As repair nears, scientists say Hubble achievements already shine

November 15, 1993|By Frank D. Roylance | Frank D. Roylance,Staff Writer

At first, the most costly and audacious telescope ever built just seemed a bit out of focus.

But no matter how handlers of the orbiting Hubble Space Telescope tweaked its mirrors by remote control, they could not sharpen the smeary stars on their video screens.

In June 1990, stunned scientists were forced to admit that their $1.5 billion telescope's 94-inch primary mirror had been ground too flat. A repair mission scheduled for 1993 would be the first chance for astronauts to attempt to fix the problem.

Today -- 2 1/2 weeks before that $251 million repair mission is to be launched -- much of the universe remains beyond Hubble's reach.

But clever manipulation of the instrument and its data has produced a steady stream of important discoveries. More than 290 Hubble-based scientific papers have been published around the world, and 40 more are pending. They dominate many international astronomical conferences.

Hubble has watched swirling weather systems on Mars, Jupiter and Saturn. It has used its unmatched sensitivity to ultraviolet light to peer deep into the hottest, most violent places in the universe. It has photographed galaxies where stars appear to be drawn down the throat of a black hole, and it has begun the work of calibrating the yardsticks used to measure the size and age of the universe.

Astronauts on the shuttle Endeavour will attempt to restore the full promise of Hubble's science by replacing its Wide Field/Planetary Camera with an upgraded version that has devices to correct for the mirror flaw.

They also will deliver new solar panels, gyroscopes and other gear. And they will replace the High Speed Photometer, which measures rapid variations in starlight, with COSTAR -- a phone-booth-size package of lenses and mirrors to correct the effect of the mirror flaw on three other instruments.

Dr. James Crocker, COSTAR project manager at the Space Telescope Science Institute in Baltimore, said a repaired Hubble will see "as good or perhaps even better" than the original design. "We have some adjustment capabilities that would not have been on the original instrument."

Astrophysicist Francesco Paresci, also of the space telescope institute, said his biggest worry is not whether the new hardware will function, but whether the astronauts will get all their work done.

Hubble "was designed to be fixed in orbit," he said. "If it isn't doable, we've got real problems, not just with the space telescope, but with everything else that follows."

It will take three months to calibrate the newly installed instruments. Only then will astronomers at the institute be sure the repairs have been successful.

If they are, "I don't think we will have lost anything" from Hubble's science mission, Dr. Crocker said. "In 15 years," he said, "if we do everything from here forward correctly, you wouldn't be able to tell we had this problem, other than some reordered observations."

That would obliterate the gloom of June 1990.

"We were basically, I would say, devastated," Dr. Paresci, 53, said of that dark summer. His own plans to search for planets orbiting distant stars depended on razor-sharp focus.

Without it, he said, "it would be like looking at our solar system and not being able to see anything inside the orbit of Pluto," which is usually the farthest planet from the sun.

Hundreds of other proposals to study very dim objects, from the Earth's solar system to the farthest reaches of space, seemed doomed.

In their initial distress, astronomers say, they probably contributed to Hubble's public black eye as the billion-dollar telescope that couldn't see straight.

"The scientists rushed out expressing great disappointment without fully understanding what we had and didn't have," Dr. Crocker said. It took a month to realize that their telescope was not crippled by hopelessly "fuzzy" images.

Pulling out a large pad of paper, Dr. Crocker sought to explain.

If Hubble were perfect, light from a star would fall onto its light detectors like grains of sand, piling up like a very tall, thin mountain peak. For astronomers, a thin peak means lots of sharp detail; a tall one means plenty of light from faint objects.

But the flaw built into Hubble's primary mirror because of a testing error diverts some of the starlight. The falling "sand" builds a jumble of "foothills" around the central peak and reduces its height. Target stars appear dimmer, with confusing halos. Faint objects can't be seen.

"It took a while for people to realize what was going on here," Dr. Crocker said. But they soon understood that by digitally subtracting the "foothills" from below the "peaks," they could reveal an image that was dimmer, but packed with information.

"What we have is a loss of sensitivity," Dr. Crocker said. "We got the exquisite [data] we were looking for, but it's just very faint."

The telescope's ability to "see" ultraviolet wavelengths has been a boon. On Earth, telescopes can't see ultraviolet light.

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