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Fifth spacewalk energises Hubble Fifth spacewalk energises Hubble
(about 7 hours later)
Space shuttle astronauts have embarked on the fifth and final spacewalk to repair the Hubble Space Telescope. Shuttle Atlantis astronauts have completed the fifth and final spacewalk to repair the Hubble Space Telescope.
Mission specialists John Grunsfeld and Andrew Feustel have replaced three batteries, so that Hubble now has a brand new complement. John Grunsfeld and Drew Feustel renewed the observatory's batteries which enable it to keep operating when its solar panels are in shadow.
They have also replaced one of the telescope's three fine-guidance sensors which keep the telescope's gaze precisely fixed for observations. They also replaced a fine-guidance sensor that helps keep the telescope's gaze precisely fixed on image targets.
Space shuttle Atlantis is scheduled to return to Earth on Friday. In addition, the spacewalking pair fitted three thermal blankets protecting Hubble's electronics.
Hubble will be released from the orbiter's cargo bay on Tuesday, with the repairs and upgrades that the mission has accomplished promising at least five more years of observations.
HUBBLE SPACE TELESCOPE Named after the great US astronomer Edwin HubbleLaunched in 1990 into a 600km-high circular orbit Equipped with a 2.4m primary mirror and five instrumentsLength: 15.9m; diameter: 4.2m; Mass: 11,110kg In pictures: The best of HubbleHUBBLE SPACE TELESCOPE Named after the great US astronomer Edwin HubbleLaunched in 1990 into a 600km-high circular orbit Equipped with a 2.4m primary mirror and five instrumentsLength: 15.9m; diameter: 4.2m; Mass: 11,110kg In pictures: The best of Hubble
Among the final tasks is to replace one of the telescope's Fine Guidance Sensors, which allow the extraordinary precision and steadiness of Hubble's pointing. Monday's spacewalk lasted seven hours and two minutes.
According to Nasa, that precision is equivalent to keeping a laser beam focused on a US dime coin at a distance of 320km. The servicing mission has been a great success so far.
The servicing mission has been largely successful but not without its problems. Difficult to budge bolts and problematic tools have slowed the spacewalkers on occasions but overall they have been delighted with their progress through the list of planned refurbishments.
During Friday's spacewalk, one of the three brand-new sets of gyroscopes brought up to replace the existing units would not fit into its assigned slot. A old, refurbished set had to be installed instead. "This is a really tremendous adventure that we've been on, a very challenging mission. Hubble isn't just a satellite - it's about humanity's quest for knowledge," said Grunsfeld.
Saturday's walk successfully installed the Cosmic Origins Spectrograph, filling the instrument bay previously occupied by a corrective optics unit which has acted as Hubble's "spectacles" for 15 years, compensating for the manufacturing flaw in its main mirror. "A tour de force of tools and human ingenuity. On this mission in particular, the only way of finding the limits of the possible is by going beyond them into the impossible.
But the spacewalk failed to repair the high-resolution channel of the Advanced Camera for Surveys (ACS), Hubble's most versatile and well-used camera before its failure in 2007 due to a short-circuit. Two other channels on the ACS are working, though. "On this mission, we tried some things that some people said were impossible…. We've achieved that, and we wish Hubble the very best."
On Sunday, a handrail initially hindered the mission objective of replacing the Space Telescope Imaging Spectrograph. Hubble will be released from the orbiter's cargo bay on Tuesday, with the repairs and upgrades that the mission has accomplished promising at least five more years of observations.
Mission specialists Mike Massimino and Michael Good removed - and captured - more than 100 screws to access the spectrograph. Their spacewalk lasted 8 hours, two minutes, making it the the sixth longest spacewalk in US history. Space shuttle Atlantis is scheduled to return to Earth on Friday.
The final task of Monday's spacewalk will be to remove and replace thermal blankets protecting Hubble's electronics.