Reliability Investigation and Design Improvement of FEMTA Microthruster
The advent of nano and micro class satellites has generated new demand for compact and efficient propulsion systems. Traditional propulsion technologies have been miniaturized for the CubeSat platform and new technology solutions have been proposed to address this demand. However, each of these approaches has disadvantages when applied within the context of a CubeSat. One potential low mass and power alternative is Film-Evaporation MEMS Tunable Array (FEMTA) micropropulsion which is capable of generating 150μN of thrust using 0.65W of electrical power and ultra-pure deionized water as propellant. The FEMTA thruster is etched into a 1cm × 1cm × 0.3mm silicon substrate using standard photolithography and microfabrication techniques. Each thruster consists of a 4 μm wide nozzle and platinum resistive heaters. Capillary pressure prevents the water from leaking through the nozzle and the heaters induce film-evaporation at the fluid interface to generate thrust. FEMTA has been in development at Purdue University since 2015 under the NASA SmallSat Technology Partnership Program and is currently on its 5th generation design. While these generations of FEMTA have successfully demonstrated the viability of the propulsion technique under ideal conditions, multiple reliability and performance related issues have been identified. More specifically, high vacuum tests have shown that the current FEMTA design is susceptible to quiescent propellant mass loss due to ice generation and leaking at the nozzle. These mass ejections can limit the lifespan and performance of the thruster and can induce undesired attitude perturbations on the host spacecraft. The purpose of this researchidentify the root causes of the quiescent mass loss mechanims hrough simulation and direct experimentation. Based on the results of these investigations, a next generation design is proposed, fabricated, and tested. Microfabrication was performed at Purdue’s Birck Nanotechnology Center and vacuum and thrust stand tests were performed at the High Vacuum Lab in the Aerospace Sciences Laboratory at Purdue.