Hubble's troubles resolved

Astronauts finish telescope repairs

Endeavour astronauts finished the task of rejuvenating the Hubble Space Telescope early today, following an unprecedented record-breaking fifth spacewalk that enabled the high-flying handymen to achieve each of the repair tasks assigned them by NASA.

The possibility of a sixth excursion to deal with a puzzling telescope computer problem disappeared overnight as ground controllers traced the difficulty to a transient glitch in a satellite communications system.

"We all have big grins down here," mission control radioed Endeavour commander Dick Covey and his weary crew.

"This is just like Christmas," said Covey.

Later today, the Endeavour crew planned to raise the towering observatory from its work bench in the shuttle's cargo bay with the ship's robot arm. Arm operator Claude Nicollier was scheduled to redeploy the overhauled telescope early Friday.

The 11-day mission is scheduled to end early Monday at the Kennedy Space Center in Florida. However, mission managers have discussed the possibility of a Sunday landing.

During their final seven-hour spacewalk, astronauts Story Musgrave and Jeff Hoffman equipped the observatory with a new electronics drive motor for its winglike solar arrays. The assembly keeps the power generating arrays bathed in sunlight as the telescope circles the Earth.

The astronauts also supplied backup power cables to one of the Hubble's science instruments, makeshift covers for two electronic compasses that showed signs of shedding tiny debris that threatened to contaminate the telescope's optics.

The drive motor installation was the last of seven primary repair objectives outlined by space agency officials before Endeavour's Dec. 2 lift off. Achieving all seven of the objectives would qualify the mission as a "full" success, NASA said.

"We planned to do a lot of things on this flight, and we've done all of them and extra things," said Milt Heflin, NASA's lead flight director for the mission. "That says a whole lot to me."

Working in pairs on alternating spacewalks, astronauts Tom Akers, Kathy Thornton, Musgrave and Hoffman also achieved all four of the mission's secondary objectives. The Endeavour crew and ground controllers joined forces as well to successfully tackle nearly a half-dozen problems that arose during the spacewalks.

The number of excursions broke the previous record of four established during a dramatic 1992 satellite retrieval mission.

All of the work fell into two broad categories, those that enhanced the Hubble's science capabilities and those intended to keep the observatory's power generation and intricate pointing system intact.

Though three to four months of post-mission evaluation will be necessary, Hubble astronomers have every reason to believe the space telescope's focusing problem has been corrected with the new optical components installed by the spacewalkers.

The repair crew also installed new gyroscopes, solar arrays, magnetometers and an expanded memory for the telescope's flight computer.

Late Wednesday, Covey and shuttle pilot Ken Bowersox gave the observatory a small boost in altitude with a steering maneuver that was aborted abruptly when the telescope began to vibrate.

However, it positioned the box car-sized spacecraft at an altitude of 369 miles, well above the distorting influences of the Earth's upper atmosphere. The boost reversed a slow descent that could have allowed the spacecraft to re-enter the Earth's atmosphere after the turn of the century.

The $1.5 billion instrument was launched by a shuttle crew in April 1990. Within weeks, soaring enthusiasm among astronomers and the public for the project was jolted when the space agency announced the telescope had a flawed 94-inch wide primary mirror.

The flaw escaped pre-launch testing, which some critics claimed was inadequate.

In spite of the handicap, an international team of astronomers have employed the telescope for a number of discoveries. However, the instrument's myopia kept them from observing the faint distant objects believed to be the earliest inhabitants of the universe and other significant new phenomena.

Officials believe the observatory will function at least through 2005. Additional visits by astronauts are planned about once every three years to install updated science instruments and to perform other maintenance tasks.