The spacecraft is designed to gather more data on the planet than all previous Martian missions combined.

A glitch in computer software and sensors that monitor the fuelling of a rocket used during lift-off forced the space agency to scrub its first attempt to launch the Mars Reconnaissance Orbiter on Thursday.

Nasa officials could not explain why the sensors were reading "dry" when other data showed that the rocket was being filled with propellant.

Before the problem arose, project manager Jim Graf of the Jet Propulsion Laboratory said the powerful Atlas V rocket, being used for the first time in an interplanetary mission, would be ready to go.

"It's just a thoroughbred waiting to break the bounds that's holding it back," Graf said. "Release the reins and let it get out ... into space."

The orbiter will provide unparalleled information on Mars' weather, climate and geology, which could aid possible future human exploration of the Red Planet.

Equipped with the largest telescopic camera ever sent to another planet, the orbiter is expected to spend at least four years circling Mars, collecting data that will help Nasa plan where to land two robotic explorers later this decade.

The Phoenix Mars Scout, in search of organic chemicals, will be launched in 2007, and the Mars Science Laboratory will follow two years later.

The $720 million mission is also expected to help build on Nasa's knowledge of the history of ice on the planet.

The planet is cold and dry with large caps of frozen water at its poles. But scientists think it was a wetter and possibly warmer place eons ago, conditions that might have been conducive to life. Scientists are also trying to determine if it could support future human outposts.

The orbiter will join three other spacecraft, including a European orbiter, when it arrives at the planet in March 2006.
Two Nasa rovers launched in 2003, Spirit and Opportunity, also continue to roam the planet.