The ESA is gearing up for the end of the mission of its first spacecraft towards the Moon. SMART-1 was launched on September 27, 2003, and it reached the Moon in November 2004 after a long spiralling around Earth. So far, the mission has been a success and will end in a dramatic fashion.
Initially planned to last 6 months, the SMART-1 mission got a one year extension and further studies were completed. Now the delay is over and the spaceship will be a tool for one last experiment. Since the spacecraft is trapped by the Moon’s gravity, it will come down crashing on the Moon on September 3rd. The last bits of propellant were used to boost the orbit of SMART-1, giving it that one year extension. Out of xenon propellant, SMART-1 used its hydrazine thrusters to perform the last major manoeuvre at the end of June 2006 to further stretch the mission lifetime and win three more weeks of operations.
SMART-1 first contribution was to show that its ion engine could be used efficiently for interplanetary travel (assisted by gravity slingshots). To cover the 385,000 km distance that separates the Earth from the Moon if one travelled in a straight line, this remarkably efficient engine brought the spacecraft on a 100 million km long spiralling journey on only 60 litres of fuel!
SMART-1 also tested future deep-space communication techniques for spacecraft, techniques to achieve autonomous spacecraft navigation, and miniaturised scientific instruments, used for the first time around the Moon. Also, a small instrument on the satellite as shown the first detection from orbit of calcium on the Moon. This could help scientists determine if the Moon form from part of the Earth.
The last observations before impact will provide new impressions of the lunar landscapes.
During close lunar approaches, the AMIE camera on board SMART-1 will have oblique views of some areas that we have previously looked at only vertically, providing a sort of 3-dimensional view of the surface. However, as the impact will occur in a dark area of the Moon, it is not possible to expect to see very much by visible light during the final descent.
During the last orbits, the other instruments on-board, including the D-CIXS X-ray telescope and the SIR infrared spectrometer, will have detailed views of some lunar regions from very low altitudes.
Powerful telescopes on the Earth may see a faint flash from the impact itself, followed by a cloud of dust thrown up by the impact, perhaps 5 kilometres wide. The dust will obscure the view of part of the Moon’s surface for 5 or 10 minutes. The behaviour of the cloud will give valuable information about impact events in general, while the analysis of the light from the dust, with spectrographs in the telescopes, may detect materials dug up by the impact from just beneath the lunar surface.
The observations will rely on the faint glow of earthshine – unless some of the dust cloud is thrown more than 20 kilometres above the lunar surface. In that case, it will be lit directly by sunlight and will appear far brighter for perhaps a few minutes. Amateur astronomers may be able to spot the sunlit dust cloud with their binoculars and small telescopes.