Performance Evaluation of a Throttleable Solid Propellant Thruster Using Laser Heating

Abstract

This paper describes a solid propellant microthruster that is throttleable using laser heating. Solid propellant thrusters generally require neither tank nor valve, and accordingly have relatively high reliability due to simple structures. Nevertheless, conventional solid propellant thrusters have not been applied to attitude control or station keeping for satellites because of difficulty in throttling including start and interrupt of thrust production. Hence, we proposed to apply combustion-controllable solid propellants, and a compact and lightweight semiconductor laser to thrusters in order to develop a throttleable solid propellant microthruster. For combustion controllable solid propellants, combustion was sustained only when external heat was supplied to burning surface. In our previous study, a prototyped 0.1 N class thruster successfully produced thrust in a vacuum, but the combustion was unstable. In this paper, to stabilize combustion, we prototyped a nozzle with a reduced target combustion chamber pressure of 0.03 MPa. Mass ratio of carbon black, which was added to absorb laser beam efficiently, was varied from 0.05 wt% to 0.5 wt%. Thrust measurement showed that the prototyped thruster successfully yields a stable thrust of 0.02 N at a laser power density of 0.98 W/mm 2 .