Design, Optimization and Fabrication of a Free Molecule Micro-Resistojet for Microspacecraft Thrust Generation

摘要

Constellations or platoons of batch-fabricated micro- and nanospacecraft may offer a variety of benefits over large multi-functioning space platforms. Among the major impediments to their introduction are the thrust requirements and power limitations of micro spacecraft; low mass, power efficient microthrusters that can deliver accurately controlled micro-N-sec impulse bits must be developed. The Free Molecule Micro-Resistojet (FMMR) concept that was proposed earlier by Muntz and Ketsdever has been analyzed using direct simulation Monte Carlo numerical simulations and well-established MEMS fabrication techniques. The FMMR combines polysilicon heating elements to heat a gas expanding through long ((caret) 1 cm), narrow (1 to 100 micrometers wide) slots. Initial simulations suggest that the resistojet can attain a specific impulse of nearly 45 seconds with a thrust level of 0.25 mN for an argon propellant, 10 expansion slots and a heated wall temperature of 600 K. Higher thrust levels can be achieved by increasing the polysilicon heater temperature, changing the slot dimensions, allowing more propellant mass flow through the expanding slots or by changing the propellant. Lightweight construction, device ruggedness and relative ease of fabrication were also important design considerations. Initial fabrication of the FMMR suggests the relative ease of construction using well established MEMS techniques.