Mission Status Center

Pilot Terry Virts and then commander George Zamka just emerged from the spacecraft following the scrub. They'll head back to the crew quarters to wait out this 24-hour launch postponement that was caused by unfavorable weather.

The half-million gallons of rocket fuel will be drained from Endeavour's external tank and countdown clocks recycled back during this 24-hour delay.

Mission specialists Steve Robinson and Kay Hire have exited the shuttle's flight deck.

The astronauts are beginning to climb out of the space shuttle already. Bob Behnken and Nick Patrick have egressed from their middeck seats.

The official weather forecast for Monday's 4:14 a.m. EST launch time calls for scattered-to-broken clouds at 3,000 feet, 7 miles of visibility, launch pad winds from the north-northwest at 340 degrees of 8 peaking to 12 knots and a temperature of 51 degrees F. There's a 40 percent chance that the clouds will form a low ceiling and prohibit launch.

For Tuesday's 3:51 a.m. EST launch time, meteorologists predict scattered-to-broken clouds at 3,000 feet, 7 miles of visibility, launch pad winds from the southeast at 130 degrees of 5 peaking to 8 knots and a temperature of 65 degrees F. The chance of low clouds being a problem is 40 percent once again.

Looking to Wednesday's 3:25 a.m. EST launch time, the weather worsens to 60 percent "no go." The forecast includes a chance of rain showers, scattered-to-broken clouds at 3,000 feet, 7 miles of visibility, launch pad winds from the west at 270 degrees of 18 peaking to 25 knots and a temperature of 60 degrees F.

The Orbiter Closeout Crew has returned to the launch pad for opening Endeavour's hatch and helping the astronauts out of the shuttle.

Today's scrub of shuttle Endeavour means Tuesday's planned launch of the Atlas 5 rocket carrying the Solar Dynamics Observatory from nearby Complex 41 at Cape Canaveral will be pushed back 24 hours too.

The Eastern Range needs two days between launches of different vehicles to reset its tracking, safety and communications systems. So Endeavour's delay ripples to the Atlas.

A Wednesday launch of the Atlas would occur during a window extending from 10:26 to 11:26 a.m. EST.

Looking skyward at the planned launch time, skies are completely overcast and no stars can be seen from the Kennedy Space Center press site.

SCRUB. Low clouds hanging over the Kennedy Space Center will prevent the space shuttle Endeavour from launching today on its mission to the International Space Station.

With a launch window lasting just 10 minutes to put the shuttle on the proper path to the reach the orbiting outpost, there's no time left to wait for the weather to improve.

Another opportunity to launch Endeavour will come tomorrow at 4:14 a.m. EST. Meteorologists predict a 60 percent chance of weather cooperating then.

The poll by NASA test director Jeff Spaulding confirms there are no technical issues or constraints standing in the way of launch at 4:39 a.m. EST. But the Range is "no go" for cloud ceilings at the launch pad. And Mission Control says that weather at Kennedy Space Center's runway for the return-to-launch-site abort is "no go."

Seven minutes are remaining in this built-in hold. Final readiness polls will be conducted over the next few moments. There are no technical issues being worked by the launch team. But weather is the obstacle.

If the weather somehow improves, we're now 20 minutes from Endeavour's launch on an eight-and-a-half minute trek to space. At main engine cutoff, Endeavour will be flying on a suborbital trajectory with a high point of 136 statute miles and low point of 36 statute miles, inclined 51.6 degrees to the equator. A half-hour later, the twin orbital maneuvering engines will be fired to place the shuttle into a 142 by 98 statute mile orbit.

Current weather conditions are once again violating the cloud ceiling rule. Weather is "no go" for launch at this time.

Powering space shuttle Endeavour throughout its eight-and-a-half minute climb to orbit will be the three main engines built by Pratt & Whitney Rocketdyne. The cryogenic powerplants are fed with liquid hydrogen and liquid oxygen stored in the external fuel tank.

