Nuclear thermal propulsion

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Nuclear thermal propulsion uses a nuclear core to heat a propellant and provide propulsion to a space vehicle.

Liquid hydrogen is usually used as the propellant as it has a higher velocity for the same input power, and therefore produces a faster final velocity according to the rocket equation. An animated illustration of nuclear thermal rockets can be found at [1].

History of nuclear thermal propulsion



Propellant Liquid hydrogen
Thrust (vac.) 246,663 N (55,452 lbf)
Chamber pressure 3,861 kPa (560.0 psi)
Isp (vac.) 841 seconds (8.25 km/s)
Isp (SL) 710 seconds (7.0 km/s)
Burn time 1,680 seconds
Thrust to weigh ratio 1.36
Restarts 24
Length 6.9 meters (23 ft)
Diameter 2.59 meters (8 ft 6 in)
Dry weight 18,144 kilograms (40,001 lb)


Analysis of use


  • Higher ISP than chemical
  • Higher power energy source
  • Shorter travel time
  • Oberth effect
  • Self cooling


  • Cost
  • Cost of development
  • Risk of accident
  • Lower ISP than electric
  • Low public trust
  • Thrust to weight ratio close to 1 (cannot take off from Earth with a significant payload)


  • Solid core[3]
  • Gas core[4]
  • Nuclear light bulb, open and closed[5]
  • Nuclear salt water rockets[6]