THE Van Allen belts, which were discovered in 1958 by some of the first artificial satellites, are a bane of those satellites' successors. The outer belt, which begins at an altitude of 13,000km above Earth's surface and goes up to 60,000km, is full of energetic electrons. The inner one, at 1,000-6,000km, is full of energetic protons. Both play havoc with satellites' electronics.

But what if you could sweep them away? This is the ambition of Reinhard Friedel, a physicist at Los Alamos National Laboratory, in New Mexico, and his colleagues. Dr Friedel reckons you could do the job with radio waves. In principle this should work because the gap between the inner and outer belts is maintained by natural radio waves from things like lightning.

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Particles in the Van Allen belts are constantly on the move, following the lines of Earth's magnetic field towards the poles, gyrating as they travel. As they approach a pole, however, the laws of electrodynamics that govern the behaviour of gyrating particles force them to reverse their direction and head back towards the opposite pole. If a particle is moving towards a pole faster, it will come closer to Earth before bounding back and is more likely to hit an air molecule. If it does so it is, to use the jargon, "precipitated" into the atmosphere where it gives up its energy and never returns to space.

So the way to sweep the Van Allen belts clean of their troublesome electrons and protons is to bombard the particles with radio waves at a frequency that speeds them up as they head towards the poles. Protons are heavy and influencing them requires a lot of power. So sweeping the inner belt may be impractical. Electrons, however, are much lighter. That means a space-borne particle-sweeper for the outer Van Allen belt is a possibility, according to Dr Friedel. He reckons it would cost about $500m to launch and operate for 15 years. Not all satellites would benefit. But many, including all the geostationary communications satellites, have to contend with electrons in the outer belt. Sweeping could extend the life of all GPS satellites by two years, saving about $22m per satellite, or $660m in all.

The scheme is ambitious, but not foolhardy. Some talk of clearing larger chunks of space debris to stop them crashing into satellites. That would be hard. Sweeping away the cloud of electrons that surrounds Earth could be a better investment.