Astronauts Robert Behnken and Nicholas Patrick are gearing up for a third and final spacewalk to activate a second ammonia coolant loop for the space station's new Tranquility module and to remove insulation and launch locks securing shutters to a seven-window observation deck.

Credit: NASA

The six-and-a-half-hour spacewalk is scheduled to begin at 9:09 p.m. EST when Behnken and Patrick switch their spacesuits to battery power. For identification, Behnken will be wearing a suit with red stripes around the legs while Patrick's suit is unmarked.

This will be the 140th spacewalk devoted to station assembly and maintenance since construction began in 1998, the fourth so far this year and the third for Behnken and Patrick.

The first major task will be to open valves routing ammonia coolant to and from Tranquility. The module was tied into one of the station's two independent coolant loops during the crew's second spacewalk, allowing engineers to power up Tranquility's internal systems. Coolant loop B will be activated this evening.

The astronauts will then remove a temporary "keep-alive" power cable that is no longer needed and complete outfitting of a pressurized docking port that was moved to Tranquility's outboard port late Monday.

From there, the astronauts will make their way to the cupola on Tranquility's Earth-facing port to remove protective insulation covering the observation deck's seven windows. They also will remove launch locks securing aluminum shutters that protect against micrometeoroid impacts.

If all goes well, the windows will be uncovered for the first time, one at a time, starting around 12:30 a.m. Wednesday.

"The plan is, after the spacewalkers have removed the launch locks, we will then be able to open the shutters," said station Flight Director Bob Dempsey. "We want to open them while the spacewalkers are still out there so if there are any problems with these new shutters, they can go over and make sure they can be closed."

The cupola will provide spectacular panoramic views for Earth observation and serve as a robot arm work station, giving arm operators direct views of approaching cargo ships and maintenance sites. Robot arm computer displays and control equipment will be moved into the cupola overnight Wednesday.

Dempsey said all of the shutters will be opened during initial checkout while this evening's spacewalk is proceeding.

"At one point, we will have all the shutters open to sort of verify and get a view," Dempsey said. "The crew will be taking some video inside, we'll also see what video we can get outside with the windows during the spacewalk and after.

"I'm not sure we'll get a good view of the astronauts while they're out spacewalking from there. I hope to, but they need to be at least 10 feet away from the open shutters because the water that comes out of their evaporator cooling systems could contaminate the windows a little bit, plus we want to make sure that they're not near it so they physically don't kick or have any tools or anything that bump against the windows and possibly scratch them."

Built by Thales Alenia Space, the cupola weighs 1.6 tons, featuring six trapezoidal side windows and a 31.5-inch circular top window, the largest ever launched into space. Each window features a protective "scratch" pane on the interior side, two inch-thick pressure panes and a debris pane on the outside to protect against space debris impacts.

When not in use, the windows will be covered by the aluminum shutters, which are manually cranked open and closed by the astronauts. The greatest threat from a debris standpoint is from the front, along the direction of the station's 5-mile-per-second velocity vector. Shutters on the forward-facing windows typically will remain closed unless visibility in that direction is needed. Trailing windows can remain open for longer periods.

"We do have a very long flight rule that deals with the operations of this particular set of equipment," Dempsey said. "The two most major concerns of operating the shutters are thermal and micrometeoroid debris. ... The debris concern, obviously, is more severe. There's not a lot of debris out there but it wouldn't take much for a small piece of debris coming through and damaging these windows.

"Even though they're reinforced to prevent anything happening to the crew, we want to keep them in good pristine condition so that over a long period of time, the crew will have good views since this will be used for not only Earth observations but for things like capturing, with the robotic arm, upcoming visiting vehicles.

"So as long as we can keep within these constraints, the crew can open the windows more or less as needed," Dempsey said. "The windows that are going into the velocity vector where you're more likely to have debris come in and strike it will be closed most of the time. The large round one that faces the Earth, or the nadir, side and the two rear facing ones ... those can pretty much be open as much as the crew wants. So we anticipate that they'll have that open a lot during the crew day to look out, take pictures, whatever they want to do. The other ones, just when they need it for operations."

