Description: Busek proposes to prove the feasibility of a Mg Hall effect thruster system that would open the door for In-Situ Resource Utilization (ISRU) based solar system exploration. Elemental magnesium has favorable thermophysical properties and is very easy to ionize. The estimated specific impulse for a high efficiency magnesium Hall thruster operating off of a standard 400 V power processing unit is 5000 s. Efficiencies >50% will be possible. Although the vapor pressure of Mg is relatively low, it is believed that spacecraft interactions can be managed through the implementation of a simple plume shield. Moreover, magnesium is found abundantly in the regolith of Mars and the Moon, from which it can be readily extracted. In Phase I, we will prove the concept's feasibility through four technical tasks. In the first task, the overall architecture of a Mg Hall thruster system will be established and subsystem requirements will be identified. In the second task, Busek will integrate an magnesium vapor propellant Hall thruster with a wire feed system. In the third task, the integrated system will be tested in Busek facilities. In the fourth task, the Applied Research Laboratory (ARL) at Penn State University will develop a powder feed system capable of fueling both medium and high power thrusters. A fully integrated system sized for NASA needs will be developed and characterized in Phase II.

Benefits: Light metal Hall thruster technology may enhance many critical DoD and commercial missions such as satellite orbit maintenance, orbit raising and repositioning. Magnesium offers the possibility of efficiencies close to xenon with the possibility of lightweight, long term, low maintenance, solid propellant storage. High pressure propellant tanks will not be required and spacecraft interaction issues should be manageable. Mg Hall thrusters could also form one half of a multi-mode propulsion system that also contains a Mg based rocket. This system would provide both high thrust and high Isp. The two systems would share propellant feed system components, tanks, and fuel.

Magnesium Hall thrusters are attractive for NASA Flagship, Frontier, and Discovery class missions because Isp ~ 5000 s is possible at low voltage, enabling the use of low cost flight qualified power processors. These thrusters can also be deeply throttled. Examples mission targets include asteroids, comets, and the outer planets. Sample return missions are also enabled. Magnesium thrusters are also well suited for lunar and Martian missions. A high power cluster would support manned missions by transporting fuel and cargo. In-situ propellant utilization is possible, as is a multi-mode system incorporating a Mg based rocket. Advantages over SOA noble gas Hall thrusters include higher Isp at the same voltage, less erosion (longer lifetime) at the same Isp and power, and much lower propellant, propellant storage, and tests costs. High pressure propellant tanks will not be required. Vapor pressure curves suggest modest precautions may fully mitigate spacecraft interactions. The powdered feed system technology may also be used to develop powdered metal propellants such as Mg and Al to bipropellant rockets.