Design, Simulation and Optimisation of a Low-Pressure Micro-Resistojet for Small Satellite Missions

Incorporating propulsion in small satellites is becoming a growing trend, due to its potential for enabling new and ambitious mission objectives. One of these objectives is formation flying, that will be pursued by TU Delft for the DelFFi mission as part of the larger QB50 project. For DelFFi, two identical spacecraft will use propulsion to allow for relative positioning. Due to the intrinsic limitations in mass, volume, power and propellant choice, pico-/nanosatellite propulsion poses different challenges when compared to larger spacecraft. The design of a MEMS (Micro Electro- Mechanical Systems) resistojet using water (ice) as propellant, operating at low pressures in the range of 50 to 200 Pa (below the vapour pressure of ice at temperatures below 270 K) will be described. The main results of a set of DSMC (Direct Simulation Monte Carlo) simulations performed with the open source dsmcFoam solver, showing the influence of geometry on thruster performance, in particular thrust and specific impulse, at a given input power will be presented. The low operating pressure allows for using the vapour pressure of ice as the only method of propellant feeding. The design presented in the paper will use few moving parts — one in the thruster and two or three in the propellant storage subsystem — and two heat inputs: one in the thruster and one to maintain the propellant temperature in the tank. The simulations, performed with various geometries and propellant storage conditions, show that the proposed design represents an alternative, low risk, micro-propulsion system suitable for small satellite missions, with the pressure inside the system never exceeding 600 Pa.