To get to the P1-P3/P4 worksite, Tanner and Piper will first exit the Quest airlock, using 55-foot-long safety tethers. Crossing over a spur to the S0 truss atop the Destiny laboratory module, the spacewalkers will move across the forward face of the truss to the port side and, reaching the end of their safety lines, hook up to a different 55-foot tether. Once at the P1-P3 interface, they will swap tethers again, switching to 85-foot safety lines.

A key aspect of the spacewalk is the tight choreography between flight controllers, Tanner and Piper as the ground powers down one channel of the station's electrical system at a time to permit the astronauts to safely plug in the big umbilical cables that will route power and data to and from P3/P4.

"The ground and the crew are very highly choreographed," McCullough said. "The ground has about 100 pages of ground procedures to execute in order to power down and safe connections for the EV crew to mate the 13 umbilicals. They're done on two different channels, so we have to power down one channel first, give them a go to hook up those umbilicals, then they give us a go and we power that channel back up again. We have to complete that before we can take down the next channel so we can maintain connectivity and power to the space station.

"It takes about an hour and a half between the two sets of umbilicals and when that's complete, the second set of umbilicals will be given a go and they'll do that. In between that time, there are other activities for the crew to do to get prepared for solar array deploy on flight day six."

For astronauts in the Destiny lab module, McCullough said in an interview, "a segment of the lights are going to go out that aren't on that channel. You want to be on the cooling loop system that's supplied by the other channel, so we switch over to that. You want to make sure your air circulation system is powered. ... We want to make sure we're switched over to the other side as much as possible."

In one case, he said, the astronauts in the lab will connect a jumper cable to keep avionics rack 2 going, which houses critical command and control computers that otherwise would get shut down during the P3/P4 powerup/powerdown cycle.

Along with hooking up the umbilicals, Tanner and Piper will remove a variety of launch locks and restraints to prepare the solar arrays for deployment later in the mission and begin the process of preparing the massive SARJ for operation.

"The solar alpha rotary joint is locked in place for launch," McCullough said. "It has 16 launch locks and a lot of braces that need to be installed to support rotation and we can't deploy the arrays until all of those things are completed."

Tanner's call sign is EV-1 and he will wear a spacesuit with solid red stripes around the legs. Piper, wearing a suit with no markings, is EV-2.

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

08/30/06
Wed 05:30 AM...02...13...00...STS/ISS crew wakeup
Wed 06:00 AM...02...13...30...EVA-1: Hygiene break; prebreathe
Wed 06:15 AM...02...13...45...EVA-1: Airlock repress
Wed 06:45 AM...02...14...15...EVA-1: 10.2 depress
Wed 07:20 AM...02...14...50...EVA-1: Campout EVA preps
Wed 07:20 AM...02...14...50...SSRMS moves P3/4 to pre-install position
Wed 08:40 AM...02...16...10...SSRMS maneuver to latch position
Wed 08:50 AM...02...16...20...EVA-1: Spacesuit prebreathe
Wed 09:10 AM...02...16...40...P1/P3 bolts engaged
Wed 09:55 AM...02...17...25...EVA-1: Crew lock depressurization
Wed 10:10 AM...02...17...40...SSRMS ungrapple
Wed 10:30 AM...02...18...00...EVA-1: Airlock egress; tool setup
Wed 11:05 AM...02...18...35...EVA-1: EV1: Connect P1/P3 lower cable tray
Wed 11:05 AM...02...18...35...EVA-1: EV2: Release aft SA blanket
                                            box restraint
Wed 12:05 PM...02...19...35...EVA-1: EV1: Release aft BGA restraint
Wed 12:05 PM...02...19...35...EVA-1: EV2: Release forward SA
                                            blanket box restraint
Wed 12:30 PM...02...20...00...ISS: EVA-2 tools configured
Wed 12:50 PM...02...20...20...EVA-1: EV1: Solar alpha rotary joint prep
Wed 01:00 PM...02...20...30...EVA-1: EV1: Unstow aft SA blanket box restraint
Wed 01:05 PM...02...20...35...EVA-1: EV2: Release forward BGA restraint
Wed 01:30 PM...02...21...00...EVA-1: EV1: SARJ preps
Wed 01:50 PM...02...21...20...EVA-1: EV2: Unstow forward SA blanket box
Wed 02:05 PM...02...21...35...EVA-1: EV1: Connect P1/P3 upper cable tray
Wed 02:20 PM...02...21...50...EVA-1: EV2: SARJ prep
Wed 03:20 PM...02...22...50...EVA-1: EV1: SARJ prep
Wed 04:10 PM...02...23...40...EVA-1: Cleanup
Wed 04:50 PM...03...00...20...EVA-1: Airlock ingress/repress
Wed 06:40 PM...03...02...10...EVA-2: Procedures review
Wed 07:55 PM...03...03...25...EVA-2: EV3/EV4 campout mask prebreathe
Wed 08:40 PM...03...04...10...EVA-2: Crew lock to 10.2 psi
Wed 09:00 PM...03...04...30...ISS crew sleep begins
Wed 09:30 PM...03...05...00...STS crew sleep begins (EV3/EV4 in airlock)

