Cold Gas Microthruster Characterization in Vacuum, using a High Precision Microbalance

In the framework of the development of a cold gas micropropulsion system, pursued since 2005 in the aerospace laboratories of the II Faculty of Engineering of the University of Bologna, a microbalance was designed, assembled, calibrated and characterized. This project, entirely developed by the University of Bologna, under a contract with Carlo Gavazzi Space (CGS), was aimed at the evaluation of the thrust generated by a MEMS (micro electromechanical systems) based cold gas micropropulsion system to be flown on-board the first microsatellite of the University of Bologna (ALMASat-1)1 for attitude and orbit control experiments. The microbalance is based on the pendulum principle and makes use of a Laser Optical Displacement Sensor to measure the pendulum displacement generated by the thruster. The force exerted by the thruster, together with its own weight, identifies an equilibrium condition whose angular displacement with respect to its initial vertical position is proportional to the measured thrust. The interface between the thruster and the Optical Sensor was designed with the aim of minimizing the friction on the hinge point, so an Aluminium sheet was used. A software interface was developed in LabVIEW® environment in order to evaluate the real time thrust generated by the microthruster. This paper presents the results of the measurements, fully characterizing the balance in terms of accuracy, resolution and thrust range. Finally, the experimental results in vacuum condition (10-2 mbar) are compared to the fluid dynamic simulations carried out on the microdevices manufactured in collaboration with Carlo Gavazzi Space (CGS) and the IMM section of the Italian National Research Council (CNR) of Bologna, using a Deep Reactive Ion Etching (DRIE) technique and successive bonding.