See our Expedition 35 landing coverage.

With the airlock pressurized, Cassidy and Marshburn have floated back into the space station now, where they will take off their spacesuits.

Today marked the 168th spacewalk in support of space station assembly and maintenance, totaling 1,061 hours and 9 minutes. It was the fourth EVA each for Cassidy and Marshburn.

Today's spacewalk is officially over with the repressurization of the Quest airlock beginning at 2:14 p.m. EDT (1814 GMT). The EVA's official duration was 5 hours, 30 minutes.

The crew is back in the airlock and the hatch is closed. Now they will use a special contamination detection kit to make sure there is no ammonia on their spacesuits.

The astronauts are now back at the airlock to finish up the "bakeout" procedure, a precaution against contaminating the space station with ammonia. The spacewalk is passing the five-hour mark now.

Cassidy and Marshburn are moving back toward the airlock now, their work finished at the P6 truss.

The astronauts will go through a "bakeout" procedure in which their spacesuits will be exposed to hot sunlight for about an hour to ensure any ammonia contamination sublimates before they re-enter the airlock.

Mission control told the crew to take their time in their translation along the truss. They will also inspect their spacesuits for any ammonia.

Still no evidence of any leak from the new pump.

"I've had eyes on it and haven't seen a thing," Marshburn said.

It will take some more time to confirm there is no leak through diagnostic tests and telemetry from the ammonia system, which cools one of the space station's eight power loops. This power system was shut down after the leak intensified Thursday.

Now flying in daylight over the Pacific Ocean, Cassidy and Marshburn still see no evidence of any leak emanating from the P6 truss after the installation of a new pump module.

No sign of any ammonia so far, according to Cassidy and Marshburn.

The space station is in a night pass right now. If there is any leakage, it might be easier to spot in daytime.

"So far, so good, I guess," astronaut Mike Fincke said from mission control in Houston.

Flight controllers have turned on the new cooling pump. The spacewalkers are standing by to look for any sign of ammonia leakage. If no leaks are found, there is a good chance this replacement solved the problem.

Mission control says Cassidy and Marshburn have completed all their tasks for this spacewalk, but their day is not over. They will move to a nearby, but safe, location to see if they can spot any leaking ammonia when the new pump module is turned on in a few minutes.

The astronauts are wrapping up the stowage of the old pump and are now putting a cover over it.

The astronauts will stay in the work area to observe for any leaking ammonia when mission control activates the spare pump. If they see no ammonia, the leak may be resolved.

Mission control reports the spare pump is now powered up and being integrated into the electronics on the P6 truss segment.

The spacewalk is passing the three-hour mark.

The spacewalkers will next took their attention to stowing the old Pump Flow Control Subassembly into storage slot previously occupied by the spare pump just installed.

Cassidy is opening up fluid connectors and ammonia is now flowing into the cooling system. Marshburn reports no sign of any ammonia leakage, and NASA is hopeful this means the old pump was the cause of Thursday's leak.

Mission control will activate the pump soon to drive even more ammonia into the cooling system.

Once the new pump is hooked up, it will be activated and ammonia will flow into the space station's channel 2B cooling loop. Cassidy and Marshburn will again look for any sign of ammonia leakage as the fresh coolant is pumped through the system on the outer port end of the space station's power truss.

The space station just passed into sunrise just south of Hawaii. With the spare pump in hand, the astronauts are about to install it where they removed the suspect pump package earlier in the EVA.

The spare pump device has been extracted from its storage site on the truss.

Two hours into the spacewalk, the space station is flying over the southern Indian Ocean on a night pass. The astronauts are working on getting the spare Pump Flow Control Subassembly ready.

Running late getting out the door earlier this morning, the spacewalk is now about a half-hour ahead of the planned timeline.

Cassidy and Marshburn will pull a cover off the spare pump and move the unit to the site where the astronauts just removed the suspect coolant pump on the port-side truss of the space station.

"We're going to put the new guy in the hole, put the bad guy in the temp stow location and go home," Cassidy said, summing up the spacewalk.

Chris Cassidy examined the plumbing the P6 coolant system using a mirror inserted into the innards of the truss.

"All the pipes look shiny clean," Cassidy said.

"I can't give you any good data other than nominal, unfortunately," Cassidy told mission control, noting no smoking guns showing a clear sign as the source of the ammonia leak.

"What we're seeing is really helpful in diagnosing where problem might be," astronaut Mike Fincke said from mission control in Houston. "In this case, we know it's not here."

