RL-10A-4-1

Pratt and Whitney LOx/LH2 rocket engine. Out of production. Used on Atlas IIIA launch vehicle. First flight 2000. Version with one of engines removed; remaining engine re-positioned to center-mount; new electro-mechanical gimbals.

For Centaur IIIA, one of Centaur IIAS's two RL10A-4 engines is removed. The remaining engine is re-positioned to a center-mount, and electro-mechanical thrust vector control actuators replace the hydraulically actuated system previously in use. Guidance, tank pressurization, and propellant usage controls for both Atlas and Centaur phases are provided by the inertial navigation unit (INU) located on the forward equipment module. The first Centaur burn lasts about nine minutes after which the Centaur and its payload coast in a parking orbit. During the first burn, approximately ten seconds after ignition, the payload fairing is jettisoned. The second Centaur ignition occurs about 23 minutes into the flight, continues for about three minutes, and is followed several minutes later by the separation of the spacecraft from Centaur.

Engine: 167 kg (368 lb). Chamber Pressure: 39.00 bar. Area Ratio: 84. Thrust to Weight Ratio: 60.53.