Computer Science – Sound
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.785n&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Sound
Scientific paper
Cold gas micropropulsion is a sound choice for space missions that require extreme stabilisation, pointing precision or contamination-free operation. The use of forces in the micronewton range for spacecraft operations have been identified as a mission-critical item in several demanding space systems currently under development. The required micropropulsion systems are emerging, using various principles, e.g. field emission, colloid acceleration, solid combustion, and cold gas expulsion. Cold gas micropropulsion systems share merits with traditional cold gas systems in being of simple design, clean, safe, and robust. They do not generate net charge to the spacecraft, and typically operate on low-power. The necessary extreme miniaturisation of system parts furthermore works well to increasing other merits of these systems, making them truly competitive for state-of-the-art spacecraft: e.g. DARWIN, LISA, or high-performance nanosatellites. Silicon microsystems technology can be used for the cold gas micropropulsion system manufacture. Here, the decrease of dimensions is not restricted to fit standard components or tools. This allows for an astonishing mass reduction, e.g. 80 g for a unit comprising four independent nozzles, proportional valves, particle filters, control electronics, and housing. The minute size is also suitable for inclusion on nanosatellites. The dynamic range of a cold gas micropropulsion system can be quite wide (e.g. 1 μN - 10 mN) by using differently sized nozzles in parallel systems. Again, the microsystems technology makes this scheme possible without compromising the mass budget. The micropropulsion system benefits greatly from using a continuously proportional control on the thrust. In this system, the impulse is obtained as the difference of two opposite thrusters in the same unit. Here, the minimum impulse bit is reduced to virtually zero, while simultaneously avoiding any troubles emerging from extremely low flows at near-zero thrust from a single thruster. The same strategy can be extended to continuous operation, never closing the valves completely. In this way, leakage-induced thrust fluctuations are bypassed, and wear of the valve seats is heavily reduced. Main concerns are the low specific impulse and the consequent large amount of propellant required. System analysis shows that low delta-v missions or their equivalent (e.g. attitude control) are suitable missions for cold gas micropropulsion. The choice of propellant is naturally of prime importance - carbon dioxide is possible to store in solid form, while liquid gas may act as a cooling fluid in addition to being used as propellant. The analysis in this work shows that cold gas micropropulsion has emerged as a high-performance propulsion principle for future state-of-the-art space missions. These systems enable missions with extreme demands on stability, cleanliness, and precision, without compromising the performance or scientific return of the mission.
Köhler Jürgen
Nguyen Hoi H.
Stenmark Lars
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