Finnish space boffins have been awarded €1.7m and placed in charge on an international effort to build the fastest thing ever made by the human race – namely a spacecraft propelled by the pressure of sunlight striking an enormous electrical field.
The "electric solar wind sail" is not your common or garden solar sail, familiar to many Reg readers, in which the solar wind strikes something physical – a fabric or film, probably extremely thin and light – and the resulting minuscule pressure exerted over a large area very gradually accelerates the sail and its attached spacecraft.
No, the Finns are having none of that – the necessary vast acreage of sail fabric required to achieve even a feeble push would be too much bother, they feel.
Rather, in the electric version, the ship deploys instead 50-100 20km-long, extremely fine (25 micron thick) cables. These are arranged in a circle and the whole thing spins, keeping the wires stretched out in a huge, 40km-across disc like the spokes of a wheel. A positive potential of, say, 20,000 volts is put on the wires (requiring only a few hundred watts of power, as almost no current is actually flowing).
Thus the wires generate overlapping electrical fields which, as far as the ions of the solar wind are concerned, is a solid barrier. They hit it and are stopped or bounced back, and in the nature of things this exerts pressure on the electric-field "sail". The effect isn't nearly as strong as it would be with a physical sail, but because the electric model is so huge and so light, it can still achieve impressive results. For instance it has been calculated that an electrosail ship could reach Pluto in less than five years.
All this was worked out back in 2006 by Finnish Meteorological Institute researcher Pekka Janhunen, causing a minor stir in solar sail circles but, so far, no action. Now, however, the Institute has announced commencement of the EU-funded ESAIL project, led by the Finns but also including space scientists from Estonia, Sweden, Germany and Italy.
According to the FMI:
The ESAIL project will last for three years, its EU funding contribution is 1.7 million euros and its goal is to build the laboratory prototypes of the key components of the electric sail.
The electric solar wind sail may enable faster and cheaper access to the solar system. In the longer run it may enable an economic utilisation of asteroid resources. A related but simpler device (the so-called plasma brake) can be used for deorbiting satellites to address the space debris issue. The working principles of the electric sail and the plasma brake will be tested in the coming years by the Estonian ESTCube-1 and the Finnish Aalto-1 nanosatellites.
Though it is only a lab effort for now, the FMI boffins add expansively that the ESAIL project's "goal is to build the largest and fastest man-made device" – which, if such a sail ever flew in space, would probably be fair enough. An object 40km across travelling at perhaps 30km per second or even more would surely qualify. There's more on electric sails here. ®