In the engine No. 1 position today is the Block 2-2059 engine now making its fourth launch. It has accumulated 2,051 seconds of total firing time on the previous missions, plus ground testing. STS-117 was its debut flight.

Making its first launch is the Block 2-2061 in the engine No. 2 position. This powerplant has 1,560 seconds of firing time during ground tests.

And Block 2-2057 is engine No. 3 on Endeavour. It has four previous flights, starting with STS-114, and some 2,564 seconds of firing time.

Astronaut Chris Ferguson is flying weather reconnaissance flights around the Kennedy Space Center to evaluate the clouds and whether the current conditions obscure the view to the emergency runway available to Endeavour. Cloud ceilings also pose a problem for the Range needing to visually track the shuttle's initial climb away from the pad.

The reusable solid rocket boosters, built by ATK, provide the primary thrust to propel the space shuttle away from Earth during the initial two minutes of flight. The 11 sections on each booster flying on Endeavour are refurbished hardware. The upper cylinder on the right-hand booster, for example, flew on STS-3 in 1982. In all, the twin boosters flying today have reused segments and pieces that trace back to 64 previous shuttle launches and 14 ground test-firings.

The boosters will parachute into the Atlantic Ocean where a pair of retrieval ships are standing by to recover the rockets and tow them back to shore.

At launch, the space station will be flying 212 miles above the southern Indian Ocean at 24.5 degrees south latitude and 89.9 degrees east longitude. Liftoff at 4:39 a.m. EST is timed to place Endeavour on course to dock with the station Tuesday morning.

The official launch window, based on the latest radar tracking of the space station's orbit and subsequent revision from Mission Control, extends from 4:35:16 to 4:44:15 a.m. EST. But the liftoff is planned in the middle of the window at 4:39:50 a.m. EST when Earth's rotation carries the launch pad into the plane of the station's orbit.

T-minus 9 minutes and holding. Countdown clocks have gone into the planned 45-minute, 50-second built-in hold. Launch is targeted for 4:39:50 a.m. EST.

The launch weather officer just reported that current conditions "go" now. The ceiling rule isn't being violated any longer. But whether the low clouds will cooperate at the actual liftoff time remains to be seen.

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

Now one hour away from liftoff. Mission Control in Houston is loading Endeavour's onboard computers with the proper guidance parameters based on the projected launch time.

Pilot Terry Virts has configured the displays inside Endeavour's cockpit for launch while commander George Zamka enabled the abort steering instrumentation.

The Orbiter Closeout Crew is driving away from the pad.

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 4:39:50 a.m. EST.

Endeavour's 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.

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch is scheduled for 4:39 a.m. EST.

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.

The work to seal the shuttle's crew compartment hatch for flight is complete. And the closeout team that assisted the astronauts into Endeavour today is stowing equipment in the White Room before leaving the launch pad now.

Commander George Zamka is pressurizing the gaseous nitrogen system for Endeavour's Orbital Maneuvering System engines and pilot Terry Virts activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water spray boilers.

The launch weather rule governing low clouds has now been declared "red" or "no go" for a ceiling that's violating the criteria.

The ground pyrotechnic 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.

Initialization of the Ground Launch Sequencer has been completed. This is the master computer program that will run the final nine minutes of the countdown.

None of the launch weather rules are being violated right now. But the forecast for the 4:39 a.m. EST liftoff time calls for a 70 percent chance of a low-cloud ceiling at 3,800 feet that would be unacceptable for a space shuttle launch.

The outlook for Monday and Tuesday are 60 percent favorable both days, but low clouds at 4,000 feet will be the concern.

Endeavour's hatch has been closed and locked.

The orbiter closeout team at the launch pad is shutting Endeavour's crew module hatch for flight.

The pad crew is ready to close up Endeavour's hatch.

The astronauts have completed a series of radio communication checks with ground controllers.

