engine design for a reusable LH2/LOX rocket larger and more powerful than any other. The RS-83 was developed by Rocketdyne Propulsion and Power in Canoga Park, California to power the launch vehicle as part of the Space Launch Initiative program. This engine was designed to produce a thrust of 664000 lbf at sea level and 750000 lbf in a vacuum with an I_sp of 395 and 446 seconds (3.87 and 4.37 kN·s/kg), respectively.

The RS-83 is loosely