Assuming solar array deployment goes smoothly, Swanson and Forrester will spend the night in the Quest airlock module in preparation for a critical spacewalk to configure the SARJ for normal operation and to assist, if necessary, the retraction of the P6-2B solar array extending at right angles to the long axis of the station and the newly installed S4 arrays. P6 must be retracted 14 to 16 bays to permit the S4 arrays to rotate as required to track the sun.

But a partial retraction, while acceptable for a brief period, is not acceptable over the long haul. P6 must be moved by the station's robot arm in October to the left end of the main power truss and the solar array support masts are too fragile to withstand the sort of side-to-side forces they would experience if the move was attempted with more than just a few of the mast bays extended.

"Our whole objective with this plan is to try to reduce the overall time we spend on this array outside during the spacewalks," Beck explained. "And we're trying to complete all the planned activities we had originally had for this mission, so we're trying to minimize that time and trying to put ourselves in a good posture so we can retract it remotely, without the EVA crews assistance. So we start out doing that.

"Because we think it's very likely that the panels are not going to fold up properly, we initiate the retract (from the ground), we're going to start the morning of flight day six, right before our second spacewalk. The ground will actually do some configuration to try to minimize the tension on that array to hopefully give us the best chance for getting that panel to fold right. So the ground will actually do that before the crew ever starts their activities."

All four spacewalkers have received extensive training for assisting the retraction process during the second spacewalk and, if necessary, the third.

"If you've ever tried to fold a map, if you don't have the creases just lined up quite right it's very difficult to get it to fold up properly," Beck said. "It's a similar case here. ... That is one problem that we're anticipating with the 2B array.

Another possible problem is trouble with the guide wires that pass through grommets in each blanket slat.

"You can kind of think of these solar arrays sort of like window blinds, that these guidewires run through the center and through the edges of the array and that's to tend the solar array panels so they'll retract neatly just as if you were raising a blind, the panels on the blind would stack up," Beck said. "And so what happened is, these guidewires were getting hung up on the small rings that are attached to the arrays that the guide wires go through and it was causing the panels to retract unevenly and they were getting hung up. So what we're trying to avoid is that stack of panels being brought down towards the blanket box and possibly spilling out of the blanket box.

"We're expecting we're going to have similar problems with 2B, so our plan involves the initial retraction before we ever send the crew out of the airlock for their spacewalk. We hope to have about an hour of time to try to get the array to start the initial retraction and see if we're going to have that same backward panel folding problem that the 4B array experienced. if we do have that problem, we'll have some time that we can try to redeploy the array and then start the retraction again to see if we can correct the problem that way.

"If not, then the whole reason for doing it before that second spacewalk is that gives us the opportunity to have Pat and Steve correct that backward panel folding during their EVA.

"So once they get out the door, we'll get Pat on the station arm and Steve will also be up on the truss on the other side so that they can both assist us to get retracted," Beck said. "We're shooting for two or three mast bays because we think if we can get it retracted that far we'll have a good clear indication if the panels are folding properly. So if we need them to, we'll have them go up and push on that hinge so that the panels are allowed to fold up properly.

"Once we are done with that small amount of 2B retraction we're going to be doing during that second spacewalk, then Pat and Steve will continue on with their other tasks, which involve prepping that solar alpha rotary joint. They will be positioning the second drive lock assembly so the ground can engage that. They will be installing brace beams, which provide additional structural integrity to the element to carry on orbit loads. And then they'll also start to release the launch locks."

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

06/13/07
Wed 12:18 AM...04...04...40...EVA-2: Crew lock to 10.2 psi
Wed 12:38 AM...04...05...00...ISS crew sleep begins
Wed 01:08 AM...04...05...30...STS crew sleep begins
Wed 07:48 AM...04...12...10...MCC: P6-2B retracted 1/2 bay
Wed 09:08 AM...04...13...30...STS/ISS crew wakeup
Wed 09:48 AM...04...14...10...EVA-2: Crew lock repress to 14.7 psi
Wed 10:03 AM...04...14...25...EVA-2: Hygiene break
Wed 10:38 AM...04...15...00...EVA-2: Crew lock depress to 10.2 psi
Wed 10:58 AM...04...15...20...EVA-2: Camp out EVA preps
Wed 11:23 AM...04...15...45...SSRMS set for retraction viewing
Wed 12:03 PM...04...16...25...P6-2B retraction operations
Wed 12:28 PM...04...16...50...EVA-2: Spacesuit purge
Wed 12:43 PM...04...17...05...EVA-2: Spacesuit pre-breathe
Wed 12:58 PM...04...17...20...SSRMS maneuver
Wed 01:33 PM...04...17...55...EVA-2: Crew lock depressurization
Wed 02:08 PM...04...18...30...EVA-2: Airlock egress
Wed 02:48 PM...04...19...10...EVA-2: P6-2B retraction
Wed 03:33 PM...04...19...55...EVA-2: Deploy SARJ BR
Wed 04:03 PM...04...20...25...EVA-2: EV3: Install SARJ DLA 1
Wed 04:03 PM...04...20...25...EVA-2: EV4: SARJ locks
Wed 05:03 PM...04...21...25...EVA-2: EV3: SARJ locks
Wed 07:58 PM...05...00...20...EVA-2: Cleanup and ingress
Wed 08:33 PM...05...00...55...EVA-2: Airlock repressurization
Wed 08:48 PM...05...01...10...Spacesuit servicing

