Enhancing Performance and Efficiency of Hybrid Rocket Thrusters for Satellite Deorbiting

This study presents findings from an ongoing initiative aimed at developing hybrid rocket thruster technology as a viable alternative to hydrazine-based propulsion systems for satellite deorbiting at end-of-lifetime. The system uses 87% nitrous oxide and 13% gaseous oxygen as the oxidizer (Nytrox), with additively manufactured ABS as the fuel. When complete, the product is designed to act as an attachable deorbiting unit for small to mid-sized satellites. By employing incremental hot-fire tests and an iterative design methodology, motor combustion efficiency was enhanced from below 60% to over 95%; achieved through optimization of fuel grain length, injector configuration, and burn sequencing. Throughout the development campaign, the authors estimate that the technology readiness level of the system advanced from an initial value of approximately 4.5 to a level exceeding 6.0. Throughout the iterative design process, several experiments were carried out with cold flow gaseous nitrogen to assess different injector configurations. A full-cone injector with a 120° spray angle and internal swirl was selected for its superior atomization, thermal survivability, and uniform fuel regression properties. During a sequence of five burns with a single fuel grain, the thruster maintained a stable oxidizer-to-fuel ratio, averaging 2.60 with a 95% confidence interval of ±0.06. By putting measured impulse data from the five-burn burnout sequence into a numerical orbital simulation program, it was shown that this motor is capable of successfully deorbiting a 100 kg satellite that starts out in a 600 km circular orbit. The findings indicate that a restartable hybrid motor powered by Nytrox/ABS propellants could effectively function as a high-performance, affordable, and environmentally friendly propulsion system, potentially serving as a replacement for hydrazine systems in de-orbit missions. Adopting green hybrid propulsion in place of hydrazine substantially reduces operational costs and expands the range of application options beyond the original initial end-of-lifetime deorbit use.