Development of a nitrous oxide monopropellant thruster at BUAA: 2010

The research in 2010 for developing a nitrous oxide (N ₂O) monopropellant thruster at Beihang University (BUAA) was targeted on lowering the preheating power as well as measuring the activation temperature, life-span, and impulse magnitude of the thruster. Activation experiments and long-term hot-firing experiments were conducted respectively with a 100 mN thruster and a 1 N thruster to evaluate their activation performance and life-span. The experimental results indicated that a lower activation temperature and longer life-span could be attained by reducing the loading factor of the catalyst-bed, whereas the reaction temperature may decrease at the same time. As the influence of the loading factor on three performance parameters, i.e. the activation temperature, the reaction temperature, and the life-span) conflict, trade-off must be made when selecting the N ₂O mass flow rate for operation. Based on the analysis on the preheating process of the N ₂O monopropellant thruster and the characteristics of the N ₂O decomposition reaction in the catalyst-bed, a novel thruster employing an inner-heater was designed and fabricated. By shifting the heater from the outer wall of reaction chamber into the catalyst-bed, preheating efficiency of the heater was promoted observably. The preheating power demand of the thruster was thus successfully reduced to around 10W. Mean vacuum thrusts of 320 mN and 778 mN were attained, respectively, at the N ₂O flow rate of 0.22 g/s and 0.51 g/s. The corresponding specific impulses were around 150 s. A long term hot-firing test longer than 10000 s was attained with a loading factor of 2.45 kg/m ²·s. In addition, the pulsed operation performance of the inner-preheating thruster was studied by measuring chamber pressure. Impulses with different magnitudes were produced by adjusting the opening duration of the control valve. A minimum impulse of 81 mN·s was attained.