Experimental Investigation of TPMS Catalyst Beds and a Geometry Correction Model for ABS Hybrid Fuel Grains in Hydrogen Peroxide CubeSat Thrusters

Hydrogen peroxide (H2O2) is a promising green propellant for CubeSat propulsion and is compatible with both monopropellant and hybrid propulsion systems. This study investigates the application of silver-coated Triply Periodic Minimal Surface (TPMS) structures as catalyst supports for H2O2 monopropellant micro-thrusters and as architected fuel-grain geometries in a hybrid thruster. Four TPMS catalyst architectures Primitive, Gyroid, Diamond, and IWP were fabricated by metal additive manufacturing, coated with silver through electroplating, and experimentally compared with silver pellet and silver-coated mesh catalyst beds. Under the investigated monopropellant operating conditions, the TPMS catalyst beds generally exhibited higher steady-state chamber temperatures than the pellet catalyst and comparable temperatures to the mesh catalyst. Exhaust visualization indicated a transition toward a predominantly gaseous exhaust flow, while characteristic-velocity analysis gave an experimental-to-theoretical c* ratio of 85% for the monopropellant test, although this value is affected by heat loss, nozzle losses, flow losses, and measurement uncertainties. Post-test inspection further showed differences in the spatial distribution of visible surface changes among the catalyst configurations, providing qualitative evidence of differences in catalyst condition. For the hybrid-thruster experiments, the selected TPMS catalyst configuration was subsequently used to investigate five ABS fuel-port geometries, including straight-port, multi-port, and Gyroid TPMS designs. Under constant oxidizer mass-flow conditions, the average fuel regression rate decreased with increasing initial burning surface area. A geometry correction factor based on the ratio of the straight-port burning surface area to that of the corresponding geometry reduced the mean absolute prediction error of the classical regression-rate correlation from an average of 209% to 15%. These results demonstrate that architected TPMS geometry influences the measured thermal, flow, and surface-utilization characteristics of H2O2 catalyst beds, while fuel-port geometry strongly affects the average regression behavior of hybrid fuel grains. The findings provide an experimental basis for further development of geometry-controlled catalyst beds and hybrid fuel grains for small-satellite propulsion applications.