The Soviet RD-0120 (also designated 11D122) was the Energia core rocket engine, fueled by LH2/LOX, roughly equivalent to the Space Shuttle Main Engine (SSME). These were attached to the Energia core rather than the orbiter, so were not recoverable after a flight, but created a more modular design (the Energia core could be used for a variety of missions besides launching the shuttle). Baselined from the more mature American hydrogen–oxygen engine technology, but considerably modified with Russian innovations and methods, the RD-0120 and the SSME have both similarities and differences. The RD-0120 achieved nearly identical specific impulse and combustion chamber pressure with reduced complexity and cost, as compared to the SSME, primarily at the expense of lower thrust-to-weight ratio. It u