When completed, the international space station will feature a huge solar array truss stretching more than 300 feet from tip to tip. Two huge solar arrays on each end of the truss will track the sun as the station circles the globe, rotating and changing pitch as required to maximize electrical generation.

Finishing the main truss and wiring in the new arrays is a major element of near-term station assembly missions.

One set of arrays, P6, is already attached to the station, providing power for the U.S. segment of the outpost. It is attached to the Z1 truss that extends upward from the Unity module at right angles to the main solar array truss. It will be moved next year to its final position next to the P4 arrays being attached by Atlantis' crew.

Designed by Boeing, the P4 truss features two motor-driven telescoping masts that will pull out a pair huge solar array wings measuring 240 feet from tip to tip when fully unfurled. For launch, the arrays are folded like venetian blinds in blanket boxes measuring 15 feet long but just 20 inches thick.

The P3 truss was delivered to the Kennedy Space Center in November 1999. P4 followed suit in July 2000. The solar array blankets have not been unfolded since they were originally stowed for launch.

Prior to Columbia's launch in January 2003, the arrays were certified to operate and deploy normally when stowed for up to 45 months. Because of the extended downtime after the Columbia accident, one of the blanket boxes on P4 was removed and shipped to California for deployment tests. A replacement blanket was installed aboard P4.

As it turned out, the deployment tests went well and the blanket, which had been stowed 39 months at that point, worked normally. As a result, the certification age limit was boosted to 82 months. At launch, the P4 blankets will have been stowed for 67 and 73 months respectively.

One other consequence of the Columbia recovery and subsequent launch delays was a decision to replace all 12 batteries in P4. The 372-pound batteries were swapped out in March and August of 2005.

The solar array wings were designed by Lockheed Martin. They weigh more than 2,400 pounds and feature some 33,000 solar cells per blanket. They are designed to produce more power than the station actually needs to compensate for normal degradation as the outpost ages. The blankets must face the sun directly for maximum electrical generation and two mechanisms are in place to do just that. The wings can be rotated about their long axis by beta gimbal joints, much like the pitch of an airplane propeller can be adjusted. The SARJ rotates the arrays through 360 degrees like a waterwheel.

The P4 integrated equipment assembly, or IEA, is a cube measuring 16 feet on a side and weighing nearly 17,000 pounds. It includes direct current converters, 12 batteries, battery chargers, control computers and an ammonia cooling system to keep the electronic gear at the proper temperature. A single set of folding radiator panels will extend 44 feet when fully deployed.

Most of the work to ready the new P4 arrays for extension "is done by the flight control team," Jett said. "The EVA crew does the physical work, in terms of, positioning the arrays and releasing all the bolts and the launch restraints. But then the preparation to actually make the deployment happen, all the activation sequence and the activation of the rotary joint, is all performed by the ground team.

"When we wake up on flight day six, if everything goes well the ground is going to be ready to go. We position a few cameras so we can monitor the deployment and then we go to the computer and command the arrays to deploy. Now, hopefully, everything will go very smoothly and the problem that we had on 97 we think has been solved. Hopefully, everything will go smooth and we'll get the arrays out in a couple of orbits. The P4 arrays are identical to P6, which was attached to the space station during shuttle mission STS-97 in December 2000. When the first blanket was deployed, engineers were surprised to see several of the blanket panels had stuck together. When they jerked free, a tensioning cable jumped its guides and required repairs on a subsequent spacewalk. For the second array's deployment, the crew let the sun warm up the array and deployed it in a so-called high-tension mode. That technique worked, and the array unfurled without incident.

For the P4 deploy, flight controllers will extend a single bay of each mast - a few feet worth - while the Atlantis astronauts sleep. The crew then will extend the 4A mast to a distance of 49 percent, wait a half hour or so for additional solar heating, and then the rest of the way to full extension. They will repeat that process for the 2A mast.

"We're not too terribly concerned about stiction on the deploy," Tanner said. "We know it might happen in certain panels. The team went hard to work after STS-97 to figure out the mechanism of stiction and what we can do to reduce it. They came up with a good operational plan to nominally deploy.

"Now if for some reason one or two panels sticks after all that, then we can go out EVA, it would be on EVA 3, and actually manually peel the panels apart for the first 40 inches or so and doing a nominal deploy after that. All of our tests say they will peel open very easily. So we're not too terribly concerned about that."

