Description: A hollow reservoir cathode for use in ion and Hall thrusters which uses iodine as propellant. Reservoir cathodes have unique features not found in conventional impregnated cathodes. The critical barium reduction process occurs in the reservoir, not in the matrix, and this isolates that process from iodine poisoning. Also, the barium supply is 100 times greater than is available in conventional cathodes. This allows much higher rates of barium to flow to the cathode’s surface – enough to overcome iodine poisoning. Also, metals resistant to iodine attack can be used in the cathode matrix. We propose constructing large numbers of reservoir cathodes with various compositions and activities. We propose a systematic study of these cathodes in iodine to discover the factors which provide the successful performance. We also propose a miniature reservoir cathode for use in CubeSats, where iodine's compactness is most appealing. NASA is pursuing iodine EP because of its many advantages over xenon. These include low cost and high storage density.

Benefits: NASA's primary interest is for iodine thrusters of less than 1 KW. It is also interested in powers over 10 KW. NASA has a critical need for reliable cathodes, both for discharge and neutralization. NanoSats are the largest market with iodine supply between 1 and 10 Kg and power at about 200 watts. A 12U CubeSat sponsored by NASA Glenn Research Center will employ an iodine ion thruster. NASA Glenn and the Marshall Space Flight Center are co-sponsoring the iSat (iodine satellite) project. It, too, needs reliable cathodes. 2,000 to 2,750 small satellites are planned for this project.

Busek Co. is the main non-NASA producer of iodine thrusters. We have been in communication with it to supply cathodes if this project is successful. CubeSats are the largest non-NASA market. They are the mainstay of university and private space science projects.