BY SPACEFLIGHT NOW

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.

1558 GMT (11:58 a.m. EDT)

Hold-fire checks were just successfully conducted to verify the countdown can be halted if a problem arises.

1555 GMT (11:55 a.m. EDT)

The weather forecast for today predicts an 80 percent chance of acceptable conditions during the launch window. The two slight concerns will be anvil and cumulus clouds associated with inland thunderstorms moving within 10 miles of the launch pad and winds greater than the 14-knot liftoff limit.

The launch time conditions are expected to include some scattered low and high level clouds, thunderstorms to the west, good visibility, southeasterly winds from 120 degrees at 8 gusting to 12 knots, a temperature of 86-88 degrees F and relative humidity of 70-75 percent.

1533 GMT (11:33 a.m. EDT)

Pre-fueling operations are getting started at the pad, including pressurization system and final configuring of the pneumatics equipment at Complex 37.

1445 GMT (10:45 a.m. EDT)

A second attempt at launching the GOES-N weather spacecraft aboard the Delta 4 rocket is underway at Cape Canaveral Air Force Station today. Liftoff is set to occur at 6:32 p.m. EDT (2232 GMT).

The pressurization system concern that led to yesterday's scrub was reviewed by engineers last night and deemed not a problem for flight.

With liftoff less than 8 hours away, the launch team has started re-activating the rocket's avionics. At pad 37B, final securing work is continuing before crews clear the hazard area around the complex in the next hour or so.

Boeing says there are no problems being worked this morning.

0145 GMT (9:45 p.m. EDT Mon.)

Engineers have determined the pressure system is acceptable for flight and decided to proceed with another launch attempt on Tuesday, Boeing just announced.

"The launch team has closed out the issue," a spokesman said.

A fresh countdown will begin in the morning. Liftoff is targeted for 6:32 p.m. EDT.

0040 GMT (8:40 p.m. EDT Mon.)

"During pressure checks of the rocket's upper stage helium pressure bottles, the pressure fell below levels from previous Delta 4 missions. As a result, a decision was made to delay the launch to allow more time to understand the issue," Boeing said in a press release issued tonight.

"The launch team is meeting tonight to determine if another attempt can be made tomorrow. If so, tomorrow's launch window is 6:32 p.m. to 7:05 p.m. EDT."

MONDAY, AUGUST 15, 2005
2300 GMT (7:00 p.m. EDT)

Suspect readings from a pressurization system aboard the Boeing Delta 4 rocket prompted officials to scrub today's launch of the GOES-N weather observatory from Cape Canaveral, Florida.

The rocket's first and second stage fuel systems rely on this pressurization during launch, making it critical to a successful flight.

During today's otherwise smooth countdown, the launch team noted "abnormal readings" from the pressure system. A decision to scrub the launch attempt was made 46 minutes before blastoff time. Officials said there wasn't enough time to resolve the issue and still fly within the day's launch window.

The system uses helium, which is stored in pressure vessels on the second stage. Ironically, concerns about internal buckling of the vessels' metallic liner delayed the GOES-N launch earlier this year.

If engineers are able to quickly resolve the latest issue, another countdown will be started in the morning. Tuesday's launch window extends from 6:32 to 7:06 p.m. EDT (2232-2306 GMT).

"The launch team is performing an extensive evaluation this evening to determine the possibility of another launch attempt tomorrow," Boeing said in a post-scrub statement.

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 maneuver itself into a circular geostationary orbit 22,300 miles above the equator 11 days after launch. It will be thoroughly tested before entering an on-orbit storage mode to replace an aging U.S. weather satellite in the coming years.

2230 GMT (6:30 p.m. EDT)

The launch team is recycling the countdown for a 24-hour delay. The mobile service tower will be left in the launch position overnight given the safe weather outlook.

2210 GMT (6:10 p.m. EDT)

"NASA has chosen to scrub today's launch in order to evaluate launch vehicle gas bottles which experienced additional pressure cycles during today's countdown," Boeing spokesman Mike Woolley says. The launch team is preparing for another attempt tomorrow, if this issue can be put to rest in time.

2200 GMT (6:00 p.m. EDT)

This launch was delayed back in April because of concerns about the pressure vessels on the second stage. Technicians had to demate the stage on the launch pad to remove and replace the tanks due to concerns about an internal buckle in the vessels' metallic liner. The tanks provide helium pressure to the liquid oxygen and liquid hydrogen fuel systems on the Delta 4 rocket's first and second stages.

