Engineering news
It’s been designed for CubeSats – the tiny microsatellites that are becoming increasingly popular. They’re being launched in their thousands to take images of Earth, or provide internet connectivity to those in rural areas.
"They offer an opportunity for new missions, such as constellation flying and exploration that their larger counterparts cannot economically achieve," said Alina Alexeenko, a professor at Purdue University's School of Aeronautics and Astronautics.
However, because of their size, many don’t have any form of propulsion. Once they’re in a particular orbit, that’s where they stay. “Propulsion takes up a significant amount of space, so if you’ve got a very small CubeSat maybe even a third or half of it could be taken up with a propulsion system,” explained Jason Forshaw, a research fellow at Surrey University’s Space Centre who was not involved in the study, to PE.
This limits their potential, which is why Alexeenko has led this new research on water-based propulsion. The system is called a Film-Evaporation MEMS Tunable Array (FEMTA) thruster. It uses a teaspoon of water, and tiny nozzles just 10 micrometers in diameter.
These nozzles are small enough to harness the microscopic properties of water – with surface tension stopping it from flowing out into the vacuum of space.
When a change in a satellites trajectory is required, small heaters at the ends of each capillary would be activated, heating the water to about 50 degrees. This is enough to create water vapour that would flow out of the nozzle and provide thrust.
“There have been substantial improvements made in micro-propulsion technologies, but further reductions in mass, volume, and power are necessary for integration with small spacecraft,” Alexeenko said.
The FEMTA thruster has a thrust-to-power ratio of 230 micronewtons per watt for impulses lasting 80 seconds. “This is a very low power," Alexeenko said. "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.”
Forshaw, who works with CubeSats on his project to clean up space debris, told PE that a cheap and small propulsion system could see wide adoption in a field where it’s not a common feature. "If there is a capability to have propulsion and it was significantly cheaper and could be fitted into significantly smaller volume then yeah that's something I think people would consider for certain,” he said.