Two days after the fraught return to Earth of the space shuttle Discovery, Nasa has been forced to delay the launch of a spacecraft designed to gather unprecedented amounts of information about Mars.

With just minutes to go before the scheduled launch of the Mars Reconnaissance Orbiter today for a mission due to last at least four years, a Nasa official said: "We have scrubbed for at least 24 hours."

The mission was postponed after a glitch appeared in the computer software used for monitoring the fuelling of the rocket used for lift-off from Cape Canaveral. Nasa had already postponed the launch by a day because of a potential problem with a part of the flight control system.

The Mars Reconnaissance Orbiter is expected to spend at least four years circling the Red Planet, collecting more raw data than all previous Martian missions combined.

That information will help Nasa plan where to land two robotic explorers this decade: the Phoenix Mars Scout will be launched in 2007 to search for organic chemicals and the Mars Science Laboratory will follow two years later.

The information gathered by the orbiter also will aid possible future human exploration of Mars. "We don’t want to be hauling cement to Mars. That’s very expensive," said Richard Zurek, a project scientist at the Jet Propulsion Laboratory in Pasadena, California. "Better to know what we can make on the surface of the planet."

Thunderstoms early this morning pushed lift-off time back by an hour but the weather improved and Nasa workers began fuelling the rocket - at which point the software glitch was noticed.

The two-tonne orbiter, equipped with the largest telescopic camera ever sent to another planet, will relay information on Mars’s weather, climate and geology.

The $720 million (£399 million) mission is also expected to help build on Nasa's knowledge of the history of ice on the planet, possibly providing valuable points to climate change on Earth.

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

"With the subsurface of Mars, we’ve literally just scratched the surface and we’re trying to probe, now, more than a couple of feet into it," Mr Zurek said.

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, providing information on water on Mars.

With more instruments and higher-resolution imagery, the larger Mars Reconnaissance Orbiter will be able to offer a more comprehensive sweep of the planet. Its powerful antenna can transmit ten times more data than the current trio of satellites positioned around the planet - Nasa's Global Surveyor and Mars Odyssey and the European Space Agency’s Mars Express.

The orbiter is also loaded with two cameras that will provide high-resolution images and global maps of Martian weather, a spectrometer that will identify water-related minerals and a radiometer to measure atmospheric dust. The Italian Space Agency has provided ground-penetrating radar that will peer beneath the surface of layers of rocks or ice.

"They’re bringing their data back, we think, through a straw," Mr Graf said of the current orbiters. "We’re going to start opening up the fire hose. ... We’re going to be awash in data that will allow us to better understand the planet as a whole."

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