2147 GMT (5:47 p.m. EDT)

Today's launch attempt has been scrubbed to give engineers more time to complete an analysis on the composite-wrapped pressure tanks aboard the second stage of the Delta 4 rocket. This work cannot be completed in time to fly before the end of today's launch window. Another countdown is possible tomorrow, pending resolution of this problem.

2146 GMT (5:46 p.m. EDT)

SCRUB!

2143 GMT (5:43 p.m. EDT)

It appears a problem has developed. A scrub is possibly in the works, a Boeing spokesman says.

2142 GMT (5:42 p.m. EDT)

The first stage Common Booster Core slew tests have been finished, wrapping up this pre-launch program.

2135 GMT (5:35 p.m. EDT)

The second stage engine steering checks have been completed. The first stage tests are next.

2129 GMT (5:29 p.m. EDT)

The engine slew tests have begun -- starting with the second stage RL10 engine.

2128 GMT (5:28 p.m. EDT)

The team is now preparing to conduct the steering checks of the Delta 4 rocket's engines.

2127 GMT (5:27 p.m. EDT)

The RS-68 first stage main engine spin start pressurization operation is starting.

2120 GMT (5:20 p.m. EDT)

The Air Force-controlled Eastern Range has completed the inhibited command destruct receiver checks. This ensures safety personnel can destroy the Delta 4 rocket if it veers off course or experiences a major problem.

2110 GMT (5:10 p.m. EDT)

Health checks of the command receiver decoder devices on the rocket are underway. These units would hear the command from Range Safety and trigger the Delta 4's destruct system if a problem occurred during launch.

2102 GMT (5:02 p.m. EDT)

And we're now entering the last 90 minutes of the countdown. With fueling of the Delta 4 rocket completed and topping of all four tanks continuing normally, this phase of the count is mostly quiet. The launch team is monitoring systems and watching the clocks tick down. In a little while, the rocket's safety system will be checked and a series of engine steering tests will occur. Everything continues to proceed very well at Cape Canaveral for liftoff at 6:32 p.m. EDT.

2055 GMT (4:55 p.m. EDT)

The RF link checks between the rocket and ground have been completed and verified acceptable.

2053 GMT (4:53 p.m. EDT)

Telemetry RF link checks have started. The TEL-4 ground tracking station at the Cape will acquire the telemetry stream during this test to ensure good continuity for flight.

2049 GMT (4:49 p.m. EDT)

Using launch pad cameras, engineers have completed a check of the rocket's thermal insulation as planned with no problems reported.

2047 GMT (4:47 p.m. EDT)

Reporters and photographers are now gathering along the NASA Causeway at Cape Canaveral to cover today's launch.

2032 GMT (4:32 p.m. EDT)

Two hours to go.

2027 GMT (4:27 p.m. EDT)

The one Range radar site that had been down earlier is reported fixed and operational again. So everything is "go" for launch across the board right now.

2015 GMT (4:15 p.m. EDT)

Engineers are conducting the scheduled evaluation of the Delta 4 rocket's thermal insulation following the loading of supercold propellants into the vehicle.

The Range is working to resolve a problem with a tracking radar. Otherwise, there are no technical constraints being assessed on the Delta 4 rocket or GOES-N spacecraft. Weather conditions remain favorable.

2012 GMT (4:12 p.m. EDT)

The second stage liquid oxygen tank is now starting topping.

Fueling of the vehicle is basically complete. However, all four cryogenic propellant tanks on the Delta 4 will need to be replenished as the countdown continues to replace the fuels that boil off given their supercold nature.

2002 GMT (4:02 p.m. EDT)

Now passing Launch Minus-2 hours, 30 minutes and counting.

1953 GMT (3:53 p.m. EDT)

To recap, the first stage liquid oxygen and liquid hydrogen tanks are being topped off. The second stage oxygen remains in fast-fill and the hydrogen side is undergoing valve tests before shortly entering topping.

1953 GMT (3:53 p.m. EDT)

The first stage liquid hydrogen tank is now entering the topping phase.

1953 GMT (3:53 p.m. EDT)

We have posted a gallery of pictures taken earlier today when the mobile service tower was retracted from around the Delta 4 rocket. See the gallery here.

1950 GMT (3:50 p.m. EDT)

The second stage liquid hydrogen tank is now loaded. Checks will performed before topping commences.

