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The Mission

Rocket: Delta 4-Heavy
Payload: DemoSat
Date: December 21, 2004
Window: 2:36-5:31 p.m. EST (1936-2231 GMT)
Site: SLC-37B, Cape Canaveral, Florida
Satellite feed: AMC 9, Transponder 18, C-band

Mission preview story

Launch events timeline

Launch hazard area

D4-H story/photo archive

The Launcher

Boeing's Delta 4-Heavy vehicle is the largest, most powerful configuration in the next-generation rocket's family.

Delta 4-Heavy fact sheet

The pre-launch process

Our Delta archive

The Payload

The DemoSat satellite simulator and two university-built nanosats will be launched on the Delta 4-Heavy rocket's test flight.

Learn more


Follow the countdown and launch of the inaugural Boeing Delta 4-Heavy rocket on a demonstration test flight. Reload this page for the very latest on the mission. Use our text only page for faster downloads.

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Engineers probing the trouble experienced on the Boeing Delta 4-Heavy rocket's test flight have cleared 40 potential causes of the main engines cutting off prematurely, leaving 9 scenarios on the table, including the leading theory that bubbles formed in the liquid oxygen plumbing. Read our full story.


Investigators are theorizing that the flow of super-cold liquid oxygen in the three core boosters of Boeing's first Delta 4-Heavy rocket could have been disturbed, creating "bubbles" that tricked internal sensors into thinking the motors were out of fuel and causing them to command a premature engine shutdown, the Air Force said today. Read our full story.


Errant readings from sensors inside the inaugural Boeing Delta 4-Heavy rocket triggered the premature shutdown of its three main engines during ascent last month, causing a massive underspeed that the vehicle's upper stage could not overcome and resulting in a final orbit lower than planned, the U.S. Air Force said today. A team investigating results of the test launch are confident the problem can be resolved. Read our full story.


While stressing the positives of Tuesday's demonstration flight of the Boeing Delta 4-Heavy rocket and the mountain of data generated about the big booster's actions, Air Force officials on Wednesday acknowledged an "anomaly" occurred during the first stage and two university-built nanosats were lost after not reaching orbit. Read our full story.

1730 GMT (12:30 p.m. EST)

The DemoSat satellite simulator launched aboard the Delta 4-Heavy rocket Tuesday was delivered into an orbit 10,000 miles short of the intended altitude, according to tracking data. The payload failed to reach the proper orbit because the upper stage ran out of fuel after compensating for low performance from the first stage.

Information shows an elliptical egg-shaped orbit with a high point of 36,406 km, low point of 19,027 km and inclination of 13.5 degrees to the equator. That is 22,623 by 11,823 miles.

The rocket was supposed to inject the payload into a circular geosynchronous orbit of roughly 36,000 km with an inclination of 10 degrees.

Had the DemoSat been a real satellite relying on the rocket to reach geosynchronous orbit, it is unclear if the spacecraft's own propulsion system would have enough fuel to overcome the launch problem and climb to the proper altitude.

While the situation would likely be considered a launch failure for any operational rocket flight, Boeing terms Tuesday's Delta 4-Heavy demonstration mission a success.

"Our objective in this launch was to gather data and run through the entire mission profile. From that respect, we had a great day and a great flight," Boeing's top Delta program official, Dan Collins, told Spaceflight Now on Tuesday night.

0550 GMT (12:50 a.m. EST)

The test launch of Boeing's Delta 4-Heavy rocket began with a breath-taking blastoff from Cape Canaveral Tuesday afternoon but lower-than-expected performance during the initial minutes of flight ultimately caused the mission to fall short of its intended orbit. Nonetheless, Boeing officials called the demonstration flight a success. Read our full story.

0520 GMT (12:20 a.m. EST)

"We had a shorter than expected first stage burn. That was compensated for by longer first and second burns of the second stage. We had what I would call a good third burn of the second stage but we ended up burning to depletion and ended up on a shorter than expected final burn. I don't know the exact, final orbit or how much shorter the final burn was. We're going to look at the data and get those answers," Boeing vice president for Expendable Launch Systems, Dan Collins, said in an interview tonight.

