Effect of Carbon Black Diameter on Performance for a Throttleable Solid Propellant Microthruster Using Laser Heating

Abstract

This paper describes a solid propellant microthruster that is throttleable through laser heating. In general, solid propellant thrusters are relatively compact and reliable because the thruster requires neither tanks nor valves, and never induces propellant leakage. However, the start and interrupt of combustion is difficult because 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, wherein combustion is sustained only while external heat was supplied to burning surface, and proposed a throttleable solid propellant microthruster using semiconductor lasers as a heat source. Our previous study showed that a prototype thruster successfully started and interrupted thrust production using near-infrared 45-W laser. However, the prototype yielded ignition delay of 3-5 s. In this study, to reduce the ignition delay, carbon black (C) diameter was reduced from 50 to 10 μm such that laser beams are absorbed in a shorter depth of the propellant. Thrust measurement showed that prototype thruster yielded an ignition delay of 1.6 s, a stable thrust of 0.06 N, I_sp of 127 s at laser power density of 0.93 W/mm² for φ10-μm C.