Development of a high-temperature Solar Thermal Propulsion engine

Abstract

Miniaturization in spacecraft is an ongoing process in which the launched satellites become smaller and smaller. This trend introduces issues, such as the choice for a reliable and efficient propulsion subsystem. The implementation of engines would enable the spacecraft to perform maneuvers such as orbit changes, drag compensation and attitude control. Solar Thermal Propulsion (STP) has been identified as a promising candidate, due to its theoretical specific impulse being well above that of the best chemical thrusters when hydrogen is the propellant of choice. The concept has never been flown in space but would benefit from ground demonstrations proving that the potential can be realized. This work will focus on demonstrating the STP performance. The goal was set to reach a Sea Level (SL) specific impulse of 90.0 s at a continuous mass flow of 300 mg s−1 and input power of 250 W. During the project, a demonstration thruster named Solar Thermal Thruster 2 was designed. The resulting engine consisted of a copper heat exchanger and nozzle with a highpowered laser as the irradiation source of choice. Concurrently, a Preliminary Design Tool was developed to assess the performance of STP engines. Verification and validation was done by comparing the tool outputs to other theoretical and experimental results. Verification was completed, but for validation STT2 experimental results were required. Preliminary test results of STT2 showed that the motor had some shortcomings, due to concessions made. Erroneously, its heat exchanger had been built with a reduced number of channels, rendering the thruster unavailable for testing. Next to that, the engine suffered from leakages. For further validation of the tool, Computational Fluid Dynamics (CFD) simulations were performed. The thermal part of the tool was validated, but the pressure loss results deviated too much. As such, further experiments are required in this area. In the end, an updated design (STT3) was made of the thruster. The number of channels in the heat exchanger was increased and its mass and area was reduced. It proved to have an SL specific impulse of 84.9 s, almost meeting the goal set for the thesis. It is recommended that the engine is built and tested at Delft University of Technology (DUT) in order to complete validation of the tool and demonstrate the feasibility of STP.