CAPE CANAVERAL. Fla.-As the space shuttle Columbia poised on its launch pad yesterday, its commander, John W. Young, and pilot, Robert L. Crippen, relaxed by cruising in T-38 jets before a last sleep, and 4800 members of the press awarded like Caps mosquitos to the media site three-and-a-half mils down-range from Columbia.

Facing a grandstand full of reporters in the shadow of the 12-story Vehicle Assemble Building, officials from the National Aeronaities and Space Administration (NASA) and veteran astronauts responded to the media's occasionally critical pelts with down-home confidents.

Dke Slayton and his NASA coileagues answered the pointed questions, calmly assuring an Australian journalist that Columbia's external fuel tank would not crash and burn outside of Perth, like Skylab two years ago, and responding to a New York journalist by saying. "We are very confident in the crew's training and in the overwhelming likelihood for success."

Taking the pessimism and "what-if" of the press in stride, Slayton reminded everyone. "This is not our first time in space. We've done it before and our crew is at the peak of its training."

"There's always a risk," Slayton acknowledged as reporters pressed around him. "There's a risk standing on this stage. It may collapse."

Slayton, selected as one of the original seven astronauts for the Mercury program in 1959 but forced by a heart murmur to wait until he commanded the 1975 Apollo-Soyuz mission, was asked if he still hoped of returning. "Hell, yes, I wouldn't be here if I didn't," he replied.

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This last news conference before the launch was all smiles, all optimism and all NASA. In other press conferences, journalists in the audience ask questions that sometimes get answered, but at Cape Canaveral moderator Hugh Harris says. "I think we've had enough questions from here now. Let's go to the Johnson Space Center in Houston." A question from Houston.

"Now to the Marshal Space Flight Center in Huntsville, Alabama." Well? "No questions from Marshal. Stand by Washington."

"Do we have any questions from Washington?" Not a one. And none from DFRC--Dryden Flight Research Center in California--either, but NASA gave them a chance. Harris turns back to the assembled multitude in the grandstand.

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"Next?"

A launch wouldn't be a launch without television. CBS and NBC reopened the old studio shacks they had used during the glory days. ABC, which had closed its down, had to build a new one. But the ABC structure--complete with studio and panoramic plate-glass windows for viewing the launch--was installed backwards. It faced not pad 39A, from which the shuttle blasts off, but a swamp. So ABC had to call a crane to turn the entire two-story pine box around.

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To William Numeroff, who has painted portraits of 140 astronauts, NASA technicians and administrative leaders since the flight of Alan Shephard in 1959, the blast-off of Columbia "signals a new era of space travel."