308 ANNUAL REPORT SMITHSONIAN INSTITUTION, 196 2 



Figure 4. — Simplified schematic of a nuclear propulsion system. The H2 propellant is 

 pumped from the tank, cooling the nozzle and reactor reflector (R), before being heated 

 in the core and expelled through the nozzle. 



heavy "pusher plate," transferring momentum to the plate which is 

 coupled to the rest of the vehicle through a shock-absorbing system. 

 Space ships utilizing such a propulsion system could carry millions 

 of pounds of payload throughout the solar system with quite small 

 nuclear explosives. 



There are no workable methods of utilizing nuclear fusion (thermo- 

 nuclear) energy for space propulsion presently in sight. 



There is another class of propulsion devices which will ultimately 

 rely on nuclear energy as the power source and which is best termed 

 "electrical propulsion." This includes a wide variety of engines 

 which heat and/or, more importantly, accelerate the propellant elec- 

 trically. By accelerating the propellant directly, one can get it to 

 very high velocities (50,000 to 500,000 ft./sec.) without raising its 

 thermal (random molecular motion) energy. One volt of electrical 

 potential corresponds to 10,000°C. of thermal energy. The propel- 

 lant can consist of electrically charged ions, fine particles, gases, etc., 

 which are accelerated by electrical or magnetic fields using the same 



