BY JUSTIN RAY

Additional coverage for subscribers:
VIDEO: FULL LENGTH LAUNCH MOVIE! PLAY
VIDEO: ATLANTIS BLASTS OFF WITH COLUMBUS PLAY
VIDEO: POLLS GIVE THE FINAL "GO" TO LAUNCH PLAY
VIDEO: ASTRONAUTS ARRIVE AT LAUNCH PAD 39A PLAY
VIDEO: CREW DEPARTS QUARTERS FOR LAUNCH PAD PLAY
VIDEO: ASTRONAUTS DON THEIR SPACESUITS FOR LAUNCH PLAY
VIDEO: RUSSIAN CARGO SHIP DOCKS TO STATION THIS MORNING PLAY
VIDEO: PAD GANTRY ROLLED BACK THE NIGHT BEFORE LAUNCH PLAY
VIDEO: COLUMBUS AND ATV OVERVIEW BRIEFING PLAY
VIDEO: PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: TUESDAY MORNING'S COUNTDOWN STATUS BRIEFING PLAY
VIDEO: MONDAY'S CARGO SHIP UNDOCKING FROM STATION PLAY
VIDEO: ATLANTIS' PAYLOAD BAY DOORS CLOSED FOR FLIGHT PLAY
VIDEO: CREW RETURNS TO KENNEDY SPACE CENTER FOR LAUNCH PLAY
VIDEO: MONDAY MORNING'S COUNTDOWN STATUS BRIEFING PLAY
VIDEO: POST-FLIGHT READINESS REVIEW BRIEFING PLAY
VIDEO: STS-122 ASTRONAUT BIOGRAPHIES PLAY
VIDEO: NARRATED OVERVIEW OF ATLANTIS' MISSION PLAY
VIDEO: INSIGHTS INTO COLUMBUS SCIENCE LABORATORY PLAY
MORE: STS-122 VIDEO COVERAGE
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2212 GMT (5:12 p.m. EST)

EVA ENDS. Repressurization of the Quest airlock module began at 5:11 p.m. EST, marking the official end of today's spacewalk by Rex Walheim and Stan Love. The EVA lasted seven hours and 58 minutes.

2210 GMT (5:10 p.m. EST)

The European Space Agency's Columbus laboratory module was successfully removed from the shuttle Atlantis' cargo bay today and bolted to its permanent home on the front right side of the international space station to accomplish the primary goal of the year's first shuttle mission.

Read our update story.

2208 GMT (5:08 p.m. EST)

Both spacewalkers are back inside the airlock and the hatch has been closed.

2144 GMT (4:44 p.m. EST)

Columbus officially becomes part of the space station! Motorized bolts have engaged to firmly hold the science laboratory at its new orbital home.

2134 GMT (4:34 p.m. EST)

The robot arm has been put into its limp mode while bolts in the docking port are electrically driven to permanently attach Columbus to the station.

2129 GMT (4:29 p.m. EST)

Columbus has reached the space station. At 4:29 p.m., the four ready-to-latch indicators showed the module has arrived at the Harmony connecting port.

2123 GMT (4:23 p.m. EST)

Walheim has broken the torque on two of the four bolts. Once he finishes this job, he'll be heading back to the airlock to bring this EVA to a conclusion.

2121 GMT (4:21 p.m. EST)

Ever so slowly and carefully, Columbus is being maneuvered the final few feet to docking.

2115 GMT (4:15 p.m. EST)

Our latest update story.

2112 GMT (4:12 p.m. EST)

The robot arm has put Columbus into the "pre-install position" just outboard of Harmony.

2100 GMT (4:00 p.m. EST)

Columbus is inching ever closer to the starboard-side docking port of the Harmony module. Meanwhile, spacewalker Stan Love has discovered what appears to be a tiny impact crater on a handrail near the airlock.

2029 GMT (3:29 p.m. EST)

Given the current duration of the EVA, Mission Control has decided to have Stan Love remain at the airlock and send Rex Walheim over to the P1 truss and untorque bolts on the nitrogen tank as part of the work to prepare for Wednesday's spacewalk that will replace that tank. Tasks planned for today involving removing the nitrogen and power lines to the old tank will be postponed to Wednesday.

2017 GMT (3:17 p.m. EST)

Atlantis astronaut Leland Melvin, a former college football star drafted by the Detroit Lions, used the international space station's robot arm today to carefully pull the European Space Agency's Columbus research module out of the shuttle's cargo bay.

Read our full story.

2014 GMT (3:14 p.m. EST)

Columbus is being swung out over the starboard wing of Atlantis on its way to the docking port on the side of Italian-made Harmony connecting module.

2005 GMT (3:05 p.m. EST)

After briefly stopping at the airlock for a suit recharge, the spacewalkers will be climbing to the Port 1 truss to begin disconnecting nitrogen lines and power cables on the depleting Nitrogen Tank Assembly. That tank will be pulled out of the station on Wednesday and replaced with a fresh one.

1958 GMT (2:58 p.m. EST)

"Columbus has started its trip to the new world," astronaut Dan Tani just said.

1955 GMT (2:55 p.m. EST)

Columbus is in motion!

1953 GMT (2:53 p.m. EST)

Retension latches have been released and the station arm operators have been given a "go" to begin unberthing Columbus.

1945 GMT (2:45 p.m. EST)

Mission Control just told the crew they are a little more than an hour behind the timeline. They are facing a 7.5-hour limit for the EVA duration based on spacesuit oxygen supplies. The astronauts and ground concurred that they will press on with the planned tasks involving the nitrogen tank on the Port 1 truss.

1933 GMT (2:33 p.m. EST)

The space station's Canadian-built robotic arm has a firm grasp on the European Space Agency's Columbus laboratory module. Latches holding Columbus in the payload bay will be released shortly, allowing the arm to hoist the module toward its final home on the station.

1900 GMT (2:00 p.m. EST)

The spacewalkers have completed their prep work on Columbus after some slow-going on the connectors and exterior panels. Once the crew clears out of the way, the robot arm will reach down and capture the module for its removal from the shuttle and installation to the space station over the course of the next couple of hours. Still on the agenda for the EVA is some work to ready a depleted nitrogen tank on the station truss for its replacement during Wednesday's spacewalk.

1820 GMT (1:20 p.m. EST)

Just past the four-hour mark of today's EVA. Power cables to the grapple fixture have been hooked up and the astronauts are working to re-install the protective metal shields to the outer surface of Columbus that had been temporarily removed. These latest tasks have taken longer than anticipated, and Mission Control now says the crew is a full hour behind the timeline.

1745 GMT (12:45 p.m. EST)

The spacewalkers continue their work in the payload bay of Atlantis. Mission Control says the crew is running about a half-hour behind the timeline.

1659 GMT (11:59 a.m. EST)

Columbus has received its grapple fixture for the space station's robot arm to pick up the module and hoist it out the Atlantis' payload bay this afternoon. The spacewalkers just completed bolting the device to the lab's hull.

1602 GMT (11:02 a.m. EST)

Love has released the grapple fixture from its launch bracket. He'll carry it over to Columbus for installation.

1550 GMT (10:50 a.m. EST)

Perched on the station's extended robotic arm, Love is unbolting the grapple fixture from its stowage plate on the side of Atlantis' payload bay wall. Once Walheim has the covers removed on Columbus, the fixture will be carried over to the module and installed by the spacewalkers. Clearance issues with between the module and the payload bay doors meant the fixture must be installed in space and couldn't be installed on the ground.

1532 GMT (10:32 a.m. EST)

Walheim has begun removing one of the panels on Columbus' outer hull for the upcoming installation of the robot arm grapple fixture.

1524 GMT (10:24 a.m. EST)

A heater cable running from the shuttle payload bay to the Columbus science laboratory module has been disconnected by spacewalker Rex Walheim.

1513 GMT (10:13 a.m. EST)

Now one hour into today's EVA. Both spacewalkers have made their way from the station's Quest airlock module down to shuttle Atlantis' payload bay. They are getting set up to complete the tasks needed to prepare Columbus for its unberthing from the shuttle later today.

This is the 102nd spacewalk devoted to station assembly and maintenance since construction began in 1998, the third for Walheim and the first for Love, who is replacing German astronaut Hans Schlegel for today's excursion.

1426 GMT (9:26 a.m. EST)

Here is a revised timeline for today's spacewalk based on the actual start time (in EST and event elapsed time):

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

09:13 AM...00...00...EVA-1: Spacesuits to battery power
09:18 AM...00...05...EVA-1: Airlock egress
09:33 AM...00...20...EVA-1: Power-Data Grapple Fixture setup
11:13 AM...02...00...EVA-1: PDGF installation on Columbus module
01:28 PM...04...15...Station robot arm (SSRMS) grapples Columbus
01:28 PM...04...15...Harmony vestibule outfitting preps
01:43 PM...04...30...EVA-1 (Walheim): Nitrogen tank removal prep
01:48 PM...04...35...SSRMS unberths Columbus
01:53 PM...04...40...EVA-1 (Love): Nitrogen tank removal prep
03:13 PM...06...00...EVA-1: Cleanup and airlock ingress
03:43 PM...06...30...Columbus attachment begins
03:43 PM...06...30...EVA-1: Airlock repressurization

1414 GMT (9:14 a.m. EST)

EVA BEGINS. The airlock has been depressurized and the outer hatchway has swung open. The spacewalkers switched their suits to internal battery at 9:13 a.m. EST, marking the official start time for today's EVA by Rex Walheim and Stan Love.

1030 GMT (6:30 a.m. EST)

Astronauts Rex Walheim and Stan Love are suiting up this morning in preparation for a planned six-and-a-half-hour spacewalk to ready the European Space Agency's Columbus research module for attachment to the international space station. The excursion is scheduled to begin around 9:35 a.m. and if all goes well, astronauts Dan Tani and Leland Melvin, a former football star operating the space station's robot arm, will pull Columbus out of the shuttle Atlantis' cargo bay shortly after 2 p.m. and move it into place for robotic attachment to the lab complex.

Read our full story.

SUNDAY, FEBRUARY 10, 2008

NASA managers expect German astronaut Hans Schlegel to participate in a spacewalk Wednesday, the second of three excursions planned by the shuttle Atlantis' crew. Schlegel, a 56-year-old father of seven, originally planned to join astronaut Rex Walheim for the crew's first spacewalk Sunday. But the EVA was delayed 24 hours to Monday - and Schlegel was replaced by Stan Love - when the European Space Agency astronaut apparently became ill after launch last week.

Read our full story.

SATURDAY, FEBRUARY 9, 2008

In a surprise announcement, flight controllers Saturday told the shuttle-station astronauts shortly after Atlantis docked with the lab complex to delay a planned Sunday spacewalk - and installation of the new Columbus research module - by 24 hours, extending Atlantis' mission by one day because of a crew medical issue. German Hans Schlegel will be replaced on the EVA.

Read our full story.

1841 GMT (1:41 p.m. EST)

HATCHES OPEN. The hatchway between Atlantis and the space station was opened at 1:40 p.m. EST, and the shuttle crew is being welcomed aboard the outpost now.

1755 GMT (12:55 p.m. EST)

Wrapping up a textbook rendezvous, commander Steve Frick guided the shuttle Atlantis to a smooth docking with the international space station today after a spectacular slow-motion back flip directly below the outpost to let the lab crew photograph the ship's heat shield tiles.

Read our docking story.

1735 GMT (12:35 p.m. EST)

The docking ring between the two craft has been retracted into Atlantis' Orbiter Docking System, pulling the station to a tight mating. The hooks and latches are driving shut to firmly connect the two spacecraft.

Pressure and leak checks will be performed by the crews before the hatchway is opened.

1719 GMT (12:19 p.m. EST)

Today's docking occurred a few minutes early at 12:17 as the shuttle and station flew at an altitude of more than 200 miles over Australia.

1717 GMT (12:17 p.m. EST)

CONTACT AND CAPTURE! Atlantis has arrived at the space station to install the European Space Agency's Columbus science laboratory module.

The relative motions of the shuttle and station will be allowed to damp out over the next few minutes by the spring-loaded docking system. Later, the hooks and latches will be closed to firmly join the two craft and Atlantis' Orbiter Docking System docking ring will be retracted to form a tight seal.

The opening of hatches between the station and shuttle is expected in about 90 minutes. That will be followed by a welcoming ceremony and safety briefing.

1716 GMT (12:16 p.m. EST)

The distance to docking is now 10 feet.

1715 GMT (12:15 p.m. EST)

Now 14 feet separating the shuttle from the station. Atlantis' thrusters are programmed to fire in a post-contact maneuver to force the two docking ports together. That procedure is being armed.

1711 GMT (12:11 p.m. EST)

The final approach beginning. The alignment between docking ports on Atlantis and the space station is acceptable and no "fly out" maneuver by the shuttle is necessary.

1709 GMT (12:09 p.m. EST)

About 40 feet separate the shuttle and station. Atlantis is closing at less than one-tenth of a foot per second.

1707 GMT (12:07 p.m. EST)

The shuttle has closed to within 50 feet of the space station.

1705 GMT (12:05 p.m. EST)

Atlantis and the station are 60 feet.

1701 GMT (12:01 p.m. EST)

About 100 feet left to go.

