May 18: With Earth in the background, astronauts John Grunsfeld, rear, and Andrew Feustel work to upgrade the Hubble Space Telescope.
May 18: Astronaut John Grunsfeld is reflected on the surface of the Hubble Space Telescope.
A graphic illustrates all the planned repairs to the Hubble Space Telescope on this final maintenance mission.
May 18: Astronaut Andrew Feustel works to upgrade the Hubble Space Telescope during the shuttle mission's final spacewalk.
May 12: Space shuttle Atlantis in silhouette as it passes in front of the sun, as seen via telescope from Florida.
May 14: Astronaut Andrew Feustel works on the Hubble Space Telescope during the first of five spacewalks.
May 13: The Hubble Space Telescope suspended over ocean waves far below, as seen from space shuttle Atlantis.
Two astronauts finished up their work on the Hubble Space Telescope Monday, becoming the last two humans to ever lay hands on the orbiting observatory.
"Wow, look at Hubble," one of the astronauts said as they shut the door to the telescope's inside.
NASA is confident Hubble will be more powerful than ever for the next five to 10 years, thanks to the upgrades and repairs in five daily spacewalks that began Thursday.
Astronauts Mike Good, Andrew Feustel, John Grunsfeld and Mike Massimino gave Hubble two state-of-the-art science instruments, new batteries and new gyroscopes.
The $220 million worth of new instruments should allow the telescope to peer even deeper into space and time, as far back as 13 billion years, almost to the beginning of the universe.
"This is a real great day," Mission Control told Grunsfeld and Feustel during the final spacewalk Monday, "a great way to finish this out."
Keen on leaving the 19-year-old observatory in the best possible shape, chief mechanic John Grunsfeld and Andrew Feustel gave the telescope another fresh set of batteries Monday and a new sensor for fine pointing.
That left enough time to install steel foil sheets to protect against radiation and the extreme temperature changes of space.
It was messy work. Pieces of the old insulation broke off and floated harmlessly away.
"I was hoping to retrieve those for memories," Grunsfeld said.
As he applied the new insulation with a roller, a voice from space sang "Rollin', rollin', rollin'" to the theme song from the TV show "Rawhide."
Only one of the other four spacewalks went as smoothly. Sunday's was particularly exasperating: a stuck bolt almost prevented another team of astronauts from fixing a burned-out science instrument. Brute force saved the day, but so much time was lost that no protective sheets could be installed.
Grunsfeld and Feustel completed Sunday's missed work.
The shuttle astronauts will set Hubble free Tuesday.
During the mission, the four spacewalkers, two per team, managed to fix two science instruments that had broken down years ago and were never meant to be tinkered with in orbit, and replaced a faltering science data-handling device.
They also installed a docking device so a robotic craft can latch on and steer the telescope into the Pacific sometime in the early 2020s.
All told, this visit to Hubble cost more than $1 billion.
Hubble senior project scientist David Leckrone was hoping the spacewalkers would give the telescope a goodbye hug on behalf of the "thousands and thousands of Hubble huggers all over the world."
Grunsfeld, an astrophysicist who has spent more time working on the orbiting Hubble than anyone, was expected to do the honors. He's visited Hubble twice before, and plans to use the telescope once he's back on Earth to study the moon.
NASA hopes to crank Hubble back up by summer's end, following extensive testing of its new parts.
Already, though, scientists have gotten more than they could have hoped out of Hubble, which was launched in 1990 with a projected working lifetime of 15 years.
Once its blurred vision was corrected in 1993 and NASA's reputation was restored, the telescope began churning out breathtaking images: among other things, stars in the throes of birth and death.
Back at the launch site, meanwhile, NASA maintained its vigil in case another shuttle needed to rush to the rescue.
Atlantis escaped serious launch damage a week ago, but was susceptible to all the space junk in Hubble's 350-mile-high orbit. The astronauts will perform one last survey of their ship after releasing the telescope.
NASA took unprecedented steps to have Endeavour on the pad as a rescue ship, because the Atlantis astronauts have nowhere to seek shelter if they cannot return to Earth because of shuttle damage. The space station is in another, unreachable orbit.
The increased risk prompted NASA to cancel the mission five years ago in the wake of the Columbia accident. It was reinstated two years later.
With NASA's three remaining space shuttles set for retirement next year, there will no way for astronauts to return to Hubble.
The new spacecraft under development will be much smaller and less of a workhorse than the shuttle, and lack a big robot arm for grabbing the telescope.
Hubble's replacement, the James Webb Space Telescope, will be launched in 2014 by an unmanned rocket and placed in an orbit inaccessible to astronauts.
The Associated Press contributed to this report.