HOUSTON -
An ambitious attempt by Atlantis astronauts to fix the Hubble Space Telescope's
broken main camera has apparently met with only partial success, with one of
the instrument's three photo channels failing to recover as hoped, NASA
officials said early Sunday.
Atlantis spacewalkers
John Grunsfeld and Andrew Feustel spent 6 1/2 hours working on Hubble on Saturday
to revive the observatory's broken Advanced Camera for Surveys and install a
powerful new spectrograph. It was the third of five spacewalks planned for
their 11-day mission to overhaul
Hubble for the last time.
NASA
spokesperson Josh Byerly said engineers were unable to revive the camera's high-resolution
channel, one of three science-collecting channels it used to observe the universe
before a crippling electrical
short in 2007. That electrical short shut down the camera's high-resolution and
wide-field imager channels, though a third mode - a solar blind channel for
studying objects in the far ultraviolet realm of the light spectrum - was later
regained.
The
high-resolution channel "is likely down for good," Byerly said in a NASA TV update just before 1:00
a.m. EDT (0500 GMT). The other two channels are in fine health, which still represents a major increase in science with the return of the wide-field channel, he added.
At the time
of its 2007 failure, the survey camera was Hubble's most heavily-used instrument,
but it was never designed to be fixed in space.
Recovering
the high-resolution channel was always expected to be a long shot, with
engineers and astronauts focusing most of their efforts on the camera's
wide-field channel, which generates more science, Byerly said.
"This was
expected and there is not a surprise to the team here," Byerly said. "There is really not much that can be done at this point."
Atlantis astronauts
are in the midst of a tightly-scripted series of spacewalks that span five
consecutive days. Later today, they will begin their fourth spacewalk, an
excursion aimed at another
tough repair to revive a broken spectrograph. A fifth spacewalk on Monday
will include vital maintenance work. The mission is NASA's fifth and final
shuttle flight to Hubble before it retires its three-orbiter fleet next year.
Earlier in
the mission, they performed some much-needed maintenance and added two brand
new instruments: a powerful panchromatic
camera capable of scanning deep into the universe across the ultraviolet,
visible and near-infrared spectrum; and the most sensitive spectrograph ever
sent to space, which will use faint light from distant quasars to help measure the
chemical makeup of objects in space.
Unprecedented
fix
For Saturday's
spacewalk, NASA engineers devised custom-built tools and techniques to resurrect
the wide-field camera channel. The fix called on Grunsfeld and Feustel to
replace four electronics boards after removing a pair of cover panels and 32
screws. Despite never being done before, the spacewalk repair went off without
a hitch and power to the wide-field channel was restored.
Because of
mission time constraints, Hubble engineers chose to focus the repair on the
wide-field channel because 95 percent of the camera's science observations are
performed by that channel alone, Byerly said.
For
example, it was the camera's wide-field channel that astronomers used to
generate Hubble's Ultra Deep Field, a snapshot of one area of the sky that revealed
more than 10,000 galaxies and peered back to within 700,000 million years of
the birth of the universe. The universe is 13.7 billion years old.
The high-resolution
channel was used for smaller field of view observations, as well as studying
faint objects around bright stars. After Saturday's spacewalk repair, Hubble
engineers hoped to reroute power to the high-resolution channel through its
fixed wide-field counterpart, but were prepared if the plan didn't work, Byerly
said.
"The
outcome of these repairs is very uncertain," Hubble program manager Preston
Burch said before launch.
Hubble
engineers had suspected that a short circuit inside the high-resolution channel
from the earlier failures might prevent its recovery, Byerly added.
Even
without the high-resolution channel, Atlantis' flight has met most of NASA's mission
success criteria, which included adding two brand new cameras, vital gyroscopes
and batteries, and a critical data handling unit. The partial repair of the
main camera, and today's attempted spectrograph fix, are desirable but not
critical, mission managers said.
"There was
not that much surprise in this and not that much disappointment," Byerly said
of Hubble's science team on the partial camera repair. "They consider it a
success."
SPACE.com
is providing continuous coverage of NASA's last mission to the Hubble Space
Telescope with senior editor Tariq Malik in Houston and reporter Clara
Moskowitz in New York. Click
here for mission updates, live spacewalk coverage and SPACE.com's
live NASA TV video feed.
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