More power for Hubble

Built by the European Space Agency and fixed to the telescope in 1993, Hubble's old $40 million arrays -- which sport silicon solar cells -- have gradually degraded over time, their electrical output dropping to 65 percent of original power.

The new $19 million panels are smaller and almost twice as heavy, each stretching 25 feet (seven meters) from tip to tip and weighing 640 pounds (288 kilograms).

New Power Wing

Hubble sports a new electricity-generating solar array after the first STS-109 spacewalk was complete on March 4, 2002.

Their advanced gallium arsenide solar cells, however, will enable the new wings to produce 5,270 watts of electrical power, or 20 percent more than the old arrays.

Consequently, researchers will be able to operate as many as four Hubble science instruments simultaneously, a capability that is expected to speed the rate at which the telescope can crank out astronomical discoveries.

Another big plus: The new panels feature metal frames made of aluminum-lithium, an alloy stronger that the type typically used in spacecraft construction. As a result, they are expected to hold up better in the harsh space environment.

The rigid arrays also will wobble less than the old flexible panels, reducing the chance that vibrations from them might mar telescope observations.

The seven-hour, one-minute spacewalk largely went according to plan.

Sensors designed to beam back data on the performance of crucial systems on Grunsfeld's spacesuit failed, a situation the crew will try to troubleshoot with the help of ground controllers.

The astronauts also had some difficulty removing Hubble's new starboard wing from its cargo bay carrier, and they struggled to latch the old array to the same pallet. But the old wing came off Hubble with no trouble, and the new panel plugged into the observatory without problems.

Anchored to the end of the shuttle's robot arm, Linnehan deployed the new array while Grunsfeld watched, holding on to a handrail on the outer hull of the observatory.

"Slowly you turn, step by step," Linnehan said as he methodically unfolded the array, exposing its solar cells to orbital sunlight for the first time.

"The array looks beautiful," Grunsfeld said. "Good job."

Mission specialists James Newman and Michael Massimino aim to duplicate the feat Tuesday, swapping out Hubble's portside array. Both old arrays are to be brought back to Earth so researchers can gauge how well they fared in orbit.

The pair also plans to replace a faulty pointing control device during the planned six-and-a-half-hour spacewalk, which is slated to begin at 1:27 a.m. EST (0627 GMT) Tuesday.

The trickiest part of the electrical overhaul, however, will come Wednesday when Grunsfeld and Linnehan attempt to change out the telescope's crucial but flawed power switching station -- one of the few Hubble parts not designed for replacement.

Making matters exceptionally nerve-wracking, the telescope will have to be turned off for the first time in orbit, and there is no guarantee that the power will come back on. A failed swap-out, meanwhile, could leave Hubble a powerless piece of space junk.

To get a leg up on the crucial job, Grunsfeld and Linnehan placed thermal covers over vulnerable parts of the telescope Monday, a move meant to make sure sensitive science instruments and control systems don't freeze up or overheat while Hubble is powered down.

Two additional spacewalks also are planned this week.

Hubble is to be outfitted with an advanced planetary camera Thursday, and then astronauts will attempt to revive a dormant infrared camera and spectrometer on Friday.

If all goes well, the renovated Hubble telescope will be cast back into orbit Saturday before the shuttle crew heads off on a three-day trip back to Earth. Landing here at NASA's Kennedy Space Center remains scheduled for 4:35 a.m. EST (0935 GMT) March 12.