DISCOVERY'S ASTRONAUTS LAUNCH HUBBLE TUNEUP.

Byline: Associated Press 

Two astronauts floated out into the cargo bay of space shuttle Discovery on Thursday night to begin the Hubble Space Telescope's billion-mile tuneup.

So eager were Mark Lee and Steven Smith to get started on their spacewalk that they suited up more than an hour early. But their plans were foiled when one of Hubble's two solar panels suddenly flapped back and forth. As one of the astronauts put it, it was ``something real unusual.''

As Lee and Smith waited in the depressurizing air lock that leads from the cabin into the vacuum of space, Hubble's right solar panel moved from a horizontal position 90 degrees into a vertical position, then halfway back to horizontal, all in five seconds.

There appeared to be no damage to either of the 40-foot, power-generating solar wings, and both appeared to be fairly steady, the astronauts said.

Engineers on the ground theorized that escaping air from the depressurization of the air lock moved the solar panel, like a sheet on a clothes line caught in a breeze. An alternative method was then used to slowly lower the air lock pressure and deflect the exhaust.

It worked, and after nearly two hours inside the cramped air lock, Lee and Smith went out nearly 370 miles above Earth to install two new science instruments that will allow Hubble to peer even deeper into the far reaches of the universe. They ended up running only 15 minutes behind schedule.

``Oh my gosh. Beautiful!'' Lee said as he gazed upon the 12-ton, 43-foot-tall observatory.

Four straight nights of spacewalking were planned to install up-to-date equipment in NASA's second Hubble service call since 1993.

Twenty hours earlier, Discovery's seven-man crew hauled the telescope into the shuttle's cargo bay and latched it onto a tilt table.

``Seeing that beautiful spacecraft for the first time in three years was like seeing your best friend whom you haven't seen for three years,'' NASA's chief Hubble scientist, Ed Weiler, said on Earth. ``Not only that, but the friend doesn't seem to have aged at all.''

The only sign of age appeared to be a gouge in a dish antenna caused by a micro-meteorite. The healthy Hubble was a welcome sight; a badly warped or wobbly telescope would have forced NASA to call off the spacewalks.

Weiler considered the first spacewalk, on Thursday night, to be ``the Super Bowl'' of the series. The astronauts' job: to replace 1970s-era science instruments with start-of-the-art devices.

``If that goes well, I think it will really put Hubble into a position of having world-class scientific capability well into the 21st century,'' Weiler said.

Although this rendezvous was less urgent than the 1993 visit, when spacewalking astronauts had to install corrective lenses because of a defective mirror, it was no less nerve-racking for astronomers, fearful of an inadvertent bump that could ruin its vision again.

The $2 billion telescope has performed superbly since its full sight was restored, confirming the existence of super-massive black holes in several galaxies and bringing astronomers ever closer in determining the age of the universe.

Its vision will be even keener with the addition of the two $100 million-plus science instruments, a spectrograph with two-dimensional sensors and a near-infrared camera. Each is the size of a telephone booth.