Reservoir Scandate Cathode for Electric Propulsion

We propose to combine two revolutionary cathode technologies into a single device for use in electric space propulsion. This will overcome problems that both technologies have when operated alone. The cathode is currently the component which most limits performance and life in ion and Hall Effect thrusters. Improved cathodes are essential for NASA's next generation electric space propulsion initiative. The innovation will benefit both satellite and deep space missions. We have successfully demonstrated both stand-alone reservoir and scandate cathodes in hollow cathode geometries. Reservoir cathodes are known to provide unprecedented life and stability. Scandate cathodes dramatically lower operating temperature. By combining the two technologies, we incorporate extremely long life (greater than 10 years) and extremely low temperature (less than 850 degrees C) into a single device. The result will be a revolutionary enhancement in electric propulsion. Reservoir cathodes employ a chamber behind the emitter which contains a barium emissive material. This greatly increases the amount of barium available to the cathode. Scandate cathodes provide a scandium-containing cathode surface which lowers the work function.

NASA will use the cathode in ion thrusters for long-range space mission, such as Mars and lunar cargo missions. It will use it for voyages to more distant planets such as Jupiter and Saturn. The cathode may be used wherever long life and higher specific impulse are required. The cathode may eventually enable manned long-range missions. A higher emission cathode would enable higher power and frequency in klystrons and TWTs. This would allow higher data rate transmissions.

The cathode will improve performance and life on non-NASA ion and Hall Effect thrusters, used in near-Earth missions. Of particular interest is its use in geosynchronous satellites for circularization, attitude control and station keeping. Also, many vacuum electron devices such as klystron, traveling wave tubes and even x-ray tubes would benefit from this work. In particular, this proposal has significant effort devoted to improving the mechanical strength and geometrical stability of scandate cathode matrices. The lack of these qualities has been one reason they are not used in linear beam devices where focusing stability depends on cathode dimensional stability.

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