BY JUSTIN RAY

Follow the countdown and launch of the Boeing Delta 4 rocket with the GOES-N weather observatory. Reload this page for the very latest on the mission.

1619 GMT (12:19 p.m. EDT)

Launch weather officer Joel Tumbiolo has just given a briefing to mission managers. The situation is looking pretty good. The worries going into today's countdown were thick clouds, thunderstorms and ground winds.

The launch cannot occur if the cloud cover is greater than 4,500 feet thick. Although there is some patches of thick clouds around, the cloud cover above the launch site is thin right now. The weather reconnaissance aircraft will be dispatched later in the count to verify cloud thickness, in addition to radar information.

The weather team believes we shouldn't see thunderstorms in the local area this afternoon. Some scattered showers are moving from west but are dissipating.

Ground winds will be monitored carefully as launch time nears. The limit is 15 knots for liftoff. The forecast calls for 8 to 14 knots.

Tumbiolo is staying with a 40 percent chance of violating the launch weather rules today due to thick clouds and ground winds.

1607 GMT (12:07 p.m. EDT)

The liquid oxygen storage farm area chilldown is reported complete.

1550 GMT (11:50 a.m. EDT)

We have posted some NASA pictures taken during this morning's rollback of the mobile service tower. See the images here.

1541 GMT (11:41 a.m. EDT)

T-minus 5 hours, 15 minutes and holding. The countdown has just entered a planned 60-minute built-in hold, giving the team time to catch up on any work that could be running behind schedule. Once the clocks resume ticking at 12:41 p.m. EDT, the Terminal Countdown phase of today's launch operation will begin.

1540 GMT (11:40 a.m. EDT)

Chilldown thermal conditioning of the liquid oxygen pump in the propellant storage area of launch pad 37B is starting.

1525 GMT (11:25 a.m. EDT)

Technicians have wrapped up launch morning activities at the pad. The complex is being cleared of workers and roadblocks are being establishing.

Meanwhile, hold-fire checks are being conducted with the Range to verify the countdown can be stopped immediately if a problem arises.

Launch preparations are proceeding for liftoff at 6:11 p.m. EDT today.

1443 GMT (10:43 a.m. EDT)

At Complex 37, the Boeing launch team is busy putting the final touches on the Delta 4 rocket and completing pad securing work following mobile service tower rollback earlier this morning. The Terminal Countdown will begin at 12:41 p.m. EDT.

1200 GMT (8:00 a.m. EDT)

This morning's updated launch weather forecast is posted here.

1155 GMT (7:55 a.m. EDT)

The 330-foot tall mobile service tower has been retracted from the Boeing Delta 4 rocket at Cape Canaveral's launch pad 37B for today's liftoff to place the GOES-N weather satellite into Earth orbit.

The 9-million pound tower shielded the Delta 4 from the elements during the 15-month stay on the pad, provided workers 360-degree access to the various areas on the vehicle and was used to attach the strap-on solid motors and the payload during the launch campaign. The tower is 90-feet wide and 40-feet deep.

Crews will spend the next couple of hours securing the complex for launch before leaving the danger area around the pad. All workers must be clear of the area for the start of hazardous operations in the countdown, which include fueling the vehicle later this afternoon.

Liftoff remains scheduled for 6:11 p.m. EDT, the opening of a 60-minute window that extends to 7:11 p.m. EDT (2211-2311 GMT).

GOES-N is the first in a new series of U.S. weather satellites with sharper vision and extended life. The craft will be placed into a geosynchronous transfer orbit by the Delta rocket, then maneuvered by its onboard engine into a circular geostationary orbit 22,300 miles above the equator. It will be thoroughly tested and then put into storage mode to await its eventual job of replacing an aging weather-watching spacecraft in the coming years.

1129 GMT (7:29 a.m. EDT)

Rollback of the mobile service tower is underway right now at Cape Canaveral Air Force Station's Complex 37. The wheeled structure is moving along rail tracks to its launch position about the length of a football field away from the Delta 4 rocket in preparation for today's launch.

TUESDAY, MAY 23, 2006

The only worry heading into Wednesday's countdown to launch the GOES-N weather observatory aboard a Boeing Delta 4 rocket, ironically, is the weather.

After weeks of dry conditions in Florida, gray skies and rain have returned to the Sunshine State over the past couple of days courtesy of a weather system in the Gulf of Mexico. It could spell trouble for the launch attempt, if cloud and wind rules governing the liftoff are violated.

"We are going to be watching the thick clouds, possible thunderstorms and ground winds," said Joel Tumbiolo, the Delta launch weather officer from the Cape's 45th Weather Squadron.

The rocket is not allowed to fly through clouds thicker than 4,500 feet because of the threat that the booster can trigger its own destructive bolt of lightning.

If thunderstorms with lightning are present in the area around Cape Canaveral, the associated anvil clouds must stay at least 10 miles away from the rocket's flight path.

And in the last five minutes of the countdown, the weather team will be monitoring winds at launch pad 37B. The winds cannot exceed 15 knots, otherwise the countdown clocks will be halted.

Overall, Tumbiolo is putting the odds of acceptable launch weather at 60 percent.

The Delta 4 is targeting launch at 6:11 p.m. EDT (2211 GMT). The rocket could lift off as late as 7:11 p.m. EDT (2311 GMT). Otherwise it must wait until Thursday during the same 60-minute window, when slightly worse weather is predicted.

Managers gave approval to proceed with the mission during the launch readiness review held earlier today. This will be the fifth Delta 4 rocket to fly since debuting in November 2002.

"Right now, we are in the middle of final preparations, performing vehicle closeouts and facility closeouts," Rick Navarro, Boeing's Delta 4 launch director, said this afternoon.