"I've spent the entire day with our customer...I can tell you we've got a very, very happy customer. We demonstrated all phases of this mission and we got a huge amount of data that allows us to move forward with high confidence towards the DSP mission next summer."

We'll post a full story shortly.

0405 GMT (11:05 p.m. EST Tues.)

We're awaiting an official statement from Boeing following the third firing by the upper stage tonight. That burn was shorter than planned. DemoSat has been deployed.

0215 GMT (9:15 p.m. EST Tues.)

The Boeing Delta 4-Heavy rocket appears to have experienced lower-than-expected performance during its initial ascent today, forcing its upper stage engine to compensate and raising doubts about the mission's chances for success, sources indicate.

While it's not yet clear what might have caused the three Common Booster Core rockets to provide less total lift than anticipated or even whether the problem involved the central CBC or the two strap-ons. But the end result was the upper stage fired much longer than expected, using up more super-cold rocket fuel than planned.

The upper stage has since fired a second time, reaching a geosynchronous transfer orbit that was close to the projected altitude. A final burn scheduled for 10:27 p.m. EST would boost the stage and DemoSat dummy payload into the target orbit. However, if the upper stage does not have enough fuel remaining to complete the three-minute burn, the rocket will fall short of its intended orbit.

The purpose of this mission was testing the Delta 4-Heavy before the Air Force begins launching national security payloads on the big booster starting next summer.

We will post additional information as available.

0030 GMT (7:30 p.m. EST Tues.)

T+plus 2 hours, 40 minutes. The wait continues to learn the health of two nanosats carried into space by the Delta 4-Heavy. They were expected to be deployed about 16.5 minutes into flight. Satellite controllers report the first ground station pass heard no communciation from the tiny craft. It is suspected that since the craft were to deploy in orbital nighttime, they have not had sufficient time to recharge their solar-powered batteries in sunlight.

Another communications window is upcoming tonight.

The six-sided nanosatellites are nicknamed Ralphie and Sparky. Built in collaboration between Arizona State University, New Mexico State University and the University of Colorado at Boulder, Ralphie and Sparky will conduct imaging, micropropulsion and intersatellite communications experiments over the next one-to-two days before re-entering the atmosphere.

The canister-like nanosats were originally supposed to launch aboard a space shuttle mission in 2003. But the Columbia accident and grounding of the shuttle fleet led to the Air Force proposing an alternate route to orbit on Delta 4.

A third satellite in the trio, called Petey, was unable to fly on the Delta 4. It is bound for the National Air and Space Museum's new annex where it will be put on display for the public to see a real spacecraft.

2340 GMT (6:40 p.m. EST)

T+plus 1 hour, 50 minutes. Some additional pictures of the spectacular launch have been posted here.

2250 GMT (5:50 p.m. EST)

T+plus 60 minutes. Now one hour into this nearly six-hour flight of the Delta 4-Heavy rocket on the way to geosynchronous orbit to demonstrate the big booster's ability to carry large payloads into space. It ain't over till it's over, so there is a long way to go tonight before this mission can be declared a success. We'll continue to post updates as information is available. The rocket is quietly coasting through space until it re-ignites the upper stage about four-and-a-half hours from now.

2239 GMT (5:39 p.m. EST)

T+plus 49 minutes. We've posted a collection of images showing today's launch. See the pictures here.

2224 GMT (5:24 p.m. EST)

T+plus 34 minutes. To recap, words cannot describe the fiery liftoff that was one of the most dramatic events at Cape Canaveral in a very long time! The Delta 4-Heavy rocket has achieved orbit on this crucial test flight for the U.S. Air Force. We'll be posting video clips and pictures throughout the evening during the coast period. Watch this page for updates during the final burn and DemoSat separation at 10:40 p.m. EST.

There is still no confirmation that the two university-built Nanosats were deployed as planned.

2221 GMT (5:21 p.m. EST)

T+plus 31 minutes. This orbit achieved appears to be slightly low but within the target's margin of error.

