* Hubble observatory released into space after repairs
* Difficult overhaul replaced instruments, made upgrades
* Shuttle Atlantis due to land back in Florida on Friday
By Irene Klotz
HOUSTON, May 19 (Reuters) - Rejuvenated by hours of repairs in space, the Hubble Space Telescope floated out of shuttle Atlantis’ cargo bay on Tuesday to reclaim its place as the world’s flagship observatory for astronomical research.
Atlantis astronauts spent more than 36 hours over five marathon spacewalks to make upgrades and outfit Hubble with new instruments. These included a panchromatic wide-field camera that should be able to see objects formed just 500 million years after the universe’s birth in the big bang explosion some 13.7 billion years ago.
Using the shuttle’s robot arm, astronaut Megan McArthur gently lifted the 13-tonne observatory from a work platform in Atlantis’ payload bay where it had been positioned since Wednesday.
Holding the telescope high overhead, she released Hubble at 8:57 a.m. EDT (1257 GMT) as the spacecraft soared 350 miles (560 km) over the planet.
"Hubble isn’t just a satellite," astronaut John Grunsfeld said as he wrapped up the final spacewalk on Monday. "It’s about humanity’s quest for knowledge."
Watching Hubble resume its solitary voyage in orbit was a bittersweet moment for the U.S. space agency, which has staged five previous shuttle missions to service the observatory. The shuttle fleet is being retired next year.
The Atlantis crew completed everything NASA had planned, including the unprecedented repair of two science instruments not designed to be worked on it space. The astronauts, clad in bulky suits and gloves, sometimes struggled with the repair work, and were held up at times by stuck bolts.
"Hubble has returned to flagship status. It now has a full arsenal of instruments and tools for astronomers to make new discoveries," said Jon Morse, NASA’s chief astrophysicist.
Atlantis is due to land back at the Kennedy Space Center in Florida on Friday.
NASA plans to release the first images from the refurbished Hubble in September, following extensive tests of its cameras, light-splitting spectrographs and other systems.
"I truly believe this is a very important moment in human history, and I think it’s an important moment for science," Hubble project scientist David Leckrone said.
"Just using what Hubble’s already done as a starting point, it’s unimaginable that we won’t dramatically go further than that," he added.
Hubble already has changed astronomers’ understanding of how the universe formed and is evolving. It found ancient galaxies that formed well before scientists believed it was possible for them to exist. It also provided evidence of an anti-gravity force known as "dark energy" that is inflating all of space at a faster and faster rate.
"We have thousands of astronomers around the world waiting to get their data," Morse said. "They are chomping at the bit." (Editing by Pascal Fletcher and Will Dunham)