Tether propulsion seems to be the OLED
of the spacefaring world, carrying as it does a lot of promise but seemingly never ready for the big time. The fundamental premise is as simple as it is appealing -- a long strip of metal stretched out in space can theoretically exploit the Earth's magnetic field to maneuver itself without expending any fuel of its own. This is done by sucking up ionospheric electrons at one end and, predictably enough, spitting them out at the other, allowing current to flow through the tether. Japan's aerospace agency has recently shot off a testing vehicle for just this theory, a 300 meter-long, 2.5cm-wide ribbon, which has managed to successfully generate a current. No thrust-measuring equipment was on board and it's still very early days, but hey, there's at least the chance that one day satellites will all sprout long, elegant tails to power their way through the sky... and into our private lives.