Just 1 Little Slip And Project Was Ruined

The Telescope Teases Scientists With Pictures But Can't Show Them What They Want Most To See.

November 28, 1993|By Shirish Date of The Sentinel Staff

CAPE CANAVERAL — The very foundation of our understanding of the universe was supposed to be shaken and rebuilt three summers ago.

But an error of 50 millionths of an inch prevented us from seeing billions of light years across the cosmos, where new answers to fundamental questions are thought to be waiting.

Instead of finding those answers, the $1.5 billion Hubble Space Telescope was left with blurred vision because of a polishing error.

Now it's the telescope that must be rebuilt, while floating in orbit, because the powerful instrument was launched in April 1990 before the mistake was discovered.

''It was close to almost a disbelief, you know? How in the world could this have happened?'' astronomer and NASA astronaut Jeff Hoffman said recently.

Hubble's 8-foot-diameter primary mirror - billed as the most perfect piece of optics ever made - turned out to have a fatal flaw. During the polishing process, a calibrating tool was used incorrectly.

Its surface was left with a uniform ''spherical aberration'' of about 50 millionths of an inch - a tiny fraction of the thickness of a human hair.

The imperfection left Hubble nearsighted. The pictures most sought by astronomers - of the faintest objects at the farthest edges of the universe - come back distorted and scientifically useless.

For example, a photo taken by Hubble two years ago revealed a bright, doughnut-like shape at the heart of a star cluster. The image, much sharper than any ground-based telescope could have produced, could be an ''accretion disk'' of matter swirling into the still-unproven phenomenon known as a black hole.

But it remains only the theory, because Hubble, while able to produce a pretty picture, wasn't able to resolve, or form separate images of, any stars that appear to be revolving around the suspected black hole.

Scientists must be able to distinguish the stars individually to determine their speed. That, in turn, would allow them to calculate the mass of the hidden object in the center and help them decide if it's a black hole.

''All the things that astronomers do to figure out the physics of what is really going on out there, we just can't do those things now,'' Hoffman said. ''Eighty percent of the Priority 1 research projects were put on hold until we can fix the optics.''

Hubble is scheduled to get two new instruments during NASA's upcoming repair mission.

The Wide-Field and Planetary Camera, an upgraded version of the one already in the telescope, has dime-sized corrective mirrors to offset the errors in the main mirror. The Corrective Optics Space Telescope Axial Replacement was built specifically to correct the polishing error for the telescope's other instruments.

With the new parts in place, Hubble's vision will be 10 to 15 times better than it is now, program manager Ed Weiler said.

That would leave NASA with a telescope 70 percent as powerful as the one it was supposed to get before the flaw, Weiler said - good enough to conduct the kind of research that could answer basic questions about the age of the universe and whether it will expand forever, or eventually stop and contract.

Fixing the telescope's flaw will cost taxpayers $140 million for the two corrective instruments and $500 million for the shuttle flight itself.

Weiler, NASA's point man for handling the mistake, is eager to test the new equipment.

''Believe me, after three years of spherical aberration, I can't wait to get up there and tell you the telescope is fixed,'' he said.

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