Europe Approaches Moon

SMART-1, a tiny testbed of revolutionary technology, was successfully captured by the Moon's gravity on Monday, ESA's director of science, David Southwood, said in a teleconference from mission control in Darmstadt, western Germany.

"Our small genius is... at the Moon," a delighted Southwood declared.

The probe achieved lunar orbit at 17:53 GMT on Monday, and on Tuesday was looping the Moon at a height of 5,000-6000 kilometers (3,000-3,500 miles), SMART-1 Project Manager Giuseppe Racca said.

SMART-1 will gently spiral closer to the lunar surface, eventually stabilizing in an egg-shaped polar orbit that will vary from 300 kilometers (187 miles) at the South Pole to 3,000 kilometers (1,870 miles) at the North Pole.

The 370-kilo (814-pound) probe has been using a slow but revolutionary form of propulsion, taking it in ever-widening circles around the Earth and using terrestrial gravity as a slingshot, to get to the Moon.

It is powered by an ion engine, which converts solar power into electricity that then charges atoms of the heavy gas xenon.

These charged atoms, known as ions, are then disgorged from the back of the probe to give it thrust.

Slow, but persistent

The motor is initially slow -- launched on Sept. 27, 2003, SMART-1 took more than 13 months to make a trip achieved in three days by the chemical rockets of the Apollo era -- but speed gradually builds up in the frictionless environment of space, making ion power ideal for trips into the depths of the Solar System.

SMART-1 (photo) clocked up 332 orbits around Earth and travelled more than 84 million kilometers (52.5 million miles), "a distance comparable to an interplanetary cruise," ESA pointed out in a press statement.

It fired its engines 289 times, operating them for a total of about 3,700 hours, and sipped just 59 kilos (129.8 pounds) of its 80 kilos (176 pounds) of xenon gas. Space rockets typically carry tonnes of chemical fuel, which thus crimps the size of the payload.

So much fuel has been saved that SMART-1 will be placed in a closer approach to the Moon for the scientific phase of the mission.

"The performance [of the motor] has been better than we expected," said Giorgio Saccoccia, head of ESA Propulsion Division. "We would certainly want to have it onboard in the future."

It is only the second time that ion propulsion has been used as a space mission's primary propulsion system. The first was NASA's Deep Space 1 probe, launched in October 1998.

Scanning the Moon

After achieving its final orbit on Jan. 13, 2005, SMART-1 will start a six-month scan of the Moon, using a big payload of sensors that are also a test bench of miniaturization.

One of the spacecraft's tasks is to check out hopes that deep craters near the Moon's poles may harbour water ice, a discovery that would be a huge boost for setting up a human settlement.

And it will also explore theories as to the origin of the Moon.

The prevailing notion is that the Moon was born from the Earth -- a mass of terrestrial mantle that was smashed away when Earth was hit by a Mars-sized object in the infancy of the Solar System.

This mass of rock and debris then re-condensed to become Earth's satellite, according to this theory.

"With our X-ray eyes, we want to trace the Moon's beginnings," said Bernard Foing, SMART-1 project scientist.

Much is already known about the Moon, thanks to robot craft and the manned US missions of the early Sixties and Seventies, but scientists say there are also many unknowns.

SMART-1 is the first in a flotilla of unmanned probes to Earth's companion. Missions have been planned in the coming years by China, India, Japan and the United States.