Thermal Improvement on 1 Newton ASCENT Thruster Valve Assembly (TVA)

Traditionally, monopropellant thrusters rely on thermally conductive copper straps to shunt heat away from the injector tube or injector flange. Such passive techniques, although adequate for hydrazine thrusters, have proven difficult to implement for the new generation of green monopropellant thrusters. This is because unlike hydrazine, green monopropellants such as ASCENT are not capable of cold starts and require significant catbed preheating. During the preheat, the thermal straps contend with the catbed heater by shunting heat away. For many thruster designers, this is an accepted limitation because there is no alternative. Making matters worse, the thermal straps are often oversized for the largest thermal-load scenario (usually steady-state firing), which leads to substantial increases in catbed heater power and energy consumption during preheating. The longer heater ON time also prevents responsive start-up from the cold condition. Furthermore, passive thermal straps may be too slow to counteract fast transient heat loads (e.g., post-firing soak-backs), which in certain situations can cause a thruster to fail upon shut down or during hot restarts. Busek, with partner Exo-Atmospheric Technologies (Exo-AT), has developed a new thermal management system in Phase I that can potentially solve these industry-wide issues. The invention utilizes a thermal switching device that is “inactive” during catalyst bed pre-heat, and “turns on” after thruster ignition. In the Phase I proof-of-concept test, the new thermal switch system was installed on Busek’s existing 0.5N ASCENT green monoprop thruster BGT-X5, and a catalyst pre-heat test was performed in a simulated space environment. The thruster’s catalyst bed demonstrated the ability to heat up in less time compared to traditional copper straps. Furthermore, finite element thermal analysis (FEA) suggests that the thruster’s injector tube can maintain significantly cooler temperatures during hot fire and soak-back. In Phase II, the proof-of-concept system will be hot fire tested with BGT-X5, gathering valuable data to anchor the FEA thermal model. Then, the whole system (thermal switch and thruster) will be scaled up to the 1N level for another hot fire demonstration test.