Encyclopedia Astronautica
Delta RS-68


Lox/LH2 propellant rocket stage. Loaded/empty mass 226,400/26,760 kg. Thrust 3,312.76 kN. Vacuum specific impulse 420 seconds. Low cost expendable stage using lower performance engine. Used in Delta 4, Boeing EELV. Engine can be throttled to 60%.

Status: In production.
Gross mass: 226,400 kg (499,100 lb).
Unfuelled mass: 26,760 kg (58,990 lb).
Height: 40.80 m (133.80 ft).
Diameter: 5.10 m (16.70 ft).
Span: 5.10 m (16.70 ft).
Thrust: 3,312.76 kN (744,737 lbf).
Specific impulse: 420 s.
Specific impulse sea level: 365 s.
Burn time: 249 s.
Number: 18 .

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Associated Countries
Associated Engines
  • RS-68 Rocketdyne lox/lh2 rocket engine. 3312 kN. In production. Isp=420s. First new large liquid-fueled rocket engine developed in America in more than 25 years. Powered the Delta IV booster. First flight 2002. More...

Associated Launch Vehicles
  • Delta IV Medium+ (4.2) American orbital launch vehicle. As Delta 4 medium but with 2 x GEM-60 solid rocket boosters and a 4 m diameter payload fairing. More...
  • Delta IV Medium American orbital launch vehicle. Basic Delta-4 vehicle with no strap-ons, the core vehicle, and RL10B-1 upper stage with a 4 m diameter payload fairing. World's first all-cryogenic launch vehicle. More...
  • Delta IV Heavy American orbital launch vehicle. Heavy lift all-cryogenic launch vehicle using two Delta-4 core vehicles as first stage flanking a single core vehicle as second stage. A heavy upper stage is carried with a 5 m diameter payload fairing. More...
  • Delta IV Medium+ (5.2) American orbital launch vehicle. As Delta 4 medium but with 2 x GEM-60 solid rocket boosters and a 5 m diameter payload fairing. More...
  • Delta IV Small American orbital launch vehicle. Light launch vehicle using the Delta-4 core with the traditional Delta K and PAM-D upper stages. 2 m diameter payload fairing. Not flown as of 2008 but cancellation of the Delta II could lead to its eventual use. More...
  • Delta IV Medium+ (5.4) American orbital launch vehicle. As Delta 4 medium but with 4 x GEM-60 solid rocket boosters and a 5 m diameter payload fairing. More...

Associated Propellants
  • Lox/LH2 Liquid oxygen was the earliest, cheapest, safest, and eventually the preferred oxidiser for large space launchers. Its main drawback is that it is moderately cryogenic, and therefore not suitable for military uses where storage of the fuelled missile and quick launch are required. Liquid hydrogen was identified by all the leading rocket visionaries as the theoretically ideal rocket fuel. It had big drawbacks, however - it was highly cryogenic, and it had a very low density, making for large tanks. The United States mastered hydrogen technology for the highly classified Lockheed CL-400 Suntan reconnaissance aircraft in the mid-1950's. The technology was transferred to the Centaur rocket stage program, and by the mid-1960's the United States was flying the Centaur and Saturn upper stages using the fuel. It was adopted for the core of the space shuttle, and Centaur stages still fly today. More...

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