Effect of the Thruster Configurations on a Laser Ignition Microthruster

Abstract

Research and development of small spacecraft have advanced extensively throughout the world and propul-sion devices suitable for the small spacecraft, microthruster, is eagerly anticipated. The authors proposed a microthruster using 1–10-mm-size solid propellant. Small pellets of solid propellant are installed in small combustion chambers and ig-nited by the irradiation of diode laser beam. This thruster is referred as to a laser ignition microthruster. Solid propellant enables large thrust capability and compact propulsion system. To date theories of a solid-propellant rocket have been well established. However, those theories are for a large-size solid propellant and there are a few theories and experiments for a micro-solid rocket of 1–10 mm class. This causes the difficulty of the optimum design of a micro-solid rocket. In this study, we have experimentally investigated the effect of thruster configurations on a laser ignition microthruster. The examined parameters are aperture ratio of the nozzle, length of the combustion chamber, area of the nozzle throat, and divergence angle of the nozzle. Specific impulse dependences on those parameters were evaluated. It was found that large fraction of the uncombusted propellant was the main cause of the degrading performance. Decreasing the orifice diameter in the nozzle with a constant open aperture ratio was an effective method to improve this degradation.