NASA scrubbed the launch of its shuttle Atlantis Friday, just 31 seconds from scheduled liftoff.

On board when the postponement was announced were five astronauts and a space probe, Magellan, which the crew hoped to eject from the shuttle toward Venus - the cloud-shrouded planet that is an abiding mystery to scientists.Atlantis' countdown was five minutes behind schedule and ticking down toward a 12:29 p.m. MDT liftoff when it was interrupted at the T-minus 31-second mark because of temperature problems with main engine No. 1.

"We're out of `engine ready,' " a technician at the launch control center reported to launch director Robert Sieck.

NASA had only a 23-minute launch window for the day, and spokesman Hugh Harris said there would not be time to explore the problem and attempt a launch later in the window.

The scrub came at 2:30 p.m., six minutes after the window opened and 17 minutes after it would have closed. Harris said a recirculation pump problem had been indicated.

Atlantis and the space probe called Magellan were pronounced trouble-free until the 31-second mark, disappointing tens of thousands of spectators and many scientists who have long looked forward to the planetary mission that will follow Atlantis' flight.

Lennard Fisk, NASA's chief scientist, said the mission of the explorer craft Magellan would mark "a resurgence of America's planetary program." The last American probe to deep space was dispatched in 1978.

A number of American and foreign dignitaries were on hand for Atlantis' launch, including Russian researchers, who will help analyze the radar data from Magellan, and Igor Volk, the chief test pilot of the Soviet space shuttle Buran, which has yet to make a manned flight.

The cosmonaut's presence is believed to mark the first time a Soviet space explorer has been invited to witness an American shuttle launch.

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Shuttle flight data

Here, at a glance, are the facts and figures about the 29th space shuttle flight:

Spaceship: Atlantis, on its fourth flight.

Launch: Between 12:24 p.m. and 12:47 p.m. MDT today.

Orbit: 184 miles above Earth.

Landing: At Edwards Air Force Base, Calif., scheduled for Tuesday.

Crew: Navy Capt. David M. Walker, 44, commander; Air Force Col. Ronald J. Grabe, 43, pilot; Mary L. Cleave, 42; Norman E. Thagard, 45, and Air Force Maj. Mark C. Lee, 36.

Major goal: In the first space shuttle planetary mission, the crew is to propel the Magellan spacecraft on a 450-day journey to orbit and map the planet Venus.

Next mission: Columbia in August with a classified Defense Department payload.