Page last updated at 15:28 GMT, Tuesday, 19 May 2009 16:28 UK

Shuttle releases repaired Hubble


Shuttle Atlantis releases Hubble

Astronauts on the space shuttle Atlantis have released the Hubble Space Telescope after a series of spacewalks to repair and upgrade the observatory.

Astronaut Megan McArthur liberated the telescope from Atlantis' robotic arm at 0857 EDT (1357 BST), marking the last human contact with Hubble.

Pilot Greg Johnson then used two short burns of the shuttle's thrusters to gently back away from the telescope.

Space shuttle Atlantis is scheduled to return to Earth on Friday.

The crew will now stow the equipment that helped to hold, position, and connect to Hubble during the repairs.

Later on Tuesday, the crew will perform a further inspection of the shuttle's heat shield. An inspection on 12 May showed minor damage to the heat shield tiles.

The fifth and final Hubble servicing mission brought the number of spacewalks to repair it to 23, involving 16 astronauts in a total of 166 hours of work.

'Ready for action'

Commander Scott Altman told mission controllers in Houston that Hubble was "safely back on its journey of exploration".

He thanked everyone on the ground for their help during five gruelling spacewalks.

Hubble Space Telescope (Nasa)
Named after the great US astronomer Edwin Hubble
Launched in 1990 into a 600km-high circular orbit
Equipped with a 2.4m primary mirror and five instruments
Length: 15.9m; diameter: 4.2m; Mass: 11,110kg

"Not everything went as we planned but pulling together we've been able to do some incredible things," he said.

Mission control replied that it was "wonderful to see Hubble, the most famous scientific instrument of all time, newly upgraded and ready for action thanks to you".

Commander Altman was referring to a number of snags that occurred during the spacewalks; on Friday, one of the sets of rate sensing units, or gyroscopes, to be replaced would not fit into its bay. A refurbished unit had to be installed instead.

On Sunday, mission specialists Michael Massimino and Michael Good had to contend with a handrail blocking their access to the Space Telescope Imaging Spectrograph (STIS), resorting in the end to tearing it off with brute force.

But the repair was completed as planned. "It was a very long day supporting [Sunday's spacewalk] and testing the STIS after repair," said Ted Gull, deputy principal investigator for the STIS experiment.

"Now we have to catch up on the changes in commanding to the spacecraft to ensure we can get the best out of STIS for the future," he told BBC News.

The instrument was installed on Hubble in 1997 and worked until 2004.

"We knew the source of the failure, but the STIS was not intended to be repaired in space. And getting those 110-plus screws out, without their floating around inside the Hubble, was a major challenge," Dr Gull explained.

"(It) just shows that a combination of humans and robotics works. We hope to do it for future space missions."

Hubble will undergo many tests in the coming weeks, with observations set to resume at the end of the summer.

The hope is that the repairs and upgrades will give Hubble at least five more years of useful life.

One of the simpler tasks during the repair mission was to fit a docking ring that will serve as a point of contact with Hubble sometime after 2020.

A robotic mission will be sent to push the telescope back toward Earth's oceans - a return home for the most famous telescope the world has ever known.

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