1658 GMT (11:58 a.m. EST)

Mission Control estimates docking time will be roughly ontime at 12:25 p.m. based on the shuttle's approach rate.

1657 GMT (11:57 a.m. EST)

About 160 feet separate the shuttle and station. Atlantis is closing at about two-tenths of a foot per second.

1651 GMT (11:51 a.m. EST)

Now about 250 feet from docking.

1648 GMT (11:48 a.m. EST)

The shuttle's crew has been given a "go" for docking.

1647 GMT (11:47 a.m. EST)

The shuttle has reached the point directly in front of the station along the imaginary line called the velocity vector, or +V bar. Atlantis is 299 feet from the station.

1640 GMT (11:40 a.m. EST)

Atlantis is marking the arc from the point beneath the station to a point in front of the complex to align with the docking port on the Harmony module. Docking is about 45 minutes away.

1632 GMT (11:32 a.m. EST)

The pitch maneuver has been completed. Atlantis is back in the orientation where it started, with the payload bay looking up at the station as the craft fly over the mid-Atlantic.

1630 GMT (11:30 a.m. EST)

The main engine nozzles of Atlantis are facing the station now as the shuttle points its tail upward.

1628 GMT (11:28 a.m. EST)

This 360-degree, nose-first pirouette by Atlantis gives the station crew about 100 seconds of quality photography time to snap detailed pictures of the orbiter's black tiles in the search for any launch impact damage.

1627 GMT (11:27 a.m. EST)

The formal photo-taking period has started for the Expedition 16 crew, now that the shuttle has rotated its underside in view of the station complex.

1625 GMT (11:25 a.m. EST)

Atlantis is nose-up facing the station as the two craft fly 205 miles above the Atlantic, just off the northeastern coast of South America.

1624 GMT (11:24 a.m. EST)

The rendezvous pitch maneuver -- the 360-degree flip -- is beginning. The shuttle is the under the control of commander Steve Frick, who is flying the ship from the aft flight deck.

As the shuttle's underside rotates into view, the station's crew will photograph Atlantis' belly with handheld digital cameras equipped with 400- and 800-millimeter lenses.

The 800mm images should provide one-inch resolution for examination of landing gear door and external tank umbilical door seals. The 400mm will yield three-inch resolution.

After completing the RPM maneuver, Atlantis will fly directly ahead of the space station with the shuttle's nose facing deep space and its cargo bay pointed at the lab complex. Then Frick will guide the spacecraft to a docking with a pressurized mating adapter attached to the Harmony connecting module.

1610 GMT (11:10 a.m. EST)

Atlantis has reached a point 600 feet directly beneath the station. The shuttle will hold this position until the RPM flip occurs a few minutes from now.

1557 GMT (10:57 a.m. EST)

The shuttle is about 1,200 feet below the station. Mission Control has given the "go" for the upcoming rendezvous pitch maneuver.

1543 GMT (10:43 a.m. EST)

Another of the mid-course correction burns has been completed by the shuttle to fine-tune its path to the station.

1532 GMT (10:32 a.m. EST)

Now 15,000 feet separating the two spacecraft.

1510 GMT (10:10 a.m. EST)

Early today, one of the shuttle's four flight computers - GPC-3 - failed to properly transition from "standby" to "run" when the astronauts powered up the full redundant set.

And the space station will be in a so-called "biased" attitude, or orientation, today during docking to improve solar power generation.

Read our update story.

1509 GMT (10:09 a.m. EST)

The shuttle and station are about 7.5 miles apart now.

1459 GMT (9:59 a.m. EST)

Atlantis just completed the first in a series of available mid-course correction burns during this approach to the station.

1437 GMT (9:37 a.m. EST)

The shuttle has performed the Terminal Initiation burn. This puts the shuttle on a trajectory to directly intercept the orbiting station over the next orbit and a half. This burn is the latest in a series of maneuvers performed by Atlantis during its two days of chasing the station since launch Thursday.

Docking is anticipated at 12:25 p.m. EST.

1412 GMT (9:12 a.m. EST)

The crew has been given a "go" for the upcoming TI burn at 9:37 a.m. EST that will begin the final phase of the two-day rendezvous sequence. Atlantis is about 12 miles from the station right now.

1030 GMT (6:30 a.m. EST)

The Atlantis astronauts, closing in on the international space station, are gearing up for docking today to wrap up a two-day orbital chase. Looping below the lab complex and then up to a point directly in front of the station, commander Steve Frick plans to manually guide Atlantis to a linkup around 12:25 p.m.

Read our full story.

FRIDAY, FEBRUARY 8, 2008

Atlantis came through its eight-and-a-half-minute climb to space Thursday in good shape with no obvious signs of impact damage to the ship's protective heat shield. John Shannon, Mission Management Team chairman, said today the shuttle was operating near flawlessly and while it will take several more days to complete a detailed post-launch inspection and analysis, "it looks like we had an extremely clean launch."

Read our full story.

2030 GMT (3:30 p.m. EST)

The wing leading edge and nose cap inspections were completed today. No serious problems were identified with Atlantis, but engineers on the ground will be examining the data to make sure the heat shield is safe for reentry.

At the afternoon mission status briefing, NASA officials said Atlantis' systems are operating perfectly and the flight is progressing without any glitches.

Atlantis remains on course to reach the space station tomorrow. At present, the shuttle is 5,400 nautical miles behind the station, closing at a rate of 487 miles per orbit.

1800 GMT (1:00 p.m. EST)

The Atlantis astronauts spent the morning scrutinizing the shuttle's nose cap and wing leading edge panels in a now-standard post-Columbia inspection carried out the day after launch to look for any signs of ascent debris impact damage. The crew also broke out equipment and began readying the orbiter for docking with the international space station Saturday.

Read our full story.

1545 GMT (10:45 a.m. EST)

The Atlantis astronauts are working through a busy day in space today, setting up a critical heat shield inspection and preparing the shuttle for docking Saturday with the international space station.

Scans of the starboard wing using the Orbiter Boom Sensor System are underway right now.

This is a multi-hour job to survey the shuttle to look for any signs of launch damage. The precautionary safety inspection has become a standard activity for all post-Columbia shuttle crews.

THURSDAY, FEBRUARY 7, 2008
2235 GMT (5:35 p.m. EST)

"It was a pretty clean launch," astronaut Jim Dutton radioed from mission control. "We did see, at about MET 2:13 (two minutes 13 seconds after launch) a few piece of debris, they think at least three, that came off inboard of the LO2 (liquid oxygen) feedline just aft of the starboard bipod leg. The debris assessment team indicated they didn't identify an impact at the time and it's obviously under evaluation."

"OK, thanks for that report," commander Steve Frick replied. "We really appreciate it."

2157 GMT (4:57 p.m. EST)

The Ku-band communications antenna aboard Atlantis has been deployed and activated.

2139 GMT (4:39 p.m. EST)

The Freon cooling loops aboard the orbiter look good after door opening, Mission Control says. Before the launch there had been an issue with one of the Freon flex hoses on the right-hand door.

2135 GMT (4:35 p.m. EST)

Mission Control just gave the astronauts a "go" for on-orbit operations following today's smooth journey to space.

2135 GMT (4:35 p.m. EST)

The 60-foot-long payload bay doors have been opened.

2129 GMT (4:29 p.m. EST)

The astronauts are preparing to open the payload bay doors.

2030 GMT (3:30 p.m. EST)

Running two months late, the repaired shuttle Atlantis thundered safely into orbit today after expected storms from a weakening cold front failed to materialize. The low-level hydrogen fuel sensor circuits that derailed two launch tries in December worked normally today, clearing the way for launch of Atlantis and a European Space Agency research module bound for the international space station.

Read our full story.

2025 GMT (3:25 p.m. EST)

T+plus 39 minutes, 45 seconds. The twin Orbital Maneuvering System engines on the tail of Atlantis have been fired successfully to propel the shuttle the rest of the way to orbit. The burn occurred over the Indian Ocean.

2023 GMT (3:23 p.m. EST)

T+plus 37 minutes, 58 seconds. The maneuvering engines have ignited for the orbit raising burn.

2020 GMT (3:20 p.m. EST)

T+plus 35 minutes. Atlantis is in the correct configuration for the upcoming OMS 2 burn.

2006 GMT (3:06 p.m. EST)

T+plus 21 minutes. The two flapper doors on the belly of Atlantis are being commanded to swing shut to shield the umbilicals that had connected to the external fuel tank.

2001 GMT (3:01 p.m. EST)

T+plus 16 minutes. The three Auxiliary Power Units have been shut down as planned.

1954 GMT (2:54 p.m. EST)

T+plus 9 minutes, 19 seconds. It was a nominal MECO. A quick boost from the Orbital Maneuvering System engines is not required to reach the planned preliminary sub-orbital trajectory.

1954 GMT (2:54 p.m. EST)

T+plus 8 minutes, 55 seconds. The emptied external tank has been jettisoned from the belly of space shuttle Atlantis. The tank will fall back into the atmosphere where it will burn up harmlessly.

1954 GMT (2:54 p.m. EST)

T+plus 8 minutes, 30 seconds. MECO. Main Engine Cutoff confirmed! Atlantis has sailed into orbit with the Columbus science lab bound for the International Space Station.

1953 GMT (2:53 p.m. EST)

T+plus 7 minutes, 40 seconds. The main engines are beginning to throttle down to ensure the shuttle does not experience forces greater than 3 g's as it continues to accelerate prior to engine shutdown.

1952 GMT (2:52 p.m. EST)

T+plus 7 minutes, 10 seconds. Single engine press 104. The shuttle can reach orbit on the power from a single main engine should two fail at this point. But all three continue to fire properly.

1952 GMT (2:52 p.m. EST)

T+plus 7 minutes. Main engines, fuel cells and APUs continue to perform well as Atlantis nears the completion of powered ascent.

1951 GMT (2:51 p.m. EST)

T+plus 6 minutes, 25 seconds. "Press to MECO" Atlantis can now achieve a safe orbit on two engines. All three remain in good shape.

1951 GMT (2:51 p.m. EST)

T+plus 6 minutes. The shuttle has started rolling to a heads-up position to improve communications with the TDRS satellite network.

1950 GMT (2:50 p.m. EST)

T+plus 5 minutes, 20 seconds. "Press to ATO". Atlantis can reach an orbit, albeit a low orbit, on two engines should one shut down now. But all three powerplants are still running just fine.

1950 GMT (2:50 p.m. EST)

T+plus 5 minutes. All systems looking good on Atlantis.

1950 GMT (2:50 p.m. EST)

T+plus 4 minutes, 30 seconds. Atlantis will be tripling its speed in the next four minutes to reach orbital velocity of 17,500 mph.

1949 GMT (2:49 p.m. EST)

T+plus 4 minutes. Negative return. The shuttle has passed the point where Atlantis could turn around and make an emergency landing at Kennedy Space Center in the event of a main engine problem. Landing sites in France and Spain are now available to Atlantis in the unlikely event an abort occurs during the remainder of today's launch.

1948 GMT (2:48 p.m. EST)

T+plus 3 minutes. Commander Steve Frick just received the "Two-engine TAL" call from CAPCOM Jim Dutton in Mission Control. The call means Atlantis can now reach a Transatlantic Abort Landing site if one main engine fails. However, all three engines continue to burn normally.

1948 GMT (2:48 p.m. EST)

T+plus 2 minutes, 45 seconds. The twin Orbital Maneuvering System engines on the ship's tail have ignited to provide an extra boost in thrust in addition to Atlantis' three main engines.

1947 GMT (2:47 p.m. EST)

T+plus 2 minutes, 20 seconds. Guidance is converging as programmed. Atlantis' engine nozzles are swiveling to steer the ship toward a precise point for main engine cutoff about six minutes from now.

1947 GMT (2:47 p.m. EST)

T+plus 2 minutes, 10 seconds. A good separation of the twin solid rocket boosters has occurred. The shuttle continues its streak toward space on the power generated by the three liquid-fueled main engines.

1947 GMT (2:47 p.m. EST)

T+plus 1 minute, 45 seconds. It's a beautiful ascent for Atlantis and crew. Commander Steve Frick and pilot Alan Poindexter are joined on the flight deck by mission specialists Leland Melvin and Rex Walheim. Stanley Love and European astronauts Hans Schlegel and Leopold Eyharts are seated down on the middeck.

1947 GMT (2:47 p.m. EST)

T+plus 90 seconds. The space shuttle now weighs just half of what it did at liftoff. The solid rocket boosters are burning 11,000 pounds of propellant every second. The main engines are guzzling a half-ton of liquid fuel per second from the external tank.

1946 GMT (2:46 p.m. EST)

T+plus 70 seconds. Atlantis' three main engines have revved up to their 104 percent power setting. And Mission Control has given the "go at throttle up" call.

1946 GMT (2:46 p.m. EST)

T+plus 60 seconds. All systems are looking good one minute into the flight. Atlantis is traveling on a northeastward trajectory toward orbit, its speed already in excess of 1,000 miles per hour as the main engines and twin solid rockets generate nearly 7 million pounds of thrust.

1946 GMT (2:46 p.m. EST)

T+plus 35 seconds. Atlantis' three liquid-fueled main engines are easing back to two-thirds throttle to reduce the aerodynamic stresses on the vehicle as it powers through the dense lower atmosphere and breaks the sound barrier.

