Systems Design and Performance of Cold Gas Microthruster for Microsatellite Attitude Control

Abstract

We discuss our approach to the design and manufacturing of a cold gas micropropulsion system, using micro electromechanical systems (MEMS) devices, for an experimental attitude and orbital control system for the ALMASat microsatellite. ALMASat is a small educational spacecraft entirely designed and assembled in the aerospace laboratories of II School of Engineering of the University of Bologna. Its weight is about 12 kg, carried by a cubical bus (side 30 cm), and it is scheduled for launch from Baikonur (Kazahstan) using the DNEPR Launch Vehicle. The core of the micropropulsion system is a De Laval nozzle which accelerates the fluid, molecular nitrogen, from a plenum, through a 40 micron throat at supersonic velocity. Using the nozzle as a simple cold-gas thruster, good Isp efficiencies are demonstrated, although side-wall boundary layer contamination, no continuity effect and the limitations of MEMS fabrication technologies are clear limiting factors. The micropropulsion system consists of a high pressure tank, a pressure regulator and solenoid valves for the open/close thrusters cycles. The extruded nozzle geometry, made on silicon wafer, has been manufactured in collaboration with the Carlo Gavazzi Space (CGS) and IMM section of the Italian National Research Council (CNR) of Bologna, using a Deep Reactive Ion Etching (DRIE) technique and successive bonding.