Design and optimization of variable thrust hybrid rocket motors for sounding rockets

Besides safety and low-cost, the start/shutdown/restarting and throttling ability are the other two significant advantages of hybrid rocket motors (HRMs) compared with liquid and solid ones. In this study, a two-stage variable thrust and non-toxic 98%HP/HTPB hybrid rocket motor (VTHRM) is designed and applied in a sounding rocket, and the design parameters of the motor are analyzed and optimized. A computational program is developed to design the motor system structure, to predict the interior ballistics and the ballistic trajectory. A star grain and a wheel grain are compared. The design of experiment (DOE), variance analysis and the main effect analysis are employed to investigate the influence of the main design parameters on motor performance. The multidiscipline feasible (MDF) approach is applied to establish the optimization procedure after analyzing the system design structure matrix. A modified differential evolution algorithm is employed to maximize the load mass. The results indicate that the wheel grain could obtain a larger load mass and a lower length to diameter ratio, and that throttling markedly meliorates the motor and rocket performance. The conclusions drawn from the analysis and optimization could provide instructive guide and theoretical basis for engineering designs.