NASA's Mars Reconnaissance Orbiter (MRO) set off on an Atlas V rocket from the Kennedy Space Center in Florida. The liftoff had been postponed on Wednesday and Thursday because of problems with the rocket.

The mission, which is costing more than 700 million dollars, left three days after the space shuttle Discovery returned to Earth.

But the space agency said the MRO liftoff went well. The booster rocket shut down on schedule and fell into the Atlantic Ocean soon after the launch and the second-stage rocket engine ignited to take the orbiter on the next stage of its seven month trip to Mars.

The MRO will go into a low level orbit of Mars armed with an array of powerful cameras, monitoring and transmission equipment to search for signs of water on the Red Planet and help pick sites for possible landings in the future.

While scientists know that water existed on Mars, with oceans spread across the planet several billion years ago, they do not know if there was life.

"Dramatic discoveries ... about recent gullies, near-surface permafrost and ancient surface water have given us a new Mars in the past few years," said NASA's Mars exploration chief scientist Michael Meyer.

"Learning more about what has happened to the water will focus searches for possible Martian life, past or present," he added.

"Mars Reconnaissance Orbiter is the next step in our ambitious exploration of Mars," Douglas McCuistion, director of NASA's Mars exploration programme, said earlier this week.

"We expect to use this spacecraft's eyes in the sky in coming years as our primary tools to identify and evaluate the best places for future missions to land," he added.

Learning about the history of water distribution is also expected to shed light on possible previous Martian life forms.

The MRO will use a spectrometer that can detect minerals linked to the existence of water, a radiometer that analyzes atmospheric dust, water vapor and temperature, and an Italian radar that can look under the ground to detect water.

NASA said the craft can transmit about 10 times as much data per minute as any previous vehicle, conveying details of the Martian surface, subsurface and climate.

One of the three cameras on the MRO is the largest-diameter telescopic camera ever sent to survey a planet.

A second camera will prepare high-resolution images and a third will draw up a Mars weather map. All the information will be sent back using the biggest antenna ever sent to Mars.

The MRO will join two American orbiters, the Mars Global Surveyor and Mars Odyssey, and one European orbiter, Mars Express, that are already looking for signs of water and ice.

NASA also has two robotic rovers on the surface of Mars and the MRO will also collect information from these to send back to Earth.

A Phoenix module, carrying a new lander, is to head for Mars in 2007, and a Mars Science Laboratory will follow in 2009.

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