1945:50 GMT (2:45:50 p.m. EST)

T+plus 20 seconds. Atlantis has rolled on course for its two-day trek to the space station. The shuttle will rendezvous and dock with the station on Saturday afternoon to deliver Europe's Columbus science laboratory.

1945:30 GMT (2:45:30 p.m. EST)

T-minus 10 seconds, go for main engine start, fuel valves are opening, engine ignition, 3, 2, 1 and LIFTOFF! Liftoff of Atlantis -- a 21st century voyage of Columbus begins as the space shuttle clears the tower!

1944:59 GMT (2:44:59 p.m. EST)

T-minus 31 seconds. AUTO SEQUENCE START! The handoff has occurred from the Ground Launch Sequencer to the space shuttle. Atlantis' computers now controlling.

In the next few seconds, the solid rocket booster hydraulic steering system will be started, the orbiter's body flap and speed brake moved to their launch positions, the firing chain armed. Main engine ignition begins at T-minus 6.6 seconds.

1944:30 GMT (2:44:30 p.m. EST)

T-minus 1 minute. Computers are verifying that the main engines are ready for ignition. Sound suppression water system is armed. The system will activate at T-minus 16 seconds to suppress the sound produced at launch. And the residual hydrogen burn ignitors are armed. They will be fired at T-minus 10 seconds to burn off hydrogen gas from beneath the main engine nozzles.

Shortly, the external tank strut heaters will be turned off; Atlantis will transition to internal power; the liquid oxygen and liquid hydrogen outboard fill and drain valves will be closed; the payload bay vent doors will be positioned for the launch; and the gaseous oxygen vent arm will be verified fully retracted.

1944:00 GMT (2:44:00 p.m. EST)

Now 90 seconds from launch. All remains "go" for liftoff of Atlantis and the seven-man crew at 2:45 p.m.

1943:30 GMT (2:43:30 p.m. EST)

T-minus 2 minutes. The astronauts are being instructed to close and lock the visors on their launch and entry helmets.

At T-minus 1 minute, 57 seconds the replenishment to the flight load of liquid hydrogen in the external tank will be terminated and tank pressurization will begin.

1943:00 GMT (2:43:00 p.m. EST)

T-minus 2 minutes, 30 seconds. The external tank liquid oxygen vent valve has been closed and pressurization of the LOX tank has started.

Atlantis' power-producing fuel cells are transfering to internal reactants. The units will begin providing all electricity for the mission beginning at T-50 seconds.

And pilot Alan Poindexter has been asked to clear the caution and warning memory system aboard Atlantis. He will verify no unexpected errors in the system.

In the next few seconds, the gaseous oxygen vent hood will be removed from atop the external tank. Verification that the swing arm is fully retracted will be made by the ground launch sequencer at the T-minus 37 second mark.

1942:30 GMT (2:42:30 p.m. EST)

T-minus 3 minutes. Orbiter steering check is now complete; the main engine nozzles are in their start positions.

1942:00 GMT (2:42:00 p.m. EST)

T-minus 3 minutes, 30 seconds. The main engine nozzles now being moved through a computer controlled test pattern to demonstrate their readiness to support guidance control during launch today.

1941:30 GMT (2:41:30 p.m. EST)

T-minus 4 minutes. Activation of the APUs is complete. The three units are up and running normally.

And the final helium purge sequence is underway in the main propulsion system. This procedure readies fuel system valves for engine start. In the next few seconds, the aerosurfaces of Atlantis will be run through a pre-planned mobility test to ensure readiness for launch. This is also a dress rehearsal for flight of the orbiter's hydraulic systems.

1940:30 GMT (2:40:30 p.m. EST)

T-minus 5 minutes. The "go" has been given for for Auxiliary Power Unit start. Pilot Alan Poindexter is now flipping three switches in Atlantis' cockpit to start each of the three APU's. The units, located in the aft compartment of Atlantis, provide the pressure needed to power the hydraulic systems of the shuttle. The units will be used during the launch and landing phases of the mission for such events as moving the orbiter's aerosurfaces, gimbaling the main engine nozzles and deploying the landing gear.

Over the course of the next minute, the orbiter's heaters will be configured for launch by commander Steve Frick, the fuel valve heaters on the main engines will be turned off in preparation for engine ignition at T-6.6 seconds and the external tank and solid rocket booster safe and arm devices will be armed.

1940:00 GMT (2:40:00 p.m. EST)

T-minus 5 minutes, 30 seconds. APU pre-start is complete and the units are ready for activation. The orbiters flight data recorders have gone into the record mode to collect measurements of shuttle systems performance during flight.

1939:30 GMT (2:39:30 p.m. EST)

T-minus 6 minutes. Pilot Alan Poindexter has been asked by the orbiter test conductor to pre-start the orbiter Auxiliary Power Units. This procedure readies the three APU's for their activation after the countdown passes T-minus 5 minutes.

1938:00 GMT (2:38:00 p.m. EST)

T-minus 7 minutes, 30 seconds. The Ground Launch Sequencer has started pulling the orbiter access arm away from the crew hatch on the port side of the vehicle. The arm was the passage way for the astronauts to board Atlantis a few hours ago. The arm can be re-extended very quickly should the need arise later in the countdown.

1937:30 GMT (2:37:30 p.m. EST)

T-minus 8 minutes and counting. Pilot Alan Poindexter has flipped the switches in the cockpit of Atlantis to directly connect the three onboard fuel cells with the essential power buses. Also, the stored program commands have been issued to the orbiter.

1936:30 GMT (2:36:30 p.m. EST)

T-minus 9 minutes and counting! The Ground Launch Sequencer has been initiated. The computer program is located in a console in the Firing Room of the Complex 39 Launch Control Center. The GLS is the master of events through liftoff. During the last 9 minutes of the countdown, the computer will monitor as many as a thousand different systems and measurements to ensure that they do not fall out of any pre-determine red-line limits. At T-minus 31 seconds, the GLS will hand off to the onboard computers of Atlantis to complete their own automatic sequence of events through the final half minute of the countdown.

1935 GMT (2:35 p.m. EST)

A final pre-launch check of hydrogen ECO cutoff sensors shows all four are operating properly.

1935 GMT (2:35 p.m. EST)

At main engine cutoff, Atlantis will be flying on a suborbital trajectory with a high point of 118 nautical miles and low point of 31 nautical miles. A half-hour later, the twin orbital maneuvering engines will be fired to place the shuttle into a 123 by 105 nautical mile orbit.

1933 GMT (2:33 p.m. EST)

NASA launch director Doug Lyons has conducted his poll and given approval to resume the countdown for liftoff at 2:45 p.m. this afternoon. "Atlantis is ready to fly," he just radioed commander Steve Frick.

1932 GMT (2:32 p.m. EST)

The final readiness poll by the NASA test director Jeff Spaulding confirms there are no technical issues being addressed. The Range also reports "go" on the local weather. And Mission Control says that the abort landing site weather is acceptable, too.

1926 GMT (2:26 p.m. EST)

Ten minutes are remaining in this built-in hold. Final readiness polls will be conducted over the next few minutes.

1922 GMT (2:22 p.m. EST)

A poll of the Mission Management Team by chairman LeRoy Cain in the Firing Room indicates there are no technical issues being examined. All systems are "go" for launch.

1920 GMT (2:20 p.m. EST)

The International Space Station is orbiting 220 miles above Earth. At launch, it will be southwest of Perth, Australia. Liftoff is timed to place Atlantis on course to dock with the station at 12:25 p.m. EST on Saturday.

1918 GMT (2:18 p.m. EST)

The restricted hazard area around the Cape has been verified clear.

1915 GMT (2:15 p.m. EST)

Weather continues to be monitored. At the moment, observed conditions are "go" launch.

1907 GMT (2:07 p.m. EST)

The official launch window this afternoon opens at 2:45:30 p.m. and closes at 2:50:30 p.m. EST.

1857 GMT (1:57 p.m. EST)

Weather has just gone "no go" due to a thunderstorm developing west of Kennedy Space Center. It is hoped that storm will pass north of the Cape and not be a constraint when launch time nears.

1851 GMT (1:51 p.m. EST)

T-minus 9 minutes and holding. Countdown clocks have gone into the planned 45-minute, 30-second built-in hold. Today's launch remains set for 2:45:30 p.m. EST. And weather is still "go" at this time.

1849 GMT (1:49 p.m. EST)

Mission Control in Houston has loaded Atlantis' onboard computers with the proper guidance parameters based on the projected launch time.

1848 GMT (1:48 p.m. EST)

The Main Propulsion System helium system is being reconfigured by pilot Alan Poindexter. Soon the gaseous nitrogen purge to the aft skirts of the solid rocket boosters will be started.

1845 GMT (1:45 p.m. EST)

Now one hour away from launch of Atlantis.

Pilot Alan Poindexter is configuring the displays inside Atlantis' cockpit for launch while commander Steve Frick enables the abort steering instrumentation.

1840 GMT (1:40 p.m. EST)

T-minus 20 minutes and counting. The countdown has resumed after a 10-minute hold. Clocks will tick down for the next 11 minutes to T-minus 9 minutes where the final planned hold is scheduled to occur. The hold length will be adjusted to synch up with today's preferred launch time of 2:45:30 p.m.

Atlantis' onboard computers are now transitioning to the Major Mode-101 program, the primary ascent software. Also, engineers are dumping the Primary Avionics Software System (PASS) onboard computers. The data that is dumped from each of PASS computers is compared to verify that the proper software is loaded aboard for launch.

1835 GMT (1:35 p.m. EST)

Weather remains "go" for launch.

1833 GMT (1:33 p.m. EST)

Commander Steve Frick has pressurized the gaseous nitrogen system for Atlantis' Orbital Maneuvering System engines and pilot Alan Poindexter has activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water spray boilers.

1830 GMT (1:30 p.m. EST)

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch is scheduled for 2:45 p.m. EST. Everything is going smoothly with the countdown and current weather conditions are still looking good.

During this built-in hold, all computer programs in Firing Room 4 of the Complex 39 Launch Control Center will be verified to ensure that the proper programs are available for the countdown; the landing convoy status will be verified and the landing sites will be checked to support an abort landing during launch today; the Inertial Measurement Unit preflight alignment will be verified completed; and preparations are made to transition the orbiter onboard computers to Major Mode 101 upon coming out of the hold. This configures the computer memory to a terminal countdown configuration.

1812 GMT (1:12 p.m. EST)

The ground pyro initiator controllers (PICs) are scheduled to be powered up around this time in the countdown. They are used to fire the solid rocket hold-down posts, liquid oxygen and liquid hydrogen tail service mast and external tank vent arm system pyros at liftoff and the space shuttle main engine hydrogen gas burn system prior to engine ignition.

The shuttle's two Master Events Controllers are being tested. They relay the commands from the shuttle's computers to ignite, and then separate the boosters and external tank during launch.

1809 GMT (1:09 p.m. EST)

NASA Administrator Mike Griffin, in an interview with CBS News today, said he remains optimistic the agency can complete the international space station and retire the shuttle as planned by the end of fiscal 2010 despite recent delays to recover from hail damage and problems with critical fuel sensors.

Read our full storyhere.

1806 GMT (1:06 p.m. EST)

Crew module leak checks have been completed successfully.

1753 GMT (12:53 p.m. EST)

The shuttle's crew compartment hatch is confirmed to be closed and latched for flight.

1750 GMT (12:50 p.m. EST)

Now passing the T-minus 1 hour mark in the countdown. Two scheduled holds are planned at T-minus 20 minutes and T-minus 9 minutes, leading to the target liftoff time of 2:45:30 p.m. EST.

The final pre-flight alignment of Atlantis' guidance system inertial measurement units is underway.

1746 GMT (12:46 p.m. EST)

Just two hours remain until the planned liftoff time. The "go" was just given to close Atlantis' crew module hatch for launch.

1743 GMT (12:43 p.m. EST)

Atlantis' crew module hatch is being closed for launch.

1743 GMT (12:43 p.m. EST)

Launch weather officer Kathy Winters has added a little bit of optimism about the forecast and the odds of acceptable conditions at 2:45 p.m. today have increased from 30 percent to 40 percent.

1725 GMT (12:25 p.m. EST)

A series of routine communications checks between the Atlantis crew on various audio channels is underway.

1720 GMT (12:20 p.m. EST)

T-minus 90 minutes and counting. Countdown clocks continue to tick down to T-minus 20 minutes where the next hold is planned. Countdown activities remain on track for liftoff at 2:45 p.m. There are no technical issues being worked. Weather continues to be watched closely. A shower has developed about 9 miles west-southwest of the launch pad.

At this point in the count, the Ground Launch Sequencer software that will control the final nine minutes of the countdown has been initialized. Also, the solid rocket boosters' gas generator heaters in the hydraulic power units are turned on, the aft skirt gaseous nitrogen purge is starting and the rate gyro assemblies (RGAs) are being activated. The RGAs are used by the orbiter's navigation system to determine rates of motion of the boosters during the first stage of flight.