The crew will next work on retrieving a spare pump for installation where the old pump was located.

The pump module has been removed.

"No mechanisms have ice on them," radioed astronaut Tom Marshburn.

"Can you confirm if you have seen any flakes," astronaut Mike Fincke asked from mission control.

"I have not," one of the astronauts replied.

"It looks really clean, surprisingly so," Cassidy said, noting the only thing he saw was a bit of metallic debris in one of the bolt shafts.

Cassidy is removing structural fasteners connecting the pump to the space station's truss.

Once the bolts are removed, Cassidy and Marshburn will move the Pump Flow Control Subassembly to a temporary stowage location and examine the surfaces of the module and the area it came from to look for any smoking gun of a leak.

The pump module weighs about 235 pounds and measures approximately 40 inches by 29 inches by 19 inches.

Both fluid connectors to the Pump Flow Control Subassembly have been unbolted. The astronauts noticed a few small flakes of ammonia during as the second connector was removed, but this was expected and NASA says is not indicative of a leak.

Cassidy is now setting up for the physical removal of the pump package, which will involve unscrewing two more bolts.

Marshburn is taking photos of the area to document any signs of the leak for engineers to evaluate on the ground.

The astronauts have unscrewed one of two quick-disconnect bolts on the pump package. Now starting work on the other fluid quick-disconnect connector.

Cassidy is now beginning the procedure to unbolt the pump module, which NASA believes is the most likely culprit for the ammonia leak. He will begin with removing two quick-disconnect fluid lines by unscrewing bolts with a screwdriver.

Cassidy reports no obvious evidence of anything amiss at the Pump Flow Control Subassembly on the P6 truss. He did see a brown stain on the pump module's cover.

Chris Hadfield, who is choreographing the spacewalk from inside the space station, just tweeted: "Chris and Tom are safely outside ISS, hard at work in the vacuum of space, looking for signs of the ammonia leak. THAT was a busy AM inside."

The spacewalkers have arrived at the work site on the P6 truss. The space station is in orbital darkness, but the astronauts report no sign of leaking ammonia at first glance.

Chris Cassidy is designated the EV1 crew member for the spacewalk. He is wearing the spacesuit with red stripes.

Tom Marshburn is the EV2 spacewalker and is in the all-white suit.

Both astronauts are carrying helmet cameras, with Cassidy's helmetcam numbered "20" and Marshburn's numbered "18" in video downlinked from the spacewalkers.

Chris Cassidy and Tom Marshburn have switched their spacesuits to internal battery power, marking the official start of the EVA. The crew has also opened the hatch of the Quest airlock, now preparing to exit into space.

The pressure inside the Quest airlock is near vacuum, and the astronauts will soon open the hatch.

The spacewalk officially begins when the spacesuits are switched to internal battery power.

Depressurization of the Quest airlock has begun.

Mission control in Houston has given the "go" for depressurization of the space station's Quest airlock and a "go" for the spacewalk. Here are some statistics on today's spacewalk:

• 168th spacewalk devoted to ISS assembly and maintenance
• 4th spacewalk each for Cassidy and Marshburn
• 2nd spacewalk of 2013
• 1st U.S. spacewalk of 2013

Cassidy and Marshburn conducted two spacewalks together on the STS-127 space shuttle mission in July 2009.

Cassidy has amassed 18 hours and 5 minutes of spacewalk time over three EVAs. Marshburn's accumulated spacewalk time totals 18 hours and 59 minutes going into today's EVA.

Chris Cassidy and Tom Marshburn are in their spacesuits, and the space station's Quest airlock will soon be depressurized to vacuum before the astronauts open the hatch and head outside.

The spacewalk is scheduled to last about six-and-a-half hours. Cassidy and Marshburn will first gather tools and configure their safety tethers, then crawl toward the port side of the space station's 357-foot-long truss backbone. The leaky ammonia system - the subject of today's spacewalk - is located at the outer port truss segment.

The astronauts will first inspect the area around the P6 truss Pump Flow Control Subassembly, the suspected location of the leak that appeared Thursday.

Cassidy and Marshburn will then remove the pump module, put it in a temporary stowage location, and look for evidence of ammonia flakes where the pump resided. The plan calls for retrieving a spare pump if the astronauts spot leaking ammonia. If they can't see any evidence of a leak, the astronauts will put the old pump module back in place.

NASA managers are hopeful the replacement of a pump module during an impromptu spacewalk Saturday will eliminate an ammonia leak that forced flight controllers to shut down a solar array coolant loop aboard the International Space Station, officials said Friday.

