If weather allows, the first Mars Expedition Rover is to be launched aboard a Boeing-made Delta II launcher at 2:02 pm (1802 GMT) Monday from Cape Canaveral, Florida, space officials said. A second attempt is scheduled for 38 minutes later if needed.

The spacecraft is to traverse some 500 million kilometers (300 million miles) over seven months, then drop into the Gusev crater, 15 degrees south of the Martian equator, in early January 2004.

"This will continue NASA's long goal of finding the water. On Earth, wherever we find water, we find life. There was water on Mars billions of years ago and maybe just a few hours ago," said Ed Weiler, associate administrator for space science for NASA.

The US space agency, which has chalked up two costly failures in its quest to explore Mars in recent years, warned that the task would not be easy.

"It's not a trip to the beach on a Sunday afternoon," Weiler said.

"We can have a bad day on Mars. Wind. Bad weather. We are trying to predict the weather on Mars for January 2004."

Of 30 attempted Mars missions over the past 40 years, just 12 have succeeded, he said.

The US spacecraft will be competing in the search for Martian life with a European rival already in space. Europe's Mars Express left Monday and is scheduled to finish its trip a few days before the first US spacecraft arrives.

The rivals launched their missions so close together because Mars is now at its closest position to the Earth, an event that occurs just once every 26 months.

The National Aeronautics and Space Administration is spending 800 million dollars to get this mission right.

It aims to overcome the disappointment of the Orbiter, which took off in December 1998 and disappeared on arrival, as well as the Polar Lander rocket, which crashed into the planet in 1999 when its landing system broke down.

A US Viking probe was the first vehicle to land on Mars in 1976. In the 1997 US Pathfinder mission, a small robot roamed the planet's surface to gather information.

This time, NASA has decided to revert to its Pathfinder landing system, which uses parachutes and air bags to slow down the spacecraft and cushion the impact.

Each vessel will bounce about 10 times on the Martian surface before coming to a standstill.

The two six-wheeled robots will be put out on the opposite sides of Mars and go about for three months collecting geological samples.

Powered by solar energy, the robots will be able to move 40 metersfeet) each Martian day, as much as during the whole Pathfinder mission in 1997.

The MER robot has a telescopic arm including a camera which will be able to take 360-degree color images. It also has equipment to scratch and dig into the surface.

A squad of 150 scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, will gather data transmitted by the robots to Earth via two US satellites in orbit around Mars: the Global Surveyor and Odyssey probes.

The data will help scientists on Earth decide the robots' route on Mars for the following day.

Water in its liquid form is not a feature of the Martian surface but topography that seems in part to have been crisscrossed by running water has led many researchers to believe it may have been there in the past.

SPACE.WIRE