BY JUSTIN RAY

Follow the countdown and launch of the inaugural Boeing Delta 4-Heavy rocket on a demonstration test flight.

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

With the CBC liquid hydrogen tanking continuing, the launch team has been given approval to begin chilldown conditioning of the upper stage liquid hydrogen system. This is a precursor to fueling the upper stage.

1831 GMT (1:31 p.m. EST)

Boeing says launch will not occur before 4:25 p.m. EST (2125 GMT) based on delays encountered during countdown activities this morning. Today's launch opportunity extends through 5:31 p.m. EST (2231 GMT).

1828 GMT (1:28 p.m. EST)

The loading of liquid oxygen into the Common Booster Cores has been completed. The launch team will be performing vent and relief checks following tanking and begin chilldown procedures for the upper stage liquid oxygen system.

The CBC liquid hydrogen loading is about one-third complete.

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

Hydrogen loading is passing the 10 percent level.

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

The CBC liquid oxygen filling has surpassed the 80 percent mark.

1805 GMT (1:05 p.m. EST)

The Delta 4 rocket's three Common Booster Cores are currently being loaded with super-cold liquid oxygen and liquid hydrogen propellants.

Complex 37 has two giant sphere-shaped fuel tanks to store the cryogenic liquid oxygen and liquid hydrogen. The LOX tank holds 250,000 gallons and LH2 sphere about 850,000 gallons. Complex 37 has two giant sphere-shaped fuel tanks to store the cryogenic liquid oxygen and liquid hydrogen. The LOX tank holds 250,000 gallons and LH2 sphere about 850,000 gallons.

The cryogenics are fed from the storage tanks through pipelines to the pad. For the three Common Booster Cores, the propellants are routed up to the launch table upon which the rocket sits. Tail service masts, the large box-like structures at the base of the vehicle, feed the oxygen and hydrogen to the boosters via separate umbilicals. The upper stage receives its cryos from the middle swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

1759 GMT (12:59 p.m. EST)

A "go" have been given to start slowly pumping liquid hydrogen propellant into the three Common Booster Core stages. This "slow-fill" will be sped up to "fast-fill" after a small portion of each tank is loaded.

Chilled to Minus-423 degrees Fahrenheit, the liquid hydrogen will be consumed by the RS-68 main engines along with liquid oxygen during the early minutes of launch.

1736 GMT (12:36 p.m. EST)

Now two hours from the opening of today's launch window. Fueling operations are active at pad 37B after a delay to assess a computer problem. There has been no formal word on selecting a new liftoff time. The countdown is heading to T-minus 5 minutes where clocks will stop until all is in readiness for launch.

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

The slow-fill mode for liquid oxygen loading is now underway.

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

The "go" has been given to start filling the three Common Booster Cores with liquid oxygen and commence the chilldown thermal conditioning on the liquid hydrogen side. So countdown activities are picking up after a hold lasting nearly an hour while the sequencer computer glitch troubleshooting was underway.

1704 GMT (12:04 p.m. EST)

The launch team is being instructed to posture themselves to resume fueling operations.

1654 GMT (11:54 a.m. EST)

Engineers have been troubleshooting the problem for a little over 40 minutes now. There is no further update currently available. We'll pass along additional news as possible.

1636 GMT (11:36 a.m. EST)

Today's two-hour, 55-minute launch window opens three hours from now. Given the delays in the work timeline experienced this morning, the target liftoff time will surely slip past 2:36 p.m. EST and into the window. How far into the window is unclear, pending resolution of the current glitch. Liftoff must occur by 5:31 p.m. EST (2231 GMT) today or else the mission will have to wait until tomorrow.

If needed, Wednesday's launch window is a minute longer and extends from 2:36 to 5:32 p.m. EST (1936-2232 GMT). There is a 60 percent chance of acceptable weather. Clouds, rain and winds are concerns.

The weather is excellent today.

1618 GMT (11:18 a.m. EST)

Engineers are troubleshooting a problem associated with the Terminal Countdown Sequencer Rack. The sequencer controls the final 8.5 seconds of the countdown. A glitch with the TCSR forced a scrub of this mission on December 11. While the current situation is assessed, liquid oxygen filling operations have been halted and liquid hydrogen chilldown has been paused, too.

1611 GMT (11:11 a.m. EST)

The launch team is looking at a problem. They will hold off loading liquid oxygen and liquid hydrogen into the rocket while troubleshooting occurs.

1604 GMT (11:04 a.m. EST)

With the Common Booster Cores' liquid oxygen systems properly conditioned for cryogenic temperatures, the loading of Minus-298 degree LOX into the Delta 4-Heavy rocket is about to begin. The liquid oxygen tanks in all three Common Booster Cores will be filled over the next hour or so. The oxidizer will be consumed by the RS-68 main engines during launch.

1551 GMT (10:51 a.m. EST)

The liquid oxygen chilldown is starting in advance of feeding the cryogenic oxidizer into the Delta 4-Heavy rocket this morning. Also, the cold gas chilldown conditioning of the Common Booster Cores for liquid hydrogen fueling is beginning.

