BY JUSTIN RAY

Follow the countdown and launch of the Boeing Delta 2-Heavy rocket with NASA's MESSENGER probe that will orbit Mercury. Reload this page for the very latest on the mission.

0608 GMT (2:08 a.m. EDT)

Boeing mission director Rich Murphy has received an update from weather officer Joel Tumbiolo. The situation does not look good for a launch this morning. Managers are discussing how to proceed.

0607 GMT (2:07 a.m. EDT)

A second weather rule is now being broken. Both the anvil and thick cloud rules are being violated.

0605 GMT (2:05 a.m. EDT)

The NASA management team has verified its readiness for launch, pending resolution of the weather problems. The anvil cloud rule is still being violated.

0602 GMT (2:02 a.m. EDT)

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for today's launch attempt. During this planned 10-minute hold, officials will poll the various team members in the soft blockhouse, Range Operations Control Center and Mission Directors Center.

The weather conditions are the key problem this morning. If the situation should improve, the countdown will resume for liftoff at 2:16 a.m. EDT.

0600 GMT (2:00 a.m. EDT)

The launch weather officer reports that conditions remain "no go" for liftoff today due to anvil clouds over the Cape.

0556 GMT (1:56 a.m. EDT)

Initial word from the weather aircraft on the anvil clouds is not positive, NASA launch manager Chuck Dovale says. However, official information is upcoming in another weather briefing at T-minus 6 minutes.

0553 GMT (1:53 a.m. EDT)

Inhibited checks are underway for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course and malfunction during the launch.

0546 GMT (1:46 a.m. EDT)

T-minus 20 minutes and counting. The planned hold in the countdown has been released. Clocks will proceed to T-minus 4 minutes where the final hold is planned, lasting for 10 minutes.

0542 GMT (1:42 a.m. EDT)

The Goldstone tracking station in California has reported it is ready to acquire MESSENGER's signal following deployment from the Delta rocket later this morning.

0542 GMT (1:42 a.m. EDT)

The launch crew has voiced its readiness to press on with the countdown as scheduled.

0539 GMT (1:39 a.m. EDT)

The NASA management team has been polled by the space agency's launch manager, Chuck Dovale, for approval to continue the countdown. Aside from the weather concerns, there are no technical issues with the Delta rocket or MESSENGER spacecraft this morning.

The Boeing launch team will be polled in the next few minutes before clocks resume ticking.

0536 GMT (1:36 a.m. EDT)

Now half-way through this built-in hold at T-minus 20 minutes.

Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.

0530 GMT (1:30 a.m. EDT)

Launch weather officer Joel Tumbiolo is telling mission managers that the weather reconnaissance aircraft is flying at an altitude of 30,000 feet. However, the plane needs to get up to 35,000 or 40,000 feet to get the information needed on the anvil clouds. So there is no additional information on the anvil cloud situation at this time.

The weather team is awaiting clearance for the aircraft to ascend higher.

0528 GMT (1:28 a.m. EDT)

Radio frequency link checks with the Delta 2 rocket's second stage were just performed.

0526 GMT (1:26 a.m. EDT)

T-minus 20 minutes and holding. The countdown has entered the 20-minute built-in hold. This pause is designed to give the launch team a chance to work any problems or catch up on activities that might be running behind schedule. Engineers will also have time to examine all the data from the just-completed steering tests.

Launch remains targeted for 2:16:11 a.m. EDT at the opening of a 12-second window from pad 17B at Cape Canaveral Air Force Station, Florida.

0523 GMT (1:23 a.m. EDT)

The first stage steering tests are finished.

Meanwhile, the anvil cloud rule continues to be violated. The clouds from Tropical Storm Alex northeast of the launch site have drifted down to cover Cape Canaveral. Meteorologists are examining the clouds to determine if the Delta 2 rocket can launch safely this morning. The anvils cause worry due to the potential for triggered lightning as the rocket powers through the clouds.

0519 GMT (1:19 a.m. EDT)

The second stage engine checks have been completed.

0516 GMT (1:16 a.m. EDT)

Liftoff is now 60 minutes away, weather permitting.

The launch team is about to begin the "slew" or steering checks of the first and second stage engines. These are gimbal tests of the nozzles on the first stage main engine and twin vernier engines and second stage engine to ensure the rocket will be able to steer itself during launch.

0502 GMT (1:02 a.m. EDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been completed. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels last week. The nine strap-on boosters and third stage are solid-propellant.

