Cathode for Electric Space Propulsion Utilizing Iodine as Propellant

We propose a hollow reservoir cathode suitable for use in ion or Hall thrusters which utilizes iodine as a propellant. Reservoir cathodes have several unique features which will allow them to resist the corrosive effects of iodine. Chief amongst these is that the barium-emission-material-containing reservoir is isolated from the iodine flow. This allows free barium to be produced in an environment free of iodine. Furthermore, barium production rates in reservoir cathodes can be adjusted to very high levels -- high enough to overcome the deleterious effects of iodine at the cathode's emitting surface. Reservoir cathodes carry a barium supply that is 100 times that of conventional cathodes. Furthermore, the reservoir cathode inserts can be made of materials other than tungsten. This is not possible with impregnated cathodes. These materials can be selected for their resistance to iodine attack. They include osmium, rhodium, and iridium. NASA is pursuing iodine EP because of iodine's advantages over xenon, especially for small satellite propulsion. Most important are its low cost and its high storage density. Also, it requires no high-pressure, large and heavy pressure vessels.

NASA's primary interest is for iodine thrusters of less than 1 KW. It is also interested in powers over 10 KW. Nanosats are the biggest 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. It has a crucial need for reliable cathodes, both for discharge and neutralization. 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.

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