Read our full story.

Flight controllers are monitoring an ammonia coolant leak in the International Space Station's left-side power truss, NASA officials said late Thursday.

The leak, apparently located in the outboard port-six (P6) solar array truss segment, was reported by the station crew around 11:30 a.m. EDT (GMT-4). Downlinked video, sources said, showed a stream of white flakes dissipating in the vacuum of space.

Read our full story.

Welcome aboard! The newest residents have floated into the International Space Station from their Soyuz capsule for the formal ceremony.

The hatchway between the Soyuz spacecraft and the station was opened at 12:35 a.m. EDT, some 7 hours and 52 minutes after launching from the pad at Baikonur Cosmodrome.

The outpost's Expedition 35 crew is comprised of the Canadian astronaut commander, three Russians and two Americans. The station is back to the full 6-person-strong operating team.

The docking probe on the front of Soyuz has retracted, allowing the hooks and latches to close and form a seal between the capsule and station. Pressure and leak checks will be performed over the next orbit before the hatchway is opened for the crew to enter into the station in a couple of hours.

This was unprecedented for the International Space Station program, launching a crew and docking them on the day. Soyuz TMA-08M needed just four orbits and five hours, 45 minutes from liftoff to linkup.

The Russians tested the single-day operation on three earlier cargo resupply ships for the ISS. Today tried it for the first time on a human launch. It required the crew to remain suited throughout the flight and they will be awake nearly 21 hours, but it avoids living in the cramped Soyuz for two days in pursuit of docking under the typical plan.

The docking occurred about four minutes early as the space station flew 250 miles above the Pacific Ocean off the coast of Peru.

Over the next few minutes, the Soyuz docking probe will retract to allow hooks and latches to bring the spacecraft to a firm seal with the station. Hatches between the two vehicles will be opened around 12:10 a.m. EDT.

DOCKING! The Soyuz TMA-08M spacecraft has docked to the Poisk module of the space station, delivering Russian cosmonauts Pavel Vinogradov and Alexander Misurkin and NASA's Chris Cassidy to the international outpost for their 167-day mission.

The new Expedition 35 residents join Chris Hadfield from the Canadian Space Agency, NASA's Tom Marshburn and Russian cosmonaut Roman Romanenko.

The capsule remains on course and lined up for docking. A steady, stable approach using Soyuz's automated rendezvous system continues.

Now inside 50 feet and closing.

Less than 100 feet to go.

Now coming into an orbital sunset and the capsule's headlight has been turned on.

The range between Soyuz and station is 130 feet.

Just 200 feet left to go.

Distance now 300 feet.

Inside 400 feet and closing.

A few minutes ahead of schedule, the Russian flight control team has given approval for the final approach to commence.

The Soyuz completed the flyaround to align with the docking port. It's now in the stationkeeping hold about while controllers verify all is in readiness for final approach.

Just 675 feet separate the two craft now.

The flyaround has begun. Soyuz is flying itself around the international outpost to get into the approach corridor leading to the Poisk module's docking port.

The Soyuz is less than 2,300 feet from the station

Now completing breaking maneuvers, the range is just 3,100 feet now.

Now just 1.1 miles between the two spacecraft.

The Soyuz is 2 miles from the station.

The approaching spacecraft is 4 miles away, closing at 35 mph.

The Soyuz is about 18.5 miles away from the International Space Station. The crew reports it can see the orbiting complex out the window.

The Soyuz spacecraft carrying three new residents for the International Space Station continues on its course to intercept the orbiting complex for docking tonight.

Flight controllers have granted approval to press ahead with this rapid rendezvous, deciding not to take the offramp to default back to the two-day process.

Soyuz TMA-08M was launched today at 4:43:20 p.m. EDT, the precise moment when the Earth's rotation brought the Baikonur pad into alignment with the International Space Station's orbital plane, riding its three-stage booster into a preliminary orbit.

The day's first four major rendezvous engine firings occurred in the first two-and-a-half hours of flight and the automated rendezvous sequence aboard the Russian-built crew transport capsule began at 8:26 p.m. to control the activities via autopilot.

The two spacecraft should be within 10 miles of each other by 9:46 p.m.

The television camera on the nose of Soyuz will be turned on at 9:53 p.m. to provide views of the docking.

A series of maneuvers between 10:00 and 10:08 p.m. will dramatically slow the Soyuz's closure rate, ultimately leading to the spacecraft beginning a flyaround of the space station at 10:11 p.m. to align with the Poisk module's docking port.

