Space Probe Paves Way for European Moon Landing

A space probe the size of a washing machine driven by a Star Trek drive no more powerful than a puff of breath is about to explore one of the solar system's oldest mysteries and pave the way for a European landing on the moon.

Smart-1, a £77m European Space Agency probe carrying a British instrument which will settle questions about what the moon is made of, will be launched aboard an Ariane 5 rocket from Kourou, in French Guiana, on September 3.

Once in high orbit, its array of solar panels will unfold like the wingspan of an albatross, to collect the electrical power for an ion drive propulsion system. This will fire a stream of electrically charged xenon atoms to provide a push of no more than a few grams - the weight of a postcard or sheet of paper. Think of an ion drive as a neon lightbulb with one end removed, says Manuel Grande, of the Rutherford Appleton Laboratory in Oxfordshire, and one of the principal investigators for the mission.

But ion drive has a huge advantage over chemical rockets. A stream of xenon ions shoots away from the spacecraft at 10 times the speed of any rocket. So an ion drive spaceship can go 10 times as fast - or set off with one tenth of the fuel.

Smart-1 will take 15 months to get into orbit around the moon. But over a much greater distance, the same technology will knock four years off a planned European voyage later in the decade to the solar system's most mysterious planet. Mercury is a kind of iron cannonball which, even though it is so close to the sun, should be cool and, in effect, dead. But it has a powerful magnetic field. This implies that against all the odds, its interior has stayed molten.

"Mercury is one of those things that many scientists wish wasn't there. It is a real nuisance. It is very hard to get to," said David Southwood, director of science for the European Space Agency.

"It is small and, despite being near the sun, it should have cooled down right to the centre many, many millions of years ago. Objects that have magnetic fields have to have something inside them - dynamos that are churning around to keep the magnetic field there. Mercury is doing this against all the rules of planetary science."

Smart-1, though a rehearsal for a mission to Mercury, will first of all put the moon under the microscope. Apollo astronauts brought armfuls of moon rocks back to Earth 35 years ago. There have been visits by two US spacecraft since then. In the next six years, there could be lunar missions from Japan, China, India and the US. But Smart-1 will lead the way and answer some of the more basic questions about a celestial companion which revolves once every 28 days - coincidentally the period of its orbit around Earth - and keeps its dark side always hidden.

A British instrument the size of an electric toaster will measure the x-rays from the sun as they bombard the moon and then monitor the fluorescence from the lunar rocks. "This is exactly the same as if you are in a disco. The ultraviolet light shines on your shirt, and your shirt glows," said Prof Grande. "The moon glows in x-rays and each x-ray colour indicates unambiguously the presence of a particular element in the lunar surface. If you see the aluminium x-ray colour, you know there is aluminium there."

A precise measurement of the abundance of the elements that make up the surface rocks should throw light on the history of the moon, thought to have been formed in a cosmic collision between Earth and another large object early in the history of the solar system. But Smart-1's optical camera will also examine the topography of the surface, looking first for a suitable site for a robotic lander, and perhaps even for a human foothold on the moon.

"There is no doubt one could have a manned presence on the moon in 20 years. It is a question of wanting to do it. The issue is not so much for the scientists and technologists as for the people to decide they want to do it - that this frontier needs to have a human presence," said Professor Southwood.