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REMEMBER the furore in 1990 when the first pictures beamed down from the Hubble Space Telescope were just unfocused smudges? While an innovative repair job—effectively a pair of spectacles—allowed the short-sighted flying eye to focus, space telescopes of the future could face a similar problem. But it’s got nothing to do with poorly engineered optics.

Instead, scientists now worry that exhaust plumes from telescopes’ positioning rockets could fog sensitive mirrors, clouding cosmological images. Future telescopes will need these rockets because they are likely to be made up of a number of separate units: giant mirrors, image sensors and control systems that all fly separately but in tight formation (¿ìè¶ÌÊÓƵ, 23 February, p 20).

Getting around this problem could be easy, says David Miller, a formation flight specialist at the Massachusetts Institute of Technology. His answer? Magnets. Instead of gas-guffing rocket power, he suggests using solar-powered electromagnets to attract and repel the separate units, keeping them in tight formation. Such a system would have the added benefit of never running out of fuel—unlike rocket motors.

Electromagnets embedded in spacecraft will allow them to move closer together, further apart, or rotate around each other, says Miller. Rotation is an important manoeuvre for missions that involve pointing a formation at an object like a distant galaxy.

Solar panels would provide the electricity, while nuclear power could be used for missions that journey far from the Sun. NASA is already redoubling its efforts to create useful nuclear reactors for spacecraft and probes. But electromagnets can only be used to control the relative movements of an array of spacecraft. Getting the craft into the right orbit, for example, still requires a more conventional propulsion system.

Miller’s group is still working on a prototype, but one idea is to join three electromagnets at their midpoints so that they are perpendicular to each other, forming a six-pronged device embedded in the spacecraft, Miller says he can create useful magnetic fields that extend 100 metres into space, which is plenty for setting up an optical telescope, or even a radar array for detecting space junk. He will present his idea at the IEEE Aerospace Conference This Week in Big Sky, Montana, and hopes to test a prototype in a microgravity environment on the International Space Station in 2004.

Frank Bauer, a NASA expert on flying spacecraft in formation, says the idea looks promising. However, there’s a risk that the electromagnets may try to align themselves with the Earth’s magnetic field instead, he says.