HOUSTON --
A pair of expansive new solar arrays is due to creep slowly out of storage
boxes outside the International Space Station (ISS) today after a successful installation by NASA astronauts on Monday.
Atlantis
shuttle spacewalkers Jim Reilly II and Danny Olivas set the
stage for today's planned solar array deployment Monday, when they freed
much of the hardware slated to move into action today from the restraints that
locked it in place for the launch spaceward. But there will be no going outside
the ISS to unfurl the new solar wings today.
"The deploy
both tonight and tomorrow is all ground commanded," Joel Montalbano, NASA's ISS
mission operations representative, told reporters late Monday of the first
steps in loosing the new arrays. The remainder of the new
Starboard 3/Starboard 4 arrays, which will stretch some 240 feet (73
meters) from tip
to tip at full extension, can be unfolded remotely by the astronauts inside
the ISS, he added.
Reilly, an
STS-117 mission specialist aboard Atlantis, is due to be at the switch,
starting and stopping the deployment as needed.
"Every
person on the crew will have a role because there are a number of things that
we'll be watching for," Reilly said in a NASA interview. The astronauts will be
watching the tension in the arrays' wires, the panels themselves, and a tension
bar at the base of each panel to ensure they reel out properly, he added.
Built by
Lockheed Martin, the S3/S4 solar array wings (or SAWs) are each 115 feet (35
meters) long and 38 feet (11.5 meters) wide with a gap between them at their
hub. Each wing weighs some 2,400 pounds (1,088 kilograms) and carries about
32,800 solar cells to generate power from sunlight. The arrays themselves are
designed to produce about one-fourth the total U.S. power supply for the ISS.
Commanded
by veteran spaceflyer Rick Sturckow, Atlantis' seven-astronaut crew launched towards
the ISS on June 8 to deliver the new S3/S4 truss segments, solar arrays and a
new crewmember to the orbital laboratory. The astronauts are due to return to
Earth June 21 after a 13-day mission.
Staged
deployment
Rather than
unfurl all at once, the S3/S4 solar arrays will take baby steps to their
deployment.
The process
was actually due to begin while the joint ISS-shuttle crew slumbered to extend
each solar array out of its erector set-like mast of pop-up
battens one full section. In all, there are more than 30 or so mast sections, or bays.
Each new
solar wing is expected to be partially deployed before the STS-117 crew awakes,
then unfolded to about the halfway mark during the day to bake in the Sun.
"As you
warm them, it tends to release and lets the panels separate," Kelly Beck, NASA's
lead ISS flight director for the STS-117 mission, said before the spaceflight.
The stickiness
between individual solar panels after long stowed periods, dubbed "stiction" by
NASA, first arose in during the space agency's STS-97
mission in 2000, which delivered the first U.S. arrays to the ISS on the now
half-furled Port 6 (P6) solar wings. The first P6 array was deployed under a
low-tension mode without warming and suffered
severe stiction that ultimately pulled one tension wire free of its spool,
prompting a spacewalk repair.
In
September 2006, the STS-115 astronaut crew installed the Port 3/Port 4 solar
array trusses to the ISS. Those solar wings deployed without incident thanks to
the warming and high-tension technique.
"So all
this is based on lessons learned," Montalbano said.
By the end
of the day, flight controllers on Earth should be able to tell whether the new
S3/S4 solar arrays are generating their own power, Montalbano said. But they
will have to wait until an older P6 solar wing, which currently extends to
starboard over the S3/S4 truss, is hauled in later this week to activate the
new solar array's Sun-tracking rotation, he added.
In its
current configuration the older, starboard-reaching P6 solar wing crosses the
S4 element's rotational path. Only once it is folded back into its
storage boxes will the new starboard wings begin operations as planned.
"After the
activities [today] you'll get a feel for the functionality of the hardware,"
Montalbano said. "But we won't be able to fully use it until we get the P6
array retracted."
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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