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

Officials have given a "go" for fueling operations. The launch team will start thermal conditioning steps to ready equipment for pumping the super-cold liquid oxygen and liquid hydrogen propellants into the Delta 4-Heavy rocket today. Loading of liquid oxygen into the Common Booster Cores begins first.

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

The launch window opens in four hours. It is unclear if the target liftoff time will have to be adjusted because of the delays experienced this morning.

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

The launch pad has been verified clear of all workers.

1529 GMT (10:29 a.m. EST)

Propellant pre-loading preps are starting as a precursor to fueling the Delta 4-Heavy rocket.

1521 GMT (10:21 a.m. EST)

Technicians report the troubleshooting efforts involving the engine cooling water system has been completed and the crew is preparing to leave launch pad 37B. This should permit countdown activities to get underway again after a delay this morning.

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

There is no further update available at this time. Fueling has been delayed this morning while engineers work to resolve a technical problem at pad 37B. We'll continue to post additional information as it becomes available.

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

A Boeing spokesman says this glitch involves the pad's cooling system and it should be corrected shortly.

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

The troubleshooting crew continues its work at pad 37B to resolve a system problem. The glitch has been isolated, the team reports, and further measures to examine some equipment is underway.

1406 GMT (9:06 a.m. EST)

T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has commenced for this inaugural launch of the Delta 4-Heavy rocket. With one planned hold at T-minus 5 minutes, liftoff is still targeted for 2:36 p.m. EST. The launch window extends two hours and 55 minutes, meaning liftoff could occur as late as 5:31 p.m. EST today.

The multi-step process of loading all eight cryogenic propellant tanks in the rocket was scheduled to begin in the next half hour. However, those operations will be placed on hold until a problem is resolved at the launch pad and the troubleshooting team has cleared the hazard area around Complex 37.

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

A crew is at the launch pad troubleshooting a technical issue. The countdown will resume ticking at the end of this hold as planned. However, fueling cannot start until the pad is cleared of all workers.

1352 GMT (8:52 a.m. EST)

The Boeing launch conductor has just completed a poll of the various launch team members to ensure everyone is ready to begin Terminal Count at the end of this built-in hold.

About 14 minutes remain in this planned hold.

1340 GMT (8:40 a.m. EST)

Launch weather officer Kathy Winters is providing management with a briefing on the forecast in advance of the go/no go decision to begin fueling the Delta 4-Heavy rocket. There continues to be a 90 percent chance of good conditions today. The only slight concern is ground-level winds.

Winds are currently 12 knots and the temperatures have warmed to 51 degrees.

The launch time forecast calls for scattered clouds at 4,000 feet, 10 miles visibility, easterly winds at 8 gusting to 12 knots and a temperature of 63 degrees F.

The wind limit at launch time is 16 knots for the particular direction expected this afternoon. That assures safety of the rocket as it climbs off the pad.

1306 GMT (8:06 a.m. EST)

T-minus 5 hours, 15 minutes and holding. Countdown clocks are entering a planned one-hour hold in today's launch operation at Cape Canaveral's Complex 37. During this hold, the full launch team will be seated at their consoles, the launch pad will be verified clear of workers and readiness polls will be conducted by mission management to ensure everyone is ready to proceed with the count.

The Terminal Countdown begins when the clocks resume ticking at 9:06 a.m. EST.

1248 GMT (7:48 a.m. EST)

The hold-fire checks are underway. This test verifies safety personnel can halt the countdown if a problem arises.

1236 GMT (7:36 a.m. EST)

Countdown is entering the final seven hours to liftoff time. The launch team is beginning propellant system preparations in advance of fueling the rocket, which is scheduled to start later this morning.

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

Launch day has arrived for the Delta 4-Heavy rocket. The sun is rising at chilly Cape Canaveral as the countdown gets underway for today's planned 2:36 p.m. EST (1936 GMT) liftoff. The mobile service tower has been retracted from around the rocket and pre-launch preps are continuing at pad 37B.

MONDAY, DECEMBER 20, 2004

The maiden flight of Boeing's Delta 4-Heavy rocket is set to occur Tuesday at 2:36 p.m. EST (1936 GMT) from Cape Canaveral, Florida. The day's available window for liftoff extends nearly three hours. Weather forecasters predict a 90 percent of favorable conditions.

Here is a full preview of the countdown, originally written for the first launch attempt but now updated to reflect tomorrow's liftoff time.

Workers pulling night-owl duty will begin countdown activities in the predawn hours Tuesday, prepping the debut Delta 4-Heavy rocket, its Cape launch site and ground systems for fueling and liftoff.

The 33-story mobile service tower enclosing the rocket at pad 37B is scheduled for retraction before sunrise as the 9-million pound structure is wheeled 100 yards away from the Delta booster's launch mount.

