Ice makes unlikely rocket fuel for CubeSats

Ice would make a fine rocket fuel, if you're a CubeSat.

These lightweight, low-cost satellites are made up of 1 litre modules, making them popular for student projects. Once they have hitched a ride into Earth orbit, they can do real science, such as monitoring the atmosphere or searching for extrasolar planets.

But they are limited by the lack of a good propulsion system to keep them aloft longer and under control, says Angelo Cervone at Delft University of Technology in the Netherlands. "We have reached the maximum level of what you can do with small satellites without one."

So Cervone and his colleagues designed an ice-propelled rocket. The CubeSat would contain 100 grams of water ice. Once in space the ice would sublimate and release vapour molecules. These would then bounce against a hot plate to gain speed before escaping, causing a propulsion force. A prototype may fly in a few years.

Challenges ahead

Ice-powered propulsion could work well, says Paulo Lozano, director of the Space Propulsion Lab at the Massachusetts Institute of Technology, who is developing a CubeSat propulsion system based on accelerating charged particles.

"It's based on solid propellant, and that is always a good idea," he says. "If you have something that can explode, it would pose a threat to the main payload. The challenge will be to keep the ice as ice all the time."

Cervone and his team are still working on how to keep the ice frozen while the satellite is waiting for lift-off, which could mean days on the launch pad. Freezing it after arrival in orbit is an option, but would complicate the design.

The CubeSat propulsion field is becoming crowded – in addition to ice rockets and Lozano's "Electrospray Thruster", a group at the University of Michigan is developing a third rocket using charged particles.

But different types of CubeSat propulsion may coexist, says Cervone, because the demands made on rockets are diverse. For instance, fuel efficiency is most important for travelling long distances, such as reaching asteroids and the outer planets. Charged particle propulsion might be best for this. But for orbital corrections and orientation control, you need more powerful propulsion, and your fuel only needs to last as long as the expected working life of the satellite – ice rockets might be best for that.

Journal reference: Acta Astronautica, DOI: 10.1016/j.actaastro.2014.12.003

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