Iodine Hall Thruster System Components

Electric propulsion (EP) systems performance can significantly reduce launch vehicle requirements, costs, and spacecraft mass because of its high specific impulse capability when compared to chemical propulsion. NASA Glenn is developing Hall thrusters that are enabling and enhancing to various NASA science missions. Significant investments have been made in developing Hall thrusters that operate on the inert gas xenon (Xe) due to its favorable mass and ease of ionization. However, Xe is relatively expensive and must be stored in high-pressure tanks. Furthermore, some missions require higher specific impulse (Isp) or thrust-to-power (T/P) than is provided by Xe. Consequently, a variety of alternatives to Xe have been proposed including iodine. The goal of this effort is to advance the technology readiness level (TRL) and reduce the risk of implementing iodine as propellant for Hall thrusters. The Busek Company Inc., a US developer of electric propulsion technology including Hall thrusters, pioneered the use of iodine as a propellant for Hall thrusters in the US. Research, development, and test efforts conducted by Busek have indicated that iodine fueled Hall thrusters offer benefits for some missions relative to thrusters that use Xe. The storage characteristics of iodine results in a significant reduction in the propulsion system mass and volume which is mission enabling for certain applications. The Busek Company Inc., a leading US developer of Hall thrusters, pioneered use of iodine as a propellant for Hall thrusters in the US. Busek's research, development, and test efforts indicated that use of iodine in place of Xe as a Hall thruster propellant resulted in many benefits. Replacing Xe fueled Hall thrusters with iodine fueled Hall thrusters is a "Game Changer" since it will enable us to significantly reduce the size of the propulsion system for a given mission which will result in significant cost savings. These Hall thruster developments include sub-kilowatt (kW) Hall thrusters for small spacecraft applications, a 4 kW High Voltage Hall Accelerator (HiVHAc) for NASA's Science Mission Directorate, and high power Hall thrusters (15 kW class) for NASA's Space Technology Mission Directorate sponsored Solar Electric Propulsion Technology Demonstration Mission (SEP TDM).

The proposed work at GRC along with on-going efforts at Busek seeks to address remaining technical challenges making iodine Hall thrusters a viable propulsion alternative to existing Xe thrusters. Tests at Busek with 200 W and 1.5 kW Hall thrusters (under NASA and Air Force SBIRs) have shown that iodine performance is very similar to Xe. In addition, plume measurements have shown that iodine fueled Hall thrusters have lower plume divergence angles than Xe fueled thrusters. Finally, iodine's higher density and its low storage pressure will greatly reduce the Hall propulsion system size for a given mission when compared to SOA. These reductions will apply to low, medium, and high power Hall propulsion systems. This work addresses the NASA Grand Challenges of Space Colonization, Efficient Space Transportation and All Access Mobility. Increasing the delivered mass capability (i.e, scientific instruments) to destination will result in a far greater science return and enhanced understanding of the universe origin.

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