0453 GMT (12:53 a.m. EDT)

Cryogenic tanking of the Delta rocket's first stage continues without any reports of problems. Once the liquid oxygen tank reaches the 95 percent full level, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the tank.

0446 GMT (12:46 a.m. EDT)

The countdown is entering the final 90 minutes to launch. The weather is the only problem being reported at this point. Clouds extending from Tropical Storm Alex located off shore could pose a constraint for launch this morning.

0443 GMT (12:43 a.m. EDT)

Liquid oxygen loading has passed the 10-minute mark. The bottom of the Boeing Delta 2 rocket is icing over as the super-cold liquid oxygen continues to flow into the first stage.

0433 GMT (12:33 a.m. EDT)

Super-cold liquid oxygen is flowing into the first stage of the Boeing Delta 2 rocket as the countdown continues for today's 2:16 a.m. EDT launch.

The liquid oxygen, chilled to Minus-298 degrees F, is being pumped from a storage tank at pad 17B, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel -- loaded aboard the vehicle in the past hour -- will be consumed by the first stage main engine.

0427 GMT (12:27 a.m. EDT)

The launch team has completed work to turn on and configure the Delta's onboard guidance computer -- called the Redundant Inertial Flight Control Assembly, or RIFCA.

0426 GMT (12:26 a.m. EDT)

Preparations for liquid oxygen loading operations are beginning as scheduled this morning.

0421 GMT (12:21 a.m. EDT)

NASA launch manager Chuck Dovale has just polled the space agency team for a "go" to begin liquid oxygen loading. No problems are being reported with the Delta rocket, MESSENGER spacecraft or ground equipment.

However, weather conditions have just gone "red" due to anvil clouds from Tropical Storm Alex. But the weather officials are awaiting information from a reconnaissance plane to determine the extent of the cloud situation.

0414 GMT (12:14 a.m. EDT)

The launch weather officer just provided a detailed briefing to the management team in advance of loading liquid oxygen into the Delta 2 rocket's first stage. There is still a 70 percent chance of good weather for today's launch opportunity. All weather rules are currently "go."

The concern for launch time is clouds associated with the outflow from Tropical Storm Alex located northeast of Central Florida. The weather team will be watching thunderstorm clouds on the southern fringe of the storm system that could drift too close to Cape Canaveral to permit a safe liftoff of the Delta rocket. A weather reconnaissance aircraft will be taking off at 12:30 a.m. EDT to evaluate the clouds through the countdown.

0406 GMT (12:06 a.m. EDT)

The countdown is proceeding on schedule at Cape Canaveral. There are no technical problems being worked. A weather briefing for managers is upcoming about five minutes.

0401 GMT (12:01 a.m. EDT)

The first stage fuel tank of the Boeing Delta 2 rocket has been fully loaded for today's planned 2:16 a.m. EDT launch. The tank was filled with a highly refined kerosene, called RP-1, during an 18-minute, 49-second process that concluded at 12:00:36 a.m. EDT.

The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage.

0355 GMT (11:55 p.m. EDT Sun.)

The launch team has computed that the full load for the first stage fuel tank is 9,949 gallons.

Once the tank is filled to 98 percent, or 9,750 the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

0351 GMT (11:51 p.m. EDT Sun.)

Now 10 minutes into this 20-minute process to load the rocket's first stage with kerosene fuel. Some 6,000 gallons have been loaded to this point.

The propellant will be used along with liquid oxygen -- to be pumped into the rocket a little later -- by the first stage Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

0341 GMT (11:41 p.m. EDT Sun.)

Fueling of the Delta 2 rocket's first stage has begun for tonight's launch. About 10,000 gallons of a highly refined kerosene propellant, called RP-1, are being pumped into the base of the rocket from a storage tank at pad 17B.

0336 GMT (11:36 p.m. EDT Sun.)

Boeing technicians are starting preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank. After verifying valves, sensors, flow meters and equipment are ready, the highly refined kerosene fuel will start flowing into the vehicle.

0318 GMT (11:18 p.m. EDT Sun.)

The launch team has been given approval to begin guidance system turn on.

0316 GMT (11:16 p.m. EDT Sun.)

T-minus 150 minutes and counting. The Terminal Countdown is now underway tonight's launch of the Boeing-built Delta 2-Heavy rocket and NASA's Mercury orbiter known as MESSENGER.

