EVA ENDS. Today's spacewalk ended with the start of pressurization of the Quest airlock at 11:32 a.m. EDT (1532 GMT), marking the 179th spacewalk in support of construction and maintenance of the International Space Station.

The duration of the spacewalk was 1 hour, 36 minutes.

Mastracchio and Swanson are back inside the Quest airlock. The official end of the spacewalk will be marked at the start of repressurization of the airlock.

After completing a tool inventory, Mastracchio and Swanson are heading back to the airlock to wrap up this spacewalk.

"Your R&R was successful and we have a good MDM," radioed astronaut Jeremy Hanson from mission control in Houston. "It's in diagnostic mode as expected."

"Fantastic," one of the spacewalkers replied.

Swanson is taking the opportunity to cut lanyards over two doors leading to a secondary power distribution assembly near the MDM work site. This is the only get-ahead task on this spacewalk, and it clears the way for the space station's Dextre robotic handyman to potentially replace the power unit if needed in the future, avoiding the need for another spacewalk.

Officials say the dangling lanyards prevented Dextre from completing a demonstration task last year.

Mastracchio has completed the installation of the fresh computer on the S0 truss, completing the main task of today's spacewalk. The astronauts will now move into clean-up of the work site as ground controllers prepare to power up and test the new MDM.

The spare multiplexer-demultiplexer computer is now in place as Mastracchio prepares to drive three bolts to affix the box in place.

Making quick work, Mastracchio has unbolted the failed MDM from its housing on the S0 truss.

The spacewalkers have already started removing the first of three bolts holding the failed MDM in place. There is a center "jacking bolt" and two "tie-down bolts" on each side.

Mastracchio and Swanson have arrived at the location of the failed MDM on the S0 truss. The computer is visible in views from helmet-mounted cameras on the astronauts' space suits. Mastracchio's view is denoted by the no. 20 in the lower right corner of the frame. Swanson's camera is labeled no. 18.

The astronauts have exited the Quest airlock and are configuring tethers before moving over to the S0 truss to begin today's computer changeout. Swanson is carrying a bag containing the spare multiplexer-demultiplexer to be installed in place of the faulty unit.

The MDM "black box" computer measurs 10.5 x 14.9 x 16.4 inches and weighs 50.8 pounds. It routes commands to various systems on the space station's external truss, including thermal control systems, solar array rotary joints and the robot arm's mobile transporter.

EVA BEGINS. Today's spacewalk officially began at 1356 GMT (9:56 a.m. EDT).

Rick Mastracchio is now opening the Quest airlock hatch. The official start of the EVA will be marked when the spacesuits are switched to battery power.

With Mastracchio and Swanson now inside the Quest airlock's crew lock, the airlock is being depressurized -- initially to 5 psi and then to vacuum.

Mastracchio and Swanson are inside their spacesuits as space station commander Koichi Wakata helps them prepare for today's spacewalk. Wakata is currently installing rescue jet packs on the suits.

Mastracchio will go by the call sign EV-1 for today's EVA, and his suit will be identifiable by red stripes. Swanson, or EV-2, is wearing a solid white suit.

Astronauts Rick Mastracchio and Steve Swanson are preparing to head outside the International Space Station on Wednesday to replace a failed computer on the outpost's power truss.

The excursion is due to last two-and-a-half hours, and the computer replacement will be the only task for Mastracchio and Swanson on the spacewalk.

Mastracchio and Swanson will begin their spacewalk around 9:20 a.m. EDT (1320 GMT) by switching their spacesuits to internal battery power. A few minutes later, the duo will exit the space station's Quest airlock and make their way to the S0 truss, the center piece of the space station's structural backbone holding the outpost's massive solar arrays.

They will take with them a spare computer to swap out with the failed unit inside the S0 truss.

The external multiplexer-demultiplexer, or MDM, relays commands between computers and systems outside the space station, such as the solar array rotary joints, thermal coolant loops, the robotic arm's mobile transporter, and other functions.

The MDM did not power up when commanded for a health check April 11. It was set as a redundant computer at the time of the failure, and the primary MDM is still working.

But space station managers are concerned they would lose insight and command capability to a number of critical systems if the other computer was to fail.

The sensitivity to an additional MDM failure means replacing the faulty computer is a high priority.

