The Smart 1 spacecraft has fired up its innovative solar-electric engine.
Mission controllers sent instructions to the lunar probe to start its ion drive as they checked out the health of all Smart's onboard systems.
The European spacecraft, which blasted off from French Guiana on Saturday, will take 15 months to reach the Moon.
When it arrives, Smart will use its miniaturised instruments to map the rocky body's chemical make-up to confirm theories about its creation.
The 110 million euro (£78m) spacecraft is Europe's first solo mission to the Moon.
The unmanned probe was put into its initial Earth orbit after a flawless launch on an Ariane 5 vehicle from the Kourou spaceport.
Now engineers at the European Space Agency's (Esa) operations centre in Darmstadt, Germany, are running tests on the probe's electronics and scientific instruments to make sure they survived the shaking they received as the Ariane hurtled skywards.
The ion drive was switched on at 1225 GMT on Tuesday.
"We took it at very low level to start with and then we stepped it up to full throttle," Mike McKay, the flight operations director for Smart 1, told BBC News Online.
"Then, after firing it for a while, we shut it down and analysed the data and it looks really good."
The commissioning of the probe will continue through the week before a longer firing on the drive pushes the probe out in earnest towards the Moon.
"Everything is good - batteries are looking good, the output from the solar panels is great and those instruments we've switched on so far seem absolutely fine."
The solar-electric engine on the 375-kilogram spacecraft is the mission's key feature.
If the engine can be shown to work well, it is likely to become a standard form of propulsion on many of the inter-planetary explorers built by Esa in the coming years.
The drive works by accelerating charged xenon gas atoms - ions - out of a chamber at speeds up to 16,000 km/hour. This gives Smart a tiny push - an acceleration of just 0.2 millimetres per second per second - in the opposite direction.
This might sound feeble but on very long journeys, this type of engine should prove considerably more efficient - and end up being much faster - than the conventional chemical rockets that currently provide probes with a sudden, short-lived burst of energy.
The Small Missions for Advanced Research in Technology (Smart) has novel navigation and communications technologies on board that should also find their way on to future deep space science missions.
In addition, its Advanced/Moon Micro-Imaging Experiment (Amie) miniaturised CCD camera will provide high-resolution imagery of the Moon's surface.
A compact infrared spectrometer will map lunar materials and look for water and carbon dioxide ice in permanently shadowed craters.
UK scientists are looking for a strong performance from the Demonstration Compact Imaging X-ray Spectrometer, which together with the X-ray Solar Monitor, should provide the most comprehensive data yet obtained on the Moon's precise chemical make-up.
Researchers believe this information will confirm their favoured theory for the creation of the Moon - that it formed out of the debris kicked off the Earth when our planet collided with a Mars-sized object four and a half billion years ago.
Smart should make its first flyby of the Moon in late December 2004, entering a settled polar orbit by March 2005.
Its ion drive will progressively work the probe closer to the lunar surface and give it a more circular orbit.
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.