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STS-120 day 5 highlights

Highlights from Flight Day 5 see the astronauts enter into the newly-installed Harmony module.

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STS-120 day 4 highlights

The Flight Day 4 highlights movie shows Harmony's attachment to the station and the Discovery mission's first spacewalk.

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STS-120 day 3 highlights

This movie shows the highlights from Flight Day 3 as Discovery docked to the space station.

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STS-120 day 2 highlights

Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights.

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STS-120 launch videos

Check out all angles of space shuttle Discovery's launch with our extensive video collection.

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STS-120 day 1 highlights

The highlights from shuttle Discovery's launch day are packaged into this movie.

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STS-120: Crew arrival

The space shuttle Discovery astronauts arrive at the Kennedy Space Center for their countdown to launch.

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STS-120: The programs

In advance of shuttle Discovery's STS-120 mission to the station, managers from both programs discuss the flight.

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STS-120: The mission

Discovery's trip to the station will install the Harmony module and move the P6 solar wing truss. The flight directors present a detailed overview of STS-120.

 Part 1 | Part 2

STS-120: Spacewalks

Five spacewalks are planned during Discovery's STS-120 assembly mission to the station. Lead spacewalk officer Dina Contella previews the EVAs.

 Full briefing
 EVA 1 summary
 EVA 2 summary
 EVA 3 summary
 EVA 4 summary
 EVA 5 summary

The Discovery crew

The Discovery astronauts, led by commander Pam Melroy, meet the press in the traditional pre-flight news conference.

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Spacewalker finds debris in critical station truss joint
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 28, 2007

Space station engineers are scrambling to determine the source of unexpected debris in a critical solar array rotary joint and considering whether to order an additional, more thorough spacewalk inspection to figure out what sort of downstream repair work might be necessary.

The international space station's right-side solar alpha rotary joint, or SARJ - a 10-foot-wide, 2,500-pound motorized gear used to turn outboard arrays to keep them face on to the sun - needs to work normally to generate the electricity required by the growing space station's myriad systems.

The Discovery astronauts attached a new module to the station Friday that will serve as the attachment point for European and Japanese research labs scheduled for launch in December, February and April.

Mike Suffredini, manager of the space station program at the Johnson Space Center in Houston, said the starboard SARJ can be locked in place in the near term while engineers study the contamination problem and its possible solution. He said even with the starboard S4 solar arrays locked in place, they would generate enough power, in concert with two set of arrays on the left side of the station's main truss, to permit launch of the European Space Agency's Columbus module Dec. 6 as planned.

But at some point over the next few months, the problem must be resolved or the station might not be able to provide the required power when two Japanese research modules are attached in February and April.

"We have lots of time to work through this problem, it's not an immediate issue," Suffredini said. "The system is robust in terms of providing the power we need. We know how to operate around it so we can get all the power that we require. So we can pamper, if you will, the joint while we sort through the anomaly and make sure we fully understand it before we go back to nominal operation."

The space station ultimately will be equipped with four sets of huge solar arrays, two on each end of a beam the length of a football field. A SARJ on each side of the truss rotates the outboard solar arrays like giant paddle wheels as the station circles the Earth to maximize electrical generation.

The station currently is equipped with one set of arrays on each side of the power truss: S4, or starboard 4, on the right and P4 on the left. A third set of arrays, P6, initially was mounted at the center of the station to provide power during the initial stages of construction. That 35,000-pound segment, with its arrays stowed, was detached today and will be installed on the far left end of the power truss during a spacewalk Tuesday. The fourth and final set of arrays, S6, is scheduled for launch next Fall.

The port SARJ has operated normally since its installation last year and the starboard joint, installed last June, showed no immediate problems. But just under two months ago, engineers began noticing higher vibration levels and power usage. While the port SARJ motor operates at an average of 0.1 amps, its counterpart on the right side has been averaging 0.2 to 0.3 amps with peaks up to 0.9 amps.

