The next-generation of small satellites ('nanosats') will feature masses <10 kg and require miniaturised propulsion systems capable of providing extremely low levels of thrust. The emergence of viscous, thermal and/or rarefaction effects on the micro-scale can significantly impact the flow behaviour in supersonic micronozzles resulting in performance characteristics which differ substantially from traditional macro-scale nozzle designs. In this paper, we provide an overview of key findings obtained from computational studies of supersonic micronozzle flow and discuss the implications for future micro-scale nozzle design and optimisation.

In this study, we numerically examine thrust performance of the linear aerospike nozzle micro-thruster for various nozzle spike lengths and flow parameters in order to identify optimal geometry(s) and operating conditions. Decomposed hydrogen-peroxide is used as the monopropellant in the studies. Performance is characterized for different flow rates (Reynolds numbers) and aerospike lengths, and the impact of micro-scale viscous forces is assessed. It is found that 2-D full micro-aerospike efficiencies can exceed axisymmetric micro-nozzle efficiencies by as much as 10%; however, severe penalties are found to occur for truncated spikes at low Reynolds numbers.

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