Pratt & Whitney Space Propulsion

Pratt & Whitney Space Propulsion (now operating as Aerojet Rocketdyne following its 2013 acquisition by GenCorp, and subsequently as L3Harris's Aerojet Rocketdyne following the 2023 acquisition) is the West Palm Beach, Florida heritage site for Pratt & Whitney's rocket engine development, most famous for producing the RL10 — the world's most flight-proven upper stage engine with over 500 successful space missions.

The RL10 uses liquid hydrogen and liquid oxygen in an expander cycle (where fuel is heated by the engine chamber to drive the turbopump, with no separate preburner), achieving specific impulse of 450-465 seconds — the highest Isp of any production liquid rocket engine — making it the gold standard for upper stages where maximum efficiency per kilogram of propellant is paramount. RL10 variants (A-4, B-2, C-1, C-3) power the Centaur upper stage of Atlas V and Vulcan, Boeing's DCSS (Delta Cryogenic Second Stage), and have been selected for ULA's new Vulcan Centaur as RL10Cs.

The RS-25 (Space Shuttle Main Engine, SSME) — the world's most sophisticated liquid rocket engine — was developed at what is now Aerojet Rocketdyne's Canoga Park facility, now refurbished for NASA's Space Launch System (SLS): each SLS launches with four RS-25s producing 490,000 lbs thrust each at near-maximum efficiency. Pratt & Whitney also developed the RL50, COBRA, and various advanced concepts for upper stage applications.

The company's space propulsion heritage, concentrated in the RL10 engine which has accumulated thousands of starts and hundreds of upper stage missions without a single in-flight failure attributable to the engine, represents one of the most reliable engineering achievements in launch vehicle history.