1706 GMT (12:06 p.m. EST)

The final crewmember just boarded Atlantis. Rex Walheim serves as mission specialist No. 2, flight engineer and lead spacewalker on STS-122. He will ride in the flight deck's aft-center seat.

Read his biography here.

1703 GMT (12:03 p.m. EST)

The cloud ceiling weather rule, which had been red, is back to a "go" status again. So for the moment, all weather conditions are acceptable right now.

1656 GMT (11:56 a.m. EST)

Stanley Love has entered the shuttle to take the center seat on the middeck. The rookie is mission specialist No. 4 for STS-122.

Read his biography here.

1651 GMT (11:51 a.m. EST)

Rookie astronaut Leland Melvin is mission specialist No. 1 for Atlantis. He is climbing to the flight deck's aft-right seat.

Read his biography here.

1645 GMT (11:45 a.m. EST)

Three hours and counting until liftoff time. Current weather conditions are "no go" due to low clouds that have rolled into the Kennedy Space Center area. This isn't much of a surprise. Meteorologists have been predicting that weather would be troublesome today.

1643 GMT (11:43 a.m. EST)

German astronaut Hans Schlegel serves as mission specialist No. 3 on Atlantis' STS-122 flight. He just entered the orbiter to take the middeck's left seat.

Read his biography here.

1638 GMT (11:38 a.m. EST)

Alan Poindexter, a Navy captain and the rookie astronaut pilot of Atlantis, is making his way to the flight deck's front-right seat.

Read his biography here.

1631 GMT (11:31 a.m. EST)

Station-bound crewmember Leopold Eyharts, an astronaut representing the European Space Agency, has boarded Atlantis to take the middeck's right-side seat. He will move aboard the station for an extended stay as part of the Expedition 16 crew, replacing astronaut Dan Tani.

Read his biography here.

1625 GMT (11:25 a.m. EST)

Commander Steve Frick is the first astronaut to board the shuttle. He is taking the forward-left seat on the flight deck.

The navy captain has flown one previous shuttle mission -- as pilot of STS-110 that delivered the S0 central truss segment of the space station. Read his biography here.

1615 GMT (11:15 a.m. EST)

The inspection team is preparing to leave the launch pad. They'll be giving a report to launch director Doug Lyons once back at the Firing Room. However, there were no significant issues reported in real-time during the inspections.

1612 GMT (11:12 a.m. EST)

Atlantis' crew arrived at launch pad 39A at 11:12 a.m. The AstroVan came to a stop on the pad surface near the Fixed Service Structure tower elevator that will take the seven-man crew to the 195-foot level to begin boarding the shuttle.

1606 GMT (11:06 a.m. EST)

The AstroVan is passing the 52-story Vehicle Assembly Building where Atlantis was attached to its external tank and solid rocket boosters and the adjacent Launch Control Center.

The Press Site is located across the street, and reporters went outside to watch at the passing convoy. This is a launch day tradition to say farewell and good luck to the astronaut crews.

1556 GMT (10:56 a.m. EST)

Commander Steve Frick, pilot Alan Poindexter and mission specialists Leland Melvin, Rex Walheim, Hans Schlegel, Stanley Love and Leopold Eyharts just departed the Kennedy Space Center crew quarters to board the AstroVan for the 20-minute ride from the Industrial Area to launch pad 39A on the edge of the Atlantic Ocean.

1550 GMT (10:50 a.m. EST)

T-minus 3 hours and counting. The countdown clocks are ticking again after the planned two-and-a-half hour built-in hold. Clocks will proceed to T-minus 20 minutes when the next hold is scheduled. A final hold occurs at the T-minus 9 minute mark to synch up with the 2:45 p.m. EST launch time.

1532 GMT (10:32 a.m. EST)

The crew has donned the day-glow orange launch and entry partial pressure spacesuits. After final adjustments and pressure checks, the astronauts will depart the suitup room and take the elevator down to the ground level of the Operations and Checkout Building to board the AstroVan for the trip to launch pad 39A around 10:55 a.m.

1515 GMT (10:15 a.m. EST)

Commander Steve Frick, pilot Alan Poindexter and flight engineer Rex Walheim are receiving a weather briefing on expected conditions at the Kennedy Space Center and the primary abort landing sites. Meanwhile, the rest of the crew is moving into the suitup room to start donning their suits.

The astronauts were awakened at 4:15 a.m. this morning to begin Flight Day 1 of the STS-122 mission. They had breakfast and underwent final medical exams.

Schedules call for the seven astronauts to depart crew quarters at 10:55 a.m. for the trip out to the launch pad.

1500 GMT (10:00 a.m. EST)

The Final Inspection Team is performing its observations of Atlantis this morning.

The team is responsible for checking the shuttle and launch pad one last time prior to liftoff. The team is comprised of engineers and safety officials from NASA, United Space Alliance and tank-builder Lockheed Martin. At the conclusion of their two-hour tour-of-duty, the team will have walked up and down the entire fixed service structure and mobile launcher platform.

The team is on the lookout for any abnormal ice or frost build-up on the vehicle and integrity of the external tank foam insulation.

The team uses a portable infrared scanner that gathers temperature measurements on the surface area of the shuttle and can spot leaks. The scanner will be used to obtain temperature data on the external tank, solid rocket boosters, space shuttle orbiter, main engines and launch pad structures. The scanner can also spot leaks of the cryogenic propellants, and due to its ability to detect distinct temperature differences, can spot any dangerous hydrogen fuel that is burning. The team member also is responsible for photo documentation.

The team wears the highly visible day-glow orange coveralls that are anti-static and flame resistant. Each member also has a self-contained emergency breathing unit that holds about 10 minutes of air.

1445 GMT (9:45 a.m. EST)

The docking probe on the front-end of Progress was retracted and the latches have engaged, bringing the cargo vessel to a firm connection with the station.

1430 GMT (9:30 a.m. EST)

Contact and capture! The 28th Progress resupply ship launched to the International Space Station has successfully arrived. Docking occurred at 9:30 a.m. EST.

The freighter is loaded with 2,925 pounds of dry cargo, 1,165 pounds of propellant, 925 pounds of water and more than 100 pounds of air and oxygen for transfer to the station.

1428 GMT (9:28 a.m. EST)

About 75 feet to go. The unmanned Progress is making this docking with its autopilot in control. If there is a problem, station commander Yuri Malenchenko can take over manual control and complete the docking using joysticks and video screens aboard the outpost. But all is going well this morning.

1423 GMT (9:23 a.m. EST)

Progress is about 100 yards away from the station, now on final approach to the docking port.

1420 GMT (9:20 a.m. EST)

While Atlantis' countdown continues here at the Kennedy Space Center, the crew living aboard the International Space Station is awaiting arrival of a Russian-made cargo delivery ship a few minutes from now. The Progress M-63 craft will dock with the station's Pirs module at 9:38 a.m.

1410 GMT (9:10 a.m. EST)

Here is the countdown timeline for today's launch (in EST):

09:45 AM......NASA television launch coverage begins
10:15 AM......Final crew weather briefing
10:25 AM......Crew suit up begins
10:50 AM......Resume countdown (T-minus 3 hours)

10:55 AM......Crew departs O&C building
11:25 AM......Crew ingress
12:15 PM......Astronaut comm checks
12:30 PM......Hatch closure
01:10 PM......White room closeout

01:30 PM......Begin 10-minute built-in hold (T-minus 20m)
01:40 PM......NASA test director countdown briefing
01:40 PM......Resume countdown (T-minus 20m)

01:41 PM......Backup flight computer to OPS 1
01:45 PM......KSC area clear to launch

01:50 PM......Begin final built-in hold (T-minus 9m)
02:21 PM......NTD launch status verification
02:36:25 PM...Resume countdown (T-minus 9m)

02:37:55 PM...Orbiter access arm retraction
02:40:25 PM...Launch window opens
02:40:25 PM...Hydraulic power system (APU) start
02:40:30 PM...Terminate LO2 replenish
02:41:25 PM...Purge sequence 4 hydraulic test
02:41:25 PM...Navigation system activated
02:41:30 PM...Aerosurface profile
02:41:55 PM...Main engine steering test
02:42:30 PM...LO2 tank pressurization
02:42:50 PM...Fuel cells to internal reactants
02:42:55 PM...Clear caution-and-warning memory
02:43:25 PM...Crew closes visors
02:43:28 PM...LH2 tank pressurization
02:44:35 PM...Booster joint heater deactivation
02:44:54 PM...Shuttle flight comptuers take control of countdown
02:45:04 PM...Booster steering test
02:45:18 PM...Main engine start (T-6.6 seconds)
02:45:25 PM...Booster ignition (LAUNCH)

1350 GMT (8:50 a.m. EST)

The countdown for the launch of space shuttle Atlantis remains on schedule for a liftoff at 2:45 p.m. EST today, weather permitting. Skies are looking good right now, but cumulus clouds and showers from the inbound cold front are expected later this morning.

The ECO system is working correctly and "we're ready to go fly," launch director Doug Lyons says. All four hydrogen cutoff sensors have responded to the pre-launch testing with proper readings.

"Once we got fully tanked, around 8:15, we went to a sensor confidence test ... and I'm pleased to say all the sensors functioned as designed and we have a good ECO system and we're ready to go fly," said Lyons. "Now, we'll continue to monitor the system throughout the countdown. A final confidence check is performed at T-minus nine minutes but again, we have high confidence that that'll be successful."

Liquid hydrogen fueling was completed a 7:56 a.m., followed by liquid oxygen at 8:18 a.m. EST. Both tanks have entered stable replenish mode to continually keep the tanks topped off through the final minutes of the countdown.

With the hazardous tanking operation completed, the Orbiter Closeout Crew and Final Inspection Team have been given the OK to go out to the pad to perform their jobs. The closeout crew will ready Atlantis' crew module for the astronauts' ingress in a couple of hours; and the inspection team will give the entire vehicle a check for any ice formation following fueling.

1240 GMT (7:40 a.m. EST)

Fueling of Atlantis is nearing completion. The liquid hydrogen tank is in topping mode and the liquid oxygen tank is in the final stages of fast-fill.

Shuttle weather officer Kathy Winters says the showers associated with the approaching cold front are about 45 miles away. That front is expected to be directly over the Kennedy Space Center area at launch time this afternoon.

Clouds, rain and crosswinds are the main concerns for violating the launch weather rules this afternoon. The odds of acceptable conditions -- just 30 percent.

1156 GMT (6:56 a.m. EST)

All of the pre-planned tests on the ECO system were completed and the sensors are operating successfully this morning. A NASA spokesman says engineers will wait until the sensors are cycled once the tank filling is completed around 8:20 a.m. before declaring victory. But at this point, all four hydrogen sensors are reading correctly unlike the problems experienced during the two launch attempts and subsequent fueling test conducted in December.

1150 GMT (6:50 a.m. EST)

The propulsion console operators said they'd like to run one more suite of tests on the ECO system.

1138 GMT (6:38 a.m. EST)

So far, no ECO problems have been reported by the launch team. But there is one additional test to run before the overall health of the system can be confirmed this morning, a NASA spokesman says.

1130 GMT (6:30 a.m. EST)

The liquid hydrogen and liquid oxygen tanks are about 25 percent full.

1115 GMT (6:15 a.m. EST)

The propulsion console in Firing Room 4 of the Launch Control Center reports that testing of the ECO sensor system is about to begin.

1112 GMT (6:12 a.m. EST)

Both liquid hydrogen and liquid oxygen loading have entered the "fast-fill" mode.

There are two tanks inside the shuttle's external fuel tank. The liquid oxygen tank occupies the top third of the bullet-shaped tank. It will be filled with 143,000 gallons of liquid oxygen chilled to minus 298 degrees Fahrenheit. The liquid hydrogen tank is contained in the bottom two-thirds of the external tank. It holds 385,000 gallons of liquid hydrogen chilled to minus 423 degrees Fahrenheit.

1058 GMT (5:58 a.m. EST)

Liquid oxygen loading has transitioned from chilldown to the "slow-fill" mode.

1054 GMT (5:54 a.m. EST)

The liquid hydrogen low-level engine cutoff sensors in the bottom of the external tank have been submerged by the propellant as the fuel continues to flow into the shuttle. A short time from now, the launch team will send commands to test the health of the sensors. That will be the ultimate test to ensure the repairs to the system made since the December launch scrubs have worked.

1032 GMT (5:32 a.m. EST)

The liquid hydrogen loading has transitioned from chilldown to the "slow-fill" mode. This fills a small fraction of the tank, then the loading switches to "fast-fill" mode.

1026 GMT (5:26 a.m. EST)

FUELING UNDERWAY. The filling of space shuttle Atlantis' external fuel tank with a half-million gallons of supercold propellants has begun at launch pad 39A.

The tanking operation commenced with the chilldown thermal conditioning process at 5:21 a.m.

1020 GMT (5:20 a.m. EST)

T-minus 6 hours and counting. Clocks have just resumed ticking following another of the countdown's planned built-in holds. The next hold occurs at the T-minus 3 hour mark.

1020 GMT (5:20 a.m. EST)

The Mission Management Team has completed its pre-fueling meeting and given the launch team a "go" to begin filling space shuttle Atlantis' external tank with its cryogenic propellants as planned this morning. There are no technical issues being addressed and liftoff remains on schedule for 2:45 p.m. today.

