Characterization of the FEMTA Microthruster for CubeSat Proximity Operations

<p dir="ltr">Significant effort is being directed toward enabling autonomous rendezvous and proximity operations (RPO) for nanosatellites, unlocking capabilities such as on-orbit inspection and servicing, debris removal, and formation flying. A key barrier to this advancement is the development of compact, configurable, and highly precise six-degree-of-freedom propulsion systems. Cold and warm-gas propulsion have been demonstrated for this application; however, improved controllability is needed to reduce propellant waste and extend mission lifetimes.</p><p dir="ltr">The Film-Evaporation MEMS Tunable Array (FEMTA) microthruster is a promising technology for RPO applications. FEMTA produces highly tunable thrust output in the single to hundreds of micronewtons range, with specific impulse comparable to cold-gas systems, while utilizing ultra-pure water as propellant. Each device has a compact 1 cm x 1 cm x 1 mm form factor, making it well suited for integration of many thruster units into a single propulsion system.</p><p dir="ltr">FEMTA generates thrust by controlling the evaporation rate of free liquid surfaces within an array of micrometer-scale capillaries. However, fluid behavior within these capillaries is difficult to predict due to heterogeneous surface properties, transitional flow regimes, and complex thermal interactions. Existing models fail to fully explain observed behavior, and experimental access to micrometer-scale thermofluid properties has been limited.</p><p dir="ltr">This research experimentally characterizes FEMTA fluid interface dynamics and propulsive performance across a range of thermal and pressure conditions to refine physical models and inform future designs. Sixth-generation FEMTA thruster devices were developed to enable direct visualization of liquid–vapor interfaces during operation. Measurements of liquid retention behavior, interface stability, and thrust output were used to develop improved modeling frameworks that incorporate surface heterogeneity and non-continuum effects. Finally, a fully functional six-degree-of-freedom FEMTA propulsion system was built and tested with integrated thermal management and zero-gravity propellant feed, laying the groundwork for future orbital demonstrations.</p>