Patched-conic approximation: A trajectory model that treats motion as a sequence of two-body gravitational arcs around different bodies. It approximates the flyby as a shift from the Sun’s gravity to the planet’s and back.
Mariner 10: A NASA spacecraft that used a Venus flyby to reach Mercury and became the first spacecraft to visit it. Its 1974 Venus encounter demonstrated gravity-assisted interplanetary flight.
Two-body problem: The idealized problem of predicting the gravitational motion of two interacting masses. A flyby’s basic geometry is often analyzed as a two-body encounter.
Rocket engine: A device that produces thrust by expelling propellant. Unlike a rocket burn, an ideal gravity assist redirects velocity without consuming spacecraft propellant.
Hyperbolic trajectory: An unbound orbit that approaches and leaves a gravitating body along a hyperbola. A spacecraft follows this path during a typical planetary flyby.
Voyager 2: A NASA spacecraft launched in 1977 that explored the outer planets and continues into interstellar space. A sequence of planetary flybys enabled its tour of the outer solar system.
Sphere of influence (astrodynamics): An approximate region around a celestial body where its gravity dominates spacecraft trajectory calculations. It marks where mission analyses switch between planet-centered and Sun-centered descriptions.
Aerobraking: A maneuver that uses atmospheric drag to reduce a spacecraft’s orbital energy. It changes trajectory through atmospheric interaction rather than a body's orbital motion.
B-plane: A plane perpendicular to an incoming asymptotic trajectory, used to specify a spacecraft’s approach to a target body. Its aim point determines the flyby’s closest approach and outgoing direction.
Galileo (spacecraft): A NASA mission that studied Jupiter and its moons from orbit between 1995 and 2003. It used repeated Earth and Venus flybys to gain enough energy to reach Jupiter.

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