RS-68

RS-68
	An RS-68 engine undergoing hot-fire testing at NASA's Stennis Space Center during its developmental phase.
Country of origin	United States
First flight	2002
Manufacturer	Rocketdyne ; Pratt & Whitney Rocketdyne ; Aerojet Rocketdyne
Application	First stage engine for the Delta IV rocket
Status	Retired
Liquid-fuel engine
Propellant	Liquid oxygen / Liquid hydrogen
Configuration
Nozzle ratio	21.5
Performance
Thrust, sea-level	RS-68: 660,000 lbf (2,950 kN); RS-68A: 705,000 lbf (3,137 kN)
Thrust-to-weight ratio	RS-68: 45.3; RS-68A: 47.4
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)
Dimensions
Length	17.1 ft (5.20 m)
Diameter	8 ft 0 in (2.43 m)
Dry weight	RS-68: 14,560 lb (6,600 kg); RS-68A: 14,870 lb (6,740 kg)
Used in
	Delta IV

The Aerojet Rocketdyne 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 power cycle. It was the largest hydrogen-fueled rocket engine ever flown.^[3]

Its 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 cancellation of the rocket and the Constellation Program in 2010.

^ ^a ^b "DELTA IV". United Launch Alliance. Archived from the original on July 20, 2014. Retrieved July 13, 2014.
^ "Delta IV User's Guide" (PDF). United Launch Alliance. June 2013. Archived (PDF) from the original on July 10, 2014. Retrieved July 13, 2014.
^ "ATK Propulsion and Composite Technologies Help Launch National Reconnaissance Office Satellite" (Press release). Alliant Techsystems. January 19, 2009. Archived from the original on February 22, 2014.

[ula-delta4-1] "DELTA IV". United Launch Alliance. Archived from the original on July 20, 2014. Retrieved July 13, 2014.

[2] "Delta IV User's Guide" (PDF). United Launch Alliance. June 2013. Archived (PDF) from the original on July 10, 2014. Retrieved July 13, 2014.

[3] "ATK Propulsion and Composite Technologies Help Launch National Reconnaissance Office Satellite" (Press release). Alliant Techsystems. January 19, 2009. Archived from the original on February 22, 2014.

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