Experimental Investigation of a Direct-drive Hall Thruster and Solar Array System at Power Levels up to 10 kW

As NASA considers future exploration missions, high-power solar electric propulsion plays a prominent role in achieving many mission goals. Studies of high-power systems (i.e. tens to hundreds of kilowatts) suggest that significant mass savings may be realized by implementing direct-drive power systems, so NASA recently established the National DirectDrive Testbed to resolve technical issues identified by previous direct-drive investigations. The testbed includes a 12-kW solar array and a power control station designed to power single or multiple Hall thrusters over a wide range of voltages and currents. In this paper, single Hall thruster operation directly from the solar array at discharge voltages of 200 to 450 V and discharge powers of 1 to 10 kW is reported. Hall thruster operation and control is shown to be simple and no different than for operation on conventional power supplies. Thruster and power system electrical oscillations were investigated over a large range of operating conditions and with different filter capacitances between the solar array and thruster. Thruster oscillations were the same as for conventional power supplies, did not adversely affect solar array operation, and were independent of filter capacitance from 8 to 80 µF. Solar array current and voltage oscillations were very small compared to their mean values and showed a modest dependence on capacitor size. Significantly, no instabilities or anomalous behavior were observed in the thruster or power system at any operating condition investigated, including near and at the array peak power point at power levels up to 10 kW. Thruster startup using the anode propellant flow as the power ‘switch’ was shown to be simple and reliable with system transients mitigated by the proper selection of filter capacitance size. Thruster shutdown via cutoff of propellant flow was also demonstrated. A simple electrical circuit model was developed and is shown to have good agreement with the experimental data.

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