![]() An RS-68 engine undergoing hot-fire testing at NASA's Stennis Space Center during its developmental phase. | |
Country of origin | ![]() |
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First flight | 20 November 2002 |
Last flight | 9 April 2024 |
Designer | Rocketdyne |
Manufacturer |
|
Application | First stage engine |
Associated LV | Delta IV · Delta IV Heavy |
Status | Retired |
Liquid-fuel engine | |
Propellant | LOX / LH2 |
Cycle | Gas-generator |
Configuration | |
Nozzle ratio | 21.5:1 |
Performance | |
Thrust, sea-level | RS-68: 2,950 kN (660,000 lbf) RS-68A: 3,137 kN (705,000 lbf)[1] |
Thrust-to-weight ratio | RS-68: 45.3:1 RS-68A: 47.4:1 |
Chamber pressure | 1,488 psi (10.26 MPa) |
Specific impulse, vacuum | RS-68: 410 s (4.0 km/s) RS-68A: 411.9 s (4.039 km/s)[2] |
Dimensions | |
Length | 5.20 m (17.1 ft) |
Diameter | 2.43 m (8 ft 0 in) |
Dry mass | RS-68: 6,600 kg (14,560 lb) RS-68A: 6,740 kg (14,870 lb)[1] |
The RS-68 (Rocket System-68) was a liquid-fuel rocket engine that used liquid hydrogen (LH2) and liquid oxygen (LOX) as propellants in a gas-generator cycle. It was the largest hydrogen-fueled rocket engine ever flown.[3]
Designed and manufactured in the United States by Rocketdyne (later Pratt & Whitney Rocketdyne and Aerojet Rocketdyne). Development started in the 1990s with the goal of producing a simpler, less costly, heavy-lift engine for the Delta IV launch system. Two versions of the engine have been produced: the original RS-68 and the improved RS-68A. A third version, the RS-68B, was planned for the National Aeronautics and Space Administration's (NASA) Ares V rocket before the cancellation of the rocket and the Constellation Program in 2010.