Ice-propelled nanosatellites

In a paper in Acta Astronautica, published recently, Angelo Cervone, Barry Zandbergen and their team of researchers at the Faculty of Aerospace Engineering described a simple and reliable propulsion system that uses water ice for nanosatellites. Once in space, the ice, stored at very low pressure (less than 1% of the atmospheric pressure at sea level), sublimates and releases vapour molecules. Some of these water molecules bounce against a hot plate to gain speed before escaping into outer space, thereby generating thrust.

Nanosatellites are spacecraft with a launch mass lower than 10 kg. They are cheap and popular for student projects. After they’ve hitched a ride into orbit from a large commercial rocket, their potential for scientific research is enormous. It ranges from Earth remote sensing and earthquake detection to climatology, from atmosphere and magnetic field characterization to bioengineering and micro-gravity genetics experiments.

It is estimated that about 200 nanosatellites are currently in orbit, two of which are from TU Delft; Delfi-C3and Delfi-n3Xt. They were launched in 2008 and 2013 respectively.

“The current challenge faced by design teams of nanosatellite missions is to add more functionalities to the small spacecraft and to improve their performance”, said Cervone. “One of the key technologies to this respect is micro-propulsion, which can provide the possibility for precisely orienting and navigating the spacecraft with forces as little as a few milli-Newton.”

While most research groups in this field focus on accelerating charged particles (typically of an inert gas) as a means of thrust, the Delft researchers thought of water. “We did calculations and simulations proving that our micropropulsion device using ice can deliver an excellent performance”, said Cervone. “Since this propellant is kept in solid form and at low pressure there is no danger of explosion. This gives it a big advantage over many other propellants that have high risks of explosion or are nasty to work with being carcinogen, like hydrazine.”

The challenge is to keep the water frozen. “It will probably be better to keep the water in liquid state before launch. Once in space the water would then be frozen, although of course the necessary devices will add complexity to the satellite. In space, the satellite itself is still kept at ambient temperature (usually between 0 and 30 °C) by its thermal control system, but the outside environment is very cold (about -270 °C) and can help to efficiently freeze the water inside the tank.”

“It is obviously hard to say at this initial stage of our research, but I guess that within the next four or five years we will be ready to launch a nanosatellite that uses ice as propellant.”

Angelo Cervone, et., al. Conceptual design of a low-pressure micro-resistojet based on a sublimating solid propellant. Acta Astronautica, DOI: 10.1016/j.actaastro.2014.12.003