1932 GMT (3:32 p.m. EDT)

Liftoff time is just three hours away now. All critical systems remain "go" for launch.

1917 GMT (3:17 p.m. EDT)

The second stage conditioning on the liquid hydrogen side has finished. Loading of the tank is commencing. This is the last of the rocket's four cryogenic supplies to be loaded in today's countdown to launch.

1916 GMT (3:16 p.m. EDT)

The first stage liquid hydrogen tank fast-fill just ended. Vent and relief checks are upcoming.

1910 GMT (3:10 p.m. EDT)

The first stage liquid oxygen tank is now being topped off.

1907 GMT (3:07 p.m. EDT)

The first stage's liquid hydrogen tank is over three-quarters full now.

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 tanks' large supplies should allow for at least three consecutive launch attempts before having to be replenished.

The cryogenics flow from the storage tanks, through pipes to the base of the pad. For the first stage, 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 stage in separate umbilicals. The second stage receives its cryos from the middle swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

1902 GMT (3:02 p.m. EDT)

The chilldown of the second stage liquid oxygen system is being completed, clearing the way for loading the vehicle's tank.

1852 GMT (2:52 p.m. EDT)

The launch team has been given approval to start chilldown conditioning of the upper stage liquid hydrogen system.

1846 GMT (2:46 p.m. EDT)

The first stage liquid oxygen loading just finished. The tank has been loaded with its supercold oxidizer that is chilled to Minus-298 degrees F.

The liquid oxygen chilldown for the rocket's second stage is now beginning in advance of filling that tank.

1842 GMT (2:42 p.m. EDT)

The fast-fill loading of liquid oxygen into the first stage is nearing completion. The launch team will be performing vent and relief checks following tanking and begin chilldown procedures for the upper stage liquid oxygen system.

1832 GMT (2:32 p.m. EDT)

Now four hours from launch. First stage fueling is going well. Second stage filling is coming up.

1824 GMT (2:24 p.m. EDT)

First stage liquid hydrogen tanking operation is transitioning from "slow-fill" to "fast-fill" mode.

1816 GMT (2:16 p.m. EDT)

Fueling of the Delta 4 rocket's first stage with cryogenic liquid oxygen and liquid hydrogen is underway at launch pad 37B. The launch team reports there are no technical concerns threatening today's planned 6:32 p.m. EDT liftoff of the GOES-N weather satellite.

1805 GMT (2:05 p.m. EDT)

The cold gas chilldown conditioning of the liquid hydrogen system has been accomplished. Liquid hydrogen propellant is beginning to flow into the first stage. This "slow-fill" will be sped up to "fast-fill" after a small portion of the tank is loaded.

Chilled to Minus-423 degrees Fahrenheit, the liquid hydrogen will be consumed by the RS-68 main engine along with liquid oxygen during the first four minutes, 27 seconds of the launch.

1755 GMT (1:55 p.m. EDT)

The first stage liquid oxygen loading in "slow-fill" mode is formally underway.

1744 GMT (1:44 p.m. EDT)

The first stage liquid oxygen chilldown is complete. Fueling will begin in the "slow-fill" mode to load a small percentage of the tank. Then the process will speed up to the "fast-fill" mode until the tank is nearly full.

1732 GMT (1:32 p.m. EDT)

Now inside the final five hours of the GOES-N launch countdown. The Boeing launch team is not reporting any technical problems with the Delta 4 rocket, the weather conditions are favorable and activities are tracking right on the timeline today. Launch time remains set for 6:32 p.m. EDT from Cape Canaveral Air Force Station, Florida.

1729 GMT (1:29 p.m. EDT)

A "go" has been given to start the cold gas chilldown conditioning of the first stage liquid hydrogen system.

1719 GMT (1:19 p.m. EDT)

Chilldown of the first stage liquid oxygen system is starting. This preps the tank and pumping to guard against shock with the supercold oxidizer begins flowing into the rocket a short time from now.

Meanwhile, pressurization of the helium storage bottles on the rocket is underway.

1702 GMT (1:02 p.m. EDT)

T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has begun for today's launch of the Boeing Delta 4 rocket with the Geostationary Operational Environmental Satellite-N (GOES-N). With one planned hold at T-minus 5 minutes, liftoff is still targeted to occur at 6:32 p.m. EDT.

