Pulse Phase modulation for on-off thruster pair

On-Off thrusters have limitation both at minimum on-time and minimum off-time, so the output is nonlinear pulses. Use on-off thrusters to provide linear or near linear control force is a fundamental and important research topic. Existing previous works do not overcome the limitation of on-time and off-time constraints, so the output is only an approximation of demanded force output. In this paper, Pulse Phase modulation (PP) is proposed to generate linear output through on-off thruster pair. PP modulation exploited the dynamic output curve of thrusters. By adjusting phase difference of thruster pair that installed in the opposite direction, thrust output can be linear proportional to demanded force output. PP modulation breaks the limitation caused by minimum on-time and off-time, and thus achieves high continuity of thrust output. For practical engineering implementation, two approximate methods are proposed as double frequency phase modulation and quadruple frequency phase modulation. Theoretical analysis and experimental results are provided to prove that PP modulation can yield much better precision in stabilizing space vehicles.