Clearing the pad of all personnel happens at 8:06 a.m. EST as the countdown clocks enter a 60-minute planned hold. During this pause, the Boeing and Air Force management teams will conduct a series of polls to ensure all systems are ready to start the Terminal Countdown and begin loading super-cold cryogenic propellants into the rocket. Terminal Count starts at 9:06 a.m. EST from the T-minus 5-hour, 15-minute mark.

Fueling operations commence with the "chill down" thermal conditioning of the liquid oxygen systems on the three Common Booster Cores at 9:36 a.m. Once that prep work is completed, the liquid oxygen tanks in each CBC will be filled with the Minus-298 degree Fahrenheit oxidizer.

Liquid hydrogen fueling of the CBCs starts with cold gas chilldown at about 9:40 a.m. Loading of the rocket's fuel tanks with the Minus-423 degrees Fahrenheit propellant should start around 10:30 a.m. with the "slow fill" mode before transitioning later to "fast fill."

Chilling of the upper stage's liquid oxygen and liquid hydrogen systems will start shortly after 11 a.m. The liquid oxygen tank is scheduled to be loaded first, starting around 11:25 a.m. Hydrogen fill will start around 11:35 a.m.

Complex 37 has two giant sphere-shaped fuel tanks to store the cryogenic liquid oxygen and liquid hydrogen. The LOX tank holds 250,000 gallons and LH2 sphere about 850,000 gallons.

The cryogenics are fed from the storage tanks through pipelines to the pad. For the three Common Booster Cores, the propellants are routed up to the launch table upon which the rocket sits. Tail service masts, the large box-like structures at the base of the vehicle, feed the oxygen and hydrogen to the boosters via separate umbilicals. The upper stage receives its cryos from the middle swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

Once the rocket is fueled up, all eight cryogenic tanks in the CBCs and upper stage will be topped off through the final minutes of the count to replace the cryogenics that naturally boil away.

A series of engine nozzle motion checks occur at about 1:20 p.m. These "slew" tests ensure the engines will provide good steering for the rocket's ascent. Range Safety conducts tests of the command receiver decoders a half-hour later. This system would be used to destroy the vehicle if it veered off course during launch.

At 2:16 p.m., the countdown enters a planned 15-minute hold at the T-minus 5 minute mark. This offers managers a chance to perform final readiness polls of the entire launch team to verify there are no issues or concerns before entering the last phase of the countdown.

Assuming all systems are go, clocks will resume ticking at 2:31 p.m. During those final five minutes, the rocket will switch to internal power, ordnance will be armed, all eight cryogenic tanks will be secured and the Range will announce a clear-to-launch.

At T-minus 13.5 seconds, the sparkler-like radial outward firing ignitors -- or ROFIs -- are started beneath the main engine nozzles. The Terminal Countdown Sequencer will grab control at T-minus 8.5 seconds to manage events in the crucial last seconds and oversee the rocket's status. The ignition sequence for the three RS-68 powerplants follows at T-minus 5.5 seconds as the main hydrogen fuel valve in each engine is opened. As fuel floods through the engines, spectacular flame erupts at the base of the rocket as free hydrogen reaches the ROFIs.

"As that hydrogen makes it through the engine and hits those sparks, you are going to see the flame rise along the side of the rocket," said Dan Collins, the Boeing vice president of expendable launch systems.

The oxygen valves in the engines are opened at T-minus 2 seconds as the RS-68s begin roaring to life. The engines must rev up to full throttle -- 102 percent thrust level -- and undergo a rapid computer-controlled health check to ensure all parameters are met.

"If (the control sequencer) determines all three RS-68s, as well as the rest of the vehicle is in good health, at T-0 it will send the signal to release the hold-down bolts and the rocket will take off. There is a very short period of time where the rocket is under full thrust, being monitored for health, before we let it go."

If any problem is detected before T-minus 40 milliseconds, the engines will shut down and the liftoff aborted, Collins said.

A successful engine startup leads to T-0 as the 12 hold-down bolts that have been restraining the rocket to Earth finally detonate. The 23-story, 1.6-million pound vehicle blasts off at 2:36 p.m. EST (1931 GMT) to begin the maiden voyage of Boeing's Delta 4-Heavy rocket on its qualification flight.

"It will clear the tower in about the same amount of time as the (Delta 4) Medium vehicle did -- somewhere a little quicker than 20 seconds, but not a lot. In the Delta 4 family, the Medium vehicle and the Heavy -- so the ones without solid rocket motors -- tend to rise at about the same rate. They have essentially the same thrust-to-weight ratios," Collins said.

The slow-rising rocket's trajectory, coupled with conservatism for this first flight, resulted in an unusually large hazard area covering Cape Canaveral Air Force Station. Virtually the entire base will be evacuated Tuesday morning except for 437 mission-critical personnel, said Col. Mark Owen, the 45th Space Wing commander at Cape Canaveral.

"It is prudent to make sure the public safety is well taken care of. And I think what the Range has done is right in line with good engineering practice," Collins said.

Watch this page for live updates throughout the countdown and flight.