The only concern remains the weather. An approaching cold front bringing clouds and showers means there's just a 30 percent chance that weather conditions will be acceptable for launch today.

WEDNESDAY, FEBRUARY 6, 2008

The rotating service structure moved away from the space shuttle tonight, exposing Atlantis to the blindingly bright xenon flood lights at pad 39A as the countdown rolled onward to liftoff.

The Mission Management Team will meet at 4:45 a.m. EST to review the status of the count, the latest weather outlook and then decide whether to proceed with fueling the shuttle for launch.

The three-hour process to load the external tank with a half-million gallons of liquid hydrogen and liquid oxygen rocket fuel is scheduled to begin at 5:20 a.m. EST. The initial indications of whether the hydrogen engine cutoff sensors are working properly should be known within an hour.

Watch this page for live updates throughout the morning.

1745 GMT (12:45 p.m. EST)

Standard day-before-launch work is continuing at pad 39A for tomorrow's scheduled liftoff of the space shuttle Atlantis to deliver the European's Columbus science laboratory to the space station.

Atlantis' fuel cell storage tanks were successfully loaded with the liquid hydrogen and liquid oxygen reactants yesterday. Overnight, final tests of the three main engines were completed.

Countdown clocks are in the midst of the lengthy T-minus 11 hour planned hold period. The built-in hold began at 9 a.m. this morning and will last 13 hours and 20 minutes.

Today's planned activities include functional checks of the orbiter's star trackers, activating the inertial measurement units, thoroughly testing the communications network, loading the last items into the crew module, filling of the launch pad's sound suppression system water tank and installing film in pad cameras.

The giant gantry-like rotating service structure is scheduled for retracting from around Atlantis at 6 p.m., marking a key milestone to ready the shuttle and launch pad for Thursday morning's fueling of the external tank.

The only worry going into tomorrow's launch attempt is the weather forecast. Meteorologists say there's a 70 percent chance that clouds and rain could prohibit launch.

"I wish I had a better weather report for tomorrow, but we are expecting to have some significant weather in the area," weather officer Kathy Winters said. "We expect to see some cumulus clouds developing in the area, possibly some showers and there's even a potential for an inland thunderstorm. Our concern with that would be an (electrically charged) anvil coming across ... into the area. That would be a violation of one of our triggered lightning launch commit criteria. So we do have a lot of concerns for launch tomorrow."

1330 GMT (8:30 a.m. EST)

The odds of weather for Thursday's launch has worsened in the latest forecast. There's now only a 30 percent chance conditions will be acceptable for liftoff tomorrow afternoon.

"A cold front will move into the Central Florida area north of Kennedy Space Center on launch day. Winds will decrease through the day allowing a sea breeze to develop by launch time," the launch weather team reported this morning. "With the convergence along the coast combined with moisture increasing in the atmosphere, there is potential for cumulus clouds, showers, and even an isolated thunderstorm. Thunderstorms are more likely to be inland at launch time and move into the KSC area after launch. Although thunderstorms will be isolated, cool air aloft will provide a possibility of severe weather if a thunderstorm does occur, particularly when a storm interacts with the sea breeze."

The launch time forecast predicts broken cumulus clouds at 3,000 feet, broken altocumulus clouds at 8,000 feet and an overcast layer of cirrostratus clouds at 20,000 feet, 7 miles of visibility, easterly winds of 8 peaking to 12 knots and a temperature of 76 degrees F.

"Our primary concerns for launch day are cumulus clouds, showers, and an anvil from an inland thunderstorm," forecasters said.

"Meteorological models are now stalling the front in the area for a few days rather than moving it to the south; therefore, there is an increased chance of showers and ceilings for the 24- and 48- hour launch attempts."

TUESDAY, FEBRUARY 5, 2008

LeRoy Cain, manager of shuttle integration at the Kennedy Space Center, said today he is confident the redesigned connectors intended to fix on-going problems with low-level fuel sensors in the shuttle Atlantis' external tank will work properly Thursday when the ship is fueled for takeoff. But engineers will be paying close attention to the sensors and if any problems develop that might cast doubt on the fix, the shuttle will remain on the ground.

Read our full story here.

1830 GMT (1:30 p.m. EST)

The Mission Management Team completed its Launch Minus-2 Day meeting earlier today. Team chairman LeRoy Cain says all lingering topics have been resolved to proceed with Thursday's launch of Atlantis and the Columbus science module.

The launch team will spend this afternoon and early evening pumping liquid hydrogen and liquid oxygen reactants into the shuttle's fuel cell system.

"We're not working any issues...It's been a really clean count. We're hoping it'll stay that way," launch director Doug Lyons said at the pre-launch news conference a short time ago.

"Regardless of what the weather guy might tell you," Lyons joked, "we think Thursday is the day and we're certainly looking forward to it, ready to go make it happen."

A cold front will be sliding through Florida during the launch window on Thursday and meteorologists have put the odds of acceptable liftoff conditions at 40 percent.

"For launch, the front will be just about overhead," said Mike McAleenan, Air Force launch weather officer at the 45th Weather Squadron. "We're looking for some significant amount of cloud cover and maybe a 60 percent chance of KSC weather prohibiting launch."

Forecasters are expecting "possible crosswind violation, cumulus rule violation, anvil and rain showers in the area," McAleenan said.

The front should pass through the area by Friday, increasing the likelihood of acceptable weather for Friday and Saturday launch attempts to 80 percent both days.

"We're hopeful we can find a hole on Thursday," McAleenan said. "If not, Friday certainly looks good."

1520 GMT (10:20 a.m. EST)

The launch countdown is proceeding smoothly, NASA test director Steve Payne said at this morning's news briefing, and final preps are underway for servicing shuttle Atlantis' electricity-producing fuel cells later today.

The fuel cells use liquid hydrogen and liquid oxygen to generate power and drinking water during Atlantis' mission. The supercold the reactants will be loaded into storage spheres located beneath the payload bay.

The countdown entered a planned four-hour hold at 9 a.m. this morning. During the pause at T-minus 27 hours, the launch pad is cleared of all non-essential personnel for a test of the vehicle's pyrotechnic initiator controllers.

After the fuel cell loading is accomplished today, the count has another four-hour hold at T-minus 19 hours beginning at 9 p.m. tonight. That is when the fuel cell servicing equipment is disconnected from the orbiter's mid-body and stowed.

"We have no problems to report and we're all looking forward to Thursday afternoon's launch," Payne said.

The launch is targeted for 2:45:25 p.m. EST, the middle of a 10-minute window that is created when the Earth's rotation carries pad 39A into the plane of the space station's orbit.

The weather outlook for Thursday's launch attempt remains unchanged -- a 40 percent chance of acceptable conditions. A cold front moving into the area is expected to bring clouds and rain that could violate launch rules.

"High pressure will dominate the Central Florida area for the next few days, and temperatures will be above average with highs reaching the low 80s," the launch weather team reported this morning. "A cold front will move into the Central Florida area on launch day. The front will be located to the north of Kennedy Space Center by launch time bringing increased moisture and southwest flow. This increases the potential for cumulus clouds, showers, and even an isolated thunderstorm."

The launch time forecast predicts scattered cumulus clouds at 2,000 feet, broken altocumulus clouds at 8,000 feet and an overcast layer of cirrostratus clouds at 20,000 feet, 7 miles of visibility, southwesterly winds of 12 peaking to 18 knots and a temperature of 76 degrees F.

"Our primary concerns for launch day are cumulus clouds, showers and an anvil from an inland thunderstorm," the weather team said.

The front is expected to move through the area early Friday morning, leaving improved conditions in its wake. The outlook for Friday's 2:19 p.m. launch time calls for an 80 percent chance of good weather, with the chance of a low cloud ceiling and showers the concerns. Saturday's 1:57 p.m. launch time forecast is 80 percent "go" and gusty winds are the only worry that day.

Meanwhile, an unmanned resupply ship bound for the space station launched from Baikonur Cosmodrome earlier today. A Russian Soyuz rocket blasted off at 8:02:57 a.m. EST and successfully delivered the Progress M-63 freighter into orbit about 10 minutes later.

The craft is scheduled to dock with the station's Pirs module at 9:38 a.m. on Thursday, just five hours before Atlantis soars to space.

Progress is loaded with 2,925 pounds of dry cargo, 1,165 pounds of propellant, 925 pounds of water and more than 100 pounds of air and oxygen for transfer to the station.

MONDAY, FEBRUARY 4, 2008
2205 GMT (5:05 p.m. EST)

Inside Firing Room 4 of the Launch Control Center, countdown clocks have lit up and started ticking toward Thursday's planned liftoff of the space shuttle Atlantis.

Launch team members gathered for the "call to stations" at 4:30 p.m. EST, and then the three-day countdown commenced at 5 p.m. as scheduled.

Clocks read T-minus 43 hours and counting. But a series of holds are timed throughout the next few days, leading to Thursday's targeted liftoff time of 2:45 p.m. EST.

The early portion of the count involves buttoning up launch pad equipment and removing platforms inside the shuttle's crew module, reviewing flight software stored in Atlantis' mass memory units, loading backup software into the general purpose computers and testing navigation systems.

1700 GMT (12:00 p.m. EST)

Running two months late, the shuttle Atlantis and its crew are set for blastoff Thursday on a long-awaited flight to attach the European Space Agency's Columbus research lab to the space station. The module represents Europe's first manned toehold in orbit and promises to open a new era of international research with Japanese lab modules scheduled to follow in March and April.

This is our mission preview story.

1640 GMT (11:40 a.m. EST)

The Atlantis astronauts flew back to the Kennedy Space Center today for the start of a new countdown to launch Thursday on a long-awaited space station assembly mission. Running two months late because of fuel sensor problems that scrubbed two launch attempts in December, the international crew landed at the Florida spaceport at 10:30 a.m.

"We're feeling very good about this opportunity," commander Steve Frick said at the runway. "We'll keep looking at the weather, but we've very happy about the condition of Atlantis."

Read our update story here.

1530 GMT (10:30 a.m. EST)

Two months after their launch was stalled by fuel sensor troubles, the seven space shuttle Atlantis astronauts have returned to the Kennedy Space Center for another shot at rocketing into orbit.

The crew touched down at 10:29 a.m. EST following a morning flight from Ellington Field near Houston's Johnson Space Center.

Commander Steve Frick leads the all-male crew, with pilot Alan Poindexter, mission specialists Leland Melvin, Rex Walheim, Stanley Love, Hans Schlegel and Leopold Eyharts. Eyharts will fly to the station on Atlantis and exchange places with Expedition 16 resident crew member Dan Tani.

Coming up later today, the astronauts will don their bright orange launch and entry spacesuits for a final fit check and spend time reviewing flight plans. And then around 6 p.m., Frick and Poindexter will return to the KSC runway to fly some nighttime landing approaches aboard the Shuttle Training Aircraft.

1430 GMT (9:30 a.m. EST)

The seven-man crew to launch aboard space shuttle Atlantis is en route to the Cape this morning, flying from their training base in Houston as NASA prepares to begin the countdown for Thursday afternoon's liftoff.

"We are tracking no issues in our preparations at this point," said Charlie Blackwell-Thompson, a NASA test director at Kennedy Space Center.

Thursday's launch is targeted for 2:45 p.m. EST (1945 GMT), beginning the long-awaited flight to deliver the European Columbus science lab to the space station.

There is a 40 percent chance of acceptable conditions at launch time. The chance of showers and cumulus clouds in the area associated with a passing front are the main concerns, said Kathy Winters, the shuttle weather officer.

The forecast improves on Friday and Saturday, should the launch be delayed for any reason, with an 80 percent chance of good weather both days.

The astronauts, led by commander Steve Frick, are scheduled to arrive at the KSC runway around 10:30 a.m. this morning. And in the Launch Control Center, technicians are completing preps for starting the countdown at 5 p.m. today.

Last night, Atlantis' giant payload bay doors were swung shut for flight. The door closing involved an added bit of drama due to concerns with a kinked Freon flex hose on the right-hand door.

Engineers recently noticed one of four metal-jacketed flex hoses that carry Freon coolant to and from radiator panels mounted on the inside of the ship's cargo bay doors was sharply bent.

A long pole was crafted for workers to help push the hose into its retraction box as the door was closing.

"It pretty much went to plan. We closed the starboard door in eight increments. We had a hose-assist tool, which is a new tool, that we were able to actually just guide the radiator retract hose back into the retract box. We didn't have any issues," Blackwell-Thompson said.

FRIDAY, FEBRUARY 1, 2008

NASA managers today decided to press ahead with preparations for launch of the shuttle Atlantis Feb. 7 pending final work Monday to make sure a kinked Freon flex hose retracts as required when the ship's payload bay doors are closed for flight.

Assuming no other problems develop, engineers plan to restart Atlantis's countdown at 5 p.m. Monday for a launch attempt at 2:45:28 p.m. Thursday. This will be NASA's third attempt to launch Atlantis on a space station assembly mission following delays Dec. 6 and 9 because of problems with low-level fuel sensors in the shuttle's external tank.

Read our full story here.

