Mission Atlantis: Space Station to Unfurl New Solar Arrays

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.

• SPACE.com Video Interplayer: Space Station Power Up with STS-117
• STS-117 Power Play: Atlantis Shuttle Crew to Deliver ISS Solar Wings
• Complete Shuttle Mission Coverage