Bimodal Bismuth Vapor Hall Thruster

Busek proposes to develop a high power, bismuth vapor Hall thruster for bimodal and high thrust missions. Published Soviet data lists experimental thrust efficiencies of 75-80%. Maximum thrust to power may be 70% greater than possible with xenon. Thrustto thruster mass is also higher and mission enabling high thrust, Isp~1000 sec operating points are possible. Fuel efficient Isp~2500 sec operating points are also possible. A more tenuous charge exchange plasma should decrease discharge chamber erosion,increasing total impulse (longer lifetime), and mitigating spacecraft interactions. A high-power system could be tested in existing facilities, minimizing ground test costs; water cooled panels could condense the Bi, eliminating requirements for new,multi-million dollar cryogenic facilities. Challenges include possible spacecraft contamination issues and more complicated propellant handling, although propellant storage will be compact. In Phase I, Busek will design a Bi Hall thruster and propellantfeed system. We will analyze the design using our in-house suite of numerical models. Accumulation of Bi on heated and cooled surfaces will be tested under vacuum. Spacecraft interactions will be studied in cooperation with The Aerospace Corporation.In Phase II, Busek will design, build, and test a sub-scale thruster. We will also design a full-scale thruster. The development of a high thrust, bimodal bismuth Hall thruster represents a significant opportunity for Busek to capture the market forhigh thrust electric propulsion missions. Xenon Hall thrusters are typically used for station-keeping, re-positioning, and orbit transfer. But in many applications, one would like a Hall thruster with a lower specific impulse than possible with Xe to geta higher thrust to power ratio, even at the cost of using more fuel. With limited power available, mission requirements for trip time, in particular, are much better met by bimodal bismuth thrusters. Bismuth Hall thrusters will have higher thrust topower, higher thrust to thruster mass, higher total impulse, and cheaper ground test costs than Xe thruster alternatives.Likely DoD applications include fast repositioning of surveillance and communications satellites, orbit insertion, and a space tug. High power communication satellites may also use Bi thrusters for station-keeping, pending interactions issues. NASAapplications include Nuclear Electric Propulsion (NEP), space station re-boost, and boosting elements of a space solar collection satellite from LEO to GEO. For NASA and commercial applications, the cheapness of the raw propellant will be an additionalbenefit.The solid propellant feed system will have its own commercial applications; a host of other solid propellants could conceivably be used in Hall thrusters and other plasma devices for material processing applications.