Performance of a Throttleable Solid Propellant Microthruster Using Laser Heating

This paper describes the performance of a combustion-controllable solid-propellant microthruster using laser heating. Conventional solid propellant thrusters are relatively compact and reliable because the thrusters require neither tanks nor valves and never present the risk of propellant leakage during storage. On the other hand, interruption and restart of thrust production are difficult because the combustion is autonomously sustained once the propellant is ignited. Therefore, solid propellant thrusters have never been applied to orbit maintenance or attitude control. Hence, we have developed the solid propellants in which combustion is sustained only while the heat was supplied to the burning surface and proposed a throttleable solid propellant microthruster using semiconductor laser as a heat source. In our previous study, in a prototyped thruster, a laser head was moved by a linear traverser such that laser beam followed the regressing burning surface. The thruster interrupted and restarted thrust production by switching laser. However, the use of a linear traverser increased thruster weight. Hence, we redesigned a prototype, which maintained the gap between the burning surface and the laser-introducing window to prevent laser-beam attenuation due to the combustion products. Thrust measurement showed that the prototyped microthruster successfully yielded a thrust 0.06 N, Isp of 70.3 s, and ignition delay of 0.9 s.