Reservoir Scandate Cathode for Electric Propulsion

We propose to combine the two most powerful cathode technologies into one hollow cathode assembly for use in ion and Hall-effect thrusters. Together, these technologies will boost ion thruster performance and life beyond current art. Reservoir cathodes have demonstrated, in microwave tube environments, lifetimes beyond 100,000 hours with no drop in output. Scandate impregnated cathodes have demonstrated emission beyond 10 amps/cm2 at 800 degrees Cb(W) and emission levels over 100 amps/cm2 at under 1000 degrees Cb(W). This is over 200 degrees below comparable all-tungsten impregnated cathodes, the cathode normally used for space propulsion. High temperature is the great enemy of long cathode life. Longer-life cathodes are needed for interplanetary and lunar missions, as well as earth-escape and near-earth maneuvers. In Phase II, we shall continue developing the hybrid scandate reservoir cathode and perfect our stand-alone scandium-doped tungsten cathodes. We shall continue to improve our hollow reservoir technology. Then we will combine the two technologies into an integrated module.

Mars and lunar cargo missions would benefit, as would the upcoming JUNO mission to Jupiter. Also, piloted interplanetary mission become feasible with sufficient cathode output and life. Earth transfer, station-keeping and earth-escape should occur by all-electric means. It would lower cost, size, mass, and complexity. This technology would also help NASA's conventional cathode applications. Improved cathodes are needed for microwave amplifiers for space communications. The cathode is the performance-limiting component in these devices. A higher output cathode is especially needed for terahertz amplifiers and sources. The so-called "terahertz gap" is a vast region of frequency space that is unutilized, largely because of cathode technology limitations. Scandate cathodes are the key to accessing that space. In short, NASA needs higher bit rates, more power, and higher frequency for space communications and a host of other applications, and these are largely limited by the cathode.

All the applications described in NASA commercial applications apply to non-NASA markets except interplanetary space travel. More powerful thrusters are needed in commercial satellites for orbital transfer. These would allow all-electric propulsion for larger, heavier satellites operating in geo-synchronous orbits. All-electric propulsion lowers mass and size and raises efficiency. Other areas include Department of Defense radars and communications. This is the largest market for high-performance cathodes. The cathodes proposed here would increase life, performance, frequency data rates and resolution in these systems. Nongovernmental applications lie in high-speed x-ray tomography, electron beam-stimulated lasers, especially at UV, and commercial geo-synchronous satellite downlinks and propulsion. Hollow cathodes can be used as a source of high current density electrons for applications such as electron beam welding or as a source of electrons in corrosive environments. The cathodes proposed here are capable of creating electron beams of 1000 amps/cm2 or more. Even though the energy spread is high, the extraordinary current densities make for an extremely bright beam.

This is a mature technology (TRL 7) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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