HOUSTON--Astronauts aboard the International Space
Station (ISS) are due to reel in one of the orbital laboratory's expansive
solar wings as part of power grid overhaul by a
visiting shuttle crew.
The joint crews of the station's Expedition
14 mission and NASA's space
shuttle Discovery will retract one of two 115-foot (35-meter) arrays
extending from the Port
6 (P6) truss that currently sprouts up mast-like above the ISS.
"We're looking forward to a great
day with the P6 solar array retract tomorrow," Discovery's STS-116
commander Mark Polansky told flight controllers
earlier today, just before his crew went to sleep at 2:17 a.m. EST (0717 GMT).
Much is at stake for today's P6
solar array retraction.
The power-generating wing must be
reeled in at least 40 percent so that it does not block another set of solar
arrays--which sprout perpendicular to P6's panels from the station's Port
3/Port 4 (P3/P4) truss--from rotating like a paddlewheel to track the Sun later today.
Those P3/P4 arrays arrived
at the ISS in September and are expected to serve as the station's primary power
source until new solar wings arrive next year and the P6 truss is relocated to
its final position at the tip of the Port 5
(P5) spacer segment, which itself was
installed
Tuesday by STS-116
spacewalkers.
John Curry, NASA's lead ISS flight
director during Discovery's STS-116
mission, said mission controllers will power down the obstructing P6 solar
array at about 9:00 a.m. EST (1400 GMT), with the initial retraction beginning
at about 1:25 p.m. EST (1835 GMT).
The P6 solar arrays have been
extended and generating power since
December 2000, when they were installed during NASA's STS-97
mission aboard the shuttle Endeavour. Neither of the solar wings have ever
been reeled back in, a process ISS flight controllers have compared to
refolding a crusty old map back into its original compact form.
"I feel anxious, I think is the
right word," Curry said late Monday, adding that he and his team have spent
four years preparing for the next four days of work at the ISS. "I don't know
that it won't go perfect, but I can tell you for sure that this team has
trained as well as we possibly can to manage it."
Curry said that the P6 retraction
will be directly overseen by astronauts aboard the ISS and Discovery, with
flight controllers giving them signals proceed as they
see fit at various stages.
Built by Lockheed Martin, the P6
solar arrays, their P3/P4 counterparts, as well as two still unflown solar wings destined for the space station's
starboard side, are affixed to an erector set-like mast that is split into 31 ˝
bays.
Curry's plan is to initially have
the ISS and Discovery's astronauts retract P6 about three bays worth, pause to
evaluate its stability, then reel the solar wing down
to one bay before finally securing them closed.
If the P6 solar array fails to
retract automatically, STS-116 astronauts could be called upon to stage a
spacewalk in an attempt to reel it in manually, or latch and lash tight its
solar blanket boxes. If the panel jams fast, the astronaut would then have to
discard it completely.
"I would consider a jettison
unlikely," Curry said. "We don't want to lose that solar array if we don't have
to."
The P6 solar array retraction marks
the start of an intense four-day series of ISS construction to overhaul the
orbital laboratory's power system.
On Thursday, STS-116 spacewalkers Robert
Curbeam and Christer Fuglesang are due to
don their spacesuits for the second time this week to reroute two of four power
channels to plug into the P3/P4 solar arrays. The remaining two channels are
due to be routed in a planned Saturday spacewalk by Curbeam
and ISS astronaut Sunita Williams, who arrived at the station aboard
Discovery this week,
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