"While he's doing that, I'm starting to remove the launch locks on the solar array blanket boxes. The solar arrays are folded up into what we call blanket boxes. The blanket boxes are attached to a mast canister, which is attached to the four-bar linkage, which is attached to the P4 structure. In order to get that all to fit inside the shuttle bay and also have it be safe for the vibrations of launch there are a number of launch locks and bolts that just hold it all together.

"On EVA 1, I go out and start removing these bolts. The blanket boxes, instead of being out like you see them in all the pictures with the solar arrays deployed, are folded up together. They have big bolts that hold them together so I go out and I start removing all the bolts, first on the aft side and then I go to the forward side. Meanwhile, Joe's done with the umbilicals. He comes out and gets one of the solar arrays ... swings the four-bar out and then he climbs out onto the very end of the mast canister and swings the two blanket boxes out.

"While he's doing that, I'm out on the forward one, and I do the same thing. Now the blanket boxes are pretty much ready for the ground to start commanding them as far as unlatching them and making sure that all the pins that hold them in are all deploy. That gets that ready for the solar array deploys. We're not quite ready to deploy the arrays yet because, in order to get the P3/P4 to fit inside the shuttle bay, we have to have the alpha joint rotated 180 degrees. In order to rotate it back to the zero position, there are two drive mechanisms that needed to be deployed, the DLAs (drive lock assemblies). We start working on those so that they can command the SARJ. That's pretty much what EVA 1 is.

Tanner, his feet anchored in a foot restraint, will mate the first six umbilical cables working at the lower of two cable trays on P3. Piper, meanwhile, will be preparing the solar array wings for deployment, working from a foot restraint on P4 to access two sets of launch restraints, one inboard and one outboard, holding the blanket boxes in place.

Tanner will assist once the first six umbilicals are connected, releasing two restraints securing one of two beta gimbal assemblies. The BGAs are used to control the pitch of the array wings once they are deployed. After the restraints are released, the blanket boxes and the canisters holding the telescoping masts that will extend the array blankets will be rolled into their deploy positions by manually pushing open the four-bar linkages.

After stowing a massive keel pin that helped hold P3/P4 in place in the shuttle's cargo bay, Tanner will move to the mast canisters and rotate the 4A blanket boxes into position, swinging them through an arc of 90 degrees and locking them in place with a strut to hold them in position. Piper will rotate the 2A blanket boxes into place and release the restraints on the other BGA.

Once both sets of blanket boxes are extended in the deploy position, Tanner and Piper will release latches allowing the mast canisters to open. Tanner then will move up to the top of P4 to mate seven umbilical cables while Piper removes thermal covers on the SARJ and repositions one of the two drive lock assembly motors so its gears engage. She also will engage four "stiffeners" needed to provide additional structural support.

With the final set of electrical cables in place, Tanner will make his way up the Z1 truss atop the Unity module to remove a circuit interrupt device, or CID, as a get-ahead task for the next assembly mission. The CIDs act as circuit breakers in the station's electrical system. With CID-6 ion hand, Tanner will float back down the S0 truss and remove CID-8.

After temporarily stowing the two CIDs, Tanner will rejoin Piper and reposition the other DLA to engage its gears. The two DLAs are redundant and either one can drive the rotary joint and the deployed solar arrays.

Before returning to the airlock, Tanner and Piper will remove thermal shrouds around electrical components on the SARJ that are no longer needed.

"The big challenge about that EVA is timing," Tanner told CBS News. "We have to go through our tasks fairly expeditiously, I've got to get that lower tray connected as quickly as I can because that starts a clock on the ground with that 100 pages John McCullough was talking about. They've got to execute many power ups and start talking to the boxes."

Tanner was a good choice for STS-115. He and Jett flew together on an earlier station assembly mission to attach the P6 solar arrays atop the Z1 truss.

"Deploying the arrays, we've done it before, we know how that should go. I think there's going to be a little bit of a problem on the four bar deploy. On (assembly mission) 4A, we had a problem of them not wanting to go at all and Carlos (Noriega) and I had to push pretty hard just to get them to move and even brought out a special tool to pull them as far as we could. And even with that, two of the latches when we left were not engaged.

