NASA astronauts tuned up the Hubble Space Telescope for the final time Monday, equipping the aging stargazer with new batteries, a precision pointing device and solar shielding during a sentimental work session.

John Grunsfeld and Drew Feustel spent six hours refurbishing the 13.2 meter (43.5 foot) long telescope, hoisted into the cargo bay of the shuttle Atlantis last week for an ambitious final overhaul during five daily spacewalks.

The astronauts are now due to raise Hubble out of the bay with the shuttle's robot arm early Tuesday, floating the telescope back into space with no plans for any future human involvement.

NASA's shuttles, facing retirement by the end of next year, launched the space telescope in 1990. Shuttle crews returned in 1993, 1997, 1999 and 2002 to upgrade the telescope with new science instruments and replace failed parts.

Atlantis will depart with Hubble equipped for at least another five years of observations.

"It's been a great achievement up here," said Grunsfeld, an astronomer-turned-astronaut who is nearing the end of his third trip to the space telescope.

"This is a real great day," shuttle communicator Dan Burbank told the Atlantis astronauts from Mission Control in a wistful reference to their final session with Hubble. "A great way to finish this out."

The Atlantis astronauts equipped Hubble with a pair of new science instruments and repaired two others sidelined by electrical problems several years ago.

The astronauts replaced all of the gyroscopes and batteries, fortifying the pointing and power systems. They replaced a hobbled data managment computer that had carried on until last September.

To ensure they did all they could for iconic telescope, Grunsfeld and Feustel started Monday's spacewalk an hour early.

The decision created just enough time to finish all of the low as well as the high priority objectives of the shuttle crew's 11-day mission.

The lowest priorities included a task that was postponed on Sunday, when fellow spacewalkers Mike Massimino and Mike Good ran into a string of obstacles as they worked on the Space Telescope Imaging Spectrograph.

Grunsfeld and Feustel quickly replaced three batteries. They joined three batteries replaced Friday.

Next, they exchanged a fine guidance sensor, an optical device that works with the gyros to provide the observatory with precision pointing.

As their final task, Grunsfeld and Feustel attached panels of stainless steel shielding to the outside of the telescope, covering blemishes created by the bombardment of solar radiation.

Massimino and Good fell behind with that task when they encountered a stubborn bolt, which had to be wrestled loose, and other obstacles when they worked to revive Hubble's Space Telescope Imaging Spectrograph.

The spectrograph, which had been inactive for five years, responded to a round of critical tests, NASA said Monday.

No task seemed of a low priority to Grunsfeld though. As he mounted the new stainless steel shielding, the deteriorating material underneath began to flake and float away -- a symbol that all things come to an end.

"I feel so bad about the debris," said Grunsfeld in a low tone. The Atlantis astronauts will aim for a return to Earth on Friday, touching down at NASA's Kennedy Space Center in Florida at 11:41 am (1541 GMT).

After they pull away from Hubble, the Atlantis crew plans another inspection of the shuttle's heatshielding in a search for signs of damage from impacts with space debris and tiny meteoroids.

The 11-day Hubble mission carries a higher risk than NASA's usual mission to the international space station because of an accumulation of manmade space debris at the telescope's higher altitude.

earlier related report
Astronauts wrap up 4th spacewalk to repair Hubble
Two spacewalking astronauts overcame a stuck bolt, a power tool with a dead battery and other frustrations on Sunday while working aboard the shuttle Atlantis to revive a long inactive science instrument inside the Hubble Space Telescope.

The astronauts embark Monday on the last of the daily spacewalks that formed the cornerstone of NASA's ambitious strategy to extend observations with Hubble at least another five years.

Sunday's outing by Mike Massimino and Mike Good to recover an instrument that identifies super massive black holes was considered to be the most intricate of the five spacewalks.

It turned equally frustrating for the two men when they were forced to overcome a stripped bolt, a power tool with a dead battery and other obstacles that stretched their activities to more than eight hours.

"Oh, for Pete's sake," Massimino complained when the battery in the power ratchet he was holding died.

Later, the veteran astronaut cursed as he wrestled to discard the cover plate he'd pulled from the Space Telescope Imaging Spectrograph into a storage bag.

Mission Control sympathized. "This is sort of like what happens to me when I go out on the driveway and try to work on my car," said Preston Burch, NASA Hubble program manager.

"I can't tell you how many times you try something simple and the next thing you know you are dealing with bolts that have heads rounded off and what not. I certainly sensed his frustration."

Massimino and Good focused all of their efforts on the imaging spectrograph, an instrument installed in the telescope by a shuttle astronauts in 1997.

The spectrograph, which astronomers use to gather information about the chemical composition, temperature, pressure motions of celestial targets, was sidelined by a power failure in 2004.

In order to replace a failed power converter, Massimino and Good had to replace an internal circuit card. The extraction required Massimino to remove a protective cover secured by 111 small screws using an arsenal of custom made hand tools.

But access to the cover and the many tiny fasteners was obstructed by a hand rail that had to be removed first. The rail was secured by four thin bolts, one of them badly stripped.

After several failed attempts to turn the bolt with wrenches, Massimino offered to snap the hand rail off by hand.

"Okay, here we go," said Massimino as he broke it away.

"Awesome," responded Mission Control.

The two men then made quick work of removing a protective cover, replacing the bad circuit card and installing a new cover held down by a pair of latches rather than screws.

The spectrograph quickly passed an electrical test, the first step in a more thorough evaluation.

"Today, was like a dream come true for the science community," said NASA astrophysicist Jennifer Wiseman, who predicted the revived spectrograph will experience heavy use. "It has a very unique capability. That is why this is such a tremendous victory for us."

Mission Control postponed plans to patch a damaged region of the telecope's exterior until Monday.

On Saturday, spacewalkers John Grunsfeld and Drew Feustel breezed through a similar but less demanding repair of Hubble's Advanced Camera for Surveys, a heavily used seven-year-old instrument that encountered a disabling electrical short in early 2007.

The short disabled three internal imagers, though experts were able to recover one of them within a month of the power disruption.

When an overnight testing session ended on Sunday, NASA announced that Grunsfeld and Feustel had recovered one of the two long disabled internal imagers.

The revived Wide Field channel accounts for about 90 percent of the survey camera's observations, many of them focused on studies of galaxies and distant star systems used to calculate how rapidly the universe is expanding.

The High Resolution channel, which could not be recovered, was used to study the inner most regions of galaxies and the discs of dust and gas around stars where planets are forming.

Hubble will remain anchored in the payload bay of Atlantis until Tuesday.

In addition to the repairs, the Atlantis astronauts have installed a pair of new science instruments, a data management computer as well as gyroscopes and batteries to sustain the pointing and power systems.

During Monday's spacewalk, the astronauts will equip Hubble with three more batteries, a pointing sensor and external shielding.

The shuttle crew rendezvoused with Hubble on Wednesday and hoisted it into the cargo bay to start the overhaul. The shuttle's 11-day mission is scheduled to conclude Friday with a landing at the Kennedy Space Center in Florida.