正文
SPACE travel is expensive. Missions such as
Cassini
, a recently ended exploration of Saturn and its moons, and
New Horizons
, a trip to Pluto and one or two more distant objects in the far reaches of the solar system, have involved launching craft weighing hundreds or thousands of kilograms. For big, essentially unique targets such as these, that expense has proved worthwhile. But as exploration moves on to smaller and more numerous objects, like asteroids, individual visits at costs of hundreds of millions, or even billions of dollars are no longer a feasible idea. Some system of mass robotic space travel needs to be devised. And Pekka Janhunen of the Finnish Meteorological Institute in Helsinki thinks he has invented one.
In 2004 Dr Janhunen put forward the idea of a sail that harnesses the solar wind, a stream of charged particles emanating from the sun which manifests itself on Earth in the dramatic displays of the aurorae. He and his colleagues have since refined the idea. In a paper they presented to the European Planetary Science Congress, in Riga, Latvia on September 19th, they proposed that spacecraft equipped with their new propulsion system could make a round trip to the asteroid belt in little more than three years. A fleet of 50 such craft, weighing about 5kg each and thus capable of being launched by a single rocket, could visit 300 asteroids, survey them and return to Earth for a thrifty €60m ($72m) or so, including the cost of launch.
