US Astronauts Undertake 4th Spacewalk for Hubble Repairs
By VOA News
17 May 2009
U.S. astronauts are wrapping up their fourth in a series of five spacewalks to repair the Hubble Space Telescope.
Astronauts Mike Good and Mike Massimino on Sunday replaced the power supply unit for the Space Telescope Imaging Spectrograph that allows NASA to identify black holes and to monitor galaxies.
The two spacewalkers had trouble unbolting a handrail that had to be removed in order to start their repairs. While they were not able to loosen the handrail's bolts, they were able to bend it out of the way and proceed with their work.
This spacewalk has lasted more than 6.5 hours.
On Saturday, astronauts John Grunsfeld and Drew Feustel replaced an optics package on the telescope with a sophisticated instrument, the Cosmic Origins Spectrograph, used to capture images that will help explain how planets, stars and galaxies are formed.
The five spacewalks are intended to upgrade the 19-year-old telescope and to extend its life for at least five more years.
The mission is more dangerous than others because the telescope is sharing an orbit with debris left behind by satellite collisions and rocket launches.
The astronauts are further challenged because they can only work with the supplies they are able to carry with them on the shuttle. In missions to the International Space Station, astronauts have enough supplies on the station to last up to three months.
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