RS-68 (rocket engine)
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The Rocketdyne RS-68 (Rocket System 68) is the largest existing liquid hydrogen / liquid oxygen engine, producing a thrust of 650,000 lbf (2.9 MN) at sea level and 745,000 lbf (3.3 MN) in a vacuum. Developed from the late 1990s into the 2000s, the RS-68 was designed with the goal of reducing cost versus contemporary engines.
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[edit] Overview
The RS-68 was developed at Rocketdyne Propulsion and Power, located in Canoga Park, Ca. to power the Delta IV Evolved Expendable Launch Vehicle (EELV). The RS-68 was the first new American booster engine developed in over 25 years. The combustion chamber burns liquid hydrogen and liquid oxygen at 1410 lbf/in² (9.7 MPa) with a 1:6 liquid hydrogen / liquid oxygen ratio. The specific impulse is 410 s (4 kN·s/kg) in a vacuum and 365 s at sea level, at maximum thrust. The engine's mass is 14,560 lb (6,600 kg) and has a thrust to weight ratio of 51.2. The RS-68 also has hydraulically controlled gimbaling, and is capable of throttling from 58% to 100% thrust.
Simplicity of design and cost effectiveness were the primary design goals of this engine, which resulted in 80% fewer parts than the SSME (and a 10% reduction in specific impulse). The thrust to weight ratio of the RS-68 is also significantly lower than the SSME. The benefit of this design philosophy is drastically reduced construction costs. Each RS-68 for the Boeing Delta IV program costs approximately $14 million to build, compared to the SSME at $50 million. This is especially noteworthy considering the RS-68 is significantly larger and produces higher thrust.
The engine itself is a gas generator cycle engine with two independent turbopumps. The combustion chamber uses a channel-wall design, to reduce cost. This design, pioneered in the Soviet Union, features inner and outer skins brazed to middle separators, forming cooling channels. This method is heavier, but much simpler and cheaper than the tube-wall design (using hundreds of tubes, bent into the shape of the combustion chamber and brazed together) used in other engines. The lower nozzle has an expansion ratio of 21.5 and is made from an ablative material. The nozzle's lining is designed to burn away as the engine runs, dissipating heat. This is also heavier than the tube-wall nozzles used in other engines, but is also much easier and cheaper to manufacture. While the design was done at the Canoga Park facility, where the SSME is manufactured, the initial development engines were assembled at the Santa Susana facility where the Saturn V engines were developed and tested for the Apollo missions to the Moon. The RS-68 had initial testing done at Edwards Air Force Base and later at NASA's John C. Stennis Space Center. The first successful test firing was completed on September 11, 2000 and the first successful launch using the new engine and launch vehicle occurred on November 20, 2002.
The RS-68 is part of the Common Booster Core (CBC) used to create the many variants of the Delta IV family of launch vehicles. The largest of the launch vehicles includes three CBCs mounted together for the Heavy.
[edit] Future use
On May 18th, 2006 NASA announced that 5 RS-68 engines would be used instead of SSMEs on the planned Ares V (CaLV). The reason given is the reduced cost of the RS-68, which, with NASA upgrades, will cost about $20 million per engine. The modifications to the RS-68 for the Ares V include a regeneratively cooled nozzle, LH2 propellant densification, and other modification necessary to allow the RS-68 to run at a higher thrust and higher Isp – in essence, the modifications will allow the Ares V RS-68 engines to operate much like that of the current SSMEs, but with the high thrust ratio and reduced cost. [1]
[edit] References
- ^ NASA (2006-05-18). NASA's Exploration Systems Progress Report. Press release. Retrieved on 2006-05-30.
