By Helen Briggs BBC News Online science reporter

We'll do great science Prof Manuel Grande

The move was rubber stamped on Wednesday at a flight review at the European Space Agency's research centre in the Netherlands (Estec).

Smart 1 is currently in storage there but will be flown to the Kourou spaceport in French Guiana in the next few days.

"This is the go-ahead to pack the whole thing in a crate and send it to the launch site," says Manuel Grande, the leading British scientist on the project.

"All we have to do now is go to Kourou and light the blue touch paper."

Launch delay

The lunar probe should have left Earth in March but its take-off was put back following a failed rocket launch last December.

ION PROPULSION Uses electrical power provided by solar panels to accelerate a propellant to high velocity Smart 1 uses the propellant xenon, a colourless gas Electrons trapped inside a chamber by a magnetic field collide with xenon gas creating xenon ions and more electrons The resulting ion beam pushes the space craft forward The thrust produced is the same as the pressure exerted by a sheet of paper held in the palm of a hand Over long periods, it can make a space craft travel faster

The incident led to a shake-up of the Ariane 5 rocket programme and several Esa space missions were put on hold.

Smart 1 will be the first high-profile Ariane 5 launch since then. It will mark the beginning of a voyage to explore the cratered world we see every day from Earth.

The probe will map the composition of the Moon in an attempt to solve the mystery of how it was born.

It will also pave the way for travelling faster and further into deep space.

Smart 1 is using an innovative form of propulsion - an ion thruster - that will take it on a 15-month journey to the Moon.

The technology has been used only once before on an interplanetary mission by the US space agency (Nasa).

"This is Europe's first solar-powered space craft - it uses solar power instead of rocket fuel to get to the Moon," says Professor Grande, of the Rutherford Appleton Laboratory in Oxfordshire.

Faster, cheaper

Much of the technology used on Smart 1 will find its way on to Europe's Bepi-Colombo mission to Mercury which should launch at the end of this decade.

Once in orbit around the Earth's natural satellite, the craft will produce an X-ray map in an attempt to deduce precisely how the Moon was made.

One idea is that a Mars-sized object smashed into the juvenile Earth, flinging up debris which later merged to form the Moon.

If this actually happened, the Moon should contain less iron than the Earth, compared to lighter elements such as magnesium and aluminium.

By measuring the absolute amounts of these chemical elements comprehensively for the first time, Smart 1 should provide the answer.