It didn't happen easily, but the space shuttle Atlantis' astronauts installed new gyroscopes May 15 on the Hubble Space Telescope. Working in extremely tight quarters inside the Hubble, the spacewalking crew encountered a box of gyros that wouldn't align properly but successfully installed a different set.

The bulky gyroscope box delayed the timetable for the primary goal of flight day five of the 11-day mission by more than a hour. Once the gyroscopes were in place, the astronauts carefully maneuvered out of the Hubble and began installing new batteries on the telescope. It was the second of five scheduled spacewalks for the crew.

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The Hubble's six gyroscopes are part of the system that points the telescope. When all six gyroscopes are functioning, three gyroscopes are used for pointing, and the other three are held in reserve. Time has degraded the gyroscopes to the point where three have failed, two are in use, and a third is turned off to be used as an emergency backup. Astronauts Mike Massimino and Michael Good replaced all of the gyroscopes.

Hubble's batteries, which charge from solar panels during daylight and discharge at night, have worked flawlessly in the 19-year history of Hubble, but NASA decided to install new ones, particularly since this is the shuttle's final mission to the Hubble. The repairs and upgrades should keep the Hubble operational until at least 2014.

On the first spacewalk May 14, Atlantis mission specialists John Grunsfeld and Drew Feustel replaced Hubble's Science Instrument Command and Data Handling Unit, the computer that sends commands to Hubble’s science instruments and formats science data for transmission to the ground. The two also removed the Wide Field Planetary Camera 2 and replaced it with a new wide-field camera, allowing the Hubble to take large-scale, extremely clear and detailed pictures over a very wide range of colors.

Like the gyroscopes, NASA had a few anxious minutes when Grunsfeld and Feustel couldn't get a bolt attaching the Wide Field Planetary Camera 2 to budge. Finally, Fuestel muscled it loose, much to the relief of NASA, which had spent $132 million on the new Wide Field Camera 3.

Over the weekend, astronauts will install the Cosmic Origins Spectrograph, an instrument that breaks light into its component colors, revealing information about the object emitting the light. COS sees exclusively in ultraviolet light and will improve Hubble's ultraviolet sensitivity at least 10 times, and up to 70 times when observing extremely faint objects.