29 March 2012
Earth to Moon on a cup of fuel
by Will Parker
A new low-cost ionic motor could drastically reduce the cost of space exploration, with its developers saying it could propel a satellite to the Moon using just a tenth of a liter of fuel. The motor was developed by an international consortium including Ecole polytechnique fédérale de Lausanne (EPFL), SWITZERLAND; Queen Mary and Westfield College (University of London), UK; TNO, THE NETHERLANDS; SystematIC Design BV, THE NETHERLANDS and NanoSpace AB, SWEDEN.
The MicroThrust motor is specifically designed for small (1 to 100 kilogram) satellites on long missions. The motor, designed to be mounted on satellites as small as 10 cm3, is extremely compact but highly efficient. The prototype weighs only about 200 grams - including fuel and control electronics.
Small satellites are a hot research area as their manufacturing and launch costs are relatively low - about half a million dollars, compared to conventional satellites that run into the hundreds of millions. But nanosatellites currently lack an efficient propulsion system that would render them truly autonomous and thus able to carry out exploration or observation missions.
"At the moment, nanosatellites are stuck in their orbits. Our goal is to set them free," explained Herbert Shea, coordinator of the MicroThrust project and director of EPFL's Microsystems for Space Technologies Laboratory.
Instead of a combustible fuel, the new MicroThrust motor runs on an ionic liquid that is composed of electrically charged molecules. The principle of the ionic motor is that fuel is expelled, not burnt. The ions are extracted from the liquid and then ejected by means of an electric field to generate thrust.
The flow of ions is emitted from an array of tiny silicon nozzles - over 1,000 per square centimeter. The fuel is first guided by capillary action from a reservoir to the extremity of the micro-nozzles, where the ions are then extracted by an electrode held at 1,000 volts, accelerated, and finally emitted out the back of the satellite. The polarity of the electric field is reversed every second, so that all the ions - positive and negative - are ejected.
The acceleration produced is only about a 0.0001 m/s2, which is about 0 to 100 km/h in 77 hours. But in space, the developers note, steady acceleration is the way to go. "We calculated that in order to reach lunar orbit, a 1 kg nanosatellite with our motor would travel for about six months and consume 100 milliliters of fuel," explained EPFL's Muriel Richard.
The just-released prototype is expected to be employed on CleanSpace One, a satellite under development at EPFL that is designed to clean up space junk, and also on OLFAR, a swarm of Dutch nanosatellites that will record ultra-low radio-frequency signals on the far side of the Moon.