WEDNESDAY, JANUARY 30, 2008

Exhaustive testing shows the low-level fuel sensor problem that derailed two attempts to launch the shuttle Atlantis in December has been resolved, NASA managers said Wednesday. But a decision on whether to press ahead with a third launch try Feb. 7 was put off to Saturday pending results of last-minute troubleshooting to assess the health of a kinked flex hose in the ship's coolant system.

Read our full story here.

1715 GMT (12:15 p.m. EST)

Space station commander Peggy Whitson and flight engineer Dan Tani began repressurizing the Quest airlock module at 12:06 p.m. to officially end a seven-hour 10-minute spacewalk. The astronauts successfully installed a replacement solar array positioning motor and carried out additional inspections to help engineers troubleshoot problems with a large rotary joint.

Read our update story here.

1600 GMT (11:00 a.m. EST)

In a somewhat riskier than usual procedure, two spacewalking astronauts installed a replacement solar array positioning motor today aboard the international space station. Subsequent tests confirmed its ability to move the panel as required to maximize power production, clearing the way for attachment of European and Japanese research modules.

"Good news from the electrical systems officer here in mission control," NASA commentator Rob Navias reported. "A good rotation of 3 degrees of the beta gimbal assembly for the S4-1A array driven by the new motor, the new bearing motor roll ring module, that was installed a few hours ago by Peggy Whitson and Dan Tani."

Read our update story here.

1300 GMT (8:00 a.m. EST)

Working smoothly through a 35-minute pass through Earth's shadow, station commander Peggy Whitson and Dan Tani removed a faulty solar array positioning motor today and replaced it with a spare unit. If the replacement motor works as expected, the array can be moved from side to side like the station's other solar panels to maximize electrical output, clearing the way for launch of the European Space Agency's Columbus module aboard the shuttle Atlantis on Feb. 7.

Read our update story here.

1205 GMT (7:05 a.m. EST)

Peggy Whitson and Dan Tani have removed a faulty solar array positioning motor so it can be replaced by a spare unit. The new motor is needed to boost the station's electrical generation enough to support the planned launches of European and Japanese research modules in February, March and April.

Read our update story here.

1000 GMT (5:00 a.m. EST)

Floating in the international space station's Quest airlock module, commander Peggy Whitson and flight engineer Dan Tani switched their spacesuits to battery power at 4:56 a.m. today - 24 minutes ahead of schedule - to officially kick off a planned six-and-a-half-hour spacewalk. The primary goal of the excursion is to replace a faulty solar array positioning motor to improve electrical generation and clear the way for attachment of European and Japanese research modules.

Read our update story here.

TUESDAY, JANUARY 29, 2008

Space station commander Peggy Whitson and flight engineer Dan Tani are preparing for a critical, riskier-than-usual spacewalk Wednesday to replace a faulty solar array motor assembly on the right side of the lab's power truss. The motor, which malfunctioned Dec. 8, is needed to pivot a solar blanket from side to side to improve power generation. A different problem in a massive rotary joint used to turn the right-side solar panels like a giant paddle wheel will take longer to resolve. But a successful motor swap-out Wednesday should permit the station to generate the electricity needed to permit attachment of new European and Japanese research modules in February, March and April.

The spacewalk is a bit riskier than most for two reasons: A mistake managing the latches that hold the motor and its housing in place could result in the solar panel's inadvertent release; and because of the shock hazard associated with unplugging and replugging power cables that route 160-volt electricity from the array into the station. To eliminate any chance of a potentially fatal shock, the work will take place when the station is in Earth's shadow and the arrays are not generating any significant power.

"The choreography for the EVA will be very complex, both on orbit and with the ground," Tani said. "Because we're dealing with a solar array that produces kilowatts of power, we have to be very conscientious of when we're going to be opening connections that will expose us to that power. So the bulk of the activities will have to be performed at night when the solar array is not producing any power, or much power, at all."

The bearing motor roll ring module, or BMRRM (pronounced "broom"), is roughly the size of a garbage can and weighs more than 200 pounds. Replacing it is complicated, Whitson said, "because it's really the guts of what's holding the solar array in place. And so Dan and I will have to coordinate when we release and grapple onto the (motor housing) canister in order not to lose the solar array. That would lose us a whole lot of style points!"

The planned six-and-a-half-hour spacewalk, the 101st devoted to station assembly and maintenance since construction began in 1998 and the first so far this year, is scheduled to begin around 5:20 a.m. Whitson and Tani will exit the Quest airlock module and make their way to the far end of the right-side, or starboard, solar array truss segment. They will await the start of an eclipse period before beginning the repair work.

Read our full story here.

Additional coverage for subscribers:
VIDEO: PREVIEW OF THE BMRRM REPLACEMENT SPACEWALK PLAY
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FRIDAY, JANUARY 11, 2008

Russian space managers have agreed to move up the launch of an unmanned Progress supply ship by two days to Feb. 5, clearing the way for NASA to retarget launch of the shuttle Atlantis on a twice-delayed space station assembly mission for Feb. 7. NASA managers made the decision Thursday and officially announced it Friday, after consultation with the agency's international partners.

Read our full story here.

Additional coverage for subscribers:
VIDEO: POST-TANKING TEST NEWS CONFERENCE PLAY

VIDEO: DEC. 18 STATION EVA RECAP BRIEFING PLAY
VIDEO: SPACEWALK PREVIEW NEWS CONFERENCE PLAY

VIDEO: NEWS CONFERENCE AFTER DEC. 9 SCRUB PLAY
VIDEO: POST-SCRUB INTERVIEW WITH LAUNCH DIRECTOR PLAY
VIDEO: LAUNCH OF ATLANTIS SCRUBBED DEC. 9 PLAY
VIDEO: HYDROGEN SENSOR NO. 3 FAILS PLAY
VIDEO: DEC. 6 POST-SCRUB NEWS CONFERENCE PLAY
VIDEO: LAUNCH DIRECTOR GIVES UPDATE ON DEC. 6 SCRUB PLAY
VIDEO: PAD 39A ROTATING SERVICE STRUCTURE RETRACTED PLAY
VIDEO: TIME-LAPSE MOVIE OF PAD GANTRY ROLLBACK PLAY
VIDEO: STS-122 ASTRONAUT BIOGRAPHIES PLAY
VIDEO: NARRATED OVERVIEW OF ATLANTIS' MISSION PLAY
VIDEO: INSIGHTS INTO COLUMBUS SCIENCE LABORATORY PLAY
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TUESDAY, JANUARY 8, 2008

An upgraded wiring connector will be ready for installation on the shuttle Atlantis' external tank this week in a bid to eliminate the vexing open circuits that grounded the orbiter twice in December.

Read our full story here.

THURSDAY, JANUARY 3, 2008

NASA managers Thursday agreed to press ahead with work to replace suspect engine cutoff - ECO - sensor connectors on the shuttle Atlantis' external tank on the assumption parallel laboratory testing will confirm the root cause of open circuits that derailed two December launch tries.

Read our full story here.

THURSDAY, DECEMBER 27, 2007

NASA managers today cleared engineers to remove the external components of a suspect feed-through connector built into the wall of the shuttle Atlantis' external tank in a bid to fix intermittent electrical problems with engine cutoff sensors.

Read our full story here.

FRIDAY, DECEMBER 21, 2007

Engineers have been provisionally cleared to remove a suspect feed-through plug and an external connector from the shuttle Atlantis' external fuel tank for laboratory testing and a possible fix to eliminate intermittent electrical glitches with low-level engine-cutoff sensors.

Read our full story here.

WEDNESDAY, DECEMBER 19, 2007

NASA managers Wednesday reviewed options for fixing suspect low-level engine cutoff - ECO - sensors in the shuttle Atlantis' fuel tank. No final decisions were made and potential launch dates were not discussed. But shuttle Program Manager Wayne Hale, officials said, ruled out any discussion of launching Atlantis as is.

Read our full story here.

TUESDAY, DECEMBER 18, 2007

Precisely timing how electrical pulses moved back and forth through suspect engine cutoff sensor wiring during a fueling test today indicates intermittent open circuits that grounded the shuttle Atlantis on Dec. 6 and 9 were caused by problems in a critical-three part "feed-through" connector.

Read our full story here.

2130 GMT (4:30 p.m. EST)

Shuttle or space station astronauts likely will be asked to replace a faulty motor assembly on the right side of the lab's power truss early next year that is needed to pivot a solar blanket from side to side to improve power generation. A different problem in a massive rotary joint used to turn the right-side solar panels like a giant paddle wheel will take longer to resolve. But an exhaustive spacewalk inspection today gave engineers hope that near-term modifications may allow the joint to be operated in some fashion until a permanent fix can be implemented.

Read our full story here.

1802 GMT (1:02 p.m. EST)

After collecting some additional data on sensor No. 3 that just failed, offloading of propellant from the space shuttle has now begun.

1749 GMT (12:49 p.m. EST)

ECO sensor No. 3 has failed. It was one of the sensors acting intermittently this morning along with sensor No. 2.

Sensor No. 1 failed early in the fueling process, while No. 4 has worked throughout the day.

The shuttle launch team is preparing to start draining the cryogenic propellants from the external tank. All of the sensors will be monitored during the draining and afterwards as the sensor and tank temperatures rise.

1725 GMT (12:25 p.m. EST)

The troubleshooting team has captured the high-data data it wanted and configured the special equipment to gather information during this afternoon's tank draining. NASA plans a news conference later today with shuttle program manager Wayne Hale to discuss the test results and the plan going forward.

1658 GMT (11:58 a.m. EST)

EVA ENDS. Repressurization of the space station's Quest airlock began at 11:46 a.m. EST, marking the official conclusion of today's six-hour, 56-minute spacewalk by Expedition 16 commander Peggy Whitson and flight engineer Dan Tani. The repressurization began while the station was out of communications with Houston.

This was the 100th spacewalk devoted to station assembly and maintenance since construction began in 1998, the 23rd this year and the fourth by the Expedition 16 crew.

It was the fifth spacewalk for both Tani and Whitson, who now holds the record for cumulative EVA time for a female astronaut. The old record of 29 hours and 17 minutes, set by astronaut Sunita Williams earlier this year, was broken at 8:27 a.m. today. Whitson has now logged 32 hours and 36 minutes of EVA time over her five spacewalks. Tani has 32 hours and 1 minute of spacewalk time.

1628 GMT (11:28 a.m. EST)

The ECO sensor troubleshooting team is running the time domain reflectometry (TDR) testing from a location inside the mobile launcher platform at pad 39A. Data and voltage readings are being relayed to engineers in the Launch Control Center. This testing plan is expected to last a couple of hours.

1625 GMT (11:25 a.m. EST)

With all of their planned tasks completed, the spacewalkers are making their way back to the airlock for the conclusion of this 100th international space station EVA.

1600 GMT (11:00 a.m. EST)

The troubleshooting team has arrived at its station inside the mobile launcher platform beneath the shuttle. Computers and equipment has been set up within a compartment for today's special ECO testing.

1546 GMT (10:46 a.m. EST)

Next up for the spacewalkers, they will be returning to the S5 truss to reconnect a pair of cables they unhooked this morning for Mission Control to run some diagnostic tests on one of the starboard solar wing gimbals.

1536 GMT (10:36 a.m. EST)

And now fueling of space shuttle Atlantis has entered the stable replenish mode on the liquid hydrogen and liquid oxygen tanks. This is the milestone that enables the launch pad to be opened for select teams of personnel.

Heading to pad 39A will be the five-person troubleshooting team to spend the next couple of hours using special instrumentation to trace where the ECO sensor problem is originating. The test equipment has been spliced into the shuttle's ECO sensor circuitry in hopes of pinpointing the culprit.

Also bound for the pad is the seven-person Final Inspection Team to examine the external tank foam for any ice or debris concerns following the fuel loading, which is a standard procedure for any countdown. They are conducting their observations to see how the tank has performed today.

Once the sensor troubleshooting is finished, all personnel will clear the pad for draining of the external tank sometime in the early afternoon.

1534 GMT (10:34 a.m. EST)

The launch team has gotten the backup liquid oxygen pump operating. NASA says the resumption of fueling has gone much quicker than expected after the primary pump went down with a blown fuse.

1525 GMT (10:25 a.m. EST)

Trundle bearing assembly No. 5 has been removed by the spacewalkers to be brought back inside the space station for eventual return to Earth. Our story describes the interest in this bearing. The crew is about to wrap up the SARJ work on this EVA.

1520 GMT (10:20 a.m. EST)

The spacewalkers have not yet spotted a smoking gun that might explain what is causing problems with a critical solar array rotary joint on the international space station. But it appears that metallic shavings contaminating the mechanism's main gear are slightly more concentrated near two bearings on either side of a drive motor. Whether that observation by spacewalkers Peggy Whitson and Dan Tani is significant or not remains to be seen.

Read our full story here.

1515 GMT (10:15 a.m. EST)

A blown fuse caused the primary liquid oyxgen pump to go offline. Switching over to the backup pump and getting the liquid oxygen filling underway again is expected to take 45 to 60 minutes.

1510 GMT (10:10 a.m. EST)

Filling of liquid oxygen has stopped for some undetermined reason. NASA says the launch team is working to understand why the LOX pump went offline, halting the fueling. There's about 15 percent of the oxygen tank left to fill.

