Space Shuttle Closing In on Faulty Hubble Telescope : Science: The effort to capture and secure the 25,000-pound observatory is the first major hurdle in the $629-million repair mission.

After three years of recriminations, NASA worked early this morning to come directly to grips with the problems that crippled the Hubble Space Telescope as astronauts aboard the space shuttle Endeavour grappled with the $1.5-billion orbiting observatory.

If all went as planned, astronaut Claude Nicollier was to pluck the 25,000-pound telescope from space with the shuttle’s mechanical arm just after midnight PST and slowly swing it into Endeavour’s payload bay by 2 a.m., so it could be secured to a large turntable for servicing.

Later tonight, Endeavour’s astronauts are scheduled to don $10-million spacesuits, unlimber their micro-gravity wrenches and climb through the air lock for the first of an unprecedented five days of arduous spacewalks.

Working in pairs, they will try to refocus the telescope’s flawed vision and replace its flapping 39-foot solar-power panels. The telescope’s blurred focus has limited its range to objects within 4 billion light-years, instead of the 15 billion light-years designers had promised when it was launched in April, 1990.

If the astronauts are successful, the refurbished telescope could help rewrite the history of the astronomical science.

The rendezvous with the telescope, however, is the highest NASA has ever attempted with one of its shuttles, agency officials said. Endeavour, the space agency’s newest space ferry, can carry only enough fuel for one attempt, and mission officials at the Johnson Space Center were openly jittery about the possibility the shuttle could run out of propellant before completing the mission.

NASA officials, who have endured the recent loss of the Mars Observer space probe, a jammed antenna on the Galileo probe to Jupiter, and increasingly close congressional votes on funding for the space station project, worked hard to play down expectations by emphasizing the complexity of the $629-million repair mission.

“We really are expecting the unexpected at this point,” said Joseph Rothenberg, Hubble program manager at NASA’s Goddard Space Flight Center in Greenbelt, Md.

“If we can’t berth (the telescope) and get it into the payload bay, we won’t even be able to get up to bat, so to speak,” he said. “It would be tragic.”

Late Friday, nearing the end of a five-mile-per-second game of tag 360 miles above the Earth, shuttle commander Richard Covey maneuvered Endeavour to within a few miles of the 43-foot-long telescope with precisely measured bursts from the shuttle’s engines.

“Tallyho on Hubble, Houston,” Covey radioed as Endeavour made its final approach.

Covey, making his first shuttle rendezvous, took manual control of Endeavour as it neared the telescope. He was scheduled to turn the 100-ton shuttle in a slow back-flip in front of the telescope to avoid fouling its delicate instruments with rocket exhaust.

At least one of the shuttle’s steering jets apparently failed during the final approach, but mission controllers in Houston said it would not affect the flight.

While Covey rationed his fuel, astronomers from Princeton University and Johns Hopkins University on Friday used the space telescope for one last look at a distant quasar before controllers at the Goddard Space Flight Center shuttered Hubble’s single eye and battened down its antennas in anticipation of the rendezvous with Endeavour.

Tonight’s Task: The Gyroscopes

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

Astronauts: Jeffrey Hoffman and Story Musgrave

Goal: Replace two gyroscopes. If time permits: a secondary task* to be decided at the time.

Work Location: On the underside of the aft shroud, near the back of the telescope. (Near the “bottom” of the telescope as it sits upright in the shuttle cargo bay.)

Procedure: An astronaut in foot restraints on the end of the shuttle’s mechanical arm will use a power tool to unfasten four bolts and remove a panel on the side of the telescope. He will then loosen three more bolts on a star-tracker, a navigational device, and remove part of it to gain access to the gyroscopes. By removing three more bolts and unplugging two electrical connections, the spacewalker can pull one gyroscope free. The procedure will then be repeated to remove the second faulty gyroscope. Two new units will then be installed and the cover replaced. The astronauts will then go to the equipment bay to replace two gyroscope electronic control units, which are held in place by a total of four bolts and two electrical plugs.

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

* Secondary tasks include:

Installing new computer chips: To replace failed processing and memory chips, improving the speed of Hubble’s on-board computer, which is located in a compartment on the underside of the telescope about midway down its length. New electronics will be bolted atop the computer using power tools. Estimated time to complete: 1 hour 45 minutes.

Repair a high-resolution spectrograph. To compensate for a balky low-voltage power supply in the Goddard High-Resolution Spectrograph, one of the scientific instrument modules toward the rear (“bottom”) of the telescope. New relay box and cables will be installed in a hole drilled in the side of the spectrograph using a power tool.

Source: NASA