The next three hours will be spent fueling the rocket, activating systems and performing final testing before liftoff at 2:16 a.m. EDT (0616 GMT) from pad 17B at Cape Canaveral Air Force Station in Florida.

The Complex 17B area is verified cleared of workers. A warning horn will be sounded three times at the seaside complex as a precaution to alert any remaining personnel in the vicinity that they should leave immediately.

The pad clear status will allow the start of hazardous operations such as the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown currently stands at T-minus 150 minutes. However, there are a pair of holds planned at T-minus 20 minutes and T-minus 4 minutes totaling 30 minutes in duration.

Boeing officials say there are no constraints being addressed at this time and the weather outlook is still forecasting a 70 percent chance of good conditions for launch.

0307 GMT (11:07 p.m. EDT Sun.)

The launch team members have been polled for a "ready" status to resume the countdown as planned at the end of this hold. Clocks will start ticking again at 11:16 p.m. EDT as the Terminal Countdown begins.

0216 GMT (10:16 p.m. EDT Sun.)

T-minus 150 minutes and holding. Clocks are entering a planned 60-minute built-in hold in the countdown. Holds are scheduled to give workers a chance to catch up on any activities that may be running behind.

Over the next hour, all launch team members and management officials will be seated at their consoles. A series of polls will be conducted to verify everyone is ready tor enter Terminal Count at end of the built-in hold.

Liftoff of the Delta 2 rocket remains set for 2:16 a.m. EDT from pad 17B at Cape Canaveral, Florida.

0200 GMT (10:00 p.m. EDT Sun.)

The countdown is entering the final four hours to the launch of MESSENGER aboard a Delta 2 rocket. The space probe will begin its seven-year trip to Mercury with liftoff from Cape Canaveral at 2:16 a.m. EDT (0616 GMT), marking the first robotic expedition to the solar system's innermost planet since the mid-1970s.

"For nearly 30 years we've had questions that couldn't be answered until technology and mission designs caught up with our desire to go back to Mercury," said Sean Solomon, MESSENGER principal investigator. "Now we are ready. The answers to these questions will not only tell us more about Mercury, but illuminate processes that affect all the terrestrial planets."

"After launch and a long trip through the inner solar system, we still face the risky and difficult job of orbiting the planet next to the Sun," cautioned David Grant, MESSENGER project manager. "The team is confident that the spacecraft they designed, built and tested is ready for this journey and its mission to Mercury."

SUNDAY, AUGUST 1, 2004
2157 GMT (5:57 p.m. EDT)

The mobile service tower is currently being wheeled away from the Delta 2 rocket at pad 17B as countdown activities continue for tonight's launch of NASA's MESSENGER spacecraft to the planet Mercury.

The tower rollback was delayed a bit this afternoon due to concerns about bad weather in the local area.

Over the next couple of hours, workers will get the tower locked into its launch position, reconfigure the pad deck and exhaust ducts and then clear the hazard area. The Terminal Countdown is scheduled to begin at 11:16 p.m. EDT tonight for liftoff exactly three hours later.

2130 GMT (5:30 p.m. EDT)

The launch time weather forecast is still calling for a 70 percent chance of good conditions. You can see the full forecast here.

1830 GMT (2:30 p.m. EDT)

Stormy weather over Central Florida will delay rollback of the mobile service tower from around the Boeing Delta 2 rocket pad 17B this afternoon, NASA says.

The decision to keep the tower in position until later this evening was expected based upon the forecast for today. The tower retraction can be postponed several hours without delayng the scheduled launch time, Boeing says.

Liftoff is still targeted for 2:16 a.m. EDT (0616 GMT) Monday morning. Meteorologists say there is a 70 percent chance of acceptable conditions at launch time.

SATURDAY, JULY 31, 2004
1730 GMT (1:30 p.m. EDT)

The MESSENGER spacecraft's departure for its seven-year voyage to Mercury remains scheduled for blastoff at 2:16 a.m. EDT (0616 GMT) Monday aboard a Boeing Delta 2 rocket from Cape Canaveral, Florida.

"The launch team is extremely excited to get to this point," NASA launch director Chuck Dovale said today. "There is nothing more satisfying than exploration, particularly interplanetary exploration."

"MESSENGER is an extremely important mission because it is going to tell us something about the innermost planet of the solar system -- Mercury," said Ralph McNutt, the MESSENGER project scientist from Johns Hopkins University Applied Physics Laboratory. JHU-APL manages MESSENGER for NASA.

