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
HOUSTON: Two astronauts had to overcome frustrating obstacles, including snapping off a handrail, during the fourth spacewalk on the final mission to service the Hubble Space Telescope.
The fourth spacewalk of five, completed by astronauts Mike Massimino and Mike Good, was considered by NASA to be the most intricate spacewalk of the mission.
The two men were forced to contend with obstacles that required extra doses of ingenuity, patience and elbow grease and stretched their activities to just over eight hours, returning to the shuttle Atlantis Sunday at 5:47 pm EDT (Monday, 7:47 am Australian EST).
Massimino and Good focussed all of their efforts on the Space Telescope Imaging Spectrograph (STIS), which was installed in the telescope by shuttle astronauts in 1997 but has been in ‘safe mode’ since a power failure in 2004.
Frustrating obstacles
Prior to the failure, science with the STIS constituted about 30% of all Hubble observations. Its achievements have included weighing several dozen supermassive black holes at the cores of galaxies.
"Oh, for Pete's sake," Massimino complained when the battery-operated ratchet he was using lost power. Later, the veteran astronaut cursed as he wrestled to discard the cover plate he'd pulled from the STIS into a storage bag.
In order to replace a failed power converter, Massimino and Good had to replace an internal circuit card. The extraction required Massimino to remove a protective cover secured by 111 small screws using an arsenal of custom-made hand tools.
But access to the cover and the many tiny fasteners was obstructed by a handrail that had to be removed first. The rail was secured by four bolts, one of them badly stripped.
After several failed attempts to turn the bolt with wrenches, Massimino offered to snap the handrail off using some old-fashioned muscle. "Okay, here we go," said Massimino as he broke away the fixture. "Awesome," responded Mission Control.
Third spacewalk "partial success"
The spectrograph quickly passed an electrical test, but Hubble engineers planned to spend their Sunday night (Monday morning in Australia) conducting a more exhaustive test of the instrument.
NASA said efforts on the previous day to revive a second Hubble instrument, the Advanced Camera for Surveys, was a partial success. The repairs, performed by John Grunsfield and Drew Feustel, recovered two of three internal imagers.
"At this point, we are feeling really good," said Preston Burch, NASA's Hubble program manager, on Sunday. "Hubble has reached a new high in terms of capabilities. We have also made huge strides in terms of restoring the health of the observatory."
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.
