Encyclopedia Astronautica

IMIS Primary Propulsion Module
Credit: © Mark Wade
American space tug. Study 1968. The Primary Propulsion Module was the definitive 1960's design for a nuclear thermal rocket stage suitable for interplanetary operations.

The basic NERVA stage was modified to allow for docking and assembly in orbit, storage and reliquefaction of its liquid hydrogen propellant for periods of up to three years on long voyages to Mars and Venus, and to feed propellant to lower stages as needed.

Detailed mass breakdown was as follows:

  • Liquid hydrogen propellant: 174,600 kg
  • NERVA nuclear thermal engine system: 14,500 kg
  • Propellant tank: 22,700 kg
  • Stage equipment: 2700 kg
  • Meteoroid shield: 19,000 kg
  • Interstage structures: 5200 kg
  • 11% growth and contingency allowance: 6800 kg

AKA: Primary Propulsion Module.
Gross mass: 245,600 kg (541,400 lb).
Unfuelled mass: 71,000 kg (156,000 lb).
Height: 48.20 m (158.10 ft).
Diameter: 10.06 m (33.00 ft).
Thrust: 866.90 kN (194,887 lbf).
Specific impulse: 850 s.

More... - Chronology...

Associated Countries
Associated Spacecraft
  • IMIS 1968 American manned Mars expedition. Study 1968. In January 1968 Boeing issued a report that was the result of a 14 month study on manned Mars missions. More...
  • Von Braun Mars Expedition - 1969 American manned Mars expedition. Study 1969. Von Braun's final vision for a manned expedition to Mars was a robust plan that eliminated much of the risk of other scenarios. Two ships would fly in convoy from earth orbit to Mars and back. More...

Associated Engines
  • Nerva DoE nuclear/lh2 rocket engine. 266 kN. Study 1968. Early version of Nerva engine proposed for use in Saturn and RIFT configurations in 1961. Isp=800s. More...

See also
Associated Manufacturers and Agencies
  • Boeing American manufacturer of rockets, spacecraft, and rocket engines. Boeing Aerospace, Seattle, USA. 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...

  • Baker, Larry L, "Manned Interplanetary Spacecraft", Northwest Professional Engineer, Summer/Fall 1968.

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