Prescription Lenses Inserted to Focus Hubble

A floating physicist and a former high school principal fitted the myopic Hubble space telescope with $50 million worth of prescription lenses Tuesday night to put the finishing touch on optical repairs that should give the observatory its first clear view of the universe.

During the overnight spacewalk, mission specialist Kathryn C. Thornton, whose doctorate is in nuclear physics, and Thomas D. Akers, who once presided over his hometown high school, installed a 640-pound box of corrective mirrors designed to refocus the $1.5-billion telescope.

“Fingertip it,” Akers cautioned, as Thornton inched the freezer-sized instrument into the Hubble’s open service bay. “It couldn’t be in there any better. All indications are good.

“I think it is time to breathe a sigh of relief,” he said.

Once positioned, COSTAR, as the box is called, will automatically deploy a set of mechanical arms to position the mirrors where they can refocus the light falling into three of the telescope’s most important sensors. The mirrors, ranging in size from a dime to a quarter, were designed to unfold like a Swiss army knife in a space no larger than a generous slice of apple pie.

“The promise should be restored,” said COSTAR project scientist Holland Ford. “We will be able to push science to the very edge of space and time.”

The intricate procedure is the latest in a series of dramatic and demanding ventures outside the space shuttle Endeavour this week that have made NASA officials jubilant so far. Since Saturday, astronauts have given the Hubble more efficient solar-energy panels, refurbished its tracking system, and set up an advanced wide-field camera.

After a fifth spacewalk tonight, when they hope to tie up a number of loose ends--including installation of a new spectrometer and a computer processor--the astronauts expect to release the refurbished telescope back into orbit late Thursday.

Although preliminary tests by flight controllers show that the new equipment appears to be functioning properly, it will be six weeks or more before the first corrected images become available, and astronomers can be certain that the $629-million servicing mission has been worth the effort.

“You don’t measure success by installing things,” Edward J. Weiler, the Hubble chief scientist, said earlier Tuesday. “They have to work.”

When the last optical repair is finished Tuesday night, he said, “Will we be ecstatic? Of course. Will we party? No, we’ll wait.”

The caution was understandable. To collect the faint light from sources many trillions of miles away, the telescope’s original main mirror had to be almost perfectly smooth--more finely polished than any large mirror had ever been. Shortly after the Hubble was launched in April, 1990, however, scientists were shocked to discover that the primary mirror had been ground to the wrong prescription.

In October of this year, Perkin-Elmer Corp., the company that ground and polished the mirror, paid $25 million in damages, amid accusations that it deliberately ignored evidence of the problem before launch.

Even though they worried that their elation might be premature, NASA scientists Monday night could not restrain their applause when mission specialist Jeffrey A. Hoffman and payload commander F. Story Musgrave, working in almost total darkness to protect the telescope’s sensors, gently maneuvered the wedge-shaped Wide Field Planetary Camera into position and bolted it down.

The most critical task--the positioning of a palm-sized “pick-off” mirror--was left to Musgrave, who had developed a sure touch as a part-time surgeon at Denver General Hospital before completing astronaut training.

“It just glided in perfectly,” said Larry Simmons, who is in charge of the team at the Jet Propulsion Laboratory that built the $101-million instrument. “It was great.”

Simmons said he is confident that the camera will perform as designed because NASA imposed an unusually rigorous series of tests in order to avoid any repetition of Hubble’s original problems.

“We had test and retests,” he said. “We usually had three independent tests, but never less than two. So we have a great deal of confidence it will work.”

More than half of all the astronomical observations from the Hubble will be made with the wide-field camera, NASA scientists said, in part because it should enable astronomers to explore ultraviolet wavelengths of light normally blocked by the atmosphere.

Ultraviolet light typically radiates from extremely hot, dynamic celestial objects, such as the cores of active galaxies, quasars, and vast disks of dust around black holes. The most common elements in the universe--hydrogen, helium, carbon, nitrogen, oxygen and silicon--all leave spectral signatures in the ultraviolet.

“I think we hopefully have a lot of astronomers ready to use this beautiful thing,” Hoffman said as he finished securing the new camera in place.

“I’m looking forward to seeing the pictures,” he said.

* CORRECTOR MIRRORS: An obscure California company builds new Hubble mirrors on time and under budget. A18

Tonight’s Task: New Electronics

Details of tonight’s spacewalk, sometime between 9 p.m. and 3 a.m. Pacific time.

Astronauts: Jeffrey A. Hoffman and F. Story Musgrave

Goal: Replace the solar-array drive electronics. If time permits: a secondary task to be decided at the time.

Work Location: In the middle of the telescope, on the inside of a door in the central equipment bay.

Procedure: The astronauts will open the equipment-bay door on which these electronic devices are attached. Using power tools, they will remove six bolts holding one electronic package to the door, then disconnect its electrical plugs and remove it. The new unit will be installed in the reverse of this process.

Where to watch: CNN and C-SPAN will offer live coverage.

Source: NASA