After a stationkeeping hold by the Soyuz to ensure all is in readiness for docking, the spacecraft will commence final approach at 10:21 p.m. for docking about 1` minutes later.

The linkup should occur at 10:32 p.m. EDT, just after an orbital sunset.

The hatch opening and welcoming ceremony aboard the station is expected around 12:10 a.m. EDT.

A veteran Russian spacecraft commander, a rookie cosmonaut and a Navy SEAL-turned-astronaut rocketed into space Thursday aboard a Russian Soyuz spacecraft, kicking off on an abbreviated four-orbit flight to the International Space Station.

Read our launch story.

The craft is completing a programmed sequence to deploy the power-generating solar arrays, as well as antennas for navigational and communication systems.

T+plus 9 minutes. CAPSULE SEPARATION! The Soyuz spacecraft is flying free after the upper stage finished its engine firing and then separated away. The capsule is in pursuit of the International Space Station for a planned docking around 10:32 p.m. EDT tonight, just four orbits from now.

T+plus 8 minutes. About a minute remains in the propulsion by the upper stage. The motor consumes kerosene and liquid oxygen just like the Soyuz rocket's other powerplants.

T+plus 7 minutes. The four-nozzle engine of the upper stage continues to burn to inject the spacecraft into orbit.

T+plus 6 minutes. Soyuz's upper stage is firing to propel the spacecraft into a stable orbital perch around Earth on this single-day launch-to-docking trek to the International Space Station.

T+plus 5 minutes. The core stage of the Soyuz rocket has shut down and separated, leaving the upper stage to complete the job of injecting the Soyuz capsule into orbit.

T+plus 4 minutes. The core motor continues to fire on its propellant mixture of kerosene fuel and supercold liquid oxygen.

T+plus 3 minutes. The safety escape tower and launch shroud have been jettisoned from the atop the Soyuz capsule.

T+plus 2 minutes, 10 seconds. The four strap-on boosters clustered around the Soyuz rocket's main stage have burned out and separated. The core motor continues to fire.

T+plus 60 seconds. Good performance one minute into this ascent for the Soyuz rocket and its three-person crew from the Kazakh launch base. Flight engineer Alexander Misurkin is strapped into the left-hand seat serving as co-pilot, Russian cosmonaut Pavel Vinogradov is in the center seat for his role as the Soyuz commander and NASA astronaut Chris Cassidy is riding in the right-hand seat.

T+plus 20 seconds. The Soyuz rocket has maneuvered on course for a rendezvous with the space station 6 hours from now. The station currently is 254 miles over southern Russian.

LIFTOFF! Liftoff of the Russian Soyuz spacecraft on a sprint to the International Space Station!

T-minus 35 seconds. The first umbilical arm has separated from Soyuz. The second will retract in the next few seconds.

T-minus 1 minute and counting. The Soyuz has been placed on internal power.

T-minus 2 minutes and counting. Rocket propellant tank pressurization is underway. The vehicle's onboard measurement system is activated. Oxidizer and fuel drain and safety valves of the launch vehicle have been closed.

T-minus 3 minutes and counting. The nitrogen purge of the combustion chambers of side and central engine pods of the rocket is being performed in preparation for ignition.

T-minus 4 minutes. The launch key has been inserted in the bunker for liftoff.

T-minus 5 minutes and counting. Soyuz has switched to onboard control, the ground measurement system and the capsule commander's controls are being activated.

T-minus 6 minutes. The automatic program for final launch operations is being initiated.

See our Facebook page for images of the countdown and launch!

T-minus 9 minutes and counting. The crew has closed its helmet visors.

T-minus 10 minutes. The crew inside the Soyuz capsule are starting recorders to collect data during launch.

T-minus 14 minutes and counting. The Soyuz telemetry systems are being activated. They will relay real-time data back to Earth during today's launch.

T-minus 17 minutes. Now in the launch count, realignment of the Soyuz rocket's trajectory control system and checks of internal batteries should be complete. The Soyuz telemetry system will soon be activated and monitoring of Soyuz's thermal control system also will begin.

T-minus 24 minutes. The crew has completed leak checks of the Sokol launch spacesuits at this point in the countdown.

T-minus 30 minutes and counting. The emergency escape system is being armed. The system would be employed if a major malfunction occurs, propelling the Soyuz capsule off the top of the rocket to safety.

T-minus 40 minutes. At the moment of launch, the International Space Station will be 1,056 miles ahead of the Soyuz rocket. Once the spacecraft arrives in orbit nine minutes later, the station will be 2,175 miles ahead as the six-hour, four-orbit rendezvous commences.

