The first prototype of a new, ultra-compact motor that will allow small satellites to journey beyond Earth’s orbit has been developed by École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. The goal of the micro motor is to drastically reduce the cost of space exploration.
Imagine reaching the Moon using just a fraction of a liter of fuel. With their ionic motor, MicroThrust, EPFL scientists and their European partners are ushering in a new era of low-cost space exploration. The complete thruster weighs just a few hundred grams and is specifically designed to propel small (1-100 kg) satellites, enabling them to change orbit around the Earth and even voyage to more distant destinations – functions typically possible only for large, expensive spacecraft. The prototype will be used on CleanSpace One, a satellite under development at EPFL that is designed to clean up space debris, and on OLFAR, a swarm of Dutch nanosatellites that will record ultra-low radio-frequency signals on the far side of the Moon.
The motor, designed to be mounted on satellites as small as 10x10x10 cubic centimeters, is extremely compact but highly efficient. The prototype weighs only about 200 grams, including the fuel and control electronics. While small satellites require low manufacturing and launch costs, they currently lack an efficient propulsion system that would render them truly autonomous and able to carry out exploration or observation missions.
Instead of a combustible fuel, the mini motor runs on an ionic liquid; in this case, the chemical compound EMI-BF4, which is used as a solvent and an electrolyte. It is composed of electrically charged molecules (ions), except that this compound is liquid at room temperature. The ions are extracted from the liquid and then ejected by means of an electric field to generate thrust. This is the principle behind the ionic motor: fuel is not burned, it is expelled.
In the motor, 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.
After six months of acceleration, the microsatellite’s speed increases from 24,000 km/h, and its launch speed increases to 42,000 km/h. The acceleration is only about a tenth of a millimeter per square second, which translates into 0-100 km/h in 77 hours. But in space, where there is no friction to impede motion, gentle but steady acceleration is the way to go.