A winglet design is discussed from the perspectives of sonic boom suppression and drag reduction at supersonic speeds. Design parameters such as dihedral and anhedral angles that were effective in reducing drag in previous studies on low-drag designs of a winglet at transonic and supersonic speeds were used in this study, and their effects on a low-boom design are examined herein. Non-dominated solutions with respect to sonic boom loudness and drag are explored using response surfaces and a genetic algorithm. Two characteristic winglets are selected from the solutions, and their drag and sonic boom characteristics are compared. Results showed that winglets affect sonic boom signatures through the shielding, cancellation, and reflection effects. The first two effects weaken expansion waves propagating to the ground, exerting a positive impact on rear boom suppression. In terms of drag reduction, the suction force of the winglet utilizing expansion waves on the upper surface of the wing should be enhanced, and the pitch trim change should be minimized to reduce trim drag. Based on these results, design guidelines to reduce both sonic boom loudness and drag are derived.

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.

A thruster head of a water-vapor Hall thruster with a discharge channel of 15 mm in diameter and 5 mm in width was designed and developed by applying the conventional scaling law to a previously studied laboratory model. The newly designed thruster was successfully operated at discharge powers ranging from 80 to 340 W. The thrusts were estimated from the plume diagnostics, which were validated by direct measurements using a thrust stand. As a result of the performance analysis, it was revealed that the thrust exhibited a linear correlation with the discharge power, while the specific impulse and anode efficiency also varied with the discharge voltage. Unlike other internal efficiencies, higher discharge voltages did not necessarily enhance the mass utilization efficiency, especially above 250 V. This suggests that the electron temperature is less likely to increase in the high-voltage regime, possibly due to further energy losses from additional chemical processes or wall interactions.