13 May 2008—Next week, scientists will gather at the European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands, to discuss a radical idea in spacecraft propulsion. A Finnish invention known as an electric sail has been designed to propel a space probe through the solar system by repelling the protons contained in the solar wind. If successful, the electric sail would reduce the cost of launching deep-space probes that must carry heavy fuel tanks.
Invented by Pekka Janhunen, a research fellow at the Finnish Meteorological Institute, the electric sail produces thrust from the solar wind, comprising high-energy electrons and protons streaming from the sun. The electric sail is similar in some ways to the more conventional solar-sail idea. The solar sail requires a ultrathin aluminized Mylar sail 250 meters in diameter to catch the solar wind, which blows out from the sun at speeds between 400 and 800 kilometers per second. However, no one has ever deployed and tested the solar sail in space, and because of its extreme size, the sail presents a number of engineering problems. But, says Janhunen, the electric sail has many advantages over the solar sail—notably, not having to deploy a gigantic sheet of Mylar in space.