Believing an insulation panel might be rubbing against something in the mechanism, NASA managers added an inspection to today's spacewalk. Astronaut Dan Tani took a look around the perimeter of the joint and saw nothing out of the ordinary. But when he removed one of 22 insulation blankets to look inside, he was surprised to see what appeared to be metal shavings on the main bearing race and drive gear.

"We have been watching a slight increase in currents on the starboard SARJ joint," Suffredini said. "The currents indicated to us some friction increase in the joint, so that's why we asked the ops team if they would take a look. We did find what seems to be an indication of some particulate that we would not expect in the joint.

"In addition to that ... the flat surface right below the gear is the race the bearing runs on, it looks kind of mottled and it we would expect it to look shiny. There's about 1,000 pound force on that surface, so any little bit of particulate on that surface could potentially cause additional drag."

Each SARJ features two huge drive gears, one inboard and one outboard, and two drive lock assemblies, or motors, and associated electronics. Both DLAs can be positioned to engage the drive gear by remote control and both are on the outboard side of the starboard joint. Only one DLA is used at a time.

"This is a very low current motor that's driving these joints, very high precision joints," Suffredini said. "So any little bit of particulate, of course, can have an effect on the ability of the DLA's to overcome the friction in the joint. Of course, if the friction gets high enough, then we can't drive the joint. Now we're not at that point today, but it was important for us to start looking at it because we have had some peaks as high as .8 and .9 amps."

Tani described the debris in the joint as metallic shavings. Suffredini said engineers on the ground believe it may be aluminized mylar insulation, a tinfoil-like material on the interior of the 22 thermal blankets mounted around the joint. The blankets are anchored on the outboard side of the joint and extend across the drive gears like diving boards with about a half-inch of clearance. They rotate around the SARJ as the outboard truss rotates.

Suffredini said if any of the foil under one or more thermal blankets was rubbing against the outboard bearing race or gear, it would be damaged and that could explain the debris seen today. Finding the source of the debris may require removing all 22 thermal shields. How to clean up the debris that's already there could be a more difficult problem.

"We'll spend quite a bit of time trying to figure out what we should do next relative to this investigation," Suffredini said. "In the meantime, our plan is to limit use of the SARJ in what we call the auto-track function, simply the function that allows it to follow the sun as we go around the Earth. We have completed our assessment of the remainder of this mission and believe for the most part, we can keep it parked. We'll have to reposition it every so often in order to deal with a couple of thruster firings and, I believe, for undocking. But repositioning is not a big impact.

"In the meantime, the team is off assessing the ability to park the SARJ for the (period between Discovery's mission and the December launch of Columbus) and for the docked timeframe for 1E (the Columbus mission). My belief, and don't take this to the bank because the guys haven't finished their analysis, but I believe ... we'll have the power we need to limit the movement of the SARJ to the greatest extent possible and still be able to accomplish the objectives of our future missions.

"So, we have time to go work through this anomaly," he said. "We'll talk a lot about whether or not we want to modify one of the EVAs during (Discovery's) flight in order to look some more. I think the prevailing thought is the team would like to go ahead and take off the remainder of the covers. There's 22 in all, so we've looked under one, perhaps look under the other 21 and perhaps find an area where perhaps some portion of the mechanism is rubbing on one of the panels. If not, to get a complete assessment of the entire mechanism to decide what our future plan is. So the team is off working that right now."

The Discovery astronauts currently plan spacewalks Tuesday, Thursday and Friday. Tuesday's excursion is required to attach the P6 solar array to the far left end of the main power truss, a critical operation, and it would appear unlikely NASA would opt to add additional SARJ inspections to the crew's already busy timeline.

The mission's fourth spacewalk is a relatively short excursion to test a heat shield repair technique. The day after that, station commander Peggy Whitson and cosmonaut Yuri Malenchenko plan to stage a spacewalk to get the newly installed Harmony module ready for its eventual move to the front of the lab complex after Discovery departs.