The launch pad has been verified evacuated of all personnel in advance of fueling the rocket's two stages this afternoon.

1648 GMT (12:48 p.m. EDT)

The launch team has been polled to ensure all consoles are manned and ready to begin the Terminal Countdown when this hold ends at 1:02 p.m. A briefing on countdown procedures is now underway.

1617 GMT (12:17 p.m. EDT)

The Delta 4 rocket's avionics have been turned on and put through initial testing. Meanwhile, the chilldown thermal conditioning of the liquid oxygen pump in the propellant storage area of launch pad 37B is being performed.

1602 GMT (12:02 p.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 1:02 p.m. EDT, the Terminal Countdown phase of today's launch operation will begin.

1555 GMT (11:55 a.m. EDT)

Hold-fire checks are being conducted to verify the countdown can be stopped immediately if a problem arises. Launch preparations appear to be proceeding smoothly for liftoff at 6:32 p.m. EDT today.

1430 GMT (10:30 a.m. EDT)

At Complex 37, the Boeing launch team is busy with final pad closeouts and securing work following mobile service tower rollback earlier this morning. The hazard area around the pad is scheduled to be cleared of all personnel in the next hour or so as the countdown presses ahead. Also upcoming will be activation of the rocket's avionics.

1245 GMT (8:45 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 in preparation for today's liftoff to place the GOES-N weather satellite into Earth orbit.

At about 7:50 a.m. EDT, the wheeled structure began moving along its 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.

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 in preparation for the start of hazardous operations, including fueling the vehicle later this afternoon.

Liftoff remains scheduled for 6:32 p.m. EDT, the opening of a 34-minute window that extends to 7:06 p.m. EDT (2232-2306 GMT).

This fifth flight of Delta 4 has been delayed multiple times, pushing back its early May launch date to today because due to a series of rocket and payload issues. But officials say all of the problems have been resolved.

"We will launch no satellite before it's time. GOES-N is ready for launch," Steve Kirkner, GOES program manager at NOAA, told reporters at the pre-launch news conference this morning.

"The vehicle is ready to perform this mission," Delta 4 launch director Rick Navarro added.

Watch this page for live updates throughout the final hours of the countdown and tonight's flight.

SUNDAY, AUGUST 14, 2005
2015 GMT (4:15 p.m. EDT)

Mission managers gathered at Cape Canaveral for the launch readiness review this afternoon and gave final approval to begin the countdown Monday morning. The pre-flight meeting verified all systems are "go" for liftoff of the Boeing Delta 4 rocket carrying the GOES-N weather satellite, a company spokesman said.

The lingering issues with the spacecraft were put to rest and no significant problems are remaining with the rocket. The weather outlook calls for a 70 percent chance of acceptable conditions during the launch window of 6:32 to 7:06 p.m. EDT (2232-2306 GMT).

FRIDAY, AUGUST 12, 2005
2300 GMT (7:00 p.m. EDT)

Launch has been postponed to Monday. The window extends from 6:32 to 7:06 p.m. EDT (2232-2306 GMT).

FRIDAY, AUGUST 12, 2005

With NASA's newest Martian voyager now en route to the Red Planet, attention at the Cape now turns to Sunday's planned launch of a Delta 4 rocket of a next-generation weather satellite to bring home new images to be used by meteorologists in near-term forecasts.

The flight was delayed an additional day from Saturday to give this morning's Atlas 5 launch one more chance to begin Mars Reconnaissance Orbiter's journey.

The Delta 4 rocket, with a pair of strap-on solid rocket boosters to give an extra boost to orbit, has 34 minutes to get off the ground Sunday evening beginning at 6:31 p.m. EDT (2231 GMT).

Due to a power issue with the GOES-N payload, if the launch does not occur by Tuesday the satellite must wait until around October 8 for its next shot at space. GOES-N cannot launch in this timeframe because it is an eclipse period, meaning the craft's electricity-producing solar panels would not have enough sunlight to sufficiently charge its batteries during critical orbit-raising maneuvers and post-launch checkout.

Launch weather officer Joel Tumbiolo's forecast continues to show just a 30 percent chance of violating weather rules during launch opportunities Sunday and Monday. Overhanging anvils associated with distant thunderstorms that could trigger lightning during launch will be closely watched, along with puffy cumulus clouds and winds at launch complex 37's 54-foot level.

