Encyclopedia Astronautica
Centaur IIIB


Lox/LH2 propellant rocket stage. Loaded/empty mass 22,960/2,130 kg. Thrust 198.32 kN. Vacuum specific impulse 451 seconds. Dual-engine Centaur for Atlas IIIB. The Lockheed Martin manufactured Centaur IIIB upper stage is powered by two Pratt & Whitney RL10A-4-2 turbopump-fed engines burning liquid oxygen and liquid hydrogen. The changes to Centaur for Atlas IIIB are a stretched tank (1.68 m) and the addition of the second engine.

Guidance, tank pressurization, and propellant usage controls for both Atlas and Centaur phases are provided by the inertial navigation unit (INU) located on the forward equipment module. The first Centaur burn lasts about five minutes, after which the Centaur and its payload coast in a parking orbit. During the first burn, approximately eight seconds after ignition, the payload fairing is jettisoned. The second Centaur ignition occurs 27 minutes into the flight, continues for about three minutes, and is followed several minutes later by the separation of the spacecraft from Centaur.

Status: Out of production.
Gross mass: 22,960 kg (50,610 lb).
Unfuelled mass: 2,130 kg (4,690 lb).
Height: 11.68 m (38.32 ft).
Diameter: 3.05 m (10.00 ft).
Span: 3.05 m (10.00 ft).
Thrust: 198.32 kN (44,584 lbf).
Specific impulse: 451 s.
Burn time: 460 s.
Number: 4 .

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Associated Countries
Associated Engines
  • RL-10A-4-2 Pratt and Whitney lox/lh2 rocket engine. 99.1 kN. In production. Isp=451s. Used on Atlas IIIB launch vehicle. First flight 2002. Two engines; electro-mechanical thrust vector control actuators replaced earlier hydraulically actuated system. More...

Associated Launch Vehicles
  • Atlas IIIB American orbital launch vehicle. This was the first version of the Atlas to fly using Russian RD-180 engines; and the last version to fly using the original balloon-tank concept for the first stage. It differed from the Atlas IIIA in use of a stretched, two-engine upper stage, and had a brief three-year operational career in 2002-2005 before being superseded by the Atlas V. More...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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