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Next week an American military spacecraft is due to begin the first
journey to a near-Earth asteroid. During the mission, Clementine will test
technology that could one day be used to track nuclear missiles in the Earth’s
atmosphere. Although primarily a military project, the mission is a cooperative
venture between the Department of Defense and NASA. Before heading off in
late May to the tiny asteroid Geographos for a close encounter around the
end of August, Clementine will spend much of the intervening period mapping
the surface of the Moon for civilian scientists (see Diagram).

The mission, which is costing less than $80 million, was originally
conceived by the Strategic Defense Initiative Organisation as part of the
Star Wars programme. It is now controlled by the Ballistic Missiles Defense
Organisation, which replaced the SDIO last year. The BMDO admits it has
no real interest in either the Moon or Geographos, but over the past decade
Star Wars scientists have developed military technologies, such as lightweight
components and sensors for tracking missiles, that the BMDO now wants to
test in space.

Light array

For instance, parts of the spacecraft will use carbon fibres instead
of aluminium. Clementine will generate electricity using an array of solar
cells made from gallium-arsenide-germanium semiconductors – the array will
be one of the lightest ever sent into space. And it will save this energy
in a nickel hydrogen battery that has twice the storage capacity of previous
power cells. A solid state data recorder, holding three times as much information
as conventional devices, will store information from sensors designed to
detect and track incoming missiles.…