1449 GMT (9:49 a.m. EST)

The stable replenish mode has begun on the liquid hydrogen tank, while the oxygen tank is about 80 percent full.

To recap, ECO sensor No. 1 failed this morning, sensors Nos. 2 and 3 have been intermittent and sensor No. 4 has operated normally.

Meanwhile, the space station astronauts are methodically inspecting the SARJ rotary joint. They are removing cover by cover to peer inside to take photographs and collect samples of the contamination with tape.

1430 GMT (9:30 a.m. EST)

The liquid hydrogen tank is being topped off and the liquid oxygen tank is about two-thirds full. Once the external tank is fully filled, the troubleshooting team will be dispatched to pad 39A to begin testing the ECO sensor system with equipment already set up inside the mobile launcher platform.

1350 GMT (8:50 a.m. EST)

Now passing the four-hour mark in the space station EVA.

1323 GMT (8:23 a.m. EST)

Sensor No. 1 has failed. The sensors Nos. 2 and 3 remain intermittent.

1314 GMT (8:14 a.m. EST)

Liquid hydrogen sensors Nos. 2 and 3 are showing intermittent indications of failing this morning, NASA reports.

Sensor No. 3 has failed on both previous fuelings of the tank during launch attempts on Dec. 6 and 9.

Because of the timing of the malfunctions, engineers are hopeful the sensors themselves, located inside the huge external tank and not easily accessible at the launch pad, are healthy.

The problem could be due to broken or damaged wires, bent or recessed pins in critical connectors or even debris in a connector. Data collected during the tanking test today should help narrow down the location of the problem and help determine what might be needed to fix it.

1308 GMT (8:08 a.m. EST)

Both liquid oxygen and liquid hydrogen have gone into the fast-fill configuration.

1258 GMT (7:58 a.m. EST)

During fueling Dec. 6, the troublesome engine cutoff (ECO) sensors Nos. 3 and 4 "failed wet" about 35 minutes after they were submerged in liquid hydrogen at minus 423 degrees Fahrenheit. After the launch was called off, another sensor that shows when the tank is 5 percent full failed wet. After the tank was drained, ECO sensor No. 1 failed wet.

During fueling Dec. 9, ECO sensor No. 3 failed wet 24 minutes after the others were submerged.

In both cases, the sensors returned to normal operation after the tank was drained and temperatures rose.

1254 GMT (7:54 a.m. EST)

Liquid oxygen has has transitioned from chilldown to the "slow-fill" mode. The liquid hydrogen loading is continuing in slow-fill, which fills a small fraction of the tank before switching to fast-fill mode.

1249 GMT (7:49 a.m. EST)

The liquid hydrogen engine cutoff sensors are becoming wet as the level of propellant in the tank slowly rises.

1227 GMT (7:27 a.m. EST)

Today's filling of space shuttle Atlantis' external fuel tank is underway at launch pad 39A with the chilldown thermal conditioning process. This will be followed by the slow-fill mode and then the fast-fill mode to load the tank.

The unusual event is being conducted to troubleshoot the erratic behavior of the liquid hydrogen sensor system that serve as fuel gauges in the bottom of the external tank. False readings from the system forced two scrubs of Atlantis' launch on Dec. 6 and 9, pushing the space station assembly mission into January.

1218 GMT (7:18 a.m. EST)

The "go" has been given to begin fueling shuttle Atlantis.

1205 GMT (7:05 a.m. EST)

The shuttle fueling test is just about to get underway.

1200 GMT (7:00 a.m. EST)

Spacewalkers Peggy Whitson and Dan Tani found no obvious signs of damage in a mechanism used to pivot a set of space station solar arrays to keep them face on to the sun. A problem of some sort tripped circuit breakers routing power to the S4-1A beta gimbal assembly Dec. 8 and based on testing, engineers suspected possible impact damage from space debris or a micrometeoroid. But it now appears more likely the problem, whatever it might be, is internal to the mechanism or its electrical system.

Read our full story here.

1150 GMT (6:50 a.m. EST)

Detailed narration of the inspection and sampling of debris around the SARJ using pieces of tape are proceeding in the spacewalk.

1100 GMT (6:00 a.m. EST)

Tani and Whitson have moved to the SARJ to begin removing outer covers for today's detailed inspections of the rotary joint.

1040 GMT (5:40 a.m. EST)

The spacewalkers have not found a smoking gun in their continuing inspections. Whitson is now entering into the S5 truss to disconnect some cables to allow ground controllers to perform diagnostic tests this morning.

1020 GMT (5:20 a.m. EST)

"I don't see anything off-nominal here," spacewalker Dan Tani reports to Houston after his initial inspections aimed at determining what is causing the Beta Gimbal Assembly problems on the starboard solar array. The crew is looking for any damage resulting from space debris or a micrometeoroid impact.

1005 GMT (5:05 a.m. EST)

Space station commander Peggy Whitson and flight engineer Dan Tani began a planned 6.5-hour spacewalk today to inspect two critical solar array repositioning systems that are not working properly, curtailing the lab's electrical power.

This is the 100th spacewalk devoted to station assembly and maintenance since construction began in 1998, the 23rd of 2007 and the fourth for the Expedition 16 crew.

At the Kennedy Space Center, meanwhile, engineers are preparing to pump super-cold liquid hydrogen rocket fuel into the shuttle Atlantis' external tank to troubleshoot an elusive problem with low-level engine cutoff - ECO - sensors that derailed two launch attempts Dec. 6 and 9.

Special test equipment has been spliced into the ECO sensor circuitry to help pinpoint a presumed wiring or connector problem that only shows up after the system has been exposed to liquid hydrogen at minus 423 degrees Fahrenheit.

Read our full story here.

1000 GMT (5:00 a.m. EST)

Both Tani and Whitson have emerged from the airlock as the two NASA astronauts embark on the spacewalk. They'll be gathering tools and setting up equipment needed for today's inspections of the starboard-side solar array truss.

0953 GMT (4:53 a.m. EST)

EVA BEGINS. Running more than an hour ahead of schedule, Expedition 16 commander Peggy Whitson and flight engineer Dan Tani floating inside the space station's Quest airlock switched their suits to internal batter power at 4:50 a.m. EST, marking the official start time for today's spacewalk.

0220 GMT (9:20 p.m. EST Mon.)

The rotating gantry is swinging away from Atlantis at Kennedy Space Center's launch pad 39A right now as ground teams prepare for Tuesday's fueling test of the space shuttle.

The ship's giant external fuel tank will be filled with cryogenic propellant beginning at 7 a.m. EST. The fuel loading process will take three hours complete.

The unusual event is being conducted to troubleshoot the erratic behavior of the liquid hydrogen sensor system that serve as fuel gauges in the bottom of the external tank. False readings from the system forced two scrubs of Atlantis' launch on Dec. 6 and 9, pushing the space station assembly mission into January.

While the fueling test is underway, two American astronauts aboard the station will be going outside to inspect equipment on the starboard-side solar arrays of the outpost. Contamination in the rotation joint that allows the arrays to turn in paddle wheel-fashion and a problem with a gimbal assembly are preventing the power-generating wings from tracking sun.

The six-and-a-half-hour spacewalk is scheduled to begin at 6 a.m. EST. However, that start time could move up an hour if spacewalks preps go smoothly in the morning.

NASA plans to hold a post-spacewalk news conference as well as a late-afternoon briefing to recap the hydrogen sensor test.

Watch this page for updates during the day.

THURSDAY, DECEMBER 13, 2007

Launch of shuttle Atlantis on a critical space station assembly mission, delayed twice because of problems with troublesome low-level fuel sensors, will slip an additional week, from Jan. 2 to no earlier than Jan. 10, to give support personnel time off over the Christmas and New Year holidays, NASA managers said Thursday.

Read our full story here.

TUESDAY, DECEMBER 11, 2007

Engineers are drawing up plans to load the shuttle Atlantis' external tank with supercold liquid hydrogen next week in a critical test to pinpoint the source of elusive, intermittent electrical problems in low-level fuel sensors that derailed two launch attempts.

Read our full story here.

SUNDAY, DECEMBER 9, 2007

NASA's Mission Management Team today delayed launch of the shuttle Atlantis on a critical space station assembly mission to at least Jan. 2 to troubleshoot elusive, intermittent electrical problems with low-level hydrogen fuel sensors that derailed launch attempts Thursday and again this morning.

Read our full story here.

1545 GMT (10:45 a.m. EST)

With the delay of shuttle Atlantis today, Cape Canaveral is turning its attention to launching an Atlas 5 rocket at 5:04 p.m. EST (2204 GMT) Monday from Complex 41. The rocket was rolled from its assembly building to the pad this morning. It will haul a classified spacecraft into orbit for the National Reconnaissance Office. Forecasters predict an 80 percent chance of good weather.

1440 GMT (9:40 a.m. EST)

Read our story on the launch moving to January and an update on station plans.

1416 GMT (9:16 a.m. EST)

Launch of Atlantis has been postponed to January, NASA officials have decided. The December launch period ends this week and managers do not expect to reach a resolution to the sensor problems by then. The next liftoff attempt could come as early as Jan. 2 around 5:45 a.m. EST.

Mission managers are meeting for their post-scrub discussions. A news conference will follow later today.

1355 GMT (8:55 a.m. EST)

Our scrub story has been updated with comments from the launch director.

1250 GMT (7:50 a.m. EST)

The Mission Management Team will be convening a post-scrub meeting at 9 a.m.

1240 GMT (7:40 a.m. EST)

Draining of liquid oxygen is underway.

1234 GMT (7:34 a.m. EST)

Read our scrub story.

1225 GMT (7:25 a.m. EST)

SCRUB! Today's launch of space shuttle Atlantis has been called off after one of the troublesome liquid hydrogen sensors failed during fueling this morning.

1222 GMT (7:22 a.m. EST)

The launch team has been instructed to continue along the fueling plan while additional data is gathered.

1220 GMT (7:20 a.m. EST)

Presumably dashing hopes of finally launching shuttle Atlantis on a critical space station assembly mission today, one of the four low-level engine cutoff - ECO - sensors in the hydrogen section of the shuttle Atlantis' external tank failed to perform properly during initial tests after being submerged in supercold propellant. NASA managers said Saturday they would proceed with launch today only if all four sensors and associated instrumentation worked flawlessly.

Read our full story here.

1215 GMT (7:15 a.m. EST)

Officials are huddled together in the control room to discuss what sorts of troubleshooting could be performed this morning and the overall course of action to take.

1210 GMT (7:10 a.m. EST)

"So after a brief burst of elation here in the Firing Room that all four sensors were working, it was not too long thereafter before we had a failure of one of those sensors. And the Launch Commit Criteria for today do dictate that we have to have four sensors working, NASA launch commentator George Diller said.

1209 GMT (7:09 a.m. EST)

While today's launch has not yet been scrubbed, liftoff cannot proceed with this failed sensor based on the new rules in place for this countdown requiring all four engine cutoff sensors be operating properly.

1205 GMT (7:05 a.m. EST)

The Mission Management Team is having a discussion before a scrub is called.

1204 GMT (7:04 a.m. EST)

Sensor No. 3 failed in the same manner as it did during Thursday's launch attempt.

1200 GMT (7:00 a.m. EST)

To recap, fueling of space shuttle Atlantis' external fuel tank began at 5:58 a.m. EST this morning at launch pad 39A. After the liquid hydrogen reservoir was filled to the five-percent mark, tiny sensors in the bottom of the tank that have been a source of trouble began operating. Initially, all four of those ECO sensors -- engine cutoff sensors -- did function normally. But then sensor No. 3 failed.

Filling of the tank will continue for at least another half-hour while engineers and managers assess the situation.

At the press conference last night, shuttle program manager Wayne Hale said a failure in this sensor system would prohibit the launch from occurring today. The rules in place for this launch attempt require all four sensors to be working properly.

1152 GMT (6:52 a.m. EST)

"This is not good news," Diller says.

1151 GMT (6:51 a.m. EST)

Sensor No. 3 has just failed.

1150 GMT (6:50 a.m. EST)

All four liquid hydrogen sensors are working properly this morning, NASA launch commentator George Diller reports from Firing Room 4 of the Launch Control Center.

1148 GMT (6:48 a.m. EST)

Liquid hydrogen has switched to fast-fill mode. The sensor trouble on Thursday occurred 16 minutes into fast-fill.

1146 GMT (6:46 a.m. EST)

Fast-fill mode on the liquid oxygen system has begun.

There are two tanks inside the shuttle's external fuel tank. The liquid oxygen tank occupies the top third of the bullet-shaped tank. It will be filled with 143,000 gallons of liquid oxygen chilled to minus 298 degrees Fahrenheit. The liquid hydrogen tank is contained in the bottom two-thirds of the external tank. It holds 385,000 gallons of liquid hydrogen chilled to minus 423 degrees Fahrenheit.

1135 GMT (6:35 a.m. EST)

The liquid hydrogen engine cutoff sensors are becoming wet as the level of propellant in the tank slowly rises. It will be a few more minutes before the first indication of how the sensors are performing is known.

1112 GMT (6:12 a.m. EST)

Hoping for the best, engineers began pumping a half-million gallons of liquid oxygen and hydrogen rocket fuel into the shuttle Atlantis' external tank today for a second attempt to kick off a critical space station assembly mission. Launch is targeted for 3:21 p.m.