2220 GMT (5:20 p.m. EST)

T+plus 30 minutes. The rocket has begun a five-hour coast through space to reach the high point of this egg-shaped orbit about 22,000 miles above Earth. That is where the upper stage engine will ignite again at T+plus 5 hours, 37 minutes. That three-minute burn circularizes the orbit and lowers the inclination to 10 degrees.

About five hours and 50 minutes after leaving Cape Canaveral, DemoSat will be released from the Delta 4-Heavy rocket in geosynchronous orbit, completing the launch.

2218 GMT (5:18 p.m. EST)

T+plus 28 minutes, 32 seconds. Engine shutdown! Two firings complete, one more to go for the Delta 4-Heavy rocket's upper stage.

2217 GMT (5:17 p.m. EST)

T+plus 27 minutes, 45 seconds. About one minute left in the burn.

2216 GMT (5:16 p.m. EST)

T+plus 26 minutes, 10 seconds. Chamber pressures are normal, engine movement is minimual, data from the rocket indicates.

2215 GMT (5:15 p.m. EST)

T+plus 25 minutes. Boeing reports the upper stage continues its second firing. The Air Force's deployable tracking site at Sao Tome, known as COVE, soon will start receiving data from the vehicle.

2213 GMT (5:13 p.m. EST)

T+plus 23 minutes, 20 seconds. The Ascension island tracking station has acquired the rocket's telemetry stream.

2212 GMT (5:12 p.m. EST)

T+plus 22 minutes, 30 seconds. The burn continues.

2211 GMT (5:11 p.m. EST)

T+plus 21 minutes, 35 seconds. Chamber pressures have stablized after ignition.

2210 GMT (5:10 p.m. EST)

T+plus 21 minutes, 8 seconds. Ignition! The RL10B-2 powerplant has been re-started for an eight-minute burn.

2208 GMT (5:08 p.m. EST)

T+plus 18 minutes, 30 seconds. The upper stage is about two minutes away from re-igniting its engine. This second of three planned firings will raise one side of the rocket's orbit to geosynchronous altitude around 22,000 statute miles.

2208 GMT (5:08 p.m. EST)

T+plus 18 minutes. The rocket is 131 miles in altitude and traveling at 14,241 nautical miles per hour.

2206 GMT (5:06 p.m. EST)

T+plus 16 minutes, 50 seconds. Nanosats should be deployed, however confirmation could be delayed a few minutes.

2206 GMT (5:06 p.m. EST)

T+plus 16 minutes, 10 seconds. Data confirms the upper stage firing did complete.

2206 GMT (5:06 p.m. EST)

T+plus 16 minutes. Cape Verde has picked up the rocket's signal.

2205 GMT (5:05 p.m. EST)

T+plus 15 minutes. The next major event will be deployment of the two nanosats riding on the side of the DemoSat primary payload. The separation signal should be issued about 45 seconds from now. The physical release of the small craft occurs 38 seconds later.

2204 GMT (5:04 p.m. EST)

T+plus 14 minutes. The rocket has moved out of range from the Antigua tracking station. This begins a brief zone when the vehicle is not within site of any telemetry site. The Cape Verde station will acquire in about two minutes.

2203 GMT (5:03 p.m. EST)

T+plus 13 minutes, 55 seconds. Data signal is breaking up from the Antigua tracking station. Next tracking station is expected in two minutes.

2203 GMT (5:03 p.m. EST)

T+plus 13 minutes. Upper stage is still firing -- longer than expected.

2202 GMT (5:02 p.m. EST)

T+plus 12 minutes. The upper stage is reaching orbital velocity.

2201 GMT (5:01 p.m. EST)

T+plus 11 minutes. The duration of the burn is governed by the rocket's guidance system. The engine will be commanded to shut down once the desired orbit is obtained.

2200 GMT (5:00 p.m. EST)

T+plus 10 minutes. Just under three minutes remain in this engine firing.

2159 GMT (4:59 p.m. EST)

T+plus 9 minutes, 30 seconds. Chamber pressure reported normal on the RL10 engine as it continues to fire.

