Hubble gets 2nd set of 'glasses'


Mission accomplished -- again.

In their fourth successful space walk, the crew from the shuttle Endeavour outfitted the blurry-eyed Hubble Space Telescope today with its second pair of corrective lenses, extended the memory of its on-board computer and stowed a scientific instrument for return to Earth.

And they finished the work in 6 hours and 45 minutes.

"I'm happy . . ." astronaut Tom Akers said after installing a co-processor that will enhance the memory of Hubble's computer.

Tonight, astronauts F. Story Musgrave and Jeffrey Hoffman will attempt the last scheduled space walk to replace an electronics device that helps position the telescope's solar panels and install a backup power supply for the telescope's spectrograph. And NASA officials said they plan to boost the telescope higher into space tomorrow and unfurl Hubble's new solar panels.

The number of space walks planned for the 11-day Hubble servicing mission was unprecedented in the 12-year history of NASA's shuttle program.

"We're going for a slam dunk," Milt Heflin, the lead flight director for the mission, said this morning.

The Hubble telescope, discovered to have a focusing problem soon after its deployment in April 1990, now is equipped with two new instruments designed to correct the flaw in the observatory's primary 94.5-inch-wide mirror.

With practiced ease, astronauts Akers and Kathryn "KT" Thornton slid COSTAR (the acronym for Corrective Optics Space Telescope Axial Replacement) into the belly of the telescope, nudging the refrigerator-like component along a set of guard rails. This was no small feat as COSTAR was designed to fit snugly into the telescope and the astronauts had to be careful not to bump it for fear of disrupting the sensitive optics inside.

But the space walkers installed the package on the first try.

"Keep coming, coming . . . It's sliding in easy," Mr. Akers, an Air Force colonel, told his companion.

"It's in!" Dr. Thornton exclaimed when the job was done.

Designed in part by scientists at the Space Telescope Science Institute in Baltimore, COSTAR uses 10 mirrors -- some no bigger than a dime -- deployed on movable arms to correct the vision flaw in three astronomical instruments aboard Hubble.

The latest success mirrored that of astronauts Musgrave and Hoffman who yesterday replaced the telescope's Wide-Field Planetary Camera with an improved model. The camera, which accounts for half of Hubble's scientific observations, had been outfitted with new optics to compensate for Hubble's misshapen primary mirror.

The result of the repairs by the Endeavour's crew should be a telescope that will live nearly up to the original promise of getting crisp images and detailed scientific data from the faintest and oldest bodies in the universe. But it will be another six to eight weeks before Hubble scientists know whether the new instruments are working as expected.

During that time, they will be orienting the telescope, recalibrating the instruments and fine-tuning the position of the new mirrors before they can receive the first photographic evidence of Hubble's hoped-for sharper vision.

But if all goes well, David Leckrone, senior Hubble scientist, said, "We will have a complete and capable observatory with all the tools astronomers and astrophysicists need to ply their trade and go after the big questions."

With the fourth space walk completed, the Endeavour crew has exceeded the goals deemed critical to the success of the $629 million mission. Designed to be serviced in space, the telescope has been fitted with new solar panels, a pair of gyroscopes that point and track the telescope, the two corrective optics packages and one of two magnetometers, which measure Earth's magnetic field to guide the telescope.

Mr. Akers, who holds the record for the longest space walk, and Dr. Thornton ventured out of the shuttle more than an hour early and began their work about 10:15 last night. The first big item on their list was the removal of the High Speed Photometer, an instrument that accounted for the least amount of scientific work aboard Hubble, to make room for COSTAR.

Dr. Thornton, perched on the end of the mechanical arm, had no trouble pulling out the refrigerator-sized container. She slid it back and forth inside the telescope to practice the maneuver necessary to install COSTAR.

The photometer was then moved to the shuttle's cargo bay and stored for the flight home. In the weightlessness of space, it often appeared as though Dr. Thornton was moving an oversized ice chest rather than a 620-pound instrument many liken to a telephone booth.

Once COSTAR was secured inside Hubble, the astronauts headed up the side of the telescope, where they installed a much smaller box -- the co-processor -- on top of Hubble's computer. In their last assignment, they used scissors to snip insulation material from another area of the telescope. That material will be used to fashion a new cover for the old magnetometers at the top of the 43-foot long Hubble.

As the pair hovered in the cargo bay at one point, Mr. Akers encouraged his colleague to take a moment and "look under the telescope."

"Isn't that pretty?" Mr. Akers said, apparently in reference to the Earth.

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