The weather situation is worsening. There's now just a 30 percent chance that weather is going to allow Endeavour's launch at 4:39 a.m. EST due to low clouds.

The launch time outlook calls for an unacceptable broken deck of clouds at 3,800 feet, 7 miles of visibility, launch pad winds from the northwest at 310 degrees at 13 peaking to 20 knots and a temperature of 46 degrees F.

If the launch delays to Monday at 4:14 a.m. EST, the odds are 60 percent favorable due to possible a low cloud ceiling. There's also weather worries at all three overseas abort landing sites in France and Spain tomorrow too. At least one of the sites must have conditions within limits at launch time in case Endeavour had to make an emergency landing.

The final Endeavour astronaut has boarded the shuttle today. Steve Robinson, mission specialist No. 2 and flight engineer, has now entered the hatch.

Read his biography here.

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Kay Hire is getting seated in the flight deck's aft-right seat to serve as mission specialist No. 1.

Read her biography here.

Launch weather officer Kathy Winters reports that the approaching cloud cover is scattering out a bit, which is good news.

Three hours and counting until liftoff time. No significant technical issues are being reported in the countdown, but clouds and winds continue to be watched.

Nick Patrick is mission specialist No. 3 and the other spacewalker on the flight. He has boarded the shuttle to ride into orbit in the middeck's right seat.

Read his biography here.

Endeavour pilot Terry Virts is making his way to the flight deck's front-right seat right now.

Read Virts' biography here.

The Final Inspection Team has wrapped up its work at launch pad 39A.

Mission specialist is No. 4 and leader spacewalker Bob Behnken just crawled through the hatch to take the left-hand seat on the middeck.

Read his biography here.

Shuttle commander George Zamka is the first astronaut to board the shuttle today, taking the forward-left seat on the flight deck.

You can read Zamka's biography here.

After taking a few moments to gaze up at their spacecraft from the pad surface, the astronauts have ascended the tower.

Endeavour's crew has arrived at launch pad 39A. The AstroVan came to a stop on the pad surface near the Fixed Service Structure tower elevator that will take the six-person crew to the 195-foot level to begin boarding the shuttle.

The AstroVan is passing the 52-story Vehicle Assembly Building where Endeavour 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 the passing convoy. This is a launch day tradition to say farewell and good luck to the astronaut crews.

The crew of commander George Zamka, pilot Terry Virts and mission specialists Kay Hire, Steve Robinson, Nick Patrick and Bob Behnken just emerged from their quarters to board the AstroVan for the ride from the Kennedy Space Center Industrial Area to launch pad 39A on the edge of the Atlantic Ocean.

The astronauts are heading down the hallway from the suitup room to board the elevator that will take them down to the AstroVan.

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 4:39 a.m. EST launch time.

As the countdown to launch enters the final four hours, all systems remain "go" for liftoff of space shuttle Endeavour and six astronauts at 4:39 a.m. EST.

The astronauts -- five veterans and one rookie -- are donning their 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 12:49 a.m.

Over the past hour in the countdown, activities underway have included calibrations of the orbiter's inertial measurement units, powering up Endeavour's navigation systems, the pre-flight alignment of ground station antennas with the launch pad and communications checks with the Eastern Range.

Our launch webcast with Miles O'Brien, David Waters and astronaut Leroy Chiao is streaming live on the right-hand side of our page.

The odds of acceptable weather at launch time have decreased to 60 percent. Winds and clouds are the concerns for violating the shuttle's weather rules.

The revised outlook includes some scattered low clouds at 4,000 feet, good visibility, launch pad winds from the northwest at 310 degrees at 13 peaking to 20 knots and a temperature of 46 degrees F.

"Just had a good meal of steak and potato! No more tweets before launch. Go Endeavour!" mission specialist Nick Patrick just wrote on his Twitter page a short time ago.

The Final Inspection Team is out at the launch pad to scan the vehicle for any ice or debris concerns following fueling operations. 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.

A reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

With the hazardous tanking operation now completed, the Orbiter Closeout Crew and Final Inspection Team have arrived at the pad to perform their jobs. The closeout crew will ready Endeavour's 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.

TANK FULL. Liquid oxygen has entered stable replenishment mode, officially completing today's three-hour external tank filling process at 10:47 p.m. EST.

The topping phase is underway on liquid oxygen.

"Breakfast and a workout - nice to get both in on such a busy day!" Endeavour mission specialist Nick Patrick just wrote on his Twitter page from crew quarters. "Just over 6 hours to go!"

The liquid oxygen tank is above the 90 percent level. About 20 more minutes will be needed before fueling is completed.

Liquid hydrogen loading was completed at 10:18 p.m. EST. After reaching the 98 percent level, the topping sequence was performed. And now the stable replenishment mode has been activated to keep the tank full through the rest of the countdown, replacing the supercold propellant that naturally boils away.

Evaluation of the software in the space shuttle main engines' controllers has been performed as planned in the countdown.

T-minus 3 hours and holding. Clocks have entered a planned two-hour, 30-minute built-in hold. Additional pauses are scheduled at the T-minus 20 and T-minus 9 minute marks, setting up the countdown for launch at 4:39 a.m. EST.

Another safety check is underway on the pyrotechnic circuits to ensure they are in a good configuration now that the shuttle is in cryogenic conditions. This is done before the inspection team and orbiter closeout crew head to the pad.

No technical problems are being reported in the countdown and fueling is ongoing.

The weather team is watching an area of cloudiness north of the Kennedy Space Center creating overcast skies around 4,000 feet in altitude. The clouds are drifting this way, but meteorologists say the overcast could scatter out and not be a problem for launch.

The primary and secondary antennas at the MILA tracking station near the Kennedy Space Center have been aimed at the pad. MILA provides the primary source of tracking, telemetry data and voice communications from the space shuttle during the first seven-and-a-half minutes of flight.

All is going well 90 minutes into the fueling operations for space shuttle Endeavour.

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

The Merritt Island tracking station, commonly known as MILA, is beginning to align its tracking antennas with the launch pad.

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Liquid hydrogen and liquid oxygen loading have switched to the "fast-fill" mode as fueling of space shuttle Endeavour proceeds via remote control at launch pad 39A.

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.

The low-level sensors in the liquid oxygen tank are reading "wet" now, too.

Liquid oxygen loading has completed chilldown and gone into slow-fill.

The low-level sensors in the liquid hydrogen tank are reading "wet" as they get submerged by the cryogenics. The tank is about five percent fill now.

The transfer lines on the liquid oxygen side have been chilled down. The main propulsion system conditioning is underway now.

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

The fueling sequence started with the chilldown thermal conditioning of the liquid oxygen system.

FUELING UNDERWAY. Today's filling of space shuttle Endeavour's external fuel tank started at 7:47 p.m. EST. The brief delay of 33 minutes in beginning the fueling process will not impact the planned launch time since the countdown has plenty of margin to recover from issues of this nature.

A safety check has been completed on the pyrotechnic circuits to ensure they are in a good configuration before fueling. That's the final step before the tanking preps can commence.

The adjustment on that regulator for the crew cabin breathing air has been completed and the team is departing pad 39A now.

Once this repair team clears the pad area, the launch team in Firing Room 4 will begin their final preparations in advance of fueling.

NASA says the start of fueling will be delayed about 30 minutes while a team at the launch pad adjusts a regulator for Endeavour's cabin air. The work is being done on the 130-foot-level of the pad tower. Spokesman George Diller says the issue is minor and this adjustment will clear the slightly low pressure before proceeding with the countdown activities.

T-minus 6 hours and counting. The countdown has resumed ticking after a two-hour hold. The next scheduled built-in hold will occur at T-minus 3 hours.

