With NASA facing steep budget cuts after Apollo, efficiency became critical. With the development of Shuttle, they needed an engine that was powerful, highly efficient, and reusable. NASA once again turned to Rocketdyne to develop what became the RS-25 engine. Burning liquid hydrogen (LH2) and liquid oxygen (LOX) in a staged-combustion cycle, it produces 213 tons of thrust. Capable of deep throttling and reuse, the RS-25 became the first large reusable rocket engine. The RS-25 powered all 135 Shuttle missions and is now flying on the SLS. Proving its unmatched reliability and performance for the journey back to the Moon and beyond.