FOUR decades after Russian and US spacecraft started exploring the moon, the European Space Agency has launched its first lunar mission. But SMART-1 is not in a hurry. The tiny craft, which launched last weekend, is making the slowest ever trip to the moon, taking 15 months to arrive, compared with the five-day journeys of NASA鈥檚 Apollo missions in the 1960s and 70s.
The Europeans have been able to take advantage of the lunar knowledge already gathered by NASA to plan the 拢77 million project, which is part of ESA鈥檚 programme of 鈥渟maller, faster, smarter鈥� missions 鈥� in pointed contrast to NASA鈥檚 ill-fated 鈥渇aster, better, cheaper鈥� mantra. The probe鈥檚 progress over the next few years will show whether it merits the 鈥渟mart鈥� tag.
Smart-1 is going slow because it is testing a solar-powered ion engine in preparation for a more ambitious trip to Mercury. It has already unfurled its solar wings 鈥� 14-metre panels that capture the sun鈥檚 energy to ionise stored xenon atoms. The xenon ions are then shot out of the rear of the craft in a brilliant display of blue light, generating a gentle thrust.
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If the engine is successful, ESA hopes ion propulsion will enable its BepiColombo mission, planned for 2011, to reach Mercury in two-and-a-half years, compared with five years for NASA鈥檚 planned Messenger mission, which will be powered by conventional rockets. Craft powered by chemical thrusters are much faster over short periods, but ion engines generate 10 times the thrust per kilogram of fuel and so can carry enough fuel to continue at full acceleration for months or years.
鈥淢ercury is deep inside the sun鈥檚 gravity well,鈥� says Bernard Foing, the ESA scientist overseeing the Smart-1 mission. That makes it difficult to get a conventional rocket-powered craft into orbit around the planet without a lot of manoeuvres, and a lot of fuel. An ion engine should be able to get a craft closer in, using less fuel and leaving more space on board for scientific instruments.
Messenger will still beat BepiColombo to Mercury, but ESA scientists are not worried about being second. 鈥淲e will use the images they collect to focus our mission plan,鈥� says Sarah Dunkin, part of the Smart-1 team.
Although Smart-1 has a volume of only 1 cubic metre, ESA scientists have packed in a range of instruments that they are testing for the Mercury mission, including a toaster-sized X-ray spectrometer. While previous moon trips only circled the equator, Smart-1 will check out the entire surface, including the poles, creating the first global X-ray map.
The probe will also peer into deep craters reaching down into the moon鈥檚 core. ESA scientists want information about the moon鈥檚 internal composition to confirm the theory that it was created when an ancient planet crashed into the Earth.
They will also use an infrared spectrometer to probe dark areas, such as the poles and small craters, which are cold enough to perhaps contain ice. And they will check out areas high enough to catch the sun, where permanent solar panels could one day be placed to power a moon station.