SMART-1 "is in excellent health and preparing for the manoeuvres that will bring it into orbit around the Moon mid-November," an ESA press statement said.

The unmanned probe carries a 19-kilo (42-pound) payload of seven scientific instruments for remote scanning of the lunar surface and environment.

Its biggest innovation is an ion engine, a kind of solar-powered thruster that is 10 times more energy-efficient than the usual chemical systems used in space travel.

With small periods of thrust, the engine has operated for about 3,300 hours and covered some 78 million kilometers (49 million miles), with only 52 kilos (114 pounds) of propellant, ESA said.

Solar-electric propulsion does not burn fuel as chemical rockets do; instead solar panels convert sunlight into electricity and uses it to electrically charge heavy gas atoms, which are then spat out of the spacecraft at high speed.

In a chemical rocket, the burning fuel creates gases which are expelled relatively slowly compared to ion thrusters. However, in an ion engine, the gas is ejected at high velocity, thus providing more thrust for less energy.

If the prototype works, the system could provide the propulsion system for future deep-space missions.

SMART-1 was launched by a European Ariane-5 rocket on September 27 last year, the first in a series of small projects aimed at testing promising technologies.

Its remote exploration of the Moon aims at filling in gaps in knowledge about Earth's satellite, particularly areas that may hold out lingering hopes of ice.

Any water on the lunar surface would be a boon for any future permanent base.

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