Description: The proposed innovation is an advanced iodine feed system for Hall Effect Thrusters (HETs), ion engines, cathodes, and other plasma generators. This feed system features a low mass plastic propellant tank that may be manufactured through additive processes. This allows low cost, complex shapes that can maximize the use of available space inside the spacecraft. The feed system also features an innovative piezo valve that will save volume, mass, cost, and energy with respect to the state of the art alternative for iodine. Iodine stores as a solid and sublimates as the molecule I2, which allows many benefits with respect to traditional Hall Effect Thruster fuels such as xenon and krypton. These advantages include higher storage density, lower storage pressure, the ability to test high power systems at space-relevant conditions in modest facilities, the capability to store propellant in space without active regulation, and the capacity to transfer propellant at low pressure conditions in space. In a space-limited spacecraft, the use of iodine instead of state of the art xenon could increase available delta V by a factor of 3 or more. Iodine is especially beneficial for small CubeSat sized spacecraft. In Phase I, Busek will design a feed system featuring the new, advanced components. The system will then be demonstrated with an iodine fueled thruster in space relevant conditions. In Phase II, an improved feed system will be designed, built and tested.

Benefits: The proposed feed system supports iodine Hall thrusters, ion engines, hollow cathodes, and other plasma generators currently under development for NASA. Specific applications include iSat, Lunar Cube, and future Game Changing missions. The Phase II feed system will be ideally sized for a Hall thruster operating at 500 to 1000 W. This thruster would be used for orbit raising and interplanetary transfers of spacecraft up to several hundred kg. Missions of current interest include resource prospecting at the moon, Mars, asteroids, and NEOs. The technology is also applicable to much smaller spacecraft, such as CubeSats, and much larger spacecraft, such as future MW-class cargo transports supporting human exploration. The ability to flow iodine as a HET propellant is ultimately the game changer. Iodine is efficient, compact, highly storable, and an order of magnitude cheaper than xenon. Full power thruster demonstrations and throttling in space conditions are feasible because iodine is efficiently pumped by liquid nitrogen cooled panels.

The proposed feed system supports many types of plasma generators used in space and on the ground. In the near term, the innovative feed system components are most likely to be used as part of a space propulsion system. The next stage for commercial users is an all-electric satellite, where electric propulsion accomplishes all propulsion functions including orbit raising, orbit circularization, inclination changes, station-keeping and repositioning. Beyond stored density and pressure, iodine has many additional benefits with respect to xenon. For instance, a fully-fueled, non-active system may be stored on the ground or on orbit for long periods of time. This reduces the cost of on-orbit spares, and minimizes down-time in the event of a failure. Low pressure on-orbit refueling is also feasible. Due to its these and other advantages, iodine may be very attractive for commercial missions such as asteroid mining.