Developed by Pratt & Whitney in the late 1950s and first flown in 1963, the RL10 (Currently produced in Space Launch Systems lead contractor Aerojet Rocketdyne) is a liquid-fuel cryogenic rocket engine capable of producing 110 Kilonewtons of thrust in a vacuum. Powered by liquid hydrogen and liquid oxygen, the engine uses the expander cycle that uses heat from the nozzle to power a turbopump, pumping the cryogenic propellants into the combustion chamber for ignition. This leads to “very high specific impulses (I_sp) in the range of 373 to 470 s (3.66–4.61 km/s) in a vacuum. Mass ranges from 131 to 317 kg (289–699 lb.) depending on the version of the engine,’’ according to Encyclopedia Astronautica. As the first liquid hydrogen powered rocket engine developed by the United States, it has been used on the Centaur Stage of the Atlas V and the Delta Cryogenic Upper Stage of the Delta IV. It is also planned to be used in the first 3 Artemis missions, where the Interim Cryogenic Propulsion Stage on the SLS Block-1 will have 1 RL-10 that pushes the Orion spacecraft to the moon. On the much more powerful Block-1B, the Exploration Upper Stage will now house 4 RL10C-3 Engines that produce a total of 433.07884 Kilonewtons of thrust.