ALMASat-1 Cold Gas Micropropulsion System: Final Layout, Qualification and Functional Tests

In this paper the final layout, the qualification and functional tests of the ALMASat-1 micropropulsion system are presented. The ALMASat-1 project is a small educational microsatellite (its weight is about 12 kg) entirely designed and assembled in the aerospace laboratories of II School of Engineering of the University of Bologna, scheduled for launch onboard the VEGA Maiden Flight as part of the LARES payload, which launch is currently scheduled at the end of 2010. The micropropulsion system on-board the microsatellite is a nitrogen cold gas system which uses MEMS (Micro Electro-Mechanical System) devices, such as the microthrusters, in order to generate the required thrust level for the whole mission, about 0.75 mN. The use of MEMS technologies for micropropulsion systems is very attractive due to the small throat nozzle size, down to 10 micron, that can be manufactured. This reduces the thrust level and, theoretically, the impulse bits achievable using MEMS-based propulsion devices. In the field of propulsion for attitude control systems, it is very important to have the smallest possible impulse bit. The goal of the micropropulsion system is to perform three different types of experiments: three axis stabilization and target attitude maintenance; momentum wheel desaturation and pitch axis fine pointing and a small orbital maneuver, aimed at raising the S/C altitude (semi major axis). The micropropulsion system is mounted inside one of the trays of the ALMASat-1 microsatellite. The final layout, has been designed to satisfy the requirements of the specific type of propulsion selected among a variety of systems, as a result of a trade-off analysis performed in the conceptual design phase. Different types of tests have been performed on the micropropulsion system: (a) microthruster thrust measurements using a high precision microbalance in vacuum chamber in order to characterize the pressure–thrust curve; (b) microvalve tests aimed at measuring the valve gas leakage at different pressure levels (from 1 bar to 6 bar); (c) isolation valve tests, in order to qualify the valve in term of working pressure, gas leakage and power consumption; (d) burst tests on the nitrogen tank; (e) vibration and thermal vacuum tests at system and subsystem level and (f) functional tests (before and after the environmental tests). The total mass of the propulsion system, tank, isolation valve, pressure transducers, pipes, pressure regulator, twelve silicon wafer microthrusters, fourteen microthrusters control valves and thrusters pod, is less than 1.5 kg.