Spacewalkers Ronald Garan and Michael Fossum removed protective covers, released window cover launch locks and disconnected shuttle power to prepare Japan's 15-ton Kibo laboratory module for its move from Discovery to the international space station. The astronauts are running about an hour ahead of schedule, more than making up for a 50-minute late start due to problems with a headset cable.

Fossum and Garan have two more major tasks to complete, both involving the station's right-side solar alpha rotary joint, or SARJ. The station is equipped with two motor-driven SARJ mechanisms, one on each side of the lab's main power truss, to turn outboard solar arrays like giant paddle wheels to keep them face on to the sun.

The left-side SARJ works normally in "auto-track" mode, but the left-side gear has been used sparingly since last year when engineers discovered extensive metallic contamination on one of the drive gear's bearing surfaces. Engineers are not certain what's causing the problem, but they suspect it might be due to an initially small breakdown in the super-hard outer layer of the bearing surface that worsened as the gear rotated through the tight grip of 12 bearing assemblies.

During today's spacewalk, Garan will re-install trundle bearing No. 5, which was removed earlier as part of NASA's on-going troubleshooting. Fossum, meanwhile, will inspect the damaged bearing surface and attempt to clean a small section, spreading on Braycote grease to trap small shavings and other debris and then wiping it off. He plans to test several techniques and tools to see what works best.

If he is successful, future spacewalkers may attempt to clean the entire drive gear enough to permit at least partial use of the drive assembly. The SARJ is equipped with two drive gears, and the backup is pristine. But NASA does not want to change gears unless absolutely necessary because of the possibility of additional problems down the road.

"They'll start off by using the scraper," said David Beaver, lead spacewalk officer for Discovery's mission at the Johnson Space Center. "He'll first try just scraping the ring just with the scraper with no grease and see how much material does that remove. And then also try to characterize when the material comes off, is this going to cause a huge mess if we do this on the entire race ring? Or is this manageable?

"The next thing to try out is to use the Braycote grease along with the scraper and apply the grease and then try to remove it with the scraper and see does that pull up, attract more of the debris. The scraper is basically a putty knife, so you would use it to spread the grease out and then come back over it with the scraper and try to remove the grease and debris with it.?

"The final thing is to just take a wipe with grease and spread just grease with the wipe," he said. "The reason for that is, the crew reports (have indicated) there's some fine particulate on the ring as well as, obviously, there are some parts that are a little bit more substantial that are either pressed on debris or damage sites. So the question is, does going over it with the scraper remove any of this bigger stuff to help get this ring any smoother? Or does it do nothing more than what just a wipe with the grease does to remove this fine particulate?

"You don't want to waste time using a scraper if it doesn't do much for you. So really, this is just a test of several different techniques to try to narrow down which ones are most effective so we can better plan spacewalks on (future) missions."

Additional coverage for subscribers:
VIDEO: ANIMATION OF KIBO MODULE INSTALLATION PLAY
VIDEO: ANIMATION OF INSPECTION BOOM RETRIEVAL PLAY
VIDEO: NARRATED PREVIEW OF SPACEWALK NO. 1 PLAY
VIDEO: TUESDAY'S FLIGHT DIRECTOR INTERVIEW PLAY
VIDEO: THE FLIGHT DAY 3 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW'S REMARKABLE CAMCORDER FOOTAGE FROM MONDAY PLAY
VIDEO: MONDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: SHUTTLE CREW WELCOMED INTO STATION PLAY
VIDEO: DISCOVERY DOCKS TO SPACE STATION PLAY
VIDEO: SHUTTLE PERFORMS RENDEZVOUS BACKFLIP PLAY
VIDEO: THE FLIGHT DAY 2 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW'S CAMCORDER FOOTAGE FROM FLIGHT DAY 2 PLAY
VIDEO: SUNDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: THE FLIGHT DAY 1 HIGHLIGHTS MOVIE PLAY
VIDEO: EXTERNAL TANK SEEN AFTER SEPARATION PLAY
VIDEO: LAUNCH REPLAY: VAB ROOF PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-1 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-2 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-6 PLAY
VIDEO: LAUNCH REPLAY: FRONT CAMERA PLAY
VIDEO: LAUNCH REPLAY: BEACH TRACKER PLAY
VIDEO: LAUNCH REPLAY: PAD PERIMETER PLAY
VIDEO: LAUNCH REPLAY: UCS-12 TRACKER PLAY
VIDEO: LAUNCH REPLAY: UCS-23 TRACKER PLAY
VIDEO: LAUNCH REPLAY: PLAYALINDA BEACH PLAY
VIDEO: LAUNCH REPLAY: PATRICK AIR FORCE BASE PLAY
VIDEO: LAUNCH REPLAY: PRESS SITE PLAY
VIDEO: LAUNCH REPLAY: WEST TOWER 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: LIFTOFF OF DISCOVERY WITH KIBO LAB! PLAY
VIDEO: ONBOARD CAMERA FOOTAGE OF TANK FOAM FALLING PLAY
VIDEO: INSIDE MISSION CONTROL DURING LAUNCH PLAY
VIDEO: POST-LAUNCH NEWS CONFERENCE PLAY

