Retrothrust

Retrothrust refers to the application of thrust in the direction opposite to the vehicle's motion. This technique is primarily employed to slow down or decelerate a spacecraft or aircraft. In rocketry, retrothrust is crucial for orbital maneuvers such as deorbiting, where a spacecraft fires its engines to reduce its speed and enter the atmosphere, or for landing on celestial bodies. The amount and duration of retrothrust are carefully calculated to achieve the desired change in velocity.

For aircraft, retrothrust is often achieved through the use of thrust reversers, which are mechanical devices on jet engines that redirect the exhaust gases forward. This significantly reduces the aircraft's landing roll distance, enhancing safety on the runway, especially in wet or icy conditions. While the principle is the same as in rocketry, the implementation and purpose differ, focusing on aerodynamic deceleration rather than orbital mechanics. The concept of retrothrust highlights the dual nature of rocket engines and jet engines, capable of both accelerating and decelerating a vehicle.