The cupola robotic work station will be used during the next shuttle visit in April to remove a cargo carrier from Discovery's cargo bay and attach it to the station.

Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision I of the NASA television schedule):

EST........DD...HH...MM...EVENT

02/16
04:14 PM...08...12...00...STS/ISS crew wakeup
04:54 PM...08...12...40...EVA-3: 14.7 psi repress/hygiene break
05:39 PM...08...13...25...EVA-3: Airlock depress to 10.2 psi
07:19 PM...08...15...05...Cupola vestibule outfitting
07:34 PM...08...15...20...EVA-3: Spacesuit purge
07:49 PM...08...15...35...EVA-3: Spacesuit prebreathe
08:39 PM...08...16...25...EVA-3: Crew lock depressurization
08:49 PM...08...16...35...Cupola audio terminal install
09:09 PM...08...16...55...EVA-3: Spacesuits to battery power
09:14 PM...08...17...00...EVA-3: Airlock egress/setup
09:39 PM...08...17...25...EVA-3: EV1: Open loop B QDs
09:39 PM...08...17...25...EVA-3: EV2: PMA-3 HD cable install
09:49 PM...08...17...35...Cupola UDP install
10:09 PM...08...17...55...EVA-3: EV1: Node 3 LTA cable demate
10:29 PM...08...18...15...MTL sample tool install
10:39 PM...08...18...25...EVA-3: Cupola MLI removal
11:49 PM...08...19...35...EVA-3: EV1: Node 3 outfitting
11:49 PM...08...19...35...EVA-3: EV2: Cupola launch locks

02/17
12:29 AM...08...20...15...EVA-3: EV2: APFR relocation
12:34 AM...08...20...20...Cupola window shutters opened
12:44 AM...08...20...30...Cupola FSS fill
12:49 AM...08...20...35...EVA-3: EV2: VSC video cable routing
12:54 AM...08...20...40...Cupola panel install
01:09 AM...08...20...55...EVA-3: EV1: VSC video cable routing
02:09 AM...08...21...55...EVA-3: Get aheads; node 2 CBM ops
03:09 AM...08...22...55...EVA-3: Cleanup and ingress
03:39 AM...08...23...25...EVA-3: Airlock repressurization
03:54 AM...08...23...40...Spacesuit servicing
04:14 AM...09...00...00...Node 1 Airlock/ITCS reconfig
05:30 AM...09...01...16...Mission status briefing on NTV
07:44 AM...09...03...30...ISS crew sleep begins
08:14 AM...09...04...00...STS crew sleep begins
09:00 AM...09...04...46...Daily highlights reel on NTV
01:30 PM...09...09...16...Flight director's update on NTV
04:14 PM...09...12...00...Crew wakeup

Additional coverage for subscribers:
VIDEO: STEP-BY-STEP PREVIEW OF SPACEWALK NO. 3 PLAY
VIDEO: PREVIEW OF FLIGHT DAY 10 ACTIVITIES PLAY

VIDEO: FLY WITH THE ASTRONAUTS IN THE COCKPIT PLAY
VIDEO: LOOKING OUT THE PILOT'S FRONT WINDOW 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 INBOARD PLAY
VIDEO: RIGHT-HAND BOOSTER CAMERA LOOKING DOWNWARD PLAY
VIDEO: EXTERNAL TANK CAMERA FROM LIFTOFF TO SEPARATION PLAY

VIDEO: FLIGHT DAY 9 HIGHLIGHTS MOVIE PLAY
VIDEO: TUESDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: DOCKING ADAPTER PLACED ONTO TRANQUILITY PLAY
VIDEO: PREVIEW OF FLIGHT DAY 9 ACTIVITIES PLAY

