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.
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