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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