rl 550

The RL60 was a planned liquid-fuel cryogenic rocket engine designed in the United States by Pratt & Whitney, burning cryogenic liquid hydrogen and liquid oxygen propellants. The engine runs on an expander cycle, running the turbopumps with waste heat absorbed from the main combustion process. This high-efficiency, waste heat based combustion cycle combined with the high-performance liquid hydrogen fuel enables the engine to reach a very high specific impulse of up to 465 seconds in a vacuum. The engine was planned to be a more capable successor to the Aerojet Rocketdyne RL10, providing improved performance and efficiency while maintaining the installation envelope of the RL10.RL60 was planned to include major improvements to the high-thrust RL10B-2, such as up to 45 engine restarts (up from 15 for RL10B-2), 550 seconds longer engine lifetime (+15.7%), and twice the thrust. Like the RL10B-2, RL60 was planned to incorporate a radiatively cooled extendable nozzle. RL60 was designed to meet the evolving needs of expendable launch requirements and human-rated missions of the early 2000's.

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