2159 GMT (4:59 p.m. EST)

T+plus 9 minutes. Today's launch marks the first flight of Boeing's slightly larger 5-meter diameter upper stage. Earlier Delta rockets have used the 4-meter stage. This new configuration's wider dimension permits a larger liquid hydrogen tank to increase the amount of propellant the stage can carry. The liquid oxygen tank is stretched in length for added capacity. The extra fuel means the RL10 can fire longer for enhanced performance.

2158 GMT (4:58 p.m. EST)

T+plus 8 minutes, 45 seconds. The Air Force tracking station on Antigua island has acquired the rocket's signal. The site will be receiving the live telemetry stream coming from the Delta 4-Heavy rocket as it soars download and relaying that data to the engineers at Cape Canaveral.

2158 GMT (4:58 p.m. EST)

T+plus 8 minutes. No problems have been reported during the upper stage engine firing. The RL10 is burning consuming its mixture of liquid hydrogen and liquid oxygen.

2157 GMT (4:57 p.m. EST)

T+plus 7 minutes, 25 seconds. The rocket is 100 miles in altitude, traveling at 12,000 mph as it streams 600 miles east of the launch pad.

2156 GMT (4:56 p.m. EST)

T+plus 7 minutes. The RL10 is a highly-respected cryogenic upper stage engine. Developed in the 1960s, it has flown 190 rocket launches accounting for 368 engines and 693 firings in space. The RL10B-2 design used by Delta 4 the newest model in the venerable engine's history.

2156 GMT (4:56 p.m. EST)

T+plus 6 minutes, 30 seconds. The upper stage is firing at full thrust to accelerate the upper stage into orbit. It will take another six minutes to reach the initial parking orbit around the planet.

2156 GMT (4:56 p.m. EST)

T+plus 6 minutes. The 17-foot diameter, 63-foot long payload fairing has been jettisoned in two halves. The rocket's nose cone shielded the DemoSat and nanosats during atmospheric ascent. It is no longer needed, allowing the shroud to separate.

2155 GMT (4:55 p.m. EST)

T+plus 5 minutes, 55 seconds. Engine start! The Pratt & Whitney RL10B-2 cryogenic rocket engine is up and burning for the first of three firings during today's launch of the Delta 4-Heavy.

2155 GMT (4:55 p.m. EST)

T+plus 5 minutes, 40 seconds. Pyrotechnics have detonated to jettison the spent center Common Booster Core. The rocket's upper stage and attached payload are now flying free.

2155 GMT (4:55 p.m. EST)

T+plus 5 minutes, 35 seconds. Main engine cutoff! The center booster's Rocketdyne RS-68 engine has finished its job. Three of the engines had flown before today. This Delta 4-Heavy mission just doubled the RS-68 flight history.

2155 GMT (4:55 p.m. EST)

T+plus 5 minutes. In less than 20 seconds, the main engine will throttle back to 58 percent. It will operate in the minimum power level for 11 seconds in preparation for shutdown.

2154 GMT (4:54 p.m. EST)

T+plus 4 minutes, 45 seconds. Everyone associated with the Delta 4-Heavy must be breathing a bit easier at this point in the flight. Although there are many hours remaining in the trek to geosynchronous orbit, the rocket is currently flying in a configuration similar to the single-core Delta 4-Medium vehicle that has successfully launched three times.

2154 GMT (4:54 p.m. EST)

T+plus 4 minutes, 19 seconds. The center Common Booster Core's RS-68 engine has revved up to full throttle for the Delta 4-Heavy rocket's on-going journey to space. The booster is identical to the outer strap-on stages, carrying the same propellant supply and engine package, but it employed a more conservative fuel consumption strategy over the past three minutes. That has left enough cryogenic fuel to fire nearly 90 seconds longer.

2154 GMT (4:54 p.m. EST)

T+plus 4 minutes, 12 seconds. The 15-story tall starboard and port Common Booster Cores that provided the vast majority of thrust during the first four minutes of flight have expended their fuel and peeled away from the center stage. Tiny solid-fueled motors on the discarded boosters gave helpful nudges to ensure a clean separation. The boosters will tumble into the Atlantic Ocean below.

2154 GMT (4:54 p.m. EST)

T+plus 4 minutes, 5 seconds. Engine cutoff!