SUNDAY, DECEMBER 19, 2004

Meteorologists have issued their latest weather forecast for Tuesday's planned launch of the Delta 4-Heavy rocket. The forecast is available here.

SATURDAY, DECEMBER 18, 2004

The delayed launch of Boeing's inaugural Delta 4-Heavy rocket has been rescheduled for Tuesday afternoon from Cape Canaveral Air Force Station, Florida. Attempts a week ago were scrubbed by weather and technical troubles.

Liftoff is scheduled for 2:36 p.m. EST (1936 GMT) at the opening of a two-hour, 55-minute window extending to 5:31 p.m. EST (2231 GMT).

The weather outlook calls for near-perfect conditions. See the forecast here.

Boeing has a backup launch opportunity on Wednesday, if needed, with a window of 2:36 to 5:32 p.m. EST.

The big booster will carry a satellite payload mockup during this demonstration flight.

SUNDAY, DECEMBER 12, 2004

Equipment problems and scheduling conflicts with a rival rocket have combined to keep Boeing's Delta 4-Heavy booster grounded on its Cape Canaveral launch pad until sometime next week.

The 235-foot tall rocket has missed three consecutive launch opportunities to fly its demonstration mission. Friday's shot was spoiled by gloomy weather, trouble with the master sequencer that controls the final seconds of the countdown stopped the flight Saturday and problems with the environmental control system prevented an attempt Sunday.

Boeing was preserving the hope of trying again Monday, which was the last realistic chance of scheduling the launch ahead of a commercial Lockheed Martin Atlas 5 rocket flight slated for this Friday from the Cape. But by Sunday evening, Boeing officials acknowledged that the Delta 4 would have a longer wait.

All launches from the spaceport require tracking, safety and communications services from the Air Force-controlled Eastern Range. The vast network needs time between launches of different rockets to reset its equipment and computer systems. As a result, the Delta 4-Heavy is forced to take the next available slot on the Range, which is on or about Tuesday, December 21. The exact date will be determined by when the Atlas goes and the Range turnaround.

The Atlas 5 will carry the AMERICOM 16 communications satellite into orbit during an early-morning ascent from Complex 41. Liftoff is targeted for 4:41 a.m. EST (0941 GMT). Lockheed Martin has a backup date reserved on the Range for next Saturday, if needed. (See our coverage of that launch here)

The main objective of Delta 4-Heavy's test flight is proving the extremely complex rocket works as advertised in preparation for its upcoming operational launches for the U.S. government. The Air Force awarded Boeing a $141 million contract to complete the qualification flight.

The demonstration mission carries an instrumented satellite mockup that will be deployed into geosynchronous orbit nearly six hours after liftoff. Two university nanosats hitching a ride on the dummy satellite are supposed to be ejected in low-Earth orbit about 16 minutes into flight.

If all goes well, the government plans to accomplish two operational Delta 4-Heavy mission next year -- the deployment of the final Defense Support Program missile-warning satellite in August and the launch of a classified National Reconnaissance Office payload in December.

The Delta 4-Heavy was developed under the Air Force's Evolved Expendable Launch Vehicle program. The EELV effort has created the Atlas 5 and Delta 4 next-generation rockets to provide military, scientific and commercial payloads reliable routes to space.

America's current heavy-lifting rocket, the heritage Titan 4, is being retired next year. That makes Delta 4-Heavy's debut even more critical to ensuring a way to launch the largest satellites.

"As we close a chapter on our Titan 4 program, the importance of this mission cannot be overstated in terms of assuring access to space for America's heavy-class payloads," said Col. Mark Owen, 45th Space Wing commander at Cape Canaveral.

2335 GMT (6:35 p.m. EST)

Launch of the Delta 4-Heavy rocket will not happen on Monday. Officials are tentatively targeting liftoff around December 21, which comes after the Lockheed Martin Atlas 5 rocket launch from the Cape. That commercial mission is scheduled for December 17. The Air Force-controlled Range requires some separation between launches of different rockets to reset tracking and communications equipment.

We'll post additional information as it becomes available.

2120 GMT (4:20 p.m. EST)

Troubleshooting efforts and engineering meetings are underway today to determine what caused a problem with the environmental control system for the Delta 4 rocket at launch pad 37B. Boeing says it will be this evening before a new launch date can be confirmed. The launch team is preserving the option of starting a new countdown Monday for liftoff at 2:32 p.m. EST (1932 GMT).

1637 GMT (11:37 a.m. EST)

Boeing has issued its post-scrub press statement, which provides additional details on the problem that caused today's launch postponement:

"During securing activities following yesterday's launch attempt, the environmental control system experienced a system outage. Engineers have not been able to determine the root cause of the outage. This has led mission management to decide to scrub today's attempt. This will allow the team to determine the root cause and execute any required corrective actions.

"The launch team is coordinating with the Range to determine the next available launch date."

