This story was updated at 6:40 p.m. EDT.
HOUSTON — Spacewalking astronauts finished their hands-on repairs on the Hubble Space Telescope Monday, wrapping up a five-day marathon to overhaul the much-loved observatory for the last time.
Atlantis astronauts John Grunsfeld and Andrew Feustel spent just over seven hours adding some final upgrades to 19-year-old Hubble more powerful than ever before. It was an emotional day for the astronauts, as they became the last people ever to touch the iconic space telescope.
"This is a really tremendous adventure that we've been on, a very challenging mission," said Grunsfeld, a self-described Hubble hugger making his third trip to the telescope, as he finished his work. "Hubble isn't just a satellite, it's about humanity's quest for knowledge."
Monday's spacewalk was the fifth and last for the Atlantis crew, with astronauts soaring through all of their tasks in just over seven hours. Their mission is NASA's fifth and final service call on the Hubble, and the last chance to extend its life through at least 2014 with state-of-the-art instruments.
"Hubble is returned to flagship status," said Jon Morse, director of NASA's astrophysics division. "It now has a full arsenal of instruments and tools for astronomers to make new discoveries during the next several years."
The astronauts are slated to release Hubble back into space on Tuesday. Their 11-day mission cost about $1.1 billion and caps a $10 billion investment in the Hubble Space Telescope, which launched in 1990.
Hubble's last hug
During their spacewalk, Grunsfeld and Feustel replaced Hubble's batteries, installed a new guidance sensor to fine-tune its pointing ability and added some sorely needed steel-foil insulation covers to the telescope's hull.
The covers protect Hubble from the extreme temperature swings and radiation in space. The telescope's older insulation was in bad shape, shedding shiny, harmless bits as Grunsfeld tucked it in a trash bag.
"Wow, look at Hubble," one of the spacewalkers said after installing the gleaming new metal covers.
The astronauts were determined to leave Hubble in the best condition they could. They began Monday's spacewalk an hour early in order to squeeze in time to install more insulation, including a cover NASA packed along just in case they had extra time.
After finishing their work, the astronauts took time to take photographs of Atlantis, themselves and finally Hubble.
"This is really a great day,' Mission Control radioed the spacewalkers, adding it was "a great way to close things out."
But the spacewalkers had one last, unexpected task. They had to replace an antenna cover on Hubble after one of them accidentally bumped it.
"Sorry, Mr. Hubble," Grunsfeld said. "Have a good voyage."
"Consider it a goodbye kiss, John," astronaut Michael Good called out from inside Atlantis.
A deeper view
Since their May 11 launch, Atlantis astronauts have added a powerful new wide-field camera to peer deep into the universe and installed a super-sensitive spectrograph to study the structure and composition of the cosmos.
The new $220 million additions should extend Hubble's vision back to about 500 million years after birth of the universe, which is 13.7 billion years old. Hubble could peer back to about 700 million years after the theoretical Big Bang before the Atlantis crew arrived.
Atlantis astronauts also made two unprecedented repairs to Hubble's broken advanced camera and an older, more versatile spectrograph that doubles as an imager. Both of those instruments were never designed to be fixed in space. Atlantis astronauts revived them in two nail-biting spacewalks.
"On this mission, we tried some things that some people said were impossible," Grunsfeld said. "We've achieved that, and we wish Hubble the very best."
Then there's the vital maintenance work, which replaced aging gyroscopes, batteries and finicky science data computer. The astronauts also added a docking ring to Hubble that will allow a robotic spacecraft to latch on and send it down into the Pacific Ocean when the telescope's mission ends sometime in the 2020s.
"In many ways, it is a brand new observatory," Hubble program manager Preston Burch told reporters here at NASA's Johnson Space Center. "One far more capable than what was launched in 1990."
Burch said the initial round of system checks should last through late summer, when the first results and images from the revamped Hubble should be ready.
NASA canceled the mission in 2004 after the Columbia disaster because of its risk, but reinstated it three years later once shuttle missions resumed. Part of the reasoning for the reversal is the shuttle Endeavour, which has been sitting on a launch pad in Florida poised to fly a rescue mission if needed, since Atlantis lifted off.
Astronauts visiting Hubble have no safe haven if their shuttle is damaged beyond repair. The International Space Station serves as a refuge for its visiting shuttle crews, but is beyond the reach of Hubble-bound astronauts because of its lower altitude and different orbit.
Monday's spacewalk marked the third spacewalk for Feustel and the eighth career excursion for Grunsfeld — who finished with 58 hours and 30 minutes of spacewalking time — making him the world's fourth most experienced spacewalker. Feustel ended the spacewalk with a mission total of 20 hours and 58 minutes.
It was also the 23rd spacewalk at the Hubble Space Telescope. In all, astronauts have spent 166 hours and six minutes working on the space observatory.
The Atlantis crew is due release Hubble back into space early tomorrow and land Friday at NASA's Kennedy Space Center in Florida.
SPACE.com is providing continuous coverage of NASA's last mission to the Hubble Space Telescope with senior editor Tariq Malik in Houston and reporter Clara Moskowitz in New York. Click here for mission updates, live spacewalk coverage and SPACE.com's live NASA TV video feed.