VIDEO: FLIGHT DAY 8 HIGHLIGHTS MOVIE PLAY
VIDEO: NEW YORK, ST. LOUIS AND MEMPHIS MEDIA INTERVIEWS PLAY
VIDEO: MONDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: OBSERVATION PORTAL RELOCATED TO NEW HOME PLAY
VIDEO: CUPOLA PLUCKED FROM OUTBOARD PORT PLAY
VIDEO: ROBOTIC ARM GRAPPLES CUPOLA PLAY
VIDEO: CREW'S EDUCATIONAL EVENT PLAY
VIDEO: PREVIEW OF FLIGHT DAY 8 ACTIVITIES PLAY
VIDEO: SUNDAY AFTERNOON'S FLIGHT DIRECTOR INTERVIEW PLAY

VIDEO: FLIGHT DAY 7 HIGHLIGHTS MOVIE PLAY
VIDEO: SUNDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: PREPPING CUPOLA'S NEW HOME PORT PLAY
VIDEO: SPACEWALKERS COMPLETE OTHER OUTFITTING WORK PLAY
VIDEO: AMMONIA BEGINS FLOWING TO COOL TRANQUILITY PLAY
VIDEO: PATRICK'S SPACESUIT CONTAMINATION CHECKS PLAY
VIDEO: SPACEWALKERS INSTALL SECOND COOLANT LOOP PLAY
VIDEO: FIRST SET OF AMMONIA LINES HOOKED UP PLAY
VIDEO: PREVIEW OF FLIGHT DAY 7 ACTIVITIES PLAY
VIDEO: STEP-BY-STEP PREVIEW OF SPACEWALK NO. 2 PLAY

VIDEO: FLIGHT DAY 6 HIGHLIGHTS MOVIE PLAY
VIDEO: OPENING CUPOLA'S HATCHWAY BRIEFLY PLAY
VIDEO: ENTERING TRANQUILITY FOR FIRST TIME PLAY
VIDEO: SPACEWALKERS ANSWER TWITTER QUESTIONS PLAY
VIDEO: ASSOCIATED PRESS, CBS AND REUTERS MEDIA INTERVIEWS PLAY
VIDEO: SATURDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: PREVIEW OF FLIGHT DAY 6 ACTIVITIES PLAY

VIDEO: FRIDAY AFTERNOON'S MANAGEMENT TEAM UPDATE PLAY
VIDEO: FRIDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: FLIGHT DAY 5 HIGHLIGHTS MOVIE PLAY
VIDEO: STEP-BY-STEP PREVIEW OF SPACEWALK NO. 1 PLAY
VIDEO: PREVIEW OF FLIGHT DAY 5 ACTIVITIES PLAY

VIDEO: FLIGHT DAY 4 HIGHLIGHTS MOVIE PLAY
VIDEO: WEDNESDAY NIGHT'S MISSION STATUS BRIEFING PLAY
VIDEO: SACRAMENTO, MOBILE AND ST. LOUIS MEDIA INTERVIEWS PLAY
VIDEO: WEDNESDAY AFTERNOON'S MANAGEMENT TEAM UPDATE PLAY
VIDEO: WEDNESDAY MORNING'S FLIGHT DIRECTOR INTERVIEW PLAY
VIDEO: PREVIEW OF FLIGHT DAY 4 ACTIVITIES PLAY

VIDEO: FLIGHT DAY 3 HIGHLIGHTS MOVIE PLAY
VIDEO: WEDNESDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: SHUTTLE CREW WELCOMED ABOARD STATION PLAY
VIDEO: HATCHWAY OPENED BETWEEN TWO SPACECRAFT PLAY
VIDEO: ENDEAVOUR DOCKS TO THE SPACE STATION PLAY
VIDEO: SHUTTLE FLIES OUT IN FRONT OF STATION PLAY
VIDEO: ENDEAVOUR PERFORMS 360-DEGREE BACKFLIP PLAY
VIDEO: STUNNING SHOT OF SHUTTLE AGAINST HORIZON PLAY
VIDEO: STATION'S VIEW OF SHUTTLE ENGINE FIRING PLAY
VIDEO: PREVIEW OF FLIGHT DAY 3 ACTIVITIES PLAY
VIDEO: TUESDAY AFTERNOON'S MANAGEMENT TEAM UPDATE PLAY

