This
story was updated at 9:56 a.m. EDT
HOUSTON --
A pair of astronauts will venture outside the International Space Station (ISS)
one last time Sunday to prime the orbital laboratory's newest solar wings to
rotate and track the Sun.
Atlantis
shuttle astronauts Patrick Forrester and Steven Swanson are due to begin the
final spacewalk of NASA's STS-117 mission at 12:33 p.m. EDT (1633) and spend
more than six hours working on the station's new
starboard trusses and other areas.
"There's
nothing on this EVA that I think is challenging," NASA ISS program manager Mike
Suffredini said Saturday of the extravehicular activity (EVA). "But they all will
take time, so how much of this we get done is to be determined."
Forrester
and Swanson are expected to perform a series of tasks carried over from
previous STS-117 spacewalks, including engaging a cross-wired gear on the
station's starboard side and coaxing a stubborn vent heat shield into place.
The
spacewalk is the fourth for Atlantis' STS-117 crew and an added bonus after
mission managers extended
the mission by two extra docked days last week. The extension allowed the
repair of a torn heat-resistant blanket on the orbiters left engine pod.
Inside the space
station, six Russian control and navigation computers remain operational after being
fully
activated Saturday after a major shutdown last week. Aside from the station's
Russian-built Elektron oxygen generator, which engineers are holding off on
restarting pending final checks, most of the systems affected by the glitch are
back online, mission managers said.
"We can report that things are
still improving," ISS flight director Holly Ridings said early Sunday. "We're
back to almost nominal in terms of all the systems."
On Monday,
ISS flight controllers plan to activate the station's Russian attitude control
system for about 45 minutes as a final check on the health of the computers,
Ridings added.
Clean up
crew
The primary
tasks for Forrester and Swanson revolve around the station's new starboard
Solar Alpha Rotary Joint (SARJ) that bridges the recently delivered Starboard 3
(S3) and Starboard 4 (S4) truss segments installed during the STS-117 mission.
During
their Wednesday
spacewalk, Forrester and Swanson were unable to completely remove a series
of launch restraints that secured the SARJ inside Atlantis' payload bay for its
June 8 launch. They also discovered that the two gear motors designed to drive
the SARJ's rotation were cross-wired, with command for one affecting the other,
but were unable to verify that both were engaged at the time.
The two
spacewalkers are expected to pick up where they left off on their last EVA to
prime the SARJ which, once freed, will be able to rotate its new starboard
solar arrays like a Ferris wheel to track the Sun. They will also clear the
S3/S4 segments of obstructions on rails for the station's railcar-like Mobile
Transporter, which serves as a base for the outpost's robotic arm, so it can
aid in ISS assembly tasks on the new truss.
"Those are
the two big things we need to accomplish tomorrow," Swanson said Saturday.
"Those are big keystones in building the space station."
If time
allows, the spacewalkers may also revisit a recalcitrant hydrogen vent heat shield
on the station's Destiny module. Fellow STS-117 spacewalkers James Reilly and
Danny Olivas were unable to reattach it Friday after installing
the new vent, NASA said. They are also expected to route a computer cable
along the exterior of the station's Unity node, the agency said.
Suffredini
has said that he hopes the spacewalkers will have time to install a video
camera stanchion - to free up hardware to be discarded on a future spacewalk -
and engage locks on a broken antenna so it can be returned to Earth for repair.
NASA is
broadcasting the space shuttle Atlantis' STS-117 mission live on NASA TV. Click here for mission updates and
SPACE.com's
video feed.
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