"I'm convinced we're not going to have that problem. It's not going to go too fast, it's going to go about two thirds of the way to full deployment but this time the finish will be as easy as pushing it the last little bit. So expect that to happen, I'm not worried about it."

With spacewalk No. 1 complete, Burbank and MacLean will spend the night inside Quest to prepare their bodies for a second spacewalk the next day. The objectives of the second excursion are to release 16 launch locks and six launch restraints to free the SARJ ring mechanism for rotation. Burbank and MacLean also will complete the installation of stiffeners to provide the necessary structural rigidity.

"Steve and I are going to spend the bulk of EVA 2 removing the whole series of these 16 plus six launch locks and launch restraints," Burbank said in a NASA interview. "We're going to spend most of our time right in the middle section of the P3/P4 truss driving a lot of bolts with a lot of power tools. After all that's done, we've removed all this hardware that's kept the P3 and P4 Trusses properly oriented for launch, we're going to deploy the SARJ braces, the solar alpha rotary joint braces, a series reinforcement structures that will help to stabilize that, that alpha rotary joint on both sides. So we'll spend a lot of time doing that.

"Then, time permitting, we'll be able to do some get-aheads, some of the work we're planning on doing on EVA 3. But EVA 2's kind of different. We're going out with a different kind of a CO2 scrubber in the (spacesuits) that allow us to go a little bit longer than planned if necessary. ... We've got a fairly ambitious suite of activities set up for EVA 1, and hopefully Joe and Heide will be able to get all that done, and then we've got a little bit of money in the bank on EVA 2 to go a little long if we have some problem with the hardware, because we'd really like to not have to spend another day before we deploy the solar wings here."

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

08/31/06
Thu 05:30 AM...03...13...00...STS/ISS crew wakeup
Thu 06:00 AM...03...13...30...EVA-2: Hygiene break/prebreathe
Thu 06:15 AM...03...13...45...EVA-2: Crew lock repress
Thu 06:45 AM...03...14...15...EVA-2: Crew lock depress to 10.2 psi
Thu 07:20 AM...03...14...50...EVA-2: Campout EVA prep
Thu 08:50 AM...03...16...20...EVA-2: EMU purge
Thu 09:05 AM...03...16...35...EVA-2: EMU prebreathe
Thu 09:55 AM...03...17...25...EVA-2: Crew lock depressurization
Thu 10:30 AM...03...18...00...EVA-2: Airlock egress; setup
Thu 10:55 AM...03...18...25...SSRMS camera viewing
Thu 11:10 AM...03...18...40...EVA-2: EV3: Remove aft sequential
                                    shunt unit shroud
Thu 11:10 AM...03...18...40...EVA-2: EV4: SARJ prep
Thu 11:10 AM...03...18...40...EVA-2: EV3: SARJ prep
Thu 01:25 PM...03...20...55...ISS: Transfer operations
Thu 03:40 PM...03...23...10...EVA-2: Deploy SARJ brace
Thu 04:10 PM...03...23...40...EVA-2: Payload bay cleanup, airlock ingress
Thu 04:30 PM...04...00...00...MCC: SA/SARJ activation/checkout begins
Thu 04:30 PM...04...00...00...Transfer tagup
Thu 04:30 PM...04...00...00...EVA-2: Airlock ingress
Thu 04:50 PM...04...00...20...EVA-2: Airlock repressurization
Thu 06:30 PM...04...02...00...12A EMU swap EVA-2
Thu 09:00 PM...04...04...30...ISS crew sleep begins
Thu 09:30 PM...04...05...00...STS crew sleep begins

Burbank and MacLean will use the same tether protocol to reach the P3/P4 worksite on the left end of the truss. Once in place, they will start removing the 16 launch locks, a multi-step procedure that requires them to first release an inboard clamp; remove and temporarily stow a thermal cover; remove four bolts from the launch lock; and reinstall the thermal cover.

Once that work is done and the bolts are safely stowed in a transfer bag, the spacewalkers will remove six outboard launch restraints and install the brace beams needed to stiffen the inboard side of the SARJ interface.

"Dan and I spend a lot of time around that solar array rotary joint, making sure that it's ready so that that joint can move later on during the mission," MacLean said. "So we're removing all the launch locks associated with that, and that takes us a while because it was very important to minimize the vibration of that area during launch and we have several launch locks to take off. In addition, we will stiffen up the truss. ... Here we are, construction engineers, where we'll basically remove a brace and then bring it over and then reattach it, and that stiffens up the torsional mode of the truss. We do something similar on the, on the P4 side.

"We have some AJIS (Alpha Joint Interface Structure) struts that if Joe and Heide haven't got them done the day before we will do the AJIS struts on the P4 side, which again stiffen up the torsional mode of the P4 side."

PREVIEW REPORT PART 6 --->