Thermal Modeling of FEMTA Micropropulsion System for CubeSat Attitude Control

Nano and pico-class satellite platforms such as 1U CubeSats, PocketQubes, and ThinSats introduce unique power and volume constraints on propulsion systems. The Film-Evaporation MEMS Tunable Array(FEMTA) microthruster is one compact, low-power technology that is well suited for these applications. FEMTA thrusters are microfabricated on 1 cm x 1 cm x 1 mm silicon and glass chips. Each chip contains an array of micrometer-scale capillaries which are electrically heated to vaporize the liquid propellant and generate controlled thrust. Sixth generation FEMTA devices have been demonstrated to produce greater than 300 microNewton of thrust per 1 Watt of electrical power at 90 seconds specific impulse. Liquid ultra-pure deionized water is used as a dense, safe, and abundantly available propellant source. A complete FEMTA six degree-of-freedom propulsion system including zero-gravity propellant management is being developed at Purdue University in preparation for a future orbital flight demonstration. It is suspected that the performance and long-term reliability of FEMTA will be sensitive to temperature fluctuations within this propulsion system while in orbit. Specifically, a reduction in propellant temperature may result in ice generation within the FEMTA chips and an increase in propellant temperature will reduce total DeltaV through higher quiescent propellant loss. We present an investigation of FEMTA propulsion system thermal response in Low Earth Orbit (LEO). A generalizable analysis process was developed for LEO CubeSat missions using finite element models in ANSYS. This analysis process was applied to a preliminary CubeSat mission design to investigate FEMTA propulsion system transient-thermal behavior. Model accuracy and recommendations for future improvements to the process are discussed