May 17, 2009

Fourth Spacewalk Finished, But Not Completed

Spacewalkers during the fourth walk of the last Hubble servicing mission experienced troubles trying to dislodge a balky bolt interfering with repairs on Sunday.

Atlantis astronaut Michael Massimino used brute force to remove a bolt that was attaching a hand rail to the outside of a scientific instrument that was needing to be fixed.  The rail needed to be removed or at least bent out of the way in order to complete the task. 

This just added to other smaller problems that put the spacewalkers so far behind schedule that they had to abandon the second part of their spacewalk, which was replacing some worn insulation on the telescope.

Even with skipping a task, Massimino and Michael Good ended the spacewalk as the sixth longest U.S. spacewalk in history at eight hours and two minutes.

After several tries with a variety of expensive tools to try and pry out the stripped-out bolt, Mission Control in Houston told Massimino to go for the less precise yank.

Engineers at Goddard Space Flight Center in Maryland tested the method on a mock-up before giving Massimino the go head.

"You hope you don't get to the point where you just close your eyes and pull and hope nothing happens," said James Cooper, the Goddard mechanical systems manager for the repair mission. "But we had run out of other options."

Astronauts were careful to tape and gather pieces so they would not fly away and become potential space debris.

"This is like tying branches together in Boy Scouts," Good said.

Controllers in Houston were listening blindly, due to being out of video contact, as Massimino took a breath and pulled.

After a little bit of silence, Massimino calmly said, "disposal bag, please."

Finally, after struggling with the balky bolt for nearly two hours, the astronauts went back to the plan to bring the Space Telescope Imaging Spectrograph back from the dead.

An early test showed the spectrograph was brought back to life, after being disabled by a power failure five years ago.  However, when further tests started, the instrument put itself into "safe mode" due to temperature problems.

Out of the four spacewalks so far this mission, three have been delayed by niggling problems, like stubborn bolts and objects that would not fit.  The fifth and final spacewalk is set for Monday.

Massimino faced other problems later on when trying to install a special plate.  A battery in a tool he was using died while removing 111 tiny screws that held the instrument cover in place.  It took over half an hour for him to go back to the shuttle and swap out batteries and recharge is oxygen supply.

Once Massimino replaced the internal electronics power supply card in the spectrograph, it was already the scheduled time for the spacewalk to end.  However, over 90 minutes of clean up and close-out still work remained.

So spacewalk coordinators on the ground decided that the second part of the fourth spacewalk's task, the insulation, had to be put off until the fifth.

According to Mission Control, all the work might not be completed on Monday, but it will all be attempted.

"We're very proud of you," Atlantis astronaut John Grunsfeld told the weary spacewalkers.

Grunsfield and Andrew Feustel will pick up where the other astronauts left off on Monday, while also being the last to ever touch the 19-year-old telescope.

Atlantis will release the Hubble on Tuesday.  NASA hopes that these repairs will expand the life of the telescope another 10 years before it is steered into a watery grave.

The spectrograph that was repaired has been a big part of finding black holes and examining the atmosphere of other planets.


Image Credit: NASA


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