VIDEO: AMAZING LAUNCH FOOTAGE FROM COCKPIT CAMERA PLAY

VIDEO: FLIGHT DAY 2 HIGHLIGHTS MOVIE PLAY
VIDEO: TUESDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: TIME-LAPSE OF WING INSPECTIONS PLAY
VIDEO: INSPECTION BOOM READIED FOR USE PLAY
VIDEO: PREVIEW OF FLIGHT DAY 2 ACTIVITIES PLAY
VIDEO: NARRATED TOUR OF ENDEAVOUR'S PAYLOAD BAY PLAY

VIDEO: FLIGHT DAY 1 HIGHLIGHTS MOVIE PLAY
VIDEO: THE FULL STS-130 LAUNCH EXPERIENCE PLAY
VIDEO: SHUTTLE ENDEAVOUR BLASTS OFF! PLAY | HI-DEF
VIDEO: GO BEHIND THE SCENES IN MISSION CONTROL PLAY
VIDEO: JETTISONED EXTERNAL FUEL TANK TUMBLES AWAY PLAY
VIDEO: PAYLOAD BAY DOORS OPENED FOLLOWING LAUNCH PLAY

VIDEO: CREW FINISHES GETTING SUITED UP PLAY
VIDEO: ASTRONAUTS LEAVE CREW QUARTERS PLAY | HI-DEF
VIDEO: CREW ARRIVES AT LAUNCH PAD 39A PLAY
VIDEO: ASTRONAUTS BOARD THEIR SPACECRAFT PLAY

VIDEO: LAUNCH REPLAY: VAB ROOF PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PRESS SITE PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD PERIMETER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: BEACH TRACKER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD CAMERA 070 PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD CAMERA 071 PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: UCS-23 TRACKER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PLAYALINDA BEACH PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD FRONT CAMERA PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: BANANA CREEK SITE PLAY | HI-DEF

VIDEO: NARRATED REVIEW OF SHUTTLE'S PREPARATIONS PLAY | HI-DEF
VIDEO: NARRATED REVIEW OF PAYLOADS' PREPARATIONS PLAY | HI-DEF

VIDEO: EXPLANATION OF WEATHER PROBLEMS PLAY | HI-DEF
VIDEO: LOW CLOUDS SCRUB FIRST COUNTDOWN PLAY | HI-DEF
VIDEO: ASTRONAUTS DEPART QUARTERS FOR PAD 39A PLAY | HI-DEF
VIDEO: CREW GETS SUITED UP FOR LAUNCH ATTEMPT PLAY | HI-DEF
VIDEO: PAD SERVICE GANTRY RETRACTED PLAY | HI-DEF
VIDEO: TIME-LAPSE OF MOBILE TOWER ROLLBACK PLAY

VIDEO: INTERVIEW WITH COMMANDER GEORGE ZAMKA PLAY
VIDEO: INTERVIEW WITH PILOT TERRY VIRTS PLAY
VIDEO: INTERVIEW WITH MISSION SPECIALIST 1 KAY HIRE PLAY
VIDEO: INTERVIEW WITH MISSION SPECIALIST 2 STEVE ROBINSON PLAY
VIDEO: INTERVIEW WITH MISSION SPECIALIST 3 NICK PATRICK PLAY
VIDEO: INTERVIEW WITH MISSION SPECIALIST 4 BOB BEHNKEN PLAY

VIDEO: ENDEAVOUR'S PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: THURSDAY STATUS AND WEATHER UPDATE PLAY
VIDEO: COUNTDOWN PREVIEW BRIEFING PLAY
VIDEO: ASTRONAUTS ARRIVE FOR LAUNCH PLAY | HI-DEF

