Astronaut Andrew Feustel, tethered to the end of the remote manipulator system arm (left), navigates near the Hubble Space Telescope, during the mission's third spacewalk. Astronaut John Grunsfeld signals to his crewmate from just a few feet away.
Credit: NASA
The Advanced Camera for Surveys is a seven-year-old instrument that was crippled by a short circuit in January 2007. The breakdown left only one of three internal imagers functioning, slowing a campaign to unravel the mysteries of dark matter and dark energy. The two little understood forces influence the structure and expansion of the universe.
The still inactive high-resolution imager, which was used by astronomers for about 5% of the camera's observations, is likely unrecoverable by another means, NASA said.
In addition to the partial revival of the Advanced Camera for Surveys, they installed two new science instruments and a crucial science computer as well as replaced gyroscopes and batteries to sustain the observatory's pointing and power systems.
Computer upgrade postponed entire mission
During the first, seven-hour spacewalk, John Grunsfeld and Drew Feuste installed a new science computer on Hubble. In September 2008 the Science Instrument Command and Data Handling System experienced an electrical problem in late September. The setback prompted NASA to postpone plans to launch the Hubble mission in October so engineers could prepare a replacement.
The computer prepares each of the telescope's science instruments for astronomical observations and formats the findings for transmission to Earth.
But there were a few curve balls in the first spacewalk: the astronauts fell behind time as they tried to undo difficult bolts in order to replace the observatory's main camera; they also had to be careful not to disturb a dusting of white material that NASA feared would float free and potentially contaminate the telescope's optics.
The last spacewalk is scheduled to take place late tonight (Australian time). Astronauts will replace the final set of batteries for the telescope, replace a sensor needed for precisely pointing the telescope to gaze at its celestial targets and install another blanket on its exterior.
The 11-day mission is the final shuttle flight to NASA’s Hubble Space Telescope. The seven-member crew is putting in place advanced technology that improves the telescope’s discovery power by 10 to 70 times. If everything goes to plan, the result will be six working, complementary science instruments with new capabilities, and an extended operational lifespan through at least 2014.