Mission managers could opt to defer the tile repair demonstration and instead have spacewalkers Scott Parazynski and Doug Wheelock conduct an additional SARJ inspection in its place. To have more time for planning, managers also could opt to replace the tile repair spacewalk with Whitson's, extend the mission a day and stage a revised fifth spacewalk to look into the SARJ. No decisions have been made one way or the other.

"We would like very much to get (the Columbus) mission accomplished before the Christmas holidays," Suffredini said. "So It would be our intention to try to do whatever we can during this docked mission. If we don't figure out a way to recover nominal operations with the SARJ, we would figure out how to use it in a limited capacity to get us through the next stage and the next flight and then look at perhaps a subsequent EVA" during a future mission."

In a worst-case scenario, spacewalking astronauts could remove the drive motors and the 12 trundle bearings that press on the outboard bearing race and reposition the components on the inboard gear of the joint, effectively replacing the entire assembly. But that would require multiple spacewalks and is strictly last resort."

"If we decide this damage is great enough we don't want to live with it long term, we could choose to totally reconfigure that joint," Suffredini said. "I suspect that would be at the very end of our list of things to talk about. If we can figure out the source of the problem and reduce the contamination, if we can operate the joint without the vibrations that we're getting - and it's really not the current, it's the vibrations that are the long-term concern for us - then we'd probably try to live as is."

Vibration is more of a long-term concern, he said, because it could lead to life-limiting metal fatique.

Spaceflight Now Plus
Additional coverage for subscribers:
VIDEO: PREVIEW OF SUNDAY'S SPACEWALK PLAY
VIDEO: BIOGRAPHY MOVIE ON DISCOVERY'S ASTRONAUTS PLAY
VIDEO: BIOGRAPHY MOVIE ON EXPEDITION 16 CREW PLAY
VIDEO: BIOGRAPHY ON NEW EXPEDITION 16 MEMBER DAN TANI PLAY

VIDEO: THE FLIGHT DAY 5 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW INTERVIEWED BY CBS NEWS PLAY
VIDEO: CREW INTERVIEWED BY FOX NEWS PLAY
VIDEO: CREW INTERVIEWED BY WHAM-TV PLAY
VIDEO: SATURDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: ASTRONAUTS ENTER HARMONY FOR FIRST TIME PLAY
VIDEO: CREW COMMENTS FROM INSIDE HARMONY PLAY

VIDEO: THE FLIGHT DAY 4 HIGHLIGHTS MOVIE PLAY
VIDEO: POST-EVA MISSION STATUS BRIEFING PLAY
VIDEO: FIRST STS-120 SPACEWALK CONCLUDES PLAY
VIDEO: ROBOT ARM INSTALLS HARMONY ON THE STATION PLAY
VIDEO: HARMONY MODULE LIFTED OUT OF PAYLOAD BAY PLAY
VIDEO: S-BAND ANTENNA STOWED IN DISCOVERY'S BAY PLAY
VIDEO: WHEELOCK RIDES STATION ARM WITH ANTENNA PLAY
VIDEO: MISSION STS-120'S SPACEWALK NO. 1 BEGINS PLAY

VIDEO: ANIMATED PREVIEW OF HARMONY INSTALLATION PLAY
VIDEO: NARRATED ANIMATION OF SHUTTLE PAYLOAD BAY PLAY
VIDEO: HARMONY'S PRE-LAUNCH PREPS AT THE CAPE PLAY
VIDEO: BACKGROUND INFO ON HARMONY MODULE PLAY
VIDEO: PREVIEW OF FRIDAY'S SPACEWALK PLAY

VIDEO: THURSDAY MANAGEMENT TEAM NEWS BRIEFING PLAY
VIDEO: POST-DOCKING MISSION STATUS BRIEFING PLAY
VIDEO: INSPECTION BOOM HANDED BETWEEN ROBOT ARMS PLAY
VIDEO: SHUTTLE CREW WELCOMED ABOARD THE STATION PLAY
VIDEO: RING BETWEEN THE DOCKING PORTS RETRACTED PLAY
VIDEO: REPLAY OF DOCKING FROM PAYLOAD BAY CAMERAS PLAY
VIDEO: SHUTTLE DISCOVERY DOCKS TO THE STATION PLAY
VIDEO: DISCOVERY PERFORMS 360-DEGREE BACKFLIP PLAY
VIDEO: SHUTTLE APPROACHES STATION FROM BELOW PLAY
VIDEO: NARRATED PREVIEW OF THE DOCKING PLAY