1539 GMT (10:39 a.m. EST)

The launch team has just been informed that liftoff could be rescheduled for tomorrow. Although the Eastern Range currently is unavailable on Monday, efforts are underway to secure a reservation for liftoff at 2:32 p.m. EST. Team members were instructed to be ready for launch tomorrow if the Range can accommodate another countdown.

The Air Force-controlled Range provides tracking, safety and communications services to all Cape Canaveral launches.

1503 GMT (10:03 a.m. EST)

Problems with the environmental control system for the Delta 4-Heavy rocket at pad 37B have forced Boeing to scrub today's shot at launching the massive vehicle on its demonstration flight.

The situation prevented the countdown from proceeding into fueling operations this morning as workers wrestled with the problem. Engineers will spend the rest of today formulating plans to trace the root cause of the ECS failure, officials said.

A launch attempt on Monday is not an option. The launch team was instructed to perform an extended scrub turnaround procedure, not a 24-hour recycle of the countdown.

We will update this page as additional information becomes available.

1453 GMT (9:53 a.m. EST)

It is unclear when the next launch opportunity will be available. A try is not possible tomorrow.

1447 GMT (9:47 a.m. EST)

SCRUB! Today's countdown is being halted due to technical problems that cannot be resolved in time for launch this afternoon. Details to follow.

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

We've posted a photo gallery showing the Boeing Delta 4-Heavy rocket standing on Cape Canaveral's pad 37B in the predawn darkness December 12 awaiting another attempt at liftoff. See the photos here.

1402 GMT (9:02 a.m. EST)

T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has begun for today's shot at launching Boeing's Delta 4-Heavy rocket on its maiden voyage. With one planned hold at T-minus 5 minutes, liftoff is still targeted for 2:32 p.m. EST. The launch could occur as late as 5:28 p.m. EST today.

Engineers are working through some issues at the pad. Therefore, the countdown activities and fueling operations will be delayed until the launch complex is cleared.

1348 GMT (8:48 a.m. EST)

Members of the launch team have been polled to ensure all stations are manned and ready to begin Terminal Count at the end of this built-in hold. About 14 minutes remain in this planned hold.

1344 GMT (8:44 a.m. EST)

The launch team has completed this morning's activation of the vehicle avionics. Also, the C-band tracking beacon interrogation checks and data interrupt testing have been accomplished.

1333 GMT (8:33 a.m. EST)

The launch weather officer reports things are looking pretty good today. Winds were strong overnight, but they are trending downward this morning and should be below the 17-knot limit for launch. Also, high-altitude winds have eased since yesterday.

1302 GMT (8:02 a.m. EST)

T-minus 5 hours, 15 minutes and holding. Clocks have entered a planned 60-minute hold in today's launch operation at Cape Canaveral's Complex 37. The Terminal Countdown begins when the clocks resume ticking at 9:02 a.m. EST.

Since sunrise this morning, technicians have been working to power up the rocket's avionics, activating the guidance computer, completing pre-fueling preps and performing Range Safety hold-fire checks.

1150 GMT (6:40 a.m. EST)

A new countdown is underway this morning for the launch of Boeing's first Delta 4-Heavy rocket. The 23-story booster is scheduled for blastoff at 2:32 p.m. EST (1932 GMT) from Cape Canaveral, Florida. Poor weather cancelled Friday's launch opportunity and a glitch with the control sequencer scrubbed Saturday's try.

The vehicle stands atop pad 37B bathed in powerful flood lights. Following yesterday's scrub, the mobile service tower was left retracted in its launch position.

It is cold, crisp, clear morning here in Central Florida. The weather forecast is favorable today.

SATURDAY, DECEMBER 11, 2004
1950 GMT (2:50 p.m. EST)

The weather outlook for Sunday has improved to an 80 percent chance of favorable conditions.

"The upper-level trough over Florida today will move eastward off the coast tomorrow resulting in a decrease in winds both at the surface and at the upper levels. Cloud cover will also continue to decrease through Sunday. A slight concern remains for a violation of ground winds," the Air Force weather team reports.

1805 GMT (1:05 p.m. EST)

Today's maiden flight of the Boeing Delta 4-Heavy rocket was scrubbed because of trouble with the master sequencer that controls the crucial final seconds of the countdown.

As fueling operations got underway this morning at Cape Canaveral's pad 37B, engineers reported a problem with the Terminal Countdown Sequencer Rack computer system. Known as TCSR, this sequencer assumes control of the countdown at T-minus 8.5 seconds, overseeing ignition of the RS-68 main engines and verifying the Rocketdyne powerplants rev up to full throttle before committing the 1.6-million-pound vehicle to flight.

A 7-person troubleshooting crew was dispatched to the pad's telemetry room as officials hoped to resolve the problem. Loading of the rocket with super-cold liquid hydrogen and liquid oxygen was put on hold while the team worked at the pad.

After spending a couple of hours assessing the problem, the decision was made to postpone the mission until Sunday.

"At this time we would like to proceed with a scrub to today's operation," the Boeing launch director told the chief launch conductor. "The main activity for the rest of the day, of course, will be to address the problem at hand."