VIDEO: FINAL PRE-LAUNCH POLLS GIVE "GO" FOR LIFTOFF PLAY
VIDEO: ASTRONAUTS ARRIVE AT LAUNCH PAD 39A PLAY
VIDEO: CREW DEPARTS QUARTERS FOR LAUNCH PAD PLAY
VIDEO: ASTRONAUTS DON SPACESUITS FOR LAUNCH PLAY
VIDEO: NARRATED RECAP OF KIBO LAB'S PRE-FLIGHT CAMPAIGN PLAY
VIDEO: NARRATED RECAP OF DISCOVERY'S PRE-FLIGHT CAMPAIGN PLAY
VIDEO: LAUNCH PAD GANTRY RETRACTED FRIDAY NIGHT PLAY
VIDEO: TIME-LAPSE OF GANTRY ROLLBACK PLAY
VIDEO: FRIDAY'S COUNTDOWN STATUS BRIEFING PLAY
VIDEO: PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: BRIEFING ON KIBO LABORATORY FACILITY PLAY
VIDEO: ASTRONAUTS ARRIVE AT THE CAPE FOR LAUNCH PLAY
VIDEO: WEDNESDAY'S COUNTDOWN AND WEATHER BRIEFING PLAY
VIDEO: NARRATED MISSION PREVIEW MOVIE PLAY

VIDEO: NEWS BRIEFING FOLLOWING FLIGHT READINESS REVIEW PLAY

VIDEO: INTERVIEW WITH COMMANDER MARK KELLY PLAY
VIDEO: INTERVIEW WITH PILOT KEN HAM PLAY
VIDEO: INTERVIEW WITH MS1 KAREN NYBERG PLAY
VIDEO: INTERVIEW WITH MS2 RON GARAN PLAY
VIDEO: INTERVIEW WITH MS3 MIKE FOSSUM PLAY
VIDEO: INTERVIEW WITH MS4 AKIHIKO HOSHIDE PLAY

VIDEO: ASTRONAUTS PRACTICE EVACUATION OF SHUTTLE PLAY
VIDEO: CREW BOARDS DISCOVERY FOR PRACTICE COUNTDOWN PLAY
VIDEO: TRAINING SESSIONS AT LAUNCH PAD AND BUNKER PLAY
VIDEO: CREW NEWS CONFERENCE AT LAUNCH PAD 39A PLAY
VIDEO: ASTRONAUTS ARRIVE FOR PRACTICE COUNTDOWN PLAY

VIDEO: TIME-LAPSE OF GANTRY ENCLOSING DISCOVERY PLAY
VIDEO: PAD'S ORBITER ACCESS ARM SWUNG INTO POSITION PLAY
VIDEO: TIME-LAPSE OF CRAWLER RETREATING AFTER ROLLOUT PLAY
VIDEO: SHUTTLE DISCOVERY ROLLED TO PAD 39A PLAY

VIDEO: SHUTTLE AND STATION PROGRAM BRIEFING PLAY
VIDEO: STS-124 MISSION OVERVIEW PART 1 | PART 2
VIDEO: PREVIEW BRIEFING ON MISSION'S SPACEWALKS PLAY
VIDEO: THE ASTRONAUTS' PRE-FLIGHT NEWS BRIEFING PLAY

VIDEO: KIBO LABORATORY TRAVELS TO THE LAUNCH PAD PLAY
VIDEO: TRANSPORT CANISTER WITH KIBO ROTATED UPRIGHT PLAY
VIDEO: CRANE PLACES KIBO MODULE INTO TRANSPORT CANISTER PLAY

VIDEO: DISCOVERY HOISTED FOR ATTACHMENT TO FUEL TANK PLAY
VIDEO: THE SHUTTLE MOVES TO THE VEHICLE ASSEMBLY BUILDING PLAY
MORE: STS-124 VIDEO COVERAGE
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