RL10

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RL10

An RL10A-4 engine in London's Science Museum
Country of origin	United States
First flight	1962 (1962) (RL10A-1)
Manufacturer	Aerojet Rocketdyne
Application	Upper stage engine
Associated LV	Atlas · Delta III · Delta IV · Saturn I · SLS · Titan IIIE · Titan IV · Vulcan Centaur Canceled: DC-X · OmegA · Space Shuttle
Status	In production
Liquid-fuel engine
Propellant	LOX / LH2
Mixture ratio	5.88:1
Cycle	Expander cycle
Configuration
Nozzle ratio	84:1 or 280:1
Performance
Thrust, vacuum	110.1 kN (24,800 lbf)
Specific impulse, vacuum	465.5 s (4.565 km/s)
Dimensions
Length	4.15 m (13.6 ft) w/ nozzle extended
Diameter	2.15 m (7 ft 1 in)
Dry mass	301 kg (664 lb)
Used in
Centaur, DCSS, S-IV
References
References	[1]
Notes	Performance values and dimensions are for RL10B-2.

The RL10 is a liquid-fuel cryogenic rocket engine built in the United States by Aerojet Rocketdyne that burns cryogenic liquid hydrogen and liquid oxygen propellants. Modern versions produce up to 110 kN (24,729 lb_f) of thrust per engine in vacuum. Three RL10 versions are in production for the Centaur upper stage of the Atlas V and the DCSS of the Delta IV. Three more versions are in development for the Exploration Upper Stage of the Space Launch System and the Centaur V of the Vulcan rocket.^[2]

The expander cycle that the engine uses drives the turbopump with waste heat absorbed by the engine combustion chamber, throat, and nozzle. This, combined with the hydrogen fuel, 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.^[3][4]