The first solo European mission to the Moon is well on its way.
The Smart 1 probe blasted off from the Kourou spaceport in French Guiana at 2314 GMT.
Forty-two minutes later, ground controllers said the spacecraft had been released successfully from its Ariane 5 rocket launcher and was on its correct course.
Smart 1 will test a novel type of propulsion system on its journey to the Moon and then map the lunar body's surface features when it arrives in 2005.
"Just because the astronauts went to the Moon doesn't mean they found out everything there is to find out," said Professor David Southwood, the head of science at the European Space Agency.
The unmanned Smart 1 craft will look for water on the Moon. The probe will also gather precise data on its chemical make-up.
This information should confirm the theory that the Moon was created in a collision between Earth and another object not long after our Solar System came into being.
Two communications spacecraft were launched with Smart 1 - an Indian TV satellite, and a broadband internet platform for Europe.
Smart - short for Small Missions for Advanced Research and Technology - is Europe's first attempt at a solo Moon mission.
It is a technology demonstrator and has been built in a short time and very cheaply.
GIANT IMPACT THEORY
Suggests Mars-sized object crashed into early Earth
Debris thrown into space aggregated into the Moon
Supported by similar composition of Earth and Moon rocks
The total bill has come to just 110 million euro (£76m), including launch fees.
This has been achieved partly by using new management methods but also by using novel techniques of miniaturisation and design.
At only a metre square in size and weighing just 367 kilograms, it could almost be a space toy.
But Smart is packed with kit that will change the nature of future high-budget missions from Europe.
Of major interest is the solar-electric propulsion system that will push Smart towards the Moon.
The engine works by expelling a beam of charged xenon atoms - ions - out of the back of the probe.
This produces a thrust in the opposite direction and pushes the spacecraft forward.
The experimental engine is scheduled to be switched on on Tuesday.
The energy to feed the system comes from the solar panels, hence the term "solar-electric".
Ion drives do not produce the sudden burst of forward momentum you get from a chemical rocket. But over the long-term they are considerably more efficient and many future probes will use them.
Ion drives accelerate slower than chemical rockets
Scientists have been developing ion-drives for decades but it is only recently that they have been used in real space applications.
This is principally because new developments in photocell technology have greatly improved the effectiveness of spacecraft solar wings.
The 1998 US probe Deep Space 1 flew with an ion drive, and there is a European satellite, Artemis, that maintains its orbit with one.
Nevertheless, over short distances, ion drives are quite slow. Smart will take 15 months to reach its target.
"We will spiral out progressively ...up to the point where we will start to feel the attraction of the Moon," said Dr Bernard Foing, Smart 1 Project Scientist.
"Further, we will have a spiral down, to be closer to the Moon, and then we will reach the final science orbit, from where we can do all the observations that we want to take."
And that is where some of the new miniaturised instruments will come into play.
One of them, D-Cixs, a UK contribution to the project, developed at the Rutherton Appleton laboratory in Oxfordshire, will make the most comprehensive inventory of key chemical elements in the lunar surface.
"We think we know what the Moon is made of because the Apollo astronauts went there and brought back half a tonne of rock samples.
"But they went to the Earth side, on the equator and on the flat bits," said Professor Manuel Grande, on the instrument team.
"Those areas aren't typical and, importantly, they're not the ancient ones. What we need to do is a global survey of what the Moon is made of - and Smart 1 with our X-ray spectrometer will do that."
This information will help scientists confirm the favoured theory for the Moon's creation - that it formed out of the debris kicked up in a collision between Earth and a Mars-sized body about four and a half billion years ago.
If this is correct, D-Cixs should find that the Moon contains less iron than the Earth, in proportion to lighter elements such as magnesium and aluminium.
Smart will cut a technological path for other probes to follow
If all goes well, many of Smart's technologies - particularly its communication, navigation and propulsion systems - should find their way on to the next generation of European spacecraft.
The Bepi-Colombo mission to Mercury, for example, which should launch at the end of this decade, is set to use an ion drive.
Dr Foing said: "The goal is to get more knowledge about the universe, about the solar system, and to educate the public about our origins, about scientific challenges.
"It's also to challenge new technologies, which later will have a spin-off for the daily life of our citizens."
HOW SMART 1'S ION DRIVE ENGINE WORKS
1. Xenon gas atoms are pumped into a cylindrical chamber, where they collide with electrons from the cathode. The electrons - which are negatively charged - knock electrons off the Xenon atoms, creating Xenon ions - which are positively charged.
2. Coils outside the chamber create a magnetic field, which causes electrons from the cathode to spiral and become trapped at the mouth of the chamber.
3. The build-up of negatively-charged electrons at the mouth of the chamber attracts the positively-charged ions, accelerating them out of the chamber.
4. The stream of accelerated ions leaving the chamber thrusts the spacecraft forward. Although the force is small, over time it creates great speed in the frictionless environment of space.