Electric propulsion - An evolutionary technology

The objectives of an efficient electric propulsion (EP) system capable of meeting the requirements of the SDI Organization missions are discussed, with consideration given to each of the three EP applications, namely, the orbit raising, the on-orbit station-keeping, and the defensive maneuvering. Space experiments involving EP are being planned around the arcjet and ion thruster types, with the short-term research being focused on the NH3 arcjet for the SP-100 flight missions. Demonstrated 30 kW arcjet sustained life of the arcjet (as compared with less than 3 kW for the ion engine) and the arcjet's inherent simplicity offer low risk and minimum cost for the SP-100 flight demonstration objectives. Long-term research on high thrust-density ion propulsion is aimed at 5 to 25 kW operation in the 5000-sec specific impulse range. 30 refs.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA345760&Location=U2&doc=GetTRDoc.pdf

SDIO electric propulsion objectives and programs

An investigation was conducted to study the effect of current ripple on cathode erosion in 30 kWe class arcjets to determine the change in the cathode erosion rate for high (11 percent) and low (4 percent) current ripple. The measurements were conducted using a copper-tungsten cathode material to accelerate the cathode erosion process. It is shown that the high ripple erosion rate was initially higher than the low ripple erosion rate, but decreased asymptotically with time to a level less than half that of the low ripple value. Results suggest that high ripple extends the cathode lifetime for long duration operation, and improves arc stability by increasing the cathode attachment area.

Anthony Donaldson

Papers

Arcjet cathode erosion studies