Busek proposes to develop a novel thermal management system for its 1N ASCENT thruster valve assembly (TVA). Traditionally, monoprop thrusters rely on thermally conductive straps that shunt heat away from the injector tube or injector flange. Such passive configuration, although adequate for hydrazine thrusters, has proven difficult to implement for the new generation of green monoprop thrusters. This is because unlike hydrazine, green monoprops such as ASCENT are not capable of cold starts and require catbed preheat to >400oC. During catbed preheat, the thermal straps are inadvertently in contention with the catbed heater since they are constant heat sinks. For many thruster designers, this is an accepted limitation, and they are often forced to oversize the thermal straps for the worst thermal-load scenario (i.e., steady-state firing). This causes several issues, such as significant increase in catbed heater power and energy consumption, in order to overcome the large thermal shunt during preheat. The longer heater ON time also prevents responsive start from cold. Furthermore, passive thermal straps may be too slow to counteract post-firing soak-backs, which in certain situations can cause a thruster to fail upon shut down or during hot restarts. Having experienced these thermal difficulties first hand, Busek plans to develop a thermal switch mechanism for an ASCENT thruster that would allow for 2x faster catbed preheat, reduction of preheat energy consumption, and better protection on the injector feed tube. The Phase I work will leverage Buseks existing 1N TVA hardware known as BGT-1, which includes Buseks patented catbed design and a custom titanium micro-solenoid valve. At the conclusion of the Phase I effort, the new BGT-1 TVA will be thermally tested in vacuum to fully characterize the new thermal management system under a nominal catbed preheat condition. It will be ready for hot fire tests at the beginning of Phase II.
