H2O micropropulsion used in new CubeSat system

Engineers at Purdue University have developed a new method of micropropulsion for CubeSats, using water as the propellant.

The FEMTA (Film-Evaporation MEMS Tunable Array) thruster uses tiny heaters to create water vapour, which flows into the vacuum of space through capillaries about 10 micrometres wide. When the heaters are not operating, the water’s surface tension prevents it from escaping. The minuscule capillaries therefore act like valves when small amounts of heat are applied.

The thrusters are microscale nozzles manufactured on silicon wafers using nanofabrication techniques. A model was tested in a Purdue vacuum facility, using four thrusters that allowed the satellite to rotate on a single axis.

According to the team, the FEMTA technology demonstrated a thrust-to-power ratio of 230 micronewtons per watt for impulses lasting 80 seconds.

“This is a very low power,” said Alina Alexeenko, a professor in Purdue University’s School of Aeronautics and Astronautics.

“We demonstrate that one 180-degree rotation can be performed in less than a minute and requires less than a quarter watt, showing that FEMTA is a viable method for attitude control of CubeSats.”

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The CubeSat industry has grown considerably in recent years, with constellations of the devices, which are 10cm x 10cm x 10cm in dimension, offering a cheaper alternative to multi-million dollar satellites. However, controlling groups of CubeSats has proved difficult, and there are concerns that they will substantially add to the space debris problem. Micropropulsion systems such as FEMTA could be part of the solution.

“There have been substantial improvements made in micropropulsion technologies, but further reductions in mass, volume, and power are necessary for integration with small spacecraft,” Alexeenko said.

Funding for the project came via NASA’s SmallSat Technology Partnership programme, and the research was conducted in collaboration with the space agency’s Goddard Space Flight Centre. Though only a single-axis model has been tested so far, the team is confident that a 12-thruster, three-axis device can be developed for a CubeSat.

“What we really want to do next is integrate our system into a satellite for an actual space mission,” said Alexeenko.