The station will pass directly over the launch pad about five minutes before liftoff.

T-minus 45 minutes and counting. Retraction of the two-piece service structure that has enclosed the Soyuz rocket during its stay at the launch pad is underway as the towers rotate to a horizontal position. Several other umbilical arms connecting the rocket to the ground will be retracted at various times later in the countdown.

T-minus 60 minutes and counting. Chris Cassidy, Pavel Vinogradov and Alexander Misurkin were awakened about eight hours ago to begin launch day activities. They signed the doors at crew quarters and received religious blessings before boarding a bus that took the three crewmates the 25-mile distance into the cosmodrome. They donned their white Sokol launch and entry suits, met with officials from their respective space agencies and then headed for the pad. Crowds of well-wishers gathered to wave goodbye as the crew reached the rocket. An elevator took the trio up to the capsule-level of the tower to begin climbing aboard the cramped spacecraft.

The crew has arrived the Baikonur launch pad to begin boarding the capsule and taking their assigned seats for blastoff a little over two hours from now.

The Russian State Commission met earlier today to review readiness of the Soyuz rocket for launch before granting official approval to proceed with fueling the booster.

Clocks continue to count towards today's launch at 4:43 p.m. EDT.

Aimed to fly straight to the International Space Station on Thursday, launching and docking in a matter of hours, a three-man crew is making final preparations for blastoff aboard a Russian Soyuz capsule.

It marks a significant change to standard operating procedures for sending crew members to the orbiting outpost, opting to perform a rapid rendezvous instead of the typical two-day pursuit to catch the station and join the 35th Expedition.

The crew of Soyuz TMA-08M won't have to live in the cramped quarters of their craft for a couple of days, but the alternative is a hectic launch-to-docking timeline that lasts a mere six hours.

Pavel Vinogradov and Alexander Misurkin of the Russian Federal Space Agency and NASA's Chris Cassidy are scheduled for liftoff Thursday at 4:43 p.m. EDT (2043 GMT).

Their orbital maneuverings to reach the station include a pair of large burns within 90 minutes of liftoff, entering the automated rendezvous phase by 8:26 p.m. EDT, rapidly closing in on the station to perform a flyaround to align with the docking port at 10:11 p.m. EDT and linking up with the Poisk module at 10:32 p.m. EDT (0232 GMT).

The whole process will take five hours and 48 minutes.

The Russians successfully conducted same-day launches and dockings on their last three cargo resupply ships, giving confidence to try the sprint on a crewed vehicle.

Hatches are scheduled to open between the Soyuz and station at 12:10 a.m. Friday, boosting the outpost's resident crew back to six people.

Vinogradov, Misurkin and Cassidy will join Expedition 35 commander Chris Hadfield of the Canadian Space Agency, NASA's Tom Marshburn and Russia's Roman Romanenko.

The three-stage Soyuz booster was rolled out to the launch pad at the Baikonur Cosmodrome launch site on Tuesday morning, moving horizontally by railcar and taking the winding route from the final assembly building to the same historic pad used at the dawn of human spaceflight in 1961 to send Yuri Gagarin off the Earth.

Hydraulic pistons lifted the rocket upright on the pad and gantry swing arms moved into position to enclose the vehicle. Technicians on four levels hooked up electrical and telemetry cables between the rocket and pad.

Cassidy will be the 26th NASA astronaut to launch aboard the Russian Soyuz dating back to Norm Thagard in 1995. Two of those astronauts have gone up twice, making this NASA's 28th "seat" reserved in the capsule flights to both the Mir and the International Space Station. In addition, six Americans have paid to fly on the spacecraft as tourists to the ISS.

NASA crew members have routinely used the Soyuz to access the International Space Station since 2003 in the wake of Columbia, when full Expedition rotations were shifted away from the space shuttle and over to the Russian spacecraft.

And even when Expedition crews used the American space shuttles for launches and landings earlier in the program, the Soyuz vehicles still served as their emergency lifeboats to escape the station.

Since arriving at Baikonur earlier this month, Vinogradov, Misurkin and Cassidy have conducted final training sessions, fulfilled Russian spaceflight traditions, performed inspections of their spacecraft and participated in a full dress rehearsal that included donning Sokol spacesuits and climbing into the capsule.

They also got to see the upcoming Progress cargo ship and the new treadmill packed inside for delivery to the station.

Watch this page for live updates during the launch and docking.

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