The little-explored Mercury has been visited just once before by the Mariner 10 spacecraft in the mid-1970s. The early probe made three rapid flybys of the planet, providing brief glimpses of the planet.

Thirty years later, MESSENGER is ready to launch on its $427 million mission that will place the craft into orbit around Mercury for detailed observations lasting a full Earth year.

"The most exciting thing about MESSENGER is we've never done it before. And when I say 'we' I mean all of humanity," McNutt said.

"Like Star Trek, it is going where no one has gone before. This is pushing the envelope of the technology. This is going out beyond the edge of scientific knowledge to find out what the undiscovered country is and the science out there. How can it not be exciting?"

Countdown activities at launch pad 17B will begin Sunday afternoon. A weather briefing is planned for 3 p.m. EDT (1900 GMT) to determine if conditions will permit retraction of the mobile service tower enclosing the Delta 2 rocket.

"Whenever you launch a vehicle during the middle of summer in Florida, there are always weather concerns. This mission will be no different," said launch weather officer Joel Tumbiolo.

Tower rollback is targeted to occur after 4 p.m. EDT (2000 GMT), but afternoon thunderstorms forecast for Sunday could delay the move. Kris Walsh, Boeing's director of NASA programs, said the retraction can be delayed three-to-four hours without impacting the launch time.

Once the mobile service tower is moved back, crews will get the structure secured in its launch position and button up the pad over the following couple of hours.

The Terminal Countdown commences at 11:16 p.m. EDT (0316 GMT). The launch team will start loading a highly refined kerosene propellant into the rocket's first stage at 11:36 p.m. EDT (0336 GMT). Filling of the first stage liquid oxygen tank will follow beginning at 12:31 a.m. EDT (0431 GMT).

The final hour of the countdown will be spent conducting engine steering tests, Range Safety checks and final arming. MESSENGER switches to internal power for launch about six minutes before liftoff time, while the Delta rocket's systems transition to battery power inside the final four minutes.

The count features a pair of built-in holds at T-minus 20 minutes and T-minus 4 minutes. The first will last 20 minutes; the second extends for 10 minutes.

Weather officials continue to predict a 70 percent chance of acceptable conditions during Monday's 12-second launch opportunity. Clouds and rain in the rocket's flight path are the concerns. See the full forecast here.

Watch this page for live play-by-play reports during the countdown and the hour-long flight by the Delta 2 rocket to dispatch MESSENGER on its five-billion-mile trek to Mercury.

FRIDAY, JULY 30, 2004
1500 GMT (11 a.m. EDT)

Air Force meteorologists continue to predict a 70 percent chance of good weather for Monday's launch attempt. You can see the full forecast here.

0430 GMT (12:30 a.m. EDT)

Taking the economy route, NASA's MESSENGER spacecraft will spend six-and-a-half years just getting to its target for at least one year of scientific observations. The 4.9-billion-mile marathon will require 15 trips around the sun, six trajectory-warping planetary flybys and another half-dozen critical rocket firings. Launch is set for early Monday from Cape Canaveral, Florida. This is our four-part, 4,000-word mission preview. Read the stories here.

THURSDAY, JULY 29, 2004

Today's edition of the launch weather forecast for Monday's liftoff of MESSENGER is available here.

WEDNESDAY, JULY 28, 2004

Final pre-flight activities are underway at Cape Canaveral Air Force Station's pad 17B for Monday's early morning liftoff of NASA's MESSENGER spacecraft aboard a Boeing Delta 2 rocket.

The long-range weather forecast is calling for a 70 percent chance of favorable conditions at the 2:16 a.m. EDT (0616 GMT) launch time. Clouds over the Florida launch site and rain in the rocket's flight path are the chief concerns. Read the full forecast here.

The two halves of the Delta rocket's nose cone were installed Tuesday, enclosing MESSENGER for its launch through Earth's atmosphere. Final securing of the shroud is underway today. The fairing will be jettisoned about five minutes after liftoff.

The Flight Readiness Review is scheduled for Thursday. That meeting will give approval to continue with launch preparations, including the loading of storable hypergolic propellants into the rocket's second stage on Friday.

Saturday will be spent conducting steering system testing and Range Safety beacon checks.

