Proposal for Residual Thrust Estimation of Hybrid Thruster Using Simplified Model

This study addresses the residual thrust concept in hybrid thrusters. In this phenomenon, thrust is generated by the gasification of heated fuel post-firing, particularly after long-duration maneuvers. Residual thrust is significantly lower than nominal thrust. However, it poses challenges for attitude control and orbit design in small satellite missions because it can cause postural instability. The residual thrust in hybrid thrusters has not been evaluated to date. This study represents a pioneering study in this field. We conducted a simulation incorporating the rocket equation, unsteady heat conduction equation, fuel pyrolysis characteristics, and radiation from the nozzle and injector to the fuel. Subsequently, we estimated the residual thrust after firing. This estimation technique was applied to a single-port fuel. Simulation results indicate that the residual thrust can exceed 0.3 N for up to 6 s after firing if the fuel regression rate is 0.01 mm/s immediately after firing. The results showed that the residual thrust effect is greater for smaller regression rates. Thus, a thruster for slowly regressing fuel can generate more significant residual thrust than that for regressing fuel quickly, even if the same ΔV is designed.