Astronauts Try to Fix Hubble Power Panels

The astronauts aboard the space shuttle Endeavour Sunday night plucked a warped solar-energy panel from the Hubble Space Telescope and threw it overboard into Earth’s growing girdle of space debris.

Once the defective 39-foot-long panel was jettisoned, astronauts Kathryn C. Thornton and Thomas D. Akers started installing redesigned solar arrays that can better withstand destructive temperature changes as the telescope speeds in and out of daylight on its 96-minute orbits.

The overnight spacewalk, which started at 7:29 p.m. PST Sunday and was scheduled to end early this morning, is the second of five forays intended to restore the $1.5-billion observatory to nearly its full abilities, allowing astronomers to peer almost to the edge of space and time.

The $629-million servicing mission, called the most complex ever attempted in the space shuttle’s orbiting dry dock, has turned into a test of human brawn and ingenuity.

Early Sunday morning, during the second-longest spacewalk on record, Endeavour astronauts Jeffrey A. Hoffman and F. Story Musgrave successfully replaced two sets of faulty gyroscopes, installed new fuses and prepared the telescope’s power-generating solar arrays for removal. They were outside the space shuttle for seven hours, 54 minutes.

They started an hour early and worked overtime. Their labored breathing and terse instructions to each other underscored their concentration as they counted off each turn of a screw or bolt.

Anchored to the shuttle’s mechanical arm, Hoffman held Musgrave by the ankles as the astronaut floated upside down inside the telescope to replace the gyroscopes, his torso bent awkwardly under the navigation sensors that help the telescope locate celestial targets. Every time the astronauts shifted position, the tools, spare gloves and worn-out gyroscopes tethered to Hoffman’s workstation drifted in the low gravity like strands of seaweed rolling in a current.

Once the gyroscopes were installed, Hoffman struggled for two hours to latch a warped access doors. “Uh-oh, we’re in trouble,” he murmured at one point.

When mission controllers at Houston’s Johnson Space Center urged the astronauts to move on to other tasks, Musgrave insisted on improvising a foothold from a strap he found in the shuttle toolbox, giving him the purchase necessary to shoulder the door safely shut.

“Jeff and Story today have definitely earned their Dr. Goodwrench certificates, and service station Endeavour has qualified for a triple-A rating,” said David Leckrone, Hubble senior scientist. Flight controllers monitoring the pair’s work broke into applause three times during the night.

“We have six working gyros now. That is very good news for science. We desperately need our gyros in the observatory to accurately point to targets, to move from one point in the sky to another, and to contribute to the stabilization of the telescope,” Leckrone said.

Hoffman and Musgrave were so intent on completing their tasks that they seemed indifferent to the sights around them.

Only once did they take note of the field of stars enfolding them. Hoffman, waiting to replace a battery in his power wrench, was perched in darkness at the end of the shuttle’s mechanical arm while Musgrave, floating on a loose tether, pulled himself up on the handholds studding the side of the massive telescope.

“Oh, my goodness. Looking out the front, down to Earth, the sun’s coming up,” Musgrave said.

The astronauts’ ability to think on their feet was to be put to a more severe test Sunday night in what was expected to be a 6 1/2-hour spacewalk by Thornton and Akers.

Their work to install the redesigned solar power arrays will help stabilize the telescope and extend its working lifetime into the next century, but if the new power panels do not work or are damaged, the telescope could be left powerless.

Thornton had to take hold of the bent panel, carry it with her on the robot arm high over the space shuttle, and then let it float away into space to join about 7,000 other pieces of space junk circling Earth.

In about a year, it will drift into the atmosphere and burn up, NASA scientists said.

The solar panels are designed to roll up into storage tubes for easy transport to and from orbit. One panel, after several false starts, rolled up properly Sunday, ready to be transferred today into the shuttle’s payload bay. But the second blanket of solar cells, which had a bent supporting strut and sagging panels, defied efforts to furl it Sunday morning.

Lead flight director Milt Heflin said earlier Sunday that disposal of the solar panel should add only about 30 minutes to Thornton’s spacewalk.

“She is going to let go of it, just let go of it. Then we will perform a very gentle jettison procedure, moving the shuttle away at perhaps one foot per second,” he said. “That may not sound like much, but it adds up to a great deal over time.”

In all, more than 30 hours of spacewalks have been scheduled to carry out repairs on the telescope’s defective systems. The astronauts and NASA mission controllers are following an unusual nighttime schedule for the spacewalks, dictated by the timing of the early morning launch required for the rendezvous with the telescope.

Tonight, NASA’s schedule calls for astronauts to modernize the telescope’s stargazing sensors with a $101-million camera from Pasadena’s Jet Propulsion Laboratory, which should give it 10 times the resolution of the world’s largest ground-based telescope.

On Tuesday, the telescope is to be fitted with lenses that should sharpen the focus of its flawed 94-inch primary mirror.

“If we feel we are working the crew or the ground team too hard, we will take a day off,” Heflin said.

Tonight’s Task: Camera Replacements

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

Astronauts: Jeffrey A. Hoffman and F. Story Musgrave

Goal: Replace the wide-field and planetary camera, then replace two magnetic sensing systems.

Work Location: On the underside of the telescope, just forward (or “above”) the rate-sensing gyroscopes replaced earlier.

Procedure: The astronauts begin by opening the service-bay doors at the base of the telescope and installing a pair of guide rails. A temporary handle is then affixed to the 610-pound, wedge-shaped camera and it is slid out of the telescope like an enormous dresser drawer and temporarily stored on a special stand in the cargo bay. The handle is transferred to the new camera, which is moved on the mechanical arm from its container to the telescope. After the free-floating spacewalker removes a protective cover from the exposed “pickoff mirror,” which feeds light into the camera. Careful not to break off or bend this mirror, which would ruin the instrument, the astronauts will then slide the camera into place on the guide rails. The handle is then removed from the new camera and the service-bay doors are closed before the old camera is placed in the camera container in the cargo bay. The astronauts will then move to the top of the telescope, near the aperture door, to install two new magnetometers. These guidance instruments will be bolted to the top of existing, failed magnetometers.

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

Source: NASA