2153 GMT (4:53 p.m. EST)

T+plus 3 minutes, 35 seconds. Coming up in about 20 seconds, the outer Common Booster Cores will throttle down as a precursor to engine shutdown and jettison of the stages. It will take five seconds to ease the power setting to 58 percent. The boosters will operate at that throttle for another five seconds before the RS-68s are shut down.

2153 GMT (4:53 p.m. EST)

T+plus 3 minutes, 15 seconds. All three main engines can't and won't burn identically in respect to precise performance and fuel consumption. The rocket was designed with that fact in mind. The vehicle is programmed to accommodate and react to the differences during flight. In the event one of the outer boosters depletes its fuel tanks sooner than the other, a simultaneous engine cutoff will be commanded to prevent an unstable situation.

2153 GMT (4:53 p.m. EST)

T+plus 3 minutes. The center engine -- numbered E20007 -- remains at 58 percent thrust while the starboard Common Booster Core's engine number E20005 and port's number E20006 engine are firing at 102 percent. The outer boosters have just over one minute remaining in powered flight.

2152 GMT (4:52 p.m. EST)

T+plus 2 minutes, 40 seconds. The near-zero angle-of-attack portion of the vehicle's climb has ended and the rocket has started a 50-second rolling maneuver to position itself for "wings-level" flight.

2152 GMT (4:52 p.m. EST)

T+plus 2 minutes, 15 seconds. The rocket is following a flight azimuth of 95 degrees as it heads eastward from the Florida coastline.

2152 GMT (4:52 p.m. EST)

T+plus 2 minutes. The 8-foot diameter bell-shaped nozzles on the three main engines gimbal during flight, allowing the rocket to steer itself on the intended trajectory to space.

2151 GMT (4:51 p.m. EST)

T+plus 1 minute, 40 seconds. The outer Common Booster Cores and their RS-68 main engines continue to consume the supply of super-cold liquid hydrogen and liquid oxygen rocket fuel while firing at full throttle. The RS-68 is considered the world's largest hydrogen-fueled rocket engine. Each powerplant is capable of generating 17 million horsepower.

2151 GMT (4:51 p.m. EST)

T+plus 1 minute, 20 seconds. The vehicle is ascending through the flight regime that provides the maximum aerodynamic pressures on the rocket. This period is called Max-Q. And in the next few seconds, the Delta 4-Heavy will break the sound barrier as its speed reaches Mach 1.

2151 GMT (4:51 p.m. EST)

T+plus 1 minute, 10 seconds. No problems have been reported from the telemetry receiving station at Cape Canaveral as engineers anxiously monitor live data being transmitted from the rocket's systems.

2151 GMT (4:51 p.m. EST)

T+plus 60 seconds. The Delta 4-Heavy is an absolutely breath-taking sight as it slowly and thunderously rises away from Earth. The three distinct red-hot flames trailing three main engines are 20 stories long, backdropped against the crystal-clear blue sky.

2150 GMT (4:50 p.m. EST)

T+plus 50 seconds. The center Common Booster Core's main engine is throttling back to 58 percent thrust as a fuel conservation effort. The starboard and port boosters continue to operate at their maximum power setting of 102 percent thrust.

2150 GMT (4:50 p.m. EST)

T+plus 30 seconds. All three Rocketdyne RS-68 main engines are firing at full throttle, gulping three tons of propellant per second to produce 1.9 million pounds of thrust.

2150 GMT (4:50 p.m. EST)

T+plus 20 seconds. The rocket's closed-loop guidance and control system has assumed authority to fly the vehicle as the 23-story tall Delta 4-Heavy clears the towers at Cape Canaveral's Complex 37B.

2150 GMT (4:50 p.m. EST)

T-minus 10, 9, 8, sequencer now controlling, T-minus 6, 5, 4, 3, 2, engine ignition, 0, and LIFTOFF! Liftoff of the inaugural Boeing Delta 4-Heavy rocket on a demonstration flight to prove the powerful performance of America's newest launch vehicle!

2149 GMT (4:49 p.m. EST)

T-minus 30 seconds. The terminal countdown sequencer will take control at T-minus 8.5 seconds. Ignition of the three RS-68 powerplants will follow at T-minus 5.5 seconds. The engines power up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

2149 GMT (4:49 p.m. EST)

T-minus 40 seconds. Upper stage liquid hydrogen tank is ready.

