Characterization of film-evaporating microcapillaries for water-based microthrusters

Compact micronewton thrusters can provide attitude control for small satellites to increase mission duration and enable constellation flying. Micronewton thrust control can also enhance missions that require precision pointing such as space telescopes, laser interferometers, and laser communication relays. Film-Evaporating MEMS Tunable Array (FEMTA) is a novel micropropulsion device that generates thrust by heating a micron scale water capillary to induce controlled film-evaporation. Thrust stand tests under high vacuum have shown that FEMTA can produce controllable thrust of 150 ??N at 70 s specific impulse using 0.65 W of electrical power and ultra-pure deionized water as propellant. An undesired quiescent propellant loss rate is inherent to the current FEMTA design which limits its life span and reliability. To derive mitigations to this issue, the behavior of the fluid interface within the FEMTA micronozzle was characterized through direct experimentation. A testbed FEMTA design was created which enabled direct observation of the liquid within the micronozzles and precise control over critical nozzle dimensions. These test-bed devices were used to measure contact angle, Laplace pressure, and total quiescent propellant loss rates for multiple nozzle configurations. Finally, a next generation FEMTA design was derived from the findings of these studies and its propulsive performance was measured under high vacuum on a micronewton thrust stand. Microfabrication was performed at Purdue???s Birck Nanotechnology Center and vacuum testing was completed at Purdue???s High Vacuum Lab.

Automated summary

Compact micronewton thrusters can provide attitude control and enhance mission duration and precision pointing. The novel micropropulsion device, FEMTA, generates thrust by heating water capillary and has been tested under high vacuum. The research shows controllable thrust and long specific impulse, but the current design has an issue of undesired propellant loss rate.