High-altitude winds and gusty surface winds were concerns during today's countdown, too.

Assuming the sequencer issue can fixed by Sunday, countdown clocks will start early tomorrow morning for a fresh launch attempt. Liftoff will be possible between 2:32 to 5:28 p.m. EST (1932-2228 GMT).

Air Force meteorologists predict a 70 percent chance of good weather during the window with just some scattered clouds at 3,000 feet, visibility of 10 miles, northwesterly winds from 300 degrees at 10 gusting to 15 knots and a temperature of 64 degrees F.

This inaugural Delta 4-Heavy rocket launch will loft an instrumented satellite mockup into geosynchronous orbit during a six-hour mission designed to demonstrate the complex booster operates correctly before two national security payloads are flown next year.

1748 GMT (12:48 p.m. EST)

The launch team is beginning scrub turnaround operations to prepare for another countdown tomorrow. Sunday's launch window extends from 2:32 to 5:28 p.m. EST. The weather forecast is much improved with a 70 percent chance of good conditions. Winds will be the only concern.

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

SCRUB! Today's launch attempt has been scrubbed due to the problem with the countdown sequencer.

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

It has been two hours since the countdown sequencer problem was first reported to the full launch team. At that time, loading of liquid oxygen into the rocket's three Common Booster Cores was getting underway. The issue prompted the team to delay further activities, including loading the CBC stages with liquid hydrogen fuel. Steps to load the upper stage with its liquid oxygen and liquid hydrogen also have not commenced.

A crew is currently at the pad troubleshooting the glitch. There is still no indication when the Delta 4-Heavy rocket will blast off from Cape Canaveral Air Force Station this afternoon. A lengthy launch window extends from 2:31 to 5:27 p.m. EST, giving a good deal of margin to compensate for this delay in the work timeline.

1712 GMT (12:12 p.m. EST)

The launch team continues to wait patiently for the TCSR issue to be resolved so that the countdown work can resume. The team is located in the Delta Operations Center located about two miles southwest of the launch pad.

1655 GMT (11:55 a.m. EST)

While the countdown clocks continue to tick, pre-launch activities and fueling of the Delta 4-Heavy rocket remain on hold. Engineers are trying to resolve a problem with the computer sequencer that serves as the master controller during the last 8.5 seconds of the countdown. A team is at pad 37B working on the system. There has been no estimate on how long this could take or what time the rocket will launch this afternoon. Liftoff is possible between 2:31 and 5:27 p.m. EST.

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

About two dozen photographers were taken to Complex 37 this morning to set up cameras around the pad. The rocket's roar during engine ignition will activate the specially-outfitted cameras to begin snapping pictures of the liftoff. See a collection of photos from this morning's event here.

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

The countdown is entering the final three hours. However, a 7-person crew has been dispatched to the telemetry room at pad 37B to troubleshoot a problem with the Terminal Countdown Sequencer Rack computer system. Dubbed TCSR, the sequencer controls the final 8.5 seconds of the countdown, including ignition of the three RS-68 main engines.

While this unscheduled troubleshooting is underway, fueling of the rocket has been delayed by more than an hour. There has been no official word on pushing the target launch time into today's nearly three-hour available launch opportunity.

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

The launch weather officer has given an update to management. There remains a 70 percent chance of breaking the rules governing launch weather due to pad winds gusting over 17 knots. A little earlier, the winds hit right at the limit but did not violate the constraint. Since then, the winds have decreased a bit. However, meteorologists are expecting the winds to pick up this afternoon.

Upper level winds are a key concern too.

Meanwhile, some clouds moving westward toward the coast are being watched. They could be a problem if they are deemed too thick for the rocket to fly through. But at this point the weather officer is not too concerned about these clouds.

The weather forecast for tomorrow is much improved and calls for a 70 percent of favorable conditions. Winds remain the issue.

1608 GMT (11:08 a.m. EST)

The team is reported en route pad 37B.

1552 GMT (10:52 a.m. EST)

The special crew is being sent into the launch pad to troubleshoot a technical problem. Fueling of the rocket will remain on hold until the problem is resolved and the launch complex is again cleared of all personnel. What impact this will have on today's launch time remains to be seen.

Officials have an exceptionally long launch window to work with this afternoon. Liftoff is possible between 2:31 and 5:27 p.m. EST.

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

We've posted a collection of pictures taken this morning showing the Delta 4-Heavy rocket on pad 37B following rollback of the mobile service tower. See the photos here.

1541 GMT (10:41 a.m. EST)

The launch team is forming plans to safe the rocket and send a team of engineers into the pad for troubleshooting steps.

1521 GMT (10:21 a.m. EST)

Liquid hydrogen chilldown continues. Technicians will hold off loading the Common Booster Cores with the propellant while engineers assess an issue with the Terminal Countdown Sequencer Rack (TCSR) that controls the final 8.5 seconds of the count.

1516 GMT (10:16 a.m. EST)

A check of the ground winds at the launch pad shows that conditions have gradually gotten breezier throughout the morning. Currently, the winds are right at the 17-knot limit imposed for liftoff. The forecast for this afternoon's launch window is 15 gusting to 25 knots.