TUESDAY, AUGUST 9, 2005

DELAY. The launch of the GOES-N weather satellite has been pushed back another day due to continued pre-flight engineering reviews. Liftoff is now expected no sooner than Saturday evening during a window of 6:30 to 7:04 p.m. EDT.

NASA says the launch must occur by Sunday or else face waiting until October due to orbital lighting issues that would impact the satellite's early life in space.

Saturday's weather forecast calls for a 60 percent chance of acceptable conditions. Clouds and winds will be the chief concerns.

A backup launch opportunity is available Sunday evening. Better weather conditions are expected with a 70 percent chance of meeting the launch rules.

MONDAY, AUGUST 8, 2005

The Boeing launch team is pressing ahead with plans in advance of Friday's scheduled launch of the company's Delta 4 rocket on a weather satellite delivery mission, pending final approval of payload components that forced a delay two weeks ago.

The Delta 4 booster is slated to launch Friday at 6:29 p.m. EDT (2229 GMT) at the opening of a 35-minute window that closes at 7:04 p.m. EDT. It will take over four hours before the GOES-N weather observatory separates from the Delta 4 upper stage to begin its mission.

The rocket and satellite have been stuck on the launch pad for a couple of extra months as teams have battled problems with flight termination system batteries that would be used by Air Force safety officials to destroy the vehicle if something went awry during launch.

Once that issue was resolved, the planned July 29 liftoff was postponed to allow spacecraft engineers time to trace last-minute concerns with the payload.

"Boeing is working with NASA and NOAA to complete testing and analysis of several communications subsystem components to more thoroughly characterize their expected on-orbit performance," Boeing said in a statement.

GOES-N is the newest member of America's storied civil weather observation fleet in geostationary orbit, and its name will become GOES-13 after delivery in orbit.

The Air Force weather squadron has issued its forecast for Friday's countdown and launch attempt. It shows a 60 percent chance that conditions will prohibit a liftoff not only on Friday, but also over the weekend should Friday's attempt be called off.

"Vehicle exposure limits will be the main concern during the countdown," the outlook said. "Launch window concerns will be for thunderstorms and associated clouds within 10 nautical miles, and also for 54-foot level winds over 14 knots."

Predictions indicate skies will be littered with clouds with a level of scattered cumulus at 3,000 to 12,000 feet. A deck of broken altocumulus clouds will stretch from 12,000 to 18,000 feet, topped by an overcast layer of cirrus in the 25,000-28,000 foot range.

The temperature is forecast to be between 84 and 86 degrees, and winds will be out of the southeast at 10 to 15 knots.

Spaceflight Now will continue to provide updates as events warrant.

THURSDAY, JULY 28, 2005

A Boeing Delta 4 rocket had been scheduled for a Friday evening launch from Cape Canaveral, but an undisclosed problem with its weather spacecraft payload has put the mission on hold.

A new launch date is pending.

WEDNESDAY, JULY 27, 2005

The first Delta 4 rocket to fly this year is on track for a launch Friday evening, weather permitting, with the first of a new series of critical weather satellites designed to provide sharper images of clouds and storms over a longer lifetime.

The 4-hour, 21-minute trip to orbit begins at 6:23 p.m. EDT (2223 GMT) with a liftoff from Cape Canaveral's pad 37B situated on the Atlantic coast. The available launch window extends for another 38 minutes.

The Delta 4 Medium+ vehicle with a four-meter payload fairing and a pair of solid rocket boosters will propel its payload to a deployment orbit with an apogee, or high point, of about 18,994 nautical miles, a perigee, or low point, of 3,576 nautical miles, and an inclination of 12 degrees. See the complete ascent timeline of the marathon flight here.

However, launch weather officer Joel Tumbiolo's initial forecast, issued Wednesday morning, indicates storms and clouds have a 60 percent chance of interfering with those plans due to violations of the anvil and thick cloud rules. The forecast for Saturday is very similar.

"A frontal boundary will move into the southeastern United States Thursday morning. This will push the surface ridge axis to the south resulting in weak southwesterly flow," the outlook read.

"This usually results in sea breeze induced thunderstorms forming to our west, then slowly moving back towards the east during the afternoon and evening hours. Concerns will be for thunderstorms in the area throughout the countdown and launch window."

"Vehicle exposure limits will be the main concern during the countdown. Launch window concerns will be for thunderstorms and associated anvil clouds within 10 nautical miles."

