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Abstract
This thesis explores the application of secondary injection thrust vector control (SITVC) to spacecraft propulsion, where propellant consumption and system complexity are often increased by the need to maintain alignment of the thrust vector with the spacecraft centre of mass. SITVC involves transverse injection of a secondary fluid into the main flow of a supersonic nozzle to produce a side force. While the technique has previously been studied for atmospheric vehicles with low area-ratio nozzles, this research is focussed on the performance of SITVC in high area-ratio nozzles expanding into vacuum.
A two-dimensional numerical study was conducted to determine the influence of ambient pressure on SITVC performance. Performance was strongly affected by ambient pressure when the nozzle was overexpanded, but weakly affected when underexpanded. SITVC was modelled numerically for a three-dimensional, high area-ratio contour nozzle, where a maximum thrust vector angle of 16.4 degrees was achieved at a mass flow ratio of 0.343. The nozzle area-ratio, injector location, and injector angle were then varied to determine the effect on SITVC performance. A minor decrease in performance was observed with increasing nozzle area-ratio. SITVC efficiency was increased by moving the injector closer to the nozzle throat and by inclining it upstream, at the expense of maximum thrust vector angle.
An experimental apparatus was designed to enable validation of the numerical results. The experimental results closely matched the numerical results for mass flow ratios up to 0.17, but the maximum thrust vector angle was reached at a lower mass flow ratio. These results were used to analytically model the performance of SITVC in the context of an in-orbit servicing mission, for comparison with standard reaction thrusters and mechanical thrust vector control (MTVC). SITVC was found to be more fuel efficient than reaction thrusters for the configuration studied, and was able to compensate for a much larger range of thrust misalignment. SITVC had a lower system mass than MTVC for thrust misalignments up to 9 degrees. MTVC became competitive at larger thrust misalignments, indicating a trade-off between system mass and complexity.