Planning for Wednesday's spacewalk was tricky because it falls the same week as the arrival of a SpaceX Dragon cargo craft Sunday and a technology demonstration using a Russian Progress supply ship, which will undock from the space station about four hours before the start of the spacewalk.

The Progress spaceship will back away to a safe distance from the space station to test upgrades to its Kurs radar navigation system, leading to its return to a docking with the complex Friday.

Such complex operations as the Dragon arrival, the Progress rendezvous exercise, and a spacewalk are typically scheduled with time for breaks in between.

"This isn't a long EVA," said Brian Smith, a space station flight director. "There are certainly EVAs that are more complicated than this one. The real trick has been to figure out how to put this EVA in the same week that we're doing the Dragon mission and we're doing the 53P Progress operations.

"We know how to do each one individually and we usually keep these events spaced apart," Smith said. "In this scenario though, we need to execute them relatively close to each other."

Mastracchio will be making the ninth spacewalk of his career. Wednesday's EVA will mark Swanson's fifth spacewalk.

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

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.

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 10:55 p.m. EDT (0255 GMT).

Docking occurred 252 miles over southern Brazil.

DOCKING! The Soyuz TMA-12M spacecraft has docked to the Poisk module of the space station, delivering Russian cosmonauts Alexander Skvortsov, Oleg Artemyev, and NASA flight engineer Steve Swanson to the international outpost for their 170-day space mission.

Standing by for contact and capture momentarily.

The space station and Soyuz have passed into orbital sunset as the vehicles fly 252 miles over South America.

Range is 25 meters, or 82 feet. Everything is reported normal so far in this automated docking.

Soyuz is now about 65 meters, or 213 feet from the Poisk docking module and closing at 0.7 mph.

Range between the vehicles is now 125 meters, or about 410 feet.

Soyuz is now on a computer-controlled final approach.

Ground teams and the cosmonauts aboard the Soyuz TMA-12M spacecraft are confirming the capsule is properly aligned with the Poisk docking port.

The Soyuz completed the flyaround to align with the docking port. It's now in the stationkeeping hold about 185 meters, or about 607 feet, away from the complex about while controllers verify all is in readiness for final approach.

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. This is a 121-degree flyaround.

A live view from the Soyuz spacecraft shows spectacular imagery of the huge International Space Station looming in ahead of the capsule. Range is now 550 meters, or about 1,804 feet.

The Soyuz is now flying less than a kilometer from the space station.

We're now receiving the first views of the International Space Station from a camera on-board the Soyuz TMA-12M spacecraft at a range of about 3.5 kilometers.

The Soyuz is now 5.9 kilometers from the space station and approaching at a rate of 11 meters per second.

At the planned time of docking, the space station will be 252 miles above northern Brazil.

Range between the Soyuz TMA-12M spacecraft and the space station is now about 15 kilometers, or 9 miles.

The Soyuz is now in its automated rendezvous sequence, and the Kurs rendezvous radar system has been activated and is providing good data to the spacecraft's guidance computer.

The International Space Station has also maneuvered into its docking attitude.

Running two days late after a technical glitch forced an aborted rendezvous, two Russian cosmonauts and a NASA astronaut are approaching the International Space Station for an automated radar-guided docking.

The Soyuz TMA-12M spacecraft is set to dock with the space station's Poisk module at 7:58 p.m. EDT (2358 GMT). About three hours later, Alexander Skvortsov, Oleg Artemyev and Steve Swanson will open hatches and float into the complex, boosting the station's crew complement back to six.

The automatic rendezvous sequence is due to begin shortly, with activation of the Soyuz capsule's Kurs rendezvous radar coming around 6:20 p.m. EDT (2220 GMT).

The Soyuz will pass inside of 10 miles of the space station about an hour before docking before a series of braking burns will slow the capsule's approach to the outpost.

The spacecraft will begin a flyaround maneuver to line up with the Poisk docking port just after 7:30 p.m. EDT (2330 GMT), with final approach beginning about 10 minutes before docking.

Russian flight controllers troubleshooting a glitch aboard the Soyuz TMA-12M spacecraft that interrupted a planned four-orbit rendezvous with the International Space Station Tuesday successfully uploaded a revised 34-orbit trajectory overnight, setting up a delayed docking Thursday.

