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PPM

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PPMS IMIS Primary Propulsion Module Credit: © Mark Wade

AKA: Primary Propulsion Module. Status: Study 1968. Thrust: 866.90 kN (194,887 lbf). Gross mass: 245,600 kg (541,400 lb). Unfuelled mass: 71,000 kg (156,000 lb). Specific impulse: 850 s. Height: 48.20 m (158.10 ft). Diameter: 10.06 m (33.00 ft).

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