Encyclopedia Astronautica
Nerva Alpha


Nuclear/LH2 propellant rocket stage. Loaded/empty mass 17,783/4,969 kg. Thrust 71.70 kN. Vacuum specific impulse 860 seconds. Nuclear stage designed to fit into the space shuttle payload bay. Additional propellant modules could be added in orbit. Such propellant modules would have a mass of 23,181 kg, including 21,265 kg of usable propellant. Given goahead in 1972, it would have been flight tested by 1982.

Propellant Formulation: Nuclear/Slush Hydrogen.

Status: Development 1972.
Gross mass: 17,783 kg (39,204 lb).
Unfuelled mass: 4,969 kg (10,954 lb).
Height: 18.29 m (60.00 ft).
Diameter: 4.50 m (14.70 ft).
Span: 4.50 m (14.70 ft).
Thrust: 71.70 kN (16,119 lbf).
Specific impulse: 860 s.
Burn time: 1,500 s.

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Associated Countries
Associated Engines
  • Nerva Alpha DoE nuclear/lh2 rocket engine. 71.7 kN. Study 1972. The final Nerva Alpha flight engine reference configuration as documented at the end of its development. Isp=860s. More...

Associated Propellants
  • Nuclear/LH2 Nuclear thermal engines use the heat of a nuclear reactor to heat a propellant. Although early Russian designs used ammonia or alcohol as propellant, the ideal working fluid for space applications is the liquid form of the lightest element, hydrogen. Nuclear engines would have twice the performance of conventional chemical rocket engines. Although successfully ground-tested in both Russia and America, they have never been flown due primarily to environmental and safety concerns. 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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