Read our full story.

A veteran Russian space station commander, a rookie cosmonaut and a NASA shuttle flier rocketed smoothly into space aboard a Russian Soyuz ferry craft Tuesday, but the crew ran into problems executing a required rendezvous rocket firing, delaying docking with the International Space Station until Thursday at the earliest.

Read our full story.

Russian officials have called off the rendezvous of a Soyuz crew capsule with the International Space Station on Tuesday after a problem during a engine burn to fine-tune the spacecraft's expedited six-hour approach to the complex.

The unspecified problem occurred during the third "delta velocity" maneuver, which was scheduled for 7:48 p.m. EDT (2348 GMT).

The Soyuz TMA-12M spacecraft was on an expedited six-hour rendezvous profile, but Russian officials keep the option of reverting to a standard two-day flight to the space station in the event of a problem.

The docking opportunity Thursday is now set for 7:58 p.m. EDT (2358 GMT) with the space station's Poisk module.

"Right now, we don't understand exactly what happened," a Russian flight controller in Moscow radioed the Soyuz crew. "During this contact, we will download the whole mass of telemetry and we will analyze it and review it ... to figure out what happened.

"So you will have to be in flight for two days," a Russian official told the crew.

"Yes, I understand," one of the cosmonauts replied.

Russian cosmonauts Alexander Skvortsov and Oleg Artemyev, joined by NASA flight engineer Steve Swanson, have arrived in orbit following a good launch aboard the Soyuz TMA-12M spacecraft from the Baikonur Cosmodrome.

The solar arrays have been unfurled aboard the spacecraft to generate electricity, and the first major orbit-adjustment maneuver is planned for 6:02 p.m. EDT (2202 GMT) to begin raising the capsule's altitude to match that of the space station.

A second "delta velocity" burn is set for 6:47 p.m. EDT (2247 GMT), followed by several more firings over the next few hours to set up for rendezvous and docking.

The 7.9-ton capsule's automated rendezvous sequence, guided by its Kurs radar system, will commence at 8:54 p.m. EDT (0054 GMT).

The Soyuz should be in position to start a flyaround maneuver at about 10:39 p.m. EDT (0239 GMT) to line up with the docking port on the space station's Poisk module. Soyuz commander Alexander Skvortsov will be standing by to take over manual flying of the spacecraft if required. Final approach will begin about 10 minutes before docking, which is scheduled for 11:04 p.m. EDT (0304 GMT).

The docking should occur a mere 5 hours and 47 minutes after liftoff.

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

"Weightlessness confirmed," says Soyuz commander Alexander Skvortsov.

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 at 11:04 p.m. EDT (0304 GMT).

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 put 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 the six-hour, four-orbit trek to catch the International Space Station.

T+plus 5 minutes. The core stage of the Soyuz rocket has shut down and separated at an altitude of approximately 105 miles, 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 engine continues to fire as Soyuz streaks into space at more than 3,300 mph.

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. Russian cosmonaut Oleg Artemyev is strapped into the left-hand seat serving as co-pilot, veteran cosmonaut Alexander Skvortsov is in the center seat for his role as the Soyuz commander and NASA astronaut Steve Swanson is riding in the right-hand seat.

T+plus 30 seconds. Skvortsov, Artemyev and Swanson are beginning a 170-day expedition in space.

The Soyuz rocket has maneuvered on course for a rendezvous with the space station six hours from now. The station currently is flying 260 miles over southern Russia.

LIFTOFF! Liftoff of the Expedition 39 crew en route to the International Space Station for docking in six hours!

T-minus 40 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 4 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 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. And the launch key has been inserted in the bunker for liftoff.

Launch is set for 5:17:23 p.m. EDT (2117:23 GMT), the moment Earth's rotation carries the Baikonur Cosmodrome under the International Space Station's ground track.

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 20 minutes and counting. The three-stage Soyuz rocket will insert the 15,700-pound space capsule into a 143 by 118 mile orbit, inclined 51.6 degrees to the equator, according to NASA.

T-minus 22 minutes and counting. At the time of launch, the International Space Station will be flying 260 miles over northeast Kazakhstan. When the Soyuz TMA-12M spacecraft deploys from the Soyuz rocket's third stage, the space station will be flying 1,875 miles ahead of the Soyuz.