The Mission Management Team met for the pre-fueling meeting and gave the "go" to load a half-million gallons of supercold rocket fuel into Endeavour's external tank for launch.

Fueling is supposed to get underway in a few minutes. However, managers are reviewing the technical status of the space shuttle to determine whether to proceed.

In the latest forecast issued this evening, meteorologists continue to predict an 80 percent chance of acceptable weather conditions for launch. Winds are the only concern for the 4:39 a.m. EST liftoff time.

The outlook includes some scattered low clouds at 4,000 feet, good visibility, launch pad winds from the north-northwest at 330 degrees at 13 peaking to 20 knots and a temperature of 45 degrees F.

T-minus 6 hours and holding. The countdown has gone into the scheduled two-hour built-in hold prior to the start of fueling.

Endeavour's six astronauts spent their past day studying flight plans, going to the gym and visiting the shuttle at the pad before heading to sleep around 10 a.m. EST.

They also received a briefing on orbiter and payload status, plus the the weather forecast from the ascent team of flight controllers in Houston last night.

The crew will be awakened for launch day at 5:45 p.m. They'll have breakfast at 6:30 p.m. and then undergo final medical exams at 7 p.m. Suit up begins a little after 12 midnight and departure from crew quarters is scheduled for 12:49 a.m. in preparation for blastoff at 4:39 a.m. EST.

NASA is not abandoning efforts to develop a new heavy lift booster in the wake of the Obama administration's decision to cancel NASA's moon program, agency Administrator Charles Bolden said Saturday. But he added that any such rocket, even one using subsystems planned for the canceled Ares 5, is unlikely to fly before the 2020s at best, implying U.S. manned missions beyond low-Earth orbit are one to two decades away.

Read our full story.

See our spectacular photos of Endeavour as the launch pad gantry retracted this morning.

The official launch window, based on the latest radar tracking of the space station's orbit and subsequent revision from Mission Control, extends from 4:34:49 a.m. to 4:44:50 a.m. EST. The targeted liftoff time occurs in the middle of the window at 4:39:50 a.m. EST. That's the moment when Earth's rotation carries the launch pad into the plane of the station's orbit.

If the launch is delayed to Monday morning for some reason, a two-pane window will be available for the backup liftoff opportunity. The first pane for a Flight Day 3 rendezvous with the space station would extend from 4:09:07 to 4:19:07 a.m. EST and include a preferred launch time of 4:14:07 a.m. EST.

An additional three minutes and 11 seconds in the form a second pane of Monday's launch window exists until 4:22:18 a.m. EST. However, launching within that pane would lead to a Flight Day 4 rendezvous and docking.

Under sparkling blue skies, space shuttle Endeavour has been uncovered from the cocoon-like service gantry at launch pad 39A for Sunday morning's liftoff. Technicians will spend the next few hours getting ground equipment configured and secured in preparation for tonight's fueling operation.

Clocks will resume counting at 12:14 p.m. EST after the half-day hold at T-minus 11 hours. The orbiter's fuel cells are activated about an hour later, and the hazard area around the pad gets cleared of personnel during the afternoon.

The next planned hold is T-minus 6 hours beginning at 5:14 p.m. EST. During this two-hour pause of the clocks, the Mission Management Team convenes its pre-fueling meeting to review the status of work, the readiness of shuttle systems and the latest weather forecast.

If all goes according to plan, loading of the external tank with propellant will start at 7:14 p.m. EST. The process should take three hours to complete.

A reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

The massive gantry is clear of the shuttle now as it continues to slowly back away.

Rollback of the rotating service structure to reveal shuttle Endeavour has started at launch pad 39A. You can watch the tower retraction in our live streaming video.

The walkdown inspections at the pad prior to gantry rollback are being reported complete.

The sun is rising at the Kennedy Space Center as workers get ready to retract the service gantry away from Endeavour for tomorrow's launch. Tower rollback is slated to begin at 8 a.m. EST.


Read our earlier status center coverage.