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NASA AIMS TO GET CLEAR PICTURE OF DEFECT BLURRING HUBBLE VISION

NASA will call on experts to investigate an apparent manufacturing mistake that impaired the vision of the $1.6 billion Hubble Space Telescope and blurred what might have been the sharpest pictures ever of the universe.

National Aeronautics and Space Administration officials in Washington announced plans for the review after scientists, unable to focus a European-built faint-object camera by remote control, concluded that one of the telescope's two mirrors was deformed.

The defect virtually will eliminate the use of a key camera and halt about half of all the telescope's planned scientific work until a shuttle crew can go back to the Hubble and make repairs in 1993.

The NASA investigation of the mirrors' construction records is intended to find out who made the mistake. Disappointed scientists and engineers are scrambling to find ways to minimize the impact of the problem aboard the orbiting observatory, which, with its ground facilities in Greenbelt, Md., and Baltimore, has cost taxpayers $2.6 billion so far.

"Where we suspect the problem happened is in the technique used to measure and polish the mirrors," said Jean Olivier, deputy project manager for the telescope at Marshall Space Flight Center. "Somewhere in this complicated chain of events, there was a mistake made" in one of the two mirrors. "It was done carefully, and it was done to the wrong figure," or curvature.

The built-in flaw gives the Hubble a serious case of blurred vision. Two onboard cameras -- the workhorse Wide Field and Planetary Camera, and the European-built Faint Objects Camera, designed to take pictures in visible light -- are the most seriously affected. Four other instruments that study the heavens by gathering ultraviolet light or that for other reasons do not depend heavily on crisp, clean visible images will suffer less, officials said.

Olivier said the Hubble mirrors were tested individually on the ground but never as a combination because that would have cost "hundreds of millions of dollars."

A second generation of instruments already was being built for the Hubble, and engineers say they can be outfitted with the equivalent of prescription glasses to compensate for the defect, the same way glasses correct nearsightedness, said Ed Weiler, NASA's chief Hubble astronomer. Hubble's "glasses" will consist of adjustments in the shapes of small mirrors used to route the telescope's light rays into cameras.

Those instruments are scheduled to be installed by shuttle astronauts on missions now scheduled for 1993, 1996 and 1997. Officials said they are looking into the possibility of advancing the schedule.

"We are not losing science," Weiler said. "We are deferring science."

Engineers also plan to use actuators, or mechanical devices on the primary mirror, to change its shape slightly, but they said that only will counteract "a small fraction" of the defect.

For the short term, Weiler said, "The important question is, 'Can we still do unique and important science?' The answer is an emphatic yes."

But he acknowledged that Hubble scientists, many of whom have spent 12 or more years developing instruments for the project, are frustrated and unhappy.

The Hubble specifications had called for the mirrors to focus 70 percent of a star's light at a precise point within the telescope. "We are now getting about 20 to 25 percent, so we're a factor of 3 1/2 off," Weiler said. That is about the equivalent of what ground-based telescopes can do.

A primary claim for the Hubble was that it would provide unprecedented clarity in its images of the heavens. Its heart is its primary mirror, often described as the most optically precise large mirror ever built. It and the smaller secondary mirror were built by the Perkin-Elmer Corp., now Hughes Danbury Optical Systems of Danbury, Conn., a subsidiary of Hughes Aircraft Corp.

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