Oberth effect

The Oberth effect is the greater change in a spacecraft’s kinetic energy produced by a given rocket burn when the spacecraft is already moving faster. It makes burns near periapsis especially effective for changing orbital energy.

Vis-viva equation: An orbital relation connecting a body's speed, distance from the focus, and orbit's semimajor axis. It shows why orbital speed is greatest at periapsis, where a burn gains the most energy.
Periapsis: The point in an orbit where an object is closest to the body it orbits. A burn there takes advantage of the orbit's maximum speed.
Gravity assist: A spacecraft trajectory change that exchanges energy and momentum with a moving celestial body during a flyby. A gravity assist draws energy from a body's motion, while the Oberth effect amplifies a rocket burn's energy change.
Hermann Oberth: A German-born rocket pioneer whose 1923 book helped establish the foundations of astronautics. The effect bears his name, though the underlying energy relation follows from classical mechanics.
Impulse (physics): The change in momentum produced by a force acting over time. A rocket burn supplies impulse, changing velocity while the spacecraft is already moving.
Powered gravity assist: A planetary flyby combined with a rocket burn to alter a spacecraft's trajectory. Burning near closest approach can amplify the energy change available during a flyby.
Hohmann transfer orbit: A two-impulse orbital transfer between circular coplanar orbits using an elliptical transfer orbit. Its burns occur at specific orbital locations, but its standard analysis does not depend on the Oberth effect as a separate maneuver.
Rocket Propulsion Elements: A textbook by George Sutton and Oscar Biblarz covering rocket propulsion and spacecraft propulsion systems. Its treatments of rocket performance help place the effect within practical propulsion analysis.
Kinetic energy: The energy an object has because of its motion. The effect concerns the burn’s change in kinetic energy, not merely its change in speed.
New Horizons: NASA's spacecraft that flew past Pluto in 2015 and explored the Kuiper Belt object Arrokoth in 2019. Its launch included a high-speed departure burn that illustrates the value of the Oberth effect.

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