Spacewalkers to re-attach P6 solar array truss today
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 30, 2007
Astronauts Scott Parazynski and Doug Wheelock are gearing up for a dramatic spacewalk today to re-attach the 35,000-pound P6 solar array truss after a two-day, 145-foot move, bolting it to the far left end of the space station's main power truss where it will remain for the life of the lab complex. Parazynski also plans to carry out a brief inspection of a second solar array rotary joint to provide more insight into what might be causing contamination in a joint inspected Sunday.
P6 was the first set of U.S. solar arrays launched to the station, attached to a central truss in 2000 to provide the power needed during the early stages of construction. The lab's main power truss is now built, with solar arrays - port 4 (P4) and starboard 4 (S4) - now in place on both sides, clearing the way to move P6 to its permanent mounting point on the left end of the power truss. A fourth set of arrays, S6, will be mounted on the right end of the truss next year.
Getting the P6 arrays re-extended on the end of the port power truss is critical for continuing station assembly. Because of metallic contamination in the right-side solar array rotary joint, the S4 solar array panels on the starboard side of the station are locked in place and are not turning to track the sun, reducing the amount of power available to the station's systems.
To support the upcoming addition of European and Japanese research modules, NASA needs to get the P6 arrays re-extended and rotating alongside the P4 panels to generate as much power as possible while engineers figure out how to resolve the contamination issue in the right-side rotary joint.
The P6 truss, its two huge solar panels stowed and its electrical systems shut down, was detached during a spacewalk by Parazynski and Dan Tani on Sunday. The station's robot arm handed the segment off to the shuttle's arm on Monday, moved 80 feet to a work site at the left end of the power truss and re-grappled P6 for today's installation. The arm will be operated by Stephanie Wilson and Tani from inside the Destiny laboratory module.
To install P6, the 50-foot-long station arm will be fully extended from its position at work site No. 8 on the power truss, moving the massive segment outboard of the P4 arrays and a short spacer segment known as P5. Parazynski and Wheelock will be positioned near P5 to provide guidance cues for Wilson and Tani. Once the base of the segment is close enough to P5, Wheelock will activate a capture claw to pull the two components together before bolts at all four corners are engaged to complete the 145-foot move.
"On flight day 8 I'll be going out again with Doug Wheelock, on what I think will be our most spectacular spacewalk," Parazynski said in a NASA interview. "We'll be at the very tip of the space station, as far as you can possibly get from the comforts of the airlock, a (greater) distance then we've ever had the opportunity to go. We'll have Dan and Stephanie at the controls of the space station robotic arm. We'll be giving them verbal feedback on the precise alignment of the P6 truss relative to the P5 truss.
"Once we see everything is perfectly aligned, then they'll be issuing a command to bring the P6 into opposition with the mating interface there. Hopefully, we've given them the best insight possible, everything is perfectly aligned and we'll drive those four RTAS bolts around the corners of the truss, and then it'll be hard mated, where P6 will live for the duration of the international space station."
Parazynski will connect four power cables and both spacewalkers will remove thermal covers that were placed over critical electrical components called sequential shunt units before P6 was detached. Parazynski then plans to release restraints holding P6's ammonia radiator panels in place so the astronauts inside the station can deploy them. Wheelock will make his way back to the shuttle to move a spare 525-pound power switching unit to an external stowage platform near the station's airlock.
"Doug and I will mate several connectors, power and data, to and from the P6 truss," Parazynski said. "We'll then travel out to the very tip of P6 and remove those blankets that we installed on EVA-1 over the sequential shunt unit boxes. Doug will then depart and head back toward the center part of the space station, for the lab. He'll set up the shuttle arm with a foot restraint. And he'll get in work to transfer the MBSU, or the Main Bus Switching Unit - we have that on a side wall carrier in the payload bay - he'll bring that up to space station.
"Later in the spacewalk I'll help him attach that to a kind of a maintenance and logistics depot that we call ESP-2, or External Stowage Platform number 2. It's very close to the airlock. While he's off working with the robotic arm, Stephanie and George Zamka on the flight deck of the shuttle will be controlling that portion of the flight. I'll stay out at the tip of P6 and I'll deploy or enable deployment of the aft radiator. There's several cinches and other interfaces that I'll have to work with, to enable that. Once that's complete, I'll get out of the way and then the ground controllers are really off to the races."
Deployment of the P6 solar panels is scheduled to begin toward the end of the spacewalk and should be complete about an hour after it is over. Fully extended, the panels will stretch 240 feet from tip to tip.
"There's actually three separate teams in mission control working on the power systems of P6," Parazynski said. "Very complex choreography and sequenced events such that we can hopefully get both solar arrays deployed on flight day 8. That's our goal. So as I clear the P6 worksite, the radiator will come out and hopefully fairly soon thereafter we'll start deploying the solar array wings. Pam and Dan Tani inside will be on a PCS, a laptop display and looking at various cameras and working in close concert with folks on the ground to deploy those radiators."
In the original flight plan, Parazynski planned to leave P6 after releasing the radiator restraints and move to the P1 truss segment to activate the deployment mechanism on two large radiators, part of the station's main cooling system. But the plan was changed in the wake of Sunday's spacewalk when Tani, inspecting the starboard solar array rotary joint - used to turn outboard arrays to keep them face on to the sun - discovered metallic shavings contaminating the interior of the mechanism.