WEDNESDAY, JULY 21, 2004

NASA's MESSENGER space probe took a night owl drive early Wednesday from its processing hangar to launch pad 17B at Cape Canaveral where it was mounted atop the Boeing Delta 2-Heavy rocket in preparation for blastoff to the planet Mercury.

"MESSENGER, riding atop its spacecraft transporter, departed the Astrotech Space Operations facilities in Titusville at 12:27 a.m.," NASA said in a status report. "It arrived at pad 17B on Cape Canaveral Air Force Station at 4:30 a.m. and was hoisted atop the Boeing Delta 2 rocket at 6:20 a.m.

"The Flight Program Verification, an integrated test of the spacecraft/launch vehicle combination and the last major test before launch, is scheduled to occur on July 24."

Launch remains scheduled for August 2, and NASA says there are no technical issues or concerns with MESSENGER or the Delta 2 at this time. See the available launch windows in this chart.

MESSENGER has been undergoing final assembly and testing at Astrotech for several months. The solid-fueled motor that serves as the Delta rocket's third stage was attached to the satellite in the hangar on July 12. Workers then encapsulated the duo in the shipping container for Wednesday's move to the launch pad.

Stacking of the Delta 2 rocket at the pad started June 30 with the first stage being erected on the launch mount. Attachment of the nine strap-on solid rocket boosters in sets of three was completed July 6. The second stage was lifted into position atop the first stage on July 8.

According to NASA, the first "power-on" testing was completed on July 12. A vehicle control check was performed on July 14. This test procedure qualifies the first and second stage steering systems. A Simulated Flight (SimFlight) or flight test of the launch vehicle electrical and mechanical systems was completed on July 15. The first stage leak check, or LOX leak check, occurred on July 16 with the loading aboard of liquid oxygen. This test also exercises the first stage propulsion team using a procedure similar to that which will be during the countdown on launch day. On July 19, the first stage fuel system was then qualified by loading RP-1, a highly refined kerosene fuel.

TUESDAY, JUNE 29, 2004

Repeated delays in launching a Boeing Delta 2 rocket carrying a Global Positioning System satellite this month at Cape Canaveral have created a ripple effect by prompting NASA to postpone by three days the liftoff of the MESSENGER space probe to orbit Mercury.

The GPS mission flew from the same launch pad that MESSENGER must use, creating the schedule crunch. Technical troubles and then a stretch of bad weather kept the Air Force Delta 2 mission grounded for more than two weeks. It finally launched last Wednesday.

With pad 17B tied up with the GPS mission, workers were unable to begin erecting the Delta 2 rocket stages. The delays used up the slack in MESSENGER's pre-launch timeline, leaving no margin to deal with problems leading to a July 30 liftoff.

On Tuesday, NASA decided to move MESSENGER's target launch date to August 2.

"While the previous launch date of July 30 may have been achievable, the additional margin now being built into the schedule will provide greater confidence in meeting this new launch date," the space agency said in a statement.

"What we were trying to do is put a little bit of buffer in there," NASA spokesman George Diller said. "They just wanted a schedule that was more comfortable and more reliable for planning all of the support assets -- launch support, range, tracking, etc."

A 12-second launch window on August 2 opens at 2:16:11 a.m. EDT (0616:11 GMT).

Workers will drive the Delta rocket's first stage to pad 17B on Wednesday and hoist it atop the launch mount. The nine solid-fueled rocket boosters are scheduled for attachment in sets of three between July 1 and 6. The second stage will follow on July 8.

The MESSENGER satellite is undergoing its prelaunch testing and final assembly at the Astrotech Space Operations facilities near Kennedy Space Center. On Monday, it was moved to a hazardous processing facility in preparation for loading the spacecraft's complement of hypergolic propellants. Fueling was underway Tuesday and will conclude Thursday.

The spacecraft's two solar arrays were installed last week and a deployment test was conducted. Installation of thermal blankets continues. Spacecraft spin balance testing is planned for July 7.

The spacecraft Mission Readiness Review was completed on June 24 without any major issues remaining to be resolved.

MESSENGER must launch by August 13 or else wait until next summer before the next planetary alignment window opens.

In order to reach the solar system's innermost planet, MESSENGER will receive gravity-assisted sling-shot boosts by flying past Earth a year after launch, Venus in October 2006 and June 2007, then three flybys of Mercury in January and October 2008 and September 2009. The craft starts a year-long orbit of Mercury in March 2011 to map the planet and trace its geologic history.