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Shuttle Ready for Second Try at Launch Today

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Times Staff Writer

Space agency officials said preparations were proceeding smoothly for NASA’s second attempt this month to launch the space shuttle Challenger, which today was to begin its seven-day mission to conduct a series of astronomical and atmospheric experiments.

“We’ve got a green light for launch,” shuttle program director Jesse W. Moore said of the scheduled liftoff at 12:23 p.m. PDT. “This mission, I think, is going to yield an enormous amount of science to the program.”

No weather problems were predicted for the space center, but storms were reported in the vicinity of two emergency landing sites in Spain. Such sites are necessary in the event of engine failure before the shuttle achieves orbit, and clouds and poor visibility there could delay the launch.

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Computer Fails

Scientists reported only one problem at the space center, the failure of a computer aboard the craft that was scheduled to control some of the scientific gear and store data. A backup computer was assigned to handle those tasks.

Should the backup computer also fail, officials here say the costly mission would be greatly jeopardized. However, they said, some of the work could be completed by using a third computer.

On July 12, the Challenger’s first launch procedure was halted just three seconds before liftoff, after the engines were already firing, when a computer sensed a malfunction. The dramatic shutdown was the second time a shuttle has aborted a mission after the engines were started. Last summer, a launch was stopped four seconds before blastoff.

If the liftoff proceeds as planned today, a crew of seven led by Air Force Col. Gordon Fullerton will perform a complex array of scientific experiments involving the sun and the Earth’s ionosphere.

Around-the-Clock Work

The crew will work 24 hours a day in two 12-hour shifts to complete the studies. Scientists say they hope that the solar observations will give them clues about the relationship between the sun and weather on the Earth.

The ionospheric studies will seek to reveal details about the little-understood region of the Earth’s upper atmosphere, which protects the planet from most of the sun’s dangerous radiation.

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In the 2 1/2 weeks since the launch failure, engineers from the National Aeronautics and Space Administration have carried out many tests seeking to find the cause of the problem.

Initially, the engineers blamed a faulty valve feeding hydrogen to one of the shuttle’s three liquid-fueled engines. Those engines are separate from the huge, solid-fueled booster rockets that provide most of the thrust for the ascent.

Valve Was Working

Over the weekend, however, NASA officials said the problem may lie with the instructions given to the computer. An analysis has shown that the valve was working, albeit slowly, they said.

The response of such valves is measured in milliseconds--or thousandths of a second--by the computer, and, if the valve does not react quickly enough, the computer signals a failure.

Shuttle program director Moore said such rejection may occur too quickly, responding to sluggish behavior rather than true failure.

“We’re going to be looking at what we can do to relieve our tolerances in there,” Moore said.

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The computer now throws the switch if a valve varies by as little as 6% from its designated position.

A decision on a change in the computer’s instruction will be made later this year and will not affect today’s launch, NASA officials said. Such a change would not lower the agency’s safety standards, Moore said.

Pressure on NASA

Nonetheless, agency officials concede that they are under some pressure to demonstrate that the shuttle program can launch projects reliably and on schedule. The aborted launch earlier this month already has caused the postponement of two other missions scheduled for later this year.

Tight Schedule

Should the Challenger again fail to lift off, NASA probably would cancel this mission rather than postpone it, to avoid further erosion of the agency’s tight schedule.

The Challenger’s mission, Spacelab 2, is a joint project of NASA and the European Space Agency. The European consortium designed and built most of the $72 million worth of scientific gear aboard the craft.

In addition to Fullerton, members of the shuttle crew are Col. Roy D. Bridges Jr., the pilot; F. Story Musgrave, a NASA medical researcher; Anthony England, a NASA geophysicist; Karl Henize, a NASA astronomer; John-David Bartoe, an astrophysicist with the Naval Research Laboratory, and Loren W. Acton, an astronomer with Lockheed Corp.

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