DATE/EDT.......DD...HH...MM...EVENT

09/01/06
Fri 12:25 AM...04...07...55...MCC: 4A mast deploy (1 section)
Fri 01:55 AM...04...09...25...MCC: 2A mast deploy (1 section)
Fri 05:30 AM...04...13...00...STS/ISS crew wakeup
Fri 07:00 AM...04...14...30...SSRMS reconfig
Fri 09:05 AM...04...16...35...STS: 4A mast deploy to 49 percent
Fri 09:45 AM...04...17...15...STS: 4A mast deploy to 100 percent
Fri 10:45 AM...04...18...15...STS: 2A mast deploy to 49 percent
Fri 11:25 AM...04...18...55...STS: 2A mast deploy to 100 percent
Fri 01:00 PM...04...20...30...Crew meals begin
Fri 02:00 PM...04...21...30...SSRMS walk off reconfig
Fri 02:20 PM...04...21...50...SSRMS double walk off to lab
Fri 02:25 PM...04...21...55...Spacesuit servicing
Fri 04:30 PM...05...00...00...PAO event (STS CDR, ISS CDR, FE-2)
Fri 04:30 PM...05...00...00...EVA tool config
Fri 05:00 PM...05...00...30...Transfer tagup
Fri 05:05 PM...05...00...35...PAO event (STS CDR, MS-4)
Fri 05:05 PM...05...00...35...Infrared camera setup
Fri 05:25 PM...05...00...55...EVA-3: Procedures review
Fri 07:55 PM...05...03...25...EVA-3: Campout mask pre-breathe
Fri 08:40 PM...05...04...10...EVA-3: Crew lock 10.2 depress
Fri 09:00 PM...05...04...30...ISS crew sleep begins
Fri 09:30 PM...05...05...00...STS crew sleep begins (EV1/EV2 in airlock)

"When we wake up in the morning I will be the only one over on the shuttle, and I'm going to be providing the station with views as the solar array wings are deployed. The balance of the shuttle crew will be on the station in various capacities: Brent will be actually unfurling of the mast canister, which will pull the solar arrays from their blanket boxes. ... I'd like to think we have (the stiction) problems circumvented."

Suffredini said experience gained during the STS-97 mission in 2000 should result in a smooth deploy.

"The good news is we've done it twice before," Suffredini said. "The first time we deployed one of these arrays, we learned about a stiction issue that existed. After quite a bit of work during that mission, we deployed the second array in a little bit different technique, which allowed us to be successful. We learned a lot about techniques to get these arrays out without having the tension wire come loose, which is what happened when we tried to deploy the first one. It turns out after a lot of work ... we figured out a fix to go back in there to put it back in its original condition. And of course, the arrays have been fine ever since.

Using an engineering model, "we did quite a bit of testing on this stiction issue and how these arrays can stick together based on the silicon bead that's on the arrays and then we compress them for long periods of time before they go fly. And that was basically the cause of the problem. Over a long period of time this silicon would tend to attach itself to the back part of the array. And so we've done a number of things, largely operational changes but also on how we dealt with the arrays."

While the arrays were compressed for shipment to Florida, that pressure was relaxed until shortly before final preparations.

"Probably the largest changes were operational," Suffredini said. "We will partially deploy the array about one bay's worth and we'll let it warm up and sort of expand a little bit. Then the actual deploy process a little bit later will have us deploy the array halfway and then you'll see us sit for about 30 minutes as we warm it up and then we'll go the rest of the way.

"In addition to that, we're using what we call a high-tension mode. Instead of leaving the lower part of the array free to move up and down as the array gets deployed, we learned we need to hold it down against the bottom of the blanket box. So the new technique holds it down and then this particular deploy lets the heat warm things up, to allow the silicon to free itself, is the process we'll use to deploy. I have a lot of confidence in the deployment of the arrays."

The new solar arrays will not be rotated on the SARJ because of interference with the port wing of the P6 array and they will not provide any power to the space station until reconfigurations during the next shuttle mission in December.

With the arrays deployed, the astronauts will move the Canadarm 2 space crane from the end of the truss back to the Destiny lab module. Some of the crew members will participate in media interviews while the rest gear up for a third spacewalk the next day by Tanner and Piper.

PREVIEW REPORT PART 7 --->