A highly miniaturized uPPT thruster for attitude-orbit control

Li, Junquan and Greenland, Steve and Post, Mark and Coletti, Michele (2014) A highly miniaturized uPPT thruster for attitude-orbit control. In: 6th European CubeSat Symposium, 2014-10-14 - 2014-10-16.

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The successful miniaturization of spacecraft subsystems makes nanosatellites suitable candidates for many scientific missions, and several miniaturized electric propulsion systems on CubeSats have been studied. A Cubesat employing a Pulsed Plasma Thruster module is currently under development by Clyde Space Ltd, Mars Space Ltd and the University of Southampton under contract to ESA and is now entering final qualification testing. Pulsed Plasma Thrusters have been used in satellite attitude control studies of nadir pointing, and satellite rendezvous, docking and formation flying. This paper considers the use of the PPTCUP Pulsed Plasma Thruster in a range of different operational cases that are considered key to the success of many future nanosatellite missions, including moderate low thrust orbit inclination and altitude changes, deorbiting a satellite at the end of life, maintaining "a string of pearls" constellation, on-orbit servicing and inspection of a mother satellite, and life extension of an ISS-deployed nanosatellite. PPTCUP uses a very fast electric discharge to ablate a tiny amount of a solid propellant bar, which is then ionized and expelled at high velocity to generate thrust. To generate such a discharge, the thruster charges a high performance capacitor bank for up to a second before discharging it in few microseconds. Based on a current generation system with a mean power input of 2 W, a 40 uN thrust pulse (with a 20 N peak force) can be achieved 1 million times in succession. In order to evaluate the PPTCUP thruster performance, a simulation model has been developed and applied to the identified scenarios, leading to suggestions for baseline control laws suited for the mission. Where necessary, refinement of the design point has been performed to provide a roadmap for future PPTCUP development. We assume a nanosatellite that has a maximum mass of 4 kg at 320-380 km. Drag force and yearly velocity increments are estimated as functions of altitude, drag cross-section and solar activity. Assuming an analysis of a 3U Cubesat frame with PPTCUP, a control approach based on advanced control methods will be used to handle different operational cases. This work finds immediate application for the PPTCUP for challenges such as drag compensation, de-orbiting, and rendezvous and docking manoeuvres, and makes recommendations for future targeting of performance to further improve the capability of PPTCUP equipped satellites. In particular it is noted that advanced control design would improve the coverage of this class of thruster.