The space station will fly almost directly overhead the Baikonur Cosmodrome a few minutes before launch.

The capsule will close that distance over the next six hours, with docking to the space station's Poisk module scheduled for 11:04 p.m. EDT (0304 GMT).

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

T-minus 27 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 and counting. The two-piece service structure which enclosed the Soyuz rocket is being retracted to a horizontal position. The towers protected the rocket and provided workers and the Soyuz crew with access to the spacecraft since the rocket arrived at the launch pad at sunrise Sunday.

Several other umbilical arms connecting the rocket to the ground will be retracted at various times later in the countdown.

T-minus 55 minutes and counting. Soyuz TMA-12M commander Alexander Skvortsov, Russian flight engineer Oleg Artemyev and NASA astronaut Steve Swanson were awakened about eight hours ago to begin launch day activities.

They signed the doors at the Cosmonaut Hotel 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.

T-minus 62 minutes. Live streaming video coverage of today's rocket flight to orbit begins now.

T-minus 90 minutes. The Soyuz rocket is fueled, the crew has traveled to the launch pad and the countdown is progressing toward liftoff of the space station's Expedition 39 crew from the Baikonur Cosmodrome at 5:17 p.m. EDT (2117 GMT).

Live launch coverage and commentary begins in the stream at 4:15 p.m. EDT.

The three-man crew has arrived at Launch Pad No. 1 at the Baikonur Cosmodrome, where they will take an elevator ride to the top of the Soyuz rocket to board the Soyuz TMA-12M spacecraft for liftoff at 2117 GMT (5:17 p.m. EDT).

The crew is led by Alexander Skvortsov, a 47-year-old Russian Air Force fighter pilot selected as a cosmonaut candidate in 1997. Skvortsov logged 176 days aboard the International Space Station as Expedition 23 flight engineer and Expedition 24 commander in 2010.

Skvortsov will occupy the capsule's center seat, with cosmonaut Oleg Artemyev and NASA astronaut Steve Swanson flanking him in the left and right couches.

Artemyev will be the primary flight engineer, assisting Skvortsov with control duties during the launch and docking, which is set for 0304 GMT (11:04 p.m. EDT), less than six hours after liftoff.

The 43-year-old Artemyev was born in Latvia and holds a degree in low temperature physics and technology. Artemyev, an engineer with RSC Energia, is making his first spaceflight.

Swanson is a veteran of two space shuttle missions in 2007 and 2009, accumulating nearly 27 days in orbit. The Colorado native will assume command of the International Space Station in May.

A veteran Russian space station commander, a rookie cosmonaut and a NASA shuttle flier are set for launch aboard a Russian Soyuz ferry craft Tuesday, kicking off a four-orbit rendezvous with the International Space Station to boost the lab's crew back to six.

Read our full story.

Russian ground crews transferred a Soyuz rocket across the austere steppes of Kazakhstan on Sunday and hoisted the three-stage booster atop a concrete launch pad, marking a milestone in preparations to launch two Russian cosmonauts and an American astronaut Tuesday to the International Space Station.

Keeping with tradition dating back to the first manned space launch of Yuri Gagarin in 1961, the Soyuz launcher emerged from its assembly building on a specially-designed railroad car before sunrise Sunday.

The Soyuz rocket reached Launch Pad No. 1 at the Baikonur Cosmodrome, and technicians rotated the rocket vertical before work platforms enclosed the launcher for final flight preparations.

Liftoff is scheduled for 2117 GMT (5:17 p.m. EDT) Tuesday, or 3:17 a.m. local time at Baikonur.

Veteran Russian cosmonaut Alexander Skvortsov, first-time flier Oleg Artemyev, and NASA astronaut Steve Swanson will climb inside the Soyuz TMA-12M spacecraft about three hours before launch.

Skvortsov will be at the controls in the center seat of the spaceship as Soyuz commander, with Artemyev serving as the primary flight engineer in the left seat and Swanson in the capsule's right seat as the second flight engineer.

The trio will spend 170 days in space before returning to Earth. Landing is currently scheduled for Sept. 11.

The crew will join space station commander Koichi Wakata and flight engineers Rick Mastracchio and Mikhail Tyurin already aboard the outpost.

Check out photos of the Soyuz rollout.