VIDEO: THE FLIGHT DAY 2 HIGHLIGHTS MOVIE PLAY
VIDEO: BRIEFING ON LAUNCH IMAGERY AND TANK'S PERFORMANCE PLAY
VIDEO: WEDNESDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: HEAT SHIELD INSPECTIONS EXPLAINED PLAY
VIDEO: THE FLIGHT DAY 1 HIGHLIGHTS MOVIE PLAY
VIDEO: INSIDE MISSION CONTROL DURING LAUNCH PLAY

VIDEO: DISCOVERY'S LAUNCH AS SEEN LIVE PLAY
VIDEO: EXTERNAL TANK CAMERA FROM LIFTOFF TO ORBIT PLAY
VIDEO: LAUNCH REPLAY: VAB ROOF PLAY
VIDEO: LAUNCH REPLAY: KSC RUNWAY PLAY
VIDEO: LAUNCH REPLAY: BEACH TRACKER PLAY
VIDEO: LAUNCH REPLAY: UCS-23 WIDESCREEN PLAY
VIDEO: LAUNCH REPLAY: PLAYALINDA WIDESCREEN PLAY
VIDEO: LAUNCH REPLAY: WEST TOWER PLAY
VIDEO: LAUNCH REPLAY: PRESS SITE PLAY
VIDEO: LAUNCH REPLAY: CAMERA 009 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 041 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 049 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 050 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 051 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 054 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 060 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 061 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 063 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 070 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 071 PLAY
VIDEO: LAUNCH REPLAY: CAMERA UCS-12 PLAY
VIDEO: LAUNCH REPLAY: CAMERA UCS-15 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-1 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-2 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-6 PLAY

VIDEO: THE CREW DEPARTS QUARTERS FOR THE PAD PLAY
VIDEO: ASTRONAUTS SUITS UP ON LAUNCH MORNING PLAY
VIDEO: A LOOK BACK AT SHUTTLE DISCOVERY'S HISTORY PLAY
VIDEO: PAD 39A'S ROTATING GANTRY MOVED BACK PLAY
VIDEO: INTERVIEW CLIPS WITH THE ASTRONAUTS PLAY
VIDEO: MONDAY MORNING'S STATUS BRIEFING PLAY
VIDEO: PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: SUNDAY COUNTDOWN STATUS BRIEFING PLAY
VIDEO: SATURDAY COUNTDOWN STATUS BRIEFING PLAY
VIDEO: WATCH THE CREW'S ARRIVAL FOR LAUNCH PLAY
VIDEO: NEWS CONFERENCE AFTER FLIGHT READINESS REVIEW PLAY
VIDEO: SHUTTLE DISCOVERY ROLLS TO LAUNCH PAD 39A PLAY
VIDEO: CRANE HOISTS DISCOVERY FOR MATING TO TANK PLAY
VIDEO: DISCOVERY MOVED TO THE VEHICLE ASSEMBLY BUILDING PLAY
VIDEO: HYDRAULIC SEALS REPLACED ON LANDING GEAR STRUT PLAY
VIDEO: FUEL TANK ATTACHED TO SOLID ROCKET BOOSTERS PLAY
VIDEO: FOAM REMOVED FROM FUEL TANK FEEDLINE BRACKETS PLAY

VIDEO: STS-120 MISSION OVERVIEW BRIEFING PART 1 | PART 2
VIDEO: PREVIEW OF THE MISSION'S FIVE SPACEWALKS PLAY
VIDEO: DISCOVERY'S ASTRONAUTS MEET THE PRESS PLAY
VIDEO: BRIEFING ON SHUTTLE AND ISS PROGRAMS PLAY
MORE: STS-120 VIDEO COVERAGE
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