RS-25 Engine (Space Launch System)

The RS-25 (also known as the Space Shuttle Main Engine, SSME) is a liquid-propellant cryogenic rocket engine manufactured by Aerojet Rocketdyne, originally developed for the Space Shuttle program and now reused as the core stage engine for NASA’s Space Launch System (SLS). Each SLS core stage uses four RS-25 engines, generating a combined thrust of approximately 1,860 kN (418,000 lbf) at sea level. The engine burns liquid hydrogen (LH2) and liquid oxygen (LOX), achieving a specific impulse of 453 seconds in vacuum. The original Shuttle-era RS-25 engines were refurbished for SLS use; new production RS-25E engines are also being manufactured for later SLS missions. The RS-25 first flew on the Space Shuttle Columbia on April 12, 1981, and on the SLS during Artemis I on November 16, 2022.