US astronauts conclude spacewalk after battle with tricky bolt

May 18th, 2009 - 6:30 am ICT by IANS  

Hubble Space Telescope Washington, May 18 (DPA) Two US astronauts wrapped up a difficult spacewalk Sunday to repair a failed component on the orbiting Hubble Space Telescope.
The main goal of spacewalkers Mike Massimino and Mike Good was the repair of Hubble’s Space Telescope Imaging Spectrograph, which was first installed during a 1997 servicing

mission and was knocked out by a power supply failure in 2004.

To make the repair, the two astronauts had to replace a low-voltage power supply board, in which a power converter failed nearly five years ago. The multiple complicated steps had led NASA to compare the spacewalk to brain surgery.

The spacewalk ran into problems when a stripped bolt brought the day’s repair efforts to a standstill. The piece had to be taken out in order to remove a handrail that blocked access to the spectrograph’s critical circuit board that had to be replaced.

Ultimately, Massimino simply yanked the handrail out of place.

They then had to remove 111 fasteners that kept a cover in place, in a delicate job requiring many tools to keep pieces from floating away into space and damaging the telescope or shuttle. Massimino and Good then successfully replaced the circuit board and closed back up the telescope.

The difficulty pushed the spacewalk over its scheduled six-and-a-half hours to eight hours and two minutes, making it the sixth longest ever.

Massimino and Good were also scheduled to install new blanket-like thermal material, which is meant to extend Hubble’s life span by protecting the satellite’s electronics from temperature extremes. But that task was cut due to the length of the spacewalk.

It was the fourth of five spacewalks of the Hubble repair mission - and the second for the duo, who already worked Friday outside the shutte.

On Monday, a fifth and final spacewalk is to focus on replacing batteries and the telescope’s fine guidance sensor.

In three previous spacewalks from the shuttle Atlantis, astronauts installed a new camera and spectrograph on the ageing telescope, and replaced a computer and the gyroscopes that keep it aligned.

Scientists say the repairs and upgrades, which US space agency NASA hopes will extend Hubble’s functioning life span until at least 2014, will continue to provide clues about the origin and nature of the universe.

Since its launch in 1990, Hubble has helped scientists to place the age of the universe at 13.7 billion years, learn that black holes are at the centre of most galaxies, monitor planetary formation and discover that the universe is expanding at an ever-faster pace.

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