NASA managers decided to have Parazynski inspect the port-side solar alpha rotary joint, or SARJ, during today's spacewalk to provide a comparison and document the condition of a joint known to be operating smoothly. NASA's Mission Management Team decided Monday to extend Discovery's flight one day and to revise the crew's fourth spacewalk Thursday to include a more thorough inspection of the right-side SARJ. A fifth and final spacewalk is now planned for Saturday, by station commander Peggy Whitson and flight engineer Yuri Malenchenko, to continue outfitting the newly installed Harmony module.
Here is a timeline of today's activity. Readers are advised that as of 3 a.m., the spacewalkers were running well ahead of schedule (in EDT and mission elapsed time; include revision E of the NASA television schedule):
EDT........DD...HH...MM...EVENT 12:38 AM...06...13...00...STS/ISS crew wakeup 01:13 AM...06...13...35...EVA-3: Airlock repress to 14.7 psi; hygiene break 02:23 AM...06...14...45...EVA-3; Campout EVA preps 03:53 AM...06...16...15...EVA-3: Spacesuit purge 04:08 AM...06...16...30...EVA-3: Spacesuit oxygen pre-breathe 05:08 AM...06...17...30...EVA-3: Airlock depressurization 05:28 AM...06...17...50...EVA-3: Spacesuits to battery power 05:33 AM...06...17...55...EVA-3: Airlock egress 06:03 AM...06...18...25...EVA-3: Parazynski: Attach P6 to P5 06:18 AM...06...18...40...EVA-3: Wheelock: Attach P6 to P5 08:13 AM...06...20...35...Station arm (SSRMS): P6 ungrapple 08:13 AM...06...20...35...EVA-3: Parazynski: P5/P6 umbilical connections 08:48 AM...06...21...10...EVA-3: Wheelock: P5/P6 umbilical connections 08:53 AM...06...21...15...EVA-3: Parazynski: SSU shroud removal 09:03 AM...06...21...25...EVA-3: Wheelock: SSU shroud removal 09:28 AM...06...21...50...EVA-3: Parazynski: Radiator cinch release 10:03 AM...06...22...25...EVA-3: Wheelock: MBSU transfer 10:28 AM...06...22...50...EVA-3: Parazynski: Port SARJ inspection 10:33 AM...06...22...55...P6 radiator deployment 11:08 AM...06...23...30...EVA-3: Parazynski: Radiator squib firing unit (if time available) 11:18 AM...06...23...40...EVA-3: Parazynski: MBSU transfer 11:58 AM...07...00...20...P6 solar array deployment begins 12:03 PM...07...00...25...EVA-3: Parazynski: Airlock ingress 12:18 PM...07...00...40...EVA-3: Wheelock: Airlock ingress 12:38 PM...07...01...00...EVA-3: Airlock repressurization 12:38 PM...07...01...00...2B array 100 percent deployed 01:28 PM...07...01...50...4B array 100 percent deployed 01:48 PM...07...02...10...SSRMS powerdown 02:30 PM...07...02...52...Mission status briefing on NASA TV 04:08 PM...07...04...30...ISS crew sleep begins 04:38 PM...07...05...00...STS crew sleep begins 05:00 PM...07...05...22...Daily video highlights reel on NASA TV 10:30 PM...07...10...52...Flight director update on NASA TV
Deployment of the P6 solar arrays will be carefully monitored, in part because of problems experienced retracting the huge panels during a previous shuttle mission when frayed guidewires hung up on grommets and the arrays did not fold properly along panel hinge lines. NASA managers are confident the arrays will deploy smoothly today because like a road map, it is easier to pull the folding panels open than it is to fold them neatly into compact storage boxes.
"The mechanics of the retraction versus the deploy are very different," said flight director Derek Hassmann. "When we deploy the array, there's significantly more force, or load, on the array. So I would not expect that type of grommet sticking to be a problem. Another problem we saw in multiple places on the 2B and 4B arrays during the retraction was the folding issue where the hinges of the array did not fold in the proper direction. ... We don't expect that to be a problem on the deploy, either, because again, you're applying a consistent load across each of the solar array wings.
"So there's a fair amount of confidence and a fair amount of optimism that the deploy's going to go well. We've looked at all the failure mechanisms that we think are possible or conceivable and it's very different from a retraction. I have quite a bit of confidence this will go well. If it doesn't, we have time built into the timeline and the crew is trained to go outside and do a spacewalk and help us out if we need that kind of help."
But there is not a lot spacewalking astronauts can do if the deployment runs into problems. Because of P6's location at the far left end of the power truss, the station's robot arm does not have enough reach to position a spacewalker beyond the base of the arrays. The astronauts could manually extend the panels using power tools if necessary, but they will be unable to reach more than the lowest sections of the two array masts.
"With P6 on Z1 (in its original position), we were able to put an EVA crew member on the station robotic arm and essentially maneuver him to any place on the array where we thought we had a problem," Hassmann said. "Basically, they would identify an area of interest or perhaps a grommet snag or any other problem they might have seen, then we could maneuver them to the area of interest.
"With P6 on P5, the (station arm) simply cannot reach. We can use it for viewing, but with the mobile transporter at work site 8 and the station robotic arm extended as far as it can practically get, we can't use it to support an EVA crew member on the arm. If we do need to support any kind of contingency operations, we'll have the EVA crew basically in an extending device attached to the structure of P6 and their access will only be to the first couple of panels, essentially, and then to the blanket box. So that's one limitation we're going to have to deal with."