Astronauts leave shuttle to replace Hubble batteries, gyroscopes

Atlantis astronauts have begun the second spacewalk of their mission to repair the Hubble Space Telescope, this time with the aim of replacing the orbiting observatory's gyroscopes and batteries.

U.S. astronauts Mike Massimino and Mike Good left the shuttle at8:49 a.m. ET and will attempt to install six new gyroscopes to help keep the telescope pointing in the right direction. Three of the gyroscopes on the telescope are broken, making the replacement of all the units a priority to keep Hubble functioning.

Massimino and Good will also replace the telescope's original batteries, which have been in space now for 19 years, with a new set.

The spacewalk is scheduled to last about six and a half hours.

On Thursday, astronauts John Grunsfeld and Andrew Feustel installed Hubble's new camera and a data handling unit to replace one that had malfunctioned last fall.

Hubble has provided spectacular imagery and helped astronomers gain new insight into black holes, star formation and the early universe. But it had been seven years since the last repair of the telescope, and several of its instruments have failed or were in need of an upgrade.

NASA hopes the mission will keep Hubble running another five to 10 years.

The crew of Atlantis also received good news on Thursday evening when the shuttle was cleared for re-entry after a thorough review ofits heat shield turned up no issues.

Early Friday morning, astronaut Megan McArthur manoeuvred the shuttle's Canadarm and its camera to do a quick survey of some tiles on the ship's underbelly that were missed during an earlier inspection, but NASA said the survey was not connected to any known issues.