Page "Orbital maneuver" Paragraph 22

In astronautics, the Oberth effect is where the use of a rocket engine when travelling at high speed generates much more useful energy than one at low speed.

Oberth effect occurs because the propellant has more usable energy ( due to its kinetic energy on top of its chemical potential energy ) and it turns out that the vehicle is able to employ this kinetic energy to generate more mechanical power.

It is named after Hermann Oberth, the Austro-Hungarian-born, German physicist and a founder of modern rocketry, who apparently first described the effect.