Perched on the end of the space station's fully extended robot arm, astronaut Ronald Garan manually carried a 528-pound nitrogen tank from one side of the lab's main power truss to the other today, enjoying a spectacular there-and-back windshield-wiper ride that carried him eight stories above the research station.

"Isn't that great view?" crewmate Michael Fossum asked.

"Unbelievable."

"And Ronny, you're coming up on the coast of Peru," astronaut Kenneth Ham radioed from inside the shuttle Discovery.

"All right. Beautiful!"

Working in orbital darkness 210 miles up, Garan first carried an empty nitrogen tank from its attachment slot on the right side of the space station's main power truss to a stowage platform on the left side of the station where Fossum was waiting. After mounting the empty tank on the stowage platform, Garan took the fully-charged replacement tank back to the right-side of the truss, enjoying a daylight ride over the Pacific Ocean and northern South America.

The spacewalkers were ahead of schedule at that point and Fossum was cleared to make his way to the nearby left-side solar alpha rotary joint, or SARJ, to collect samples of presumed debris he spotted on the mechanism's drive gear during a spacewalk Thursday.

After removing a thermal cover, Fossum used Kapton tape to capture samples of a powdery material on the 10-foot-wide drive gear. The joint had been repositioned since his last inspection, but Fossum reported seeing the same grease buildups on the gear that he noticed Thursday.

"The cover's removed and I see ... the same kind of streaking we had on the other side and one of the little, uh, grease balls," he reported, peering inside the joint. "I do see another feature on datum A (surface) that is gold in color. It's near a gear tooth, I definitely recommend getting a picture of that. It's hard to get an angle on it. It is a surface deposit also, I can see it sitting on the surface."

A few moments later, he collected debris samples from the outer canted surface of the drive gear.

"OK, Mike, next you're going to remove the tape and fold it in half, sticky side to sticky side, put it in your trash bag," Ham instructed.

"Roger that."

The station is equipped with two SARJ gears to rotate outboard solar arrays like paddle wheels to track the sun. The right-side SARJ has suffered a mysterious breakdown in one of its bearing surfaces, generating extensive metallic shavings and debris. During a spacewalk Tuesday, Fossum tested techniques for eventually removing the contamination to permit normal, or near normal, operation of the mechanism.

The left-side SARJ is working normally, but astronauts have been periodically inspecting it to make sure no problems are developing. Grease buildups, presumably from one or more of the 12 bearing assemblies the gear rolls through, were seen during an inspection last October and again when Fossum looked under thermal covers Thursday. But he also saw a powder-like debris on the outer edge of the drive gear and mission managers decided to add debris collection to the list of chores planned for today's spacewalk.

WIth the nitrogen tanks exchanged and the port SARJ inspection complete, Garan and Fossum will make their way to the Japanese Kibo module to remove window cover launch locks and thermal insulation on the lab's robot arm. They also plan to re-install a repaired television camera on the station's power truss.

Additional coverage for subscribers:
VIDEO: NARRATED PREVIEW OF SPACEWALK NO. 3 PLAY
VIDEO: ANIMATION OF NITROGEN TANK REPLACEMENT PLAY

VIDEO: THE FLIGHT DAY 8 HIGHLIGHTS MOVIE PLAY
VIDEO: JAPANESE VIP CALL TO STATION PLAY
VIDEO: SATURDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: MEDIA INTERVIEWS WITH SHUTTLE AND ISS CREWS PLAY
VIDEO: KIBO LAB'S ROBOTIC ARM FLEXES FOR FIRST TIME PLAY
VIDEO: NARRATED PREVIEW OF ARM'S FIRST MOVEMENTS PLAY
VIDEO: SATURDAY'S FLIGHT DIRECTOR INTERVIEW PLAY
VIDEO: CREW'S DOWNLINKED REPLAY OF LOGISTICS MODULE MOVE PLAY

