| A micropropulsion idea called the Free Molecule Micro-Resistojet (FMMR) was studied in this research. Created for the 5–20kg class microspacecraft and constellation mission, the FMMR operates on low pressure (50–500Pa) such that a free molecular flow environment is created in the thruster. Preliminary performance was estimated by free molecular flow theory and compared with two-dimensional Direct Simulation Monte Carlo calculations that also investigated the effects of gas-surface interactions between the propellant and the heat exchanger. Fabricated using micro-electro-mechanical systems technology, the prototype FMMR heater chip consisted of a multilayer metallic thin film heater (chromium, platinum and gold) evaporated on a silicon nitride-coated single crystal silicon wafer etched with long, thin expansion slots. The temperature distribution and power consumption without propellant interaction were characterized at constant voltage in high vacuum. The chip had a non-uniform temperature distribution with the maximum chip temperature at the center. The maximum temperature was proportional to the square of the steady-state input power, while the thin film heater electrical conductivity decreased exponentially with the maximum temperature. A numerical model of the prototype heater chip was created using Abaqus, a finite element modeling software, and many sensitivity analyses were conducted on the thermophysical and interfacial properties of the FMMR. The numerical simulation steady-state results matched the experiment data within the measurement uncertainty for the most part and was used to evaluate six new thruster designs. Simulations predicted the best design could produce about 1mN per unit W of input power. The prototype heater chip will be flight-tested for survivability, duration and power consumption without propellant interaction on-board the Three Corner Sat Constellation. The flight experiment design, preparation and qualification testing were also detailed in this research. |
