The SMART-1 satellite has sent back its first close-range images of the Moon. The pictures were taken from an altitude of between 1,000 and 5,000 kilometres above the lunar surface. The pictures clearly show the Moon's craters, and the visible illumination angles are allowing scientists to establish the height of the crater rims. SMART-1 spent two months spiralling down towards the moon and testing its instruments before taking the pictures. There had been a risk of crashing into the Moon's surface as the craft was in an unstable trajectory and could have escaped the lunar orbit. The capture was therefore stabilised with the craft's electric propulsion system, or 'ion engine'.