06/14/07
Thu 12:08 AM...05...04...30...ISS crew sleep begins
Thu 12:38 AM...05...05...00...STS crew sleep begins

"If it turns out that they have some problems, they'll let us know that before we come out of the hatch and we'll grab a different set of tools and we'll head up that direction and be prepared to help with that. If things are going well, we probably are still going to go up and get into that vicinity for about the first hour of our spacewalk and be ready to help out, give direction, maybe, if we need to, help the solar array panels fold the right way.

"It's almost like folding a map in your car - you know, once you've unfolded the first time you think it would be easy to get it back but it's not, and these things have been extended for a while and they have a tendency to want to fold the wrong direction back on themselves. And so we'll just be ready to help out with whatever is required."

Using custom-built, insulated tools, the spacewalkers can push the blankets along creases to help them fold or manually push grommets along guide wires should any hang ups be spotted.

"I would push along the hinge line if it's trying to fold the wrong way," Forrester said. "The other thing is. that sometimes there's a possibility that these guide wires that help guide the solar array down into the box can get hung up on the panels themselves, in which case I'll use this same tool or another tool that they have kind of manufactured and help that, assist that along the hinges or the where the guide wires run through the panels themselves. And the other part is just watching and being up there to help direct as they're doing the commands inside the space station."

But Forrester and Swanson will only spend an hour or so on the P6 retraction. After that, even if the array remains hung up, they will turn their attention to getting the starboard SARJ activated.

"Even if we run into a lot of problems, we're only going to devote about the first hour of our spacewalk to (P6-2B retraction)," Forrester said. "At that point, they'll have enough information on the ground to begin to prepare for the next spacewalk, and we will move out to the SARJ and begin the spacewalk that we had already trained for."

And there's plenty to do.

The S3 solar alpha rotary joint, or SARJ, is equipped with two redundant motors that drive a large gear to slowly spin the outboard solar arrays so they can stay roughly face on to the sun as the station flies through each 90 minute orbit. Power from the arrays, along with data and computer commands, passes through the center of the SARJ without regard to orientation.

Before the SARJ can be activated, both motors, called drive lock assemblies, must be manually engaged and then precisely positioned by flight controllers to ensure the drive teeth mesh properly with the main gear. Braces must be positioned, launch locks and thermal shrouds removed, along with a keel pin used to help mount the S3/S4 truss segments in the shuttle's cargo bay.

In addition, the astronauts must prepare rails on the front face of the new segments to extend the "track" used by the mobile transporter to carry the station's robot arm to and from various work sites.

During the second spacewalk, Forrester and Swanson will concentrate on positioning the second DLA, removing a variety of launch locks and installing the necessary braces to stiffen the truss segment as required.

"We are going out to remove a series of launch locks," Forrester said. "There's 16 of them that are holding this rotary joint, keeping it from turning. That's mainly because of the launch loads in the shuttle. And so once we get out there, they're all covered by thermal covers, and we'll remove those covers then reach in and remove those launch locks. They are basically about a 10-by-12 steel plate being held on by four bolts. We'll remove those launch locks and then we'll put those thermal covers back on for protection, and we'll bring those 16 launch locks in.

"There are also six launch restraints that we will remove," he said. "There are several other pieces of structure that help just strengthen the actual truss section. Those were not installed for launch also, so there's a little flexibility as the shuttle kind of shakes and bends on the way up there, that the truss would not be damaged. So it's really just preparation to be able to rotate the solar array."

During installation of the P3/P4 truss segments last September, spacewalkers Dan Burbank and Steve MacLean ran into problems with supposedly captive washers that floated away during removal of the port SARJ launch locks. More troubling, it took all their combined strength and about a half hour of work to free one stuck bolt that could have prevented the SARJ from rotating.

This time around, Forrester and Swanson will be equipped with a custom-built "torque multiplier" to permit them to apply the force necessary to free tight bolts without stripping the any threads.

"They took a torque multiplier that's in the inventory, that was used for shuttle payloads, and we have modified it so that it will fit on these bolts," Forrester said. "Using that, we don't think we'll have any problem pulling any of the launch restraints off."

Continue to Part 9 -->