All compartments on the rocket are being sealed and inspections conducted, he added. Retraction of the mobile service tower from around the vehicle will occur Wednesday morning.

The GOES-N spacecraft mounted atop the rocket is the first of three next-generation weather satellites ordered by the U.S. government. Over the next several years, they will replace the existing observatories that give the critical imagery and data used to create weather forecasts. GOES' pictures of clouds are seen every day in TV newscasts.

"Here we are sitting on the eve of the GOES-N launch, NOAA's newest Geostationary Operational Environmental Satellite," said Steve Kirkner, the GOES program manager at NOAA. "This satellite will provide continuity of data and warnings for not only North America but also Central and South America, the entire Western Hemisphere and everyone that lives in that area."

"The satellite has passed all of its tests and is set for a successful launch tomorrow," said Mark Spiwak, program director at GOES-N manufacturer Boeing Satellite Systems International.

1425 GMT (10:25 a.m. EDT)

The launch readiness reviews are being held today at Cape Canaveral to confirm all systems are "go" to begin the countdown for tomorrow's launch of the Delta 4 rocket and GOES-N spacecraft. Kennedy Space Center is hosting a pre-launch news conference at 1 p.m. EDT. We'll post a complete update on this page afterward.

Meanwhile, here is the latest launch weather forecast.

MONDAY, MAY 22, 2006

The weather forecast has gotten a little bit worse for Wednesday's launch and a lot worse for Thursday's backup opportunity. Launch pad winds and cloud cover will be the two areas for concern both days. See the latest forecast here.

SUNDAY, MAY 21, 2006

The first in a new breed of advanced weather observatories for the U.S. looks to blast off this week from Cape Canaveral aboard a Boeing Delta 4 rocket.

The Geostationary Operational Environmental Satellite-N (GOES-N) has been beset by a series of technical snags that have kept it grounded for a year. The team trying to launch the craft hopes its patience will pay off with a smooth ascent to orbit Wednesday evening.

The two-stage Delta 4 rocket was rolled to launch pad 37B on February 15, 2005 for an anticipated early May 2005 liftoff. But issues with the vehicle and satellite slipped the mission to August. A pair of back-to-back countdowns were performed, the second one scrubbing less than five minutes before launch.

Expired batteries on the rocket and unfavorable orbital lighting conditions for the solar-powered GOES-N meant launch would have to wait until fall. Then, hundreds of Boeing machinists went on strike, grounding the entire Delta rocket fleet until this spring.

GOES-N was removed from atop the Delta 4 in February for a return visit to its processing building near the Cape to undergo a health checkup given the extended launch delay. The satellite went back to the pad at the end of April.

Now, all appears ready for liftoff of the $481 million mission. Wednesday's 60-minute launch window opens at 6:11 p.m. EDT (2211 GMT).

The Delta 4 Medium+ vehicle will take GOES-N on a 4-hour, 21-minute trip to orbit. This particular "4,2" version of Boeing's next-generation rocket features a four-meter payload fairing and two strap-on solid rocket boosters to propel the 6,900-pound payload. The same configuration was flown successfully during the Delta 4's maiden launch.

The Boeing-built GOES-N is designed to provide sharper images of clouds and storms over a longer lifetime compared to earlier satellites. The National Oceanic and Atmospheric Administration will use the craft, to be renamed GOES-13 after launch, from geostationary orbit about 22,300 miles above the equator.

Extensive information on the satellite and its instruments is available here.

Boeing is launching the satellite under a commercial arrangement with the government. Once in the checkout orbit about three weeks after liftoff, Boeing will hand control over to NASA and NOAA to put the craft's systems through a comprehensive suite of tests. Those checks should be complete within six months, allowing NOAA to put GOES-13 into orbital storage where it will wait to replace an aging spacecraft.

The satellite will join NOAA's Geostationary Operational Environmental Satellite system, which provides near-constant weather imagery of North America using spacecraft parked over the Pacific and Atlantic Oceans. Two satellites -- GOES-10 and GOES-12 -- are currently capturing real-time images and data, while GOES-11 is being stored as a spare. The GOES-10 is expected to retire from its lead role covering the western zone this summer, prompting GOES-11 to enter service as replacement. That would make GOES-N the only on-orbit spare for this crucial system.

Sister-satellites GOES-O and GOES-P will be launched in the coming years.

Plans for Wednesday's countdown call for the 330-foot mobile service tower to begin rolling away from the Delta 4 vehicle around sunrise in advance of the start of the Terminal Countdown. The gantry is used to gain access to the rocket during pre-launch preparation activities, in addition to use as a protective structure to shield the booster from adverse weather conditions during its stay at the pad.

Fueling operations for the Delta 4's Common Booster Core first stage and the second stage with super-cold liquid oxygen and liquid hydrogen propellants will get underway in the final five hours prior to the opening of the launch window. It takes about three hours to fully load all four tanks.

Testing of communications links between the rocket and Air Force Eastern Range will then occur. Steering checks of the first stage RS-68 engine and second stage RL10 powerplant are also on tap in the last hour of the count.

A 15-minute build-in hold is slated for T-5 minutes, during which time teams will go through final polling for launch clearance. The Delta 4 will transition to internal power as the count resumes, proceeding to RS-68 engine ignition at T-5.5 seconds and the subsequent liftoff.

Stay with Spaceflight Now for live play-by-play updates throughout the Delta 4's countdown and launch of America's newest weather satellite.

FRIDAY, MAY 19, 2006

Air Force meteorologists are predicting a 70 percent chance of acceptable weather conditions for next Wednesday's Boeing Delta 4 rocket launch from Cape Canaveral. The rocket will haul the GOES-N weather satellite into orbit. See the full forecast here.