Long-Duration Hybrid Thruster Firings with Fuel Regression and Postfiring Gasification

This study investigates the fuel regression characteristics and postfiring gasification of a hybrid thruster during long-duration operation. Firing tests of 30 and 200 s were conducted using a thruster equipped with eight circular high-density polyethylene fuel ports and gaseous oxygen as the oxidizer. The tests demonstrated stable combustion and reliable system performance in both short- and long-duration operations. Gasification of an ablator, installed for thermal protection of the combustion chamber and nozzle, was found to contribute additional mass flow during firing, thereby influencing chamber pressure. The mass consumption rate of the ablator was modeled based on impinging jet heat transfer principles, scaling with the square root of the Reynolds number. By correcting for the ablator’s contribution and accounting for postfiring gasification, the fuel regression characteristics were consistently estimated across the different firing durations. Postfiring gasification of the fuel and ablator was attributed to residual heat stored within the solid materials. This phenomenon accounted for approximately 8% and 7% of the total measured solid mass consumption in fuel and ablator, respectively, during the 200 s firings. These corrections are crucial for accurately determining thruster performance from long-duration test data.