An Air-Breathing Pulsed Plasma Thruster (AB-PPT) with the potential of supporting indefinite flight above the tropopause was developed at the Advanced Propulsion Laboratory (APL) at the University of Washington. The advantage of working at high altitudes is that the aircraft is not subject to highly variable weather conditions. With sustained flight at these altitudes, there is the potential for having continuous coverage of a region so that the aircraft acts as an "atmospheric satellite" at significantly reduced altitudes and cost relative to a low Earth orbiting spacecraft. The problem is finding an efficient lightweight propulsion system that can work at the low density of the upper atmosphere. The Air-Breathing Pulsed Plasma Thruster (AB-PPT) incorporates the innovation of a variable spacing cathode that enables consistent thruster performance over altitudes greater than 20 km. The fact that the system is air-breathing means that no fuel needs to be carried by the aircraft, and with the present system's design a thrust level of 225 mN/kW can be sustained. Laboratory demonstration of the performance of the system is presented. A 5.3 kg aircraft with the AB-PPT was also built and launched on a high-altitude burst balloon. Due to underperformance of the lift system the balloon did not quite reach the operating altitude of > 20 km, and therefore the full operational performance has yet to be demonstrated. However the demonstrated test proved that the aircraft could successfully withstand the jet stream.
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