Microsatellite plasma propulsion

Thanks to new MEMS (microelectromechanical systems) technology, the development of low-mass spacecraft—less than 20 kg—has gone well, with one notable exception: suitably miniaturized thrusters, the minirockets that steer the craft and make other flightpath adjustments. John Foster, a researcher at NASA’s Glenn Research Center in Cleveland, Ohio, has now built a tiny propulsion system that develops thrust from a pressurized gas of xenon that is ionized by energetic electrons as it escapes through 0.18-mm apertures. Foster boiled the electrons off a filament and used a cusp in a magnetic field to focus them onto the apertures. The resulting ions were then accelerated to the 50–200 eV range to generate thrust. Only about 50 mm across, the device is extremely fuel-efficient: 88% of the fuel is successfully turned into ions. The new compact plasma accelerator could also be used for modifying surface chemistry and making thin films. (J. E. Foster, Rev. Sci. Instrum. 73, 2020, 2002 http://dx.doi.org/10.1063/1.1464658 .)