VIDEO: LAUNCH DATE SET AT FLIGHT READINESS REVIEW PLAY
VIDEO: PAYLOAD BAY DOORS CLOSED FOR LAUNCH PLAY | HI-DEF
VIDEO: CREW SEES TRANQUILITY LOADED INTO SHUTTLE PLAY | HI-DEF

VIDEO: SHUTTLE EVACUATION PRACTICE PLAY | HI-DEF
VIDEO: ASTRONAUTS BOARD ENDEAVOUR PLAY | HI-DEF
VIDEO: THE LAUNCH DAY SIMULATION BEGINS PLAY | HI-DEF
VIDEO: PAD BUNKER TRAINING FOR THE CREW PLAY | HI-DEF
VIDEO: CREW BRIEFED ON EMERGENCY PROCEDURES PLAY | HI-DEF
VIDEO: TEST-DRIVING AN EMERGENCY ARMORED TANK PLAY | HI-DEF
VIDEO: NIGHTTIME APPROACHES IN TRAINING AIRCRAFT PLAY | HI-DEF
VIDEO: ASTRONAUTS CHAT WITH REPORTERS AT PAD 39A PLAY
VIDEO: SPACEWALKER UPDATES COOLING HOSE FIX PLAY | HI-DEF
VIDEO: ROBINSON'S THOUGHTS ON SHUTTLE RETIREMENT PLAY | HI-DEF
VIDEO: ASTRONAUTS ARRIVE FOR PRACTICE COUNTDOWN PLAY | HI-DEF

VIDEO: TRANQUILITY DELIVERED TO PAD 39A PLAY | HI-DEF
VIDEO: PAYLOAD TRANSPORTER GOES UPRIGHT PLAY | HI-DEF
VIDEO: PACKING UP PAYLOAD FOR LAUNCH PLAY | HI-DEF

VIDEO: SHUTTLE ENDEAVOUR'S FRIGID ROLLOUT TO PAD PLAY | HI-DEF
VIDEO: ENDEAVOUR HOISTED FOR ATTACHMENT TO TANK PLAY | HI-DEF
VIDEO: CRANE ROTATES THE ORBITER VERTICALLY PLAY | HI-DEF
VIDEO: ENDEAVOUR MOVES TO ASSEMBLY BUILDING PLAY | HI-DEF
VIDEO: TIME-LAPSE SHOWS ENDEAVOUR ASCENDING IN VAB PLAY
VIDEO: TIME-LAPSE SHOWS THE MOVE TO ASSEMBLY BUILDING PLAY

VIDEO: ORBITER READY TO LEAVE HANGAR PLAY | HI-DEF
VIDEO: EXTERNAL TANK ATTACHED TO BOOSTERS PLAY | HI-DEF
VIDEO: ENDEAVOUR'S MAIN ENGINE INSTALLATION PLAY | HI-DEF
VIDEO: ASTRONAUTS VISIT THEIR SPACECRAFT PLAY | HI-DEF
VIDEO: CREW INSPECTS MISSION PAYLOADS PLAY | HI-DEF
VIDEO: FUEL TANK UNLOADED FROM THE BARGE PLAY | HI-DEF
VIDEO: EXTERNAL TANK ARRIVES AT SPACEPORT PLAY | HI-DEF
VIDEO: FORWARD THRUSTER POD CHECKED OUT PLAY | HI-DEF
VIDEO: ENDEAVOUR TOWED OFF RUNWAY FROM STS-127 PLAY | HI-DEF

VIDEO: TRANQUILITY HATCH SEALED FOR LAUNCH PLAY | HI-DEF
VIDEO: CUPOLA ATTACHED TO TRANQUILITY PLAY | HI-DEF
VIDEO: THE SPACE STATION'S NEW CUPOLA PLAY | HI-DEF
VIDEO: TRANQUILITY UNPACKED IN FLORIDA PLAY | HI-DEF
VIDEO: NEW MODULE ARRIVES FROM EUROPE PLAY | HI-DEF
SUBSCRIBE NOW