Inexpensive and compact CubeSats are great for certain missions, but their simplicity can limit their applications. For one, most of them don't pack their own propulsion systems, instead hitchhiking into orbit aboard other satellite launches. Now, to make CubeSats more maneuverable, a team from Purdue University has developed a system that would allow the mini satellites to safely propel themselves by spraying jets of ordinary water.

The Purdue prototype was a CubeSat measuring 10 cm3 (0.6 in3) and weighing 2.8 kg (6 lb), loaded with off-the-shelf electronic components normally used for Internet of Things devices. There's a computer that wirelessly receives instructions and relays them to an inertial measurement unit that works out how to act on them. But the star of the show was the propulsion system, dubbed a Film-Evaporation MEMS Tunable Array (FEMTA) thruster.

Four of these FEMTA thrusters were built into the prototype, each one carrying about a teaspoon of ultra-purified water. The tank is full of capillaries about 10 microns wide, which is too small for the water to flow out thanks to its surface tension. To control when it escapes, small heaters around the edges of these holes can be activated on demand, warming the water into vapor and creating tiny blasts that turn the craft.

Not only is water a cheap, plentiful and safe fuel, but the system is very energy efficient as well. Tested in a vacuum chamber, the FEMTA CubeSat managed a thrust-to-power ratio of 230 micronewtons per watt for each 80 second spray.

"This is a very low power," says Alina Alexeenko, lead researcher on the project. "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."

The current model used four thrusters, allowing it to rotate along one axis, but a CubeSat in orbit would need to be able to adjust itself in three dimensions, and so would need to pack a full suite of 12 thrusters. Scaling it to an actual space mission is the ultimate goal for the team.

The researchers are presenting the prototype at the AIAA/USU Conference on Small Satellites this week, and the team describes their work in the video below.

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