The Application of Gridded Ion Thrusters to High Thrust, High Specific Impulse Nuclear-Electric Missions

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D.G. Fearn (2005), JBIS, 58, 257-267

Refcode: 2005.58.257
Keywords: Electric propulsion

Gridded ion thrusters are usually regarded as very efficient devices which can operate at high values of specific impulse (SI), of the order of 2800 to 5000 s, but with an inherently low thrust and thrust density. However, this latter limitation is due to the restricted power available from present spacecraft. It is shown in this paper that a very much enhanced thrust density can be provided if a nuclear fission power source is utilised, with an electrical output in the 100 kW to multi-MW range, and if higher values of SI can be employed. In that case, use can be made of a 4-grid ion extraction and acceleration system, permitting present thrust densities in the range 0.1 to 0.9 mN/cm2 to be increased to as much as 28 mN/cm2. Corresponding values of SI depend critically upon the propellant used and vary from about 8000 s to as high as 150,000 s. As an example of a possible application of this technology, a manned mission to Mars is considered, which employs existing space vehicles and launchers to the maximum possible extent in order to minimise cost. It is shown that such a mission is viable if a nuclear reactor system with an electrical output of about 1 MW is available, with a mass-to-power ratio of less than 20 kg/kW.

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