1508 GMT (10:08 a.m. EST)

With the Common Booster Cores' liquid oxygen systems properly conditioned for cryogenic temperatures, the loading of Minus-298 degree LOX into the Delta 4-Heavy rocket is beginning. The liquid oxygen tanks in all three Common Booster Cores will be filled over the next hour or so. The oxidizer will be consumed by the RS-68 main engines during launch.

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

Time to launch is now four-and-a-half hours. The launch team is preparing to start pumping super-cold liquid oxygen and liquid hydrogen rocket fuel into the Delta 4-Heavy vehicle at pad 37B. Chilldown conditioning is underway. The countdown is continuing on schedule. However, gusty winds at the pad and strong high-altitude winds are still major worries today.

1441 GMT (9:41 a.m. EST)

The cold gas chilldown conditioning of the Common Booster Cores for liquid hydrogen fueling is starting as scheduled.

1432 GMT (9:32 a.m. EST)

The liquid oxygen chilldown is starting in advance of feeding the cryogenic oxidizer into the Delta 4-Heavy rocket this morning.

1421 GMT (9:21 a.m. EST)

Officials have given a "go" for fueling operations. The launch team will start thermal conditioning steps to ready equipment for pumping the super-cold liquid oxygen and liquid hydrogen propellants into the Delta 4-Heavy rocket today. Loading of liquid oxygen into the Common Booster Cores begins first.

1401 GMT (9:01 a.m. EST)

T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has commenced for this inaugural launch of the Delta 4-Heavy rocket. With one planned hold at T-minus 5 minutes, liftoff is still targeted for 2:31 p.m. EST, weather permitting. The launch could occur as late as 5:27 p.m. EST today.

Ground winds at the launch pad as well as upper-altitude winds are concerns today. But the launch attempt is moving forward in hopes that the weather cooperates. Fueling of the rocket begins in the next half hour.

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

The launch pad has been cleared of all workers, the rocket's avionics have been activated and the propellant pre-loading preps have been accomplished this morning.

1347 GMT (8:47 a.m. EST)

A poll of the various launch team members has been performed to ensure everyone is "ready" to begin Terminal Count at the end of this built-in hold. No issues were reported.

About 14 minutes remain in this planned hold.

1334 GMT (8:34 a.m. EST)

Launch weather officer Kathy Winters is providing management with a briefing on today's forecast. There continues to be a 70 percent chance of unfavorable conditions due to gusty winds.

The wind limit at launch time is 17 knots. That assures safety of the rocket as it climbs off the pad. Meteorologists are predicting winds of 15 gusting to 25 knots this afternoon, prompting the high odds of violating the launch weather rules.

1301 GMT (8:01 a.m. EST)

T-minus 5 hours, 15 minutes and holding. Countdown clocks are entering a planned one-hour hold in today's launch operation at Cape Canaveral's Complex 37. During this hold, the full launch team will be seated at their consoles, the launch pad will be verified clear of workers and readiness polls will be conducted by mission management to ensure everyone is ready to proceed with the count.

The Terminal Countdown begins when the clocks resume ticking at 9:01 a.m. EST.

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

The 330-foot tall mobile service tower has slowly rolled away from the Boeing Delta 4-Heavy rocket at Cape Canaveral's launch pad 37B in preparation for today's liftoff of the demonstration mission. Weather remains a concern for the 2:31 p.m. EST launch time, but officials have decided to make an attempt at getting this flight off the ground.

The wheeled mobile service structure moves along rail tracks to its launch position about the length of a football field from the rocket's mount.

The 9-million pound tower shields the Delta 4 from the weather, provides workers 360-degree access to the various areas on the vehicle and is needed to hoist the payload atop the upper stage during the launch campaign. The tower is 90-feet wide and 40-feet deep.

Once the tower is fully retracted, crews will secure the complex for launch before leaving the danger area around the pad. All workers must be clear of the area in preparation for the start of hazardous operations, including fueling the vehicle later this morning.

0955 GMT (4:55 a.m. EST)

Pre-launch activities are underway this morning for the countdown to liftoff. The mobile service tower is slated for retraction to the launch position. News media representatives are arriving at the Cape right now to cover the event.

0230 GMT (9:30 p.m. EST Fri.)

Boeing's inaugural Delta 4-Heavy rocket is scheduled to make its thunderous departure from Cape Canaveral's pad 37B at 2:31 p.m. EST (1931 GMT) Saturday while riding 1.9-million pounds of fiery thrust generated by its three hydrogen-fueled engines.

But worries about the weather are hanging over the countdown. A cold front slowly sliding through Central Florida has bought extensive cloud cover, rain and gusty winds. The weather team predicts a 70 percent chance that conditions will prohibit liftoff during Saturday's 2:31 to 5:27 p.m. EST launch opportunity.