The forecast calls for scattered cumulus clouds at 3,000 to 12,000 feet, a level of broken altocumulus clouds from 12,000 to 18,000 feet, and another broken deck of cirrus in the upper levels at 25,000 to 28,000 feet.

Visibility is expected to be about seven miles, and ground winds are forecast to be acceptable out of the southeast at eight to twelve knots. Temperature should be around 84 to 86 degrees Fahrenheit.

Perched atop the Boeing Delta 4 some twenty stories high is the National Oceanic and Atmospheric Administration's newest addition to its weather observation fleet, dubbed GOES-N. The payload will be renamed GOES-13 after launch and operate from a geostationary orbit about 22,300 miles above the equator.

Also built by Boeing, the 6,908-pound craft will eventually settle into a circular orbit stationed at 90 degrees West longitude for testing.

Once in its checkout orbit about three weeks after launch, Boeing will hand control over to NASA and NOAA to put the craft's systems through a comprehensive suite of tests to ensure the proper health of the newly launched weather observatory. Those checks should be complete within six months, allowing NOAA to put GOES-13 into orbital storage while it awaits a call 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 are currently capturing real-time images and data, while another is being stored as a spare.

GOES-N is the first of three new satellites being manufactured for launch over the next few years. GOES-O is currently in ground storage at its Boeing factory in California, and could be launched in November 2006. GOES-P will complete assembly in April 2007, with a planned liftoff in October 2008.

Plans for Friday'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 cryogenic second stage with super-cold liquid oxygen and liquid hydrogen propellants should get underway in the final five hours prior to the opening of the launch window. Under normal circumstances, the procedure to load all four tanks should take about two hours.

Topping of the propellants will continue through the final minutes of the countdown to replenish the liquids as they naturally boil away due to their frigid temperatures.

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 at this point in the count.

A 15-minute build-in hold is slated for T-5 minutes, during which time launch teams will go through final polling for launch clearance. The GOES-N spacecraft and Delta 4 booster will be transitioned to internal power sources 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 on Friday.

TUESDAY, JUNE 21, 2005

Concerns over the onboard batteries that power the Boeing Delta 4 rocket's safety destruct system has forced another delay in launching the GOES-N civilian weather satellite. Sunday evening's planned liftoff from Cape Canaveral will be postponed until sometime in July as a result.

"Recent environmental testing of a different lot of batteries resulted in broken leads that connect the batteries' cell plates to the terminal," Boeing said in a statement announcing the delay.

The rocket carries two batteries, both mounted to its second stage, for the Range Safety's flight termination system. If the vehicle experiences a major problem during ascent or veers off course, that destruct system can be triggered to destroy the rocket.

A new launch date has not been set. Boeing says the mission will fly sometime in July.

The GOES-N satellite "remains healthy and ready for launch," the company statement said.

SUNDAY, JUNE 19, 2005

Lightning strikes uncomfortably close to Boeing's Delta 4 rocket pad at Cape Canaveral is prompting technicians to re-verify electronics and circuitry before a U.S. weather observatory can be launched into space this month.

Liftoff had been targeted for Friday, June 24 from pad 37B at the Florida spaceport. But severe thunderstorms on Thursday, June 16 brought intense lightning over the Delta 4 launch site. Managers have ordered the precautionary checks of systems before the rocket and its payload can be cleared for flight.

The launch is tentatively rescheduled for Sunday, June 26 during a 45-minute liftoff opportunity extending from approximately 6:13 to 6:58 p.m. EDT (2213-2258 GMT).

The two-stage rocket will ferry into orbit the Geostationary Operational Environmental Satellite-N, or GOES-N. The spacecraft is the latest in a long series of U.S. weather satellites that provide the imagery seen daily during news broadcasts. The combined launcher and payload are valued at $475 million.

This mission had been postponed from June 23 to June 24 to allow the replacement of a hydraulic turbopump inside the rocket's first stage main engine that is critical to operating internal valves and steering the vehicle during ascent.

"The pump uses bleed gas from the main engine to drive a turbine and hydraulic pump combination that provides pressure to control main engine valves and gimbaling of the engine's nozzle," company officials said in a statement.

It was decided to replace the pump after a "minor deviation" in speed performance was noted during a countdown dress rehearsal compared to data seen on past Delta 4 missions, Boeing said.

The pump swap is now complete, and Boeing says the subsequent testing of the new assembly was successful.

Watch this page for a complete GOES-N mission preview later this week.