PPTs have been successfully operated with the solid propellant PTFE since 1964. However, feeding the solid fuel limits the use of these thrusters in terms of achievable Av and lifetime. This work presents two different approaches how this issue can be overcome and compares them with the well-known PTFE. Each propellant's performance has been evaluated in a parametric study. The non-volatile liquid propellant PFPE shows a 20% higher impulse bit, but 3-4 times higher mass bit compared to PTFE. Its advantage is the capability to enable a propellant feeding system working on the principle of capillary motion Another approach is the utilization of residual atmospheric air for missions on very low earth orbits Two different air-fed coaxial PPT designs are introduced and their performance is discussed.
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