Mission managers were scheduled to receive a weather update at 2:30 a.m. EST to decide whether to press ahead with the countdown. Assuming officials give the "go" to proceed, rollback of the mobile service tower from around the rocket -- leaving the 23-story vehicle fully exposed to the weather -- occurs before sunrise.

The Terminal Countdown starts at 9:01 a.m. EST. Fueling of the rocket's eight cryogenic liquid hydrogen and liquid oxygen tanks begins a half-hour later. A full preview of the countdown is available here.

We will be posting live updates throughout the countdown and launch. Watch this page for the latest!

FRIDAY, DECEMBER 10, 2004
1700 GMT (12:00 p.m. EST)

Work is proceeding to tomorrow's attempt to launch the Delta 4-Heavy rocket despite the gloomy weather forecast. Boeing says senior managers will be receiving weather updates later today and again at 2:30 a.m. EST tomorrow morning in advance of mobile service tower rollback. Officials could scrub the launch if there appears to be no hope that the weather will cooperate. Otherwise, the launch remains on schedule for 2:31 p.m. EST.

Watch this page for continuing updates.

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

Today's version of the launch weather forecast has increased the odds of unacceptable conditions tomorrow. The previous forecast had predicted a 60 percent chance of violating the launch weather rules. This updated outlook says there is a 70 percent chance due to gusty winds and thick cloud cover. Sunday and Monday have much better weather expected. See the full forecast here.

0530 GMT (12:30 a.m. EST)

America's new heavy-lifting rocket takes its much-anticipated test flight Saturday, if Mother Nature cooperates. The Boeing Delta 4-Heavy rocket was supposed to launch today, but the forecast for strong winds and stormy weather at Cape Canaveral postponed the liftoff by 24 hours. Read our full story.

Workers pulling night-owl duty will begin countdown activities in the predawn hours Saturday, prepping the debut Delta 4-Heavy rocket, its Cape launch site and ground systems for fueling and liftoff. Read our countdown preview.

THURSDAY, DECEMBER 9, 2004
1940 GMT (2:40 p.m. EST)

The forecast of strong winds blowing through Cape Canaveral on Friday has forced officials to forego making an attempt to launch the inaugural Boeing Delta 4-Heavy rocket on its demonstration flight. Read our full story.

1622 GMT (11:22 a.m. EST)

SCRUB! The poor weather forecast has prompted Boeing to cancel plans to launch the Delta 4-Heavy rocket on Friday. Liftoff is rescheduled for Saturday at 2:31 p.m. EST.

The pre-launch news conference has just begun. We will post additional details shortly.

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

Today's updated weather forecast shows even more worries for tomorrow's launch attempt. The new outlook gives just a 30 percent chance of acceptable conditions due to the threat of strong winds, clouds, rain and lightning. See the full forecast here.

A pre-launch news conference is coming up at 11 a.m. EST. We'll post a full update and preview the countdown following the event. Watch this page for updates.

WEDNESDAY, DECEMBER 8, 2004

The weather outlook for Friday continues to worsen a bit. There is now only a 40 percent chance of acceptable weather for launch during the 2:31 to 5:27 p.m. EST window. See the full forecast here.

TUESDAY, DECEMBER 7, 2004

Air Force meteorologists have worsened the odds -- albeit slightly -- for acceptable weather on Friday. There is now a 60 percent chance of meeting the launch rules. The 40 percent chance of violation involves ground winds, rain in the rocket's flight path and cumulus clouds. See the full forecast here.

MONDAY, DECEMBER 6, 2004

Boeing and the U.S. Air Force continue plans to launch the inaugural Delta 4-Heavy rocket on Friday from Cape Canaveral. A Boeing spokesman says everything "looks good" for the liftoff.

The weather forecast calls for generally favorable conditions for launch during the nearly three-hour window. See the full forecast here.

WEDNESDAY, NOVEMBER 24, 2004

Launch of the first Boeing Delta 4-Heavy rocket is scheduled to occur December 10 from pad 37B at Cape Canaveral, Florida. Liftoff will be possible between 2:31 and 5:27 p.m. EST (1931-2227 GMT). We will provide comprehensive coverage of the launch.

SUNDAY, OCTOBER 31, 2004

Delta 4-Heavy launch date depends on data review
The Boeing Company is beginning an exhaustive review of testing records and data that will determine when the inaugural Delta 4-Heavy rocket will be given clearance for blastoff from Cape Canaveral, Florida. Read our full story.

Throughout this year's on-pad testing sequence, officials have focused on three key challenges created by the Delta 4-Heavy and its trio of Common Booster Cores that generate the 1.9 million pounds of thrust to propel the 23-story rocket off the launch pad. Read our full story.

SUNDAY, OCTOBER 10, 2004

The debut launch of Boeing's Delta 4-Heavy rocket has been rescheduled due to Florida's hurricane troubles this summer and three technical issues, company officials announced. Read our full story.

Additional coverage for subscribers:
VIDEO: ANIMATION PROVIDES PREVIEW OF DELTA 4-HEAVY LAUNCH QT
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