VIDEO: LEFT-HAND BOOSTER CAMERA LOOKING UPWARD PLAY
VIDEO: LEFT-HAND BOOSTER CAMERA LOOKING INBOARD PLAY
VIDEO: LEFT-HAND BOOSTER CAMERA LOOKING DOWNWARD PLAY
VIDEO: RIGHT-HAND BOOSTER CAMERA LOOKING UPWARD PLAY
VIDEO: RIGHT-HAND BOOSTER CAMERA LOOKING DOWNWARD PLAY

VIDEO: THE FLIGHT DAY 7 HIGHLIGHTS MOVIE PLAY
VIDEO: FRIDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: SHUTTLE CREW ASKED TO TAKE PHOTOS OF WING PANELS PLAY
VIDEO: JAPANESE LOGISTICS MODULE MOVED TO KIBO LAB'S ROOF PLAY
VIDEO: STATION'S ROBOT ARM GRAPPLES LOGISTICS MODULE PLAY
VIDEO: MEDIA INTERVIEWS WITH SHUTTLE AND ISS COMMANDERS PLAY
VIDEO: FRIDAY'S FLIGHT DIRECTOR INTERVIEW PLAY
VIDEO: NARRATED PREVIEW OF LOGISTICS MODULE MOVE PLAY

VIDEO: THE FLIGHT DAY 6 HIGHLIGHTS MOVIE PLAY
VIDEO: BUZZ LIGHTYEAR TOY ON THE LOOSE IN SPACE PLAY
VIDEO: ASTRONAUTS INVITE VIEWERS TO DINNER PLAY
VIDEO: THURSDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: INSPECTION OF THE PORT-SIDE SOLAR ROTARY JOINT PLAY
VIDEO: FAULTY TV CAMERA REMOVED FROM STATION PORT TRUSS PLAY
VIDEO: THERMAL SLEEVE PLACED ON KIBO TRUNNION PIN PLAY
VIDEO: LAUNCH LOCKS RELEASED ON KIBO'S UPPER PORT PLAY
VIDEO: SPACEWALKERS INSTALL PAIR OF TV CAMERAS ON KIBO PLAY
VIDEO: MIKE FOSSUM EMERGES FROM AIRLOCK FOR EVA NO. 2 PLAY
VIDEO: NARRATED PREVIEW OF SPACEWALK NO. 2 PLAY
VIDEO: THURSDAY'S FLIGHT DIRECTOR INTERVIEW PLAY

VIDEO: THE FLIGHT DAY 5 HIGHLIGHTS MOVIE PLAY
VIDEO: WEDNESDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: ASTRONAUTS ENTER THE KIBO MODULE FOR FIRST TIME PLAY
VIDEO: CEREMONY BEFORE KIBO HATCH OPENING PLAY

VIDEO: THE FLIGHT DAY 4 HIGHLIGHTS MOVIE PLAY
VIDEO: TUESDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: KIBO SCIENCE LAB ATTACHED TO THE SPACE STATION PLAY
VIDEO: KIBO MODULE UNBERTHED FROM SHUTTLE PAYLOAD BAY PLAY
VIDEO: CLOSEUP INSPECTION OF STATION'S SOLAR ROTARY JOINT PLAY
VIDEO: FOSSUM UNBOLTS LOCKS ON KIBO'S WINDOW COVERINGS PLAY
VIDEO: SPACEWALKERS REMOVE COVERS ON KIBO'S PORT PLAY
VIDEO: SHUTTLE POWER UMBILICALS UNHOOKED FROM KIBO PLAY
VIDEO: SHUTTLE INSPECTION BOOM RETRIEVED FROM THE STATION PLAY
VIDEO: SPACEWALKER RON GARAN REMOVES COVER ON BOOM PLAY
VIDEO: SPACEWALKER MIKE FOSSUM FREES ARM'S ELBOW CAMERA PLAY
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: NARRATED ANIMATION OF PREVIEWING THE DOCKING 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: ANIMATION OF THE HEAT SHIELD INSPECTIONS PLAY
VIDEO: NARRATED TOUR OF DISCOVERY'S PAYLOAD BAY 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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