With forecasters predicting an 80 percent chance of good weather, engineers will be closely monitoring the performance of four hydrogen low-level engine cutoff - ECO - sensors at the base of the external tank, on the lookout for any signs of unusual behavior.

Read our full story here.

1110 GMT (6:10 a.m. EST)

Liquid oxygen has gone into "slow-fill" mode.

1108 GMT (6:08 a.m. EST)

The liquid hydrogen loading has transitioned from chilldown to the "slow-fill" mode. This fills a small fraction of the tank, then the loading switches to "fast-fill" mode.

1100 GMT (6:00 a.m. EST)

FUELING UNDERWAY. The filling of space shuttle Atlantis' external fuel tank with a half-million gallons of supercold propellants has begun at launch pad 39A.

The tanking operation commenced with the chilldown thermal conditioning process at 5:58 a.m., some two minutes after the official "go" was given.

0305 GMT (10:05 p.m. EST Sat.)

The rotating service structure is swinging away from Atlantis right now, moving the countdown closer to Sunday morning's fueling of the space shuttle

Here is the revised countdown timeline for launch (in EST):

EST...........EVENT

12:06 AM......Fuel cell activation
12:56 AM......Booster joint heater activation
01:26 AM......MEC pre-flight bite test
01:41 AM......Tanking weather update
01:56 AM......Final fueling preps; launch area clear
02:56 AM......Red crew assembled
03:41 AM......Fuel cell integrity checks complete

03:55 AM......Begin 2-hour built-in hold (T-minus 6 hours)
04:06 AM......Safe-and-arm PIC test
05:11 AM......Mission management team tanking meeting
05:00 AM......Crew wakeup
05:26 AM......Test team ready for ET loading
05:55 AM......Resume countdown (T-minus 6 hours)

05:55 AM......LO2, LH2 transfer line chilldown
06:00 AM......NASA TV coverage of fueling begins
06:06 AM......Main propulsion system chill down
06:06 AM......LH2 slow fill
06:36 AM......LO2 slow fill
06:41 AM......Hydrogen ECO sensors go wet
06:46 AM......LO2 fast fill
06:56 AM......LH2 fast fill
08:51 AM......LH2 topping
08:56 AM......LH2 replenish
08:56 AM......LO2 replenish

08:55 AM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
08:55 AM......Closeout crew to white room
08:55 AM......External tank in stable replenish mode
09:26 AM......Astronaut support personnel comm checks
09:55 AM......Crew breakfast/photo op (recorded)
10:00 AM......NASA television coverage begins
10:01 AM......Pre-ingress switch reconfig
11:01 AM......Final crew weather briefing
11:11 AM......Crew suit up begins
11:25 AM......Resume countdown (T-minus 3 hours)

11:31 AM......Crew departs O&C building
12:01 PM......Crew ingress
12:51 PM......Astronaut comm checks
01:16 PM......Hatch closure
02:01 PM......White room closeout

02:05 PM......Begin 10-minute built-in hold (T-minus 20m)
02:16 PM......NASA test director countdown briefing
02:15 PM......Resume countdown (T-minus 20m)

02:17 PM......Backup flight computer to OPS 1
02:21 PM......KSC area clear to launch

02:26 PM......Begin final built-in hold (T-minus 9m)
02:57 PM......NTD launch status verification
03:12:00 PM...Resume countdown (T-minus 9m)

03:13:30 PM...Orbiter access arm retraction
03:16:00 PM...Launch window opens
03:16:00 PM...Hydraulic power system (APU) start
03:16:05 PM...Terminate LO2 replenish
03:17:00 PM...Purge sequence 4 hydraulic test
03:17:00 PM...IMUs to inertial
03:17:05 PM...Aerosurface profile
03:17:30 PM...Main engine steering test
03:18:05 PM...LO2 tank pressurization
03:18:25 PM...Fuel cells to internal reactants
03:18:30 PM...Clear caution-and-warning memory
03:19:00 PM...Crew closes visors
03:19:03 PM...LH2 tank pressurization
03:20:10 PM...SRB joint heater deactivation
03:20:29 PM...Shuttle GPCs take control of countdown
03:20:39 PM...SRB steering test
03:20:53 PM...Main engine start (T-6.6 seconds)
03:21:00 PM...SRB ignition (LAUNCH)

SATURDAY, DECEMBER 8, 2007

NASA's Mission Management Team today cleared the shuttle Atlantis for a second launch attempt Sunday, but agreed that any additional problems with suspect low-level hydrogen fuel sensors in the ship's external tank will trigger another delay.

Read our full story here.

2121 GMT (4:21 p.m. EST)

The briefing start time has moved back to 4:45 p.m. We'll post a complete story later today.

2100 GMT (4:00 p.m. EST)

All appears set for a launch attempt tomorrow. The management team just concluded its meeting. A press conference is coming up at 4:30 p.m.

1900 GMT (2:00 p.m. EST)

NASA and contractor managers and engineers are reviewing plans to make a second attempt to launch the shuttle Atlantis Sunday despite problems with troublesome low-level fuel tank sensors that derailed a launch try Thursday. Meanwhile, space station controllers ran into problems earlier today with circuit breaker trips.

Read our full story here.

FRIDAY, DECEMBER 7, 2007

Hoping critical fuel sensors will work properly the second time around, NASA managers Friday tentatively rescheduled the shuttle Atlantis for a delayed launch Sunday afternoon to kick off a high-profile mission to deliver Europe's Columbus research module to the international space station.

Read our full story here.

THURSDAY, DECEMBER 6, 2007

After a five-hour Mission Management Team meeting, NASA managers today decided to delay the shuttle Atlantis' launch on a space station assembly mission until Saturday at the earliest because of problems with the circuitry associated with critical engine cutoff sensors in the ship's external tank.

Read our full story here.

0055 GMT (7:55 p.m. EST Thurs.)

Space shuttle Atlantis could blast off as early as Saturday, mission managers say, if the external fuel tank hydrogen sensor problem can be resolved in time.

Officials have opted to forego a launch attempt Friday because the team needed more time to wrestle with the trouble.

The management team meeting lasting more than five hours concluded tonight with several options going forward. The shuttle could be cleared to fly Saturday with a workaround plan in place using additional instrumentation on the shuttle as a substitute for these fuel-level sensors. Another potential under discussion is conducting a fueling test to load the external tank, then draining the cryogenic propellants from the tank in an effort to collect additional data on the sensor system.

Managers will convene another meeting at 2 p.m. Friday to assess the status of the ongoing data analysis and decide how to proceed.

Launch pad teams plan to use this delay to Saturday and top off the liquid hydrogen storage tanks within the shuttle's electricity-generating fuel cell system, preserving the option to extend Atlantis' mission by two days for the addition of a fourth spacewalk at the space station.

The weather outlook for Saturday includes the possibility of scattered showers in the area and a low cloud ceiling. Meteorologists put the odds of favorable conditions at 60 percent. The forecast for Sunday and Monday calls for a 70 percent chance of good weather both days.

The launch time Saturday would be 3:43 p.m. EST, then moving earlier to 3:21 p.m. on Sunday and 2:55 p.m. on Monday.

0000 GMT (7:00 p.m. EST Thurs.)

Launch has been pushed back to Saturday. Mission managers will be briefing the news media on the situation shortly.

2353 GMT (6:53 p.m. EST)

The news conference is now planned to start at 7:30 p.m. EST.

2320 GMT (6:20 p.m. EST)

The briefing has moved to no earlier than 7 p.m.

2310 GMT (6:10 p.m. EST)

The mission management team continues its meeting to review the fuel sensor data and options for going forward. A launch attempt tomorrow has not yet been ruled out, but a further delay to Saturday is an option. A press conference will be held at Kennedy Space Center after the meeting's conclusion, expected no sooner than 6:30 p.m. EST.

1635 GMT (11:35 a.m. EST)

Engineers troubleshooting the apparent failure of two low-level hydrogen fuel sensors in the shuttle Atlantis' external tank say the problem appears to be the result of an open circuit. Whether that is true or not, and whether the problem requires repairs, is not yet known. While troubleshooting continues, however, the launch team is recycling the countdown to permit a second launch try Friday, at 4:09:13 p.m., to kick off a long-awaited flight to deliver Europe's Columbus research module to the international space station.

Read our full story here.

1520 GMT (10:20 a.m. EST)

Read our scrub story here.

1501 GMT (10:01 a.m. EST)

SCRUB! Today's launch of the space shuttle Atlantis has been postponed due to the external tank sensor problem that was uncovered during fueling this morning. The decision was made a few moments ago.

NASA officials are assessing their options for a future launch attempt of Atlantis to deliver the European Space Agency's Columbus science laboratory module to the space station. The current plan calls for another try tomorrow, after further troubleshooting on the fuel sensor system. Tomorrow's launch time would be 4:09 p.m. EST.

1435 GMT (9:35 a.m. EST)

Engineers are troubleshooting an apparent problem with two of four engine cutoff sensors in the shuttle Atlantis' hydrogen tank that apparently "failed wet" during fuel loading today. If troubleshooting confirms an actual failure, that means the sensors could falsely indicate the tank still has hydrogen in it at the end of the climb to space when, in fact, it is empty.

Read our full story here.

1425 GMT (9:25 a.m. EST)

With the shuttle Atlantis' external tank 80 percent full, engineers are troubleshooting an apparent problem with two of four engine cutoff sensors at the base of the hydrogen section of the huge tank. Sensors 3 and 4 apparently failed, or dropped off line, at the same time. It's not yet clear whether the issue can be resolved in time to complete fuel loading for a launch attempt today or whether the flight will have to be delayed.

Problems with ECO sensors during the initial post-Columbia missions caused numerous launch delays and extensive troubleshooting. It's not yet clear whether the problem today is a real sensor issue, a problem with the circuit the two sensors in questions are connected to or some other issue.

NASA says the launch has not yet been postponed. An update will be posted as soon as more information is available.

1215 GMT (7:15 a.m. EST)

FUELING UNDERWAY. The filling of space shuttle Atlantis' external fuel tank with a half-million gallons of supercold propellants has begun at launch pad 39A.

The tanking operation commenced with the chilldown thermal conditioning process at 7:06 a.m. This will be followed by the slow-fill mode and then the fast-fill mode.

The cryogenics are pumped from storage spheres at the pad, through feed lines to the mobile launcher platform, into Atlantis' aft compartment and finally into the external fuel tank.

There are two tanks inside the shuttle's external fuel tank. The liquid oxygen tank occupies the top third of the bullet-shaped tank. It will be filled with 143,000 gallons of liquid oxygen chilled to minus 298 degrees Fahrenheit. The liquid hydrogen tank is contained in the bottom two-thirds of the external tank. It holds 385,000 gallons of liquid hydrogen chilled to minus 423 degrees Fahrenheit.

There are no problems being worked in the countdown, the weather forecast still predicts a 90 percent chance of favorable conditions today and liftoff remains set for 4:31 p.m. EST.

0145 GMT (8:45 p.m. EST Wed.)

Final preparations are underway at launch pad 39A in advance of fueling space shuttle Atlantis' external tank with a half-million gallons of liquid oxygen and liquid hydrogen propellants.

The rotating service structure has been pulled back to reveal Atlantis. The gantry-like tower began retracting shortly after 8 p.m., and now technicians are performing the last steps to secure the pad for Thursday afternoon's launch.

Other activities overnight include configuring all of the switches in the cockpit, activating the shuttle's three power-producing fuel cells and clearing the blast danger area of non-essential personnel.

At 4:06 a.m., the countdown will be going into the two-hour planned hold at the T-minus 6 hour mark. The management team will be meeting to review the progress of the countdown, look at the weather and give the formal "go" to begin fueling. The three-hour fueling process should begin around 7:06 a.m.

Liftoff of Atlantis remains scheduled for 4:31 p.m. EST.

WEDNESDAY, DECEMBER 5, 2007

Engineers at the Kennedy Space Center are preparing the shuttle Atlantis for fueling and launch Thursday on a long-awaited mission to deliver Europe's Columbus research lab to the international space station.

With forecasters continuing to predict a 90 percent chance of good weather, NASA Test Director Jeff Spaulding told reporters today there are no technical problems at pad 39A that would delay the start of fueling at 7:06 a.m. Thursday. Launch is targeted for around 4:31:44 p.m.

"After lots of hard work and preparation, I'm pleased to report Atlantis and her crew are finally ready to fly with the Columbus module," Spaulding said. "The countdown is going very smoothly, really no issues to report."

Engineers loaded the shuttle's fuel cell system with hydrogen and oxygen late Tuesday, permitting up to three launch attempts in a row, if necessary, while still preserving the option to extend the mission two days to add a fourth spacewalk. The additional spacewalk is wanted for a detailed inspection of a contaminated solar array rotary joint in the space station's main power truss.

Read our full story here.

MONDAY, DECEMBER 3, 2007

The crew of the shuttle Atlantis flew to the Kennedy Space Center today for the start of the countdown to blastoff Thursday on a long-awaited mission to attach a European laboratory to the international space station. There are no technical problems of any significance at launch complex 39A and forecasters are predicting an 80 percent chance of good weather.

Read our full story here.