2149 GMT (4:49 p.m. EST)

T-minus 1 minute and counting. The ignition parameters for the RS-68 main engine are met.

2148 GMT (4:48 p.m. EST)

T-minus 70 seconds and counting. The Eastern Range has given its "go" for launch.

2148 GMT (4:48 p.m. EST)

T-minus 2 minutes and counting. The three Common Booster Core liquid hydrogen tanks are at flight level and pressure. The rocket's liquid oxygen tanks are being secured.

2147 GMT (4:47 p.m. EST)

T-minus 3 minutes and counting. The Common Booster Core propellant topping is being secured. And pressurization of the tanks has started.

2146 GMT (4:46 p.m. EST)

T-minus 4 minutes and counting. Vehicle ordnance is being armed.

2145 GMT (4:45 p.m. EST)

T-minus 4 minutes, 30 seconds. The systems of the Common Booster Cores and upper stage of the Delta 4-Heavy rocket have switched from ground-fed power to internal batteries for launch.

2145 GMT (4:45 p.m. EST)

T-minus 5 minutes and counting! The final phase of today's countdown has commenced for launch of Boeing's first Delta 4-Heavy rocket on its test flight for the U.S. Air Force. Liftoff is set to occur at 4:50 p.m. EST (2150 GMT) from pad 37B at Cape Canaveral Air Force Station, Florida.

2144 GMT (4:44 p.m. EST)

The launch director has instructed the team to start the countdown at 4:45 p.m. for liftoff five minutes later.

2143 GMT (4:43 p.m. EST)

The countdown picks up in two minutes.

2141 GMT (4:41 p.m. EST)

The team is being polled again to make sure everyone is still ready to resume the countdown from the T-minus 5 minute mark.

2138 GMT (4:38 p.m. EST)

Launch team reports the issue has been put to rest. Now 12 minutes from liftoff.

2135 GMT (4:35 p.m. EST)

NEW TIME! Liftoff has been rescheduled for 4:50 p.m. EST.

2128 GMT (4:28 p.m. EST)

The problem involves a momentary loss of signal for Range Safety equipment. Officials want to understand that problem before proceeding with the launch today.

2127 GMT (4:27 p.m. EST)

There is no estimate on the duration of this additional delayed. Boeing has until 5:31 p.m. EST (2232 GMT) to get the Delta 4-Heavy rocket off the pad today.

2125 GMT (4:25 p.m. EST)

The countdown will remain holding at T-minus 5 minutes due to an alarm. Engineers need to check the situation before clocks can resume ticking. Liftoff will be delayed pasted 4:31 p.m. EST.

2125 GMT (4:25 p.m. EST)


2125 GMT (4:25 p.m. EST)

Launch director has given final approval to resume the countdown.

2124 GMT (4:24 p.m. EST)

The countdown will resume in two minutes. Launch of the Delta 4 rocket is just seven minutes away from Cape Canaveral.

2122 GMT (4:22 p.m. EST)

The Boeing launch team has been polled for a "go" to resume the countdown. All systems were reported ready for liftoff! Launch is now 9 minutes away.

2121 GMT (4:21 p.m. EST)

Weather confirmed "go" for launch.

2118 GMT (4:18 p.m. EST)

Countdown clocks continue holding at T-minus 5 minutes. The launch team going through the final steps before the readiness polling.

2114 GMT (4:14 p.m. EST)

Now 17 minutes from launch time. Boeing is not reporting any problems standing in the way of liftoff at 4:31 p.m. EST.

2110 GMT (4:10 p.m. EST)

A series of management polls will be conducted shortly to verify all systems are ready to continue with the countdown.

2102 GMT (4:02 p.m. EST)

Using the launch pad cameras, engineers have checked the thermal insulation on the rocket. Everything appeared normal following the loading of super-cold propellants into the vehicle.

2057 GMT (3:57 p.m. EST)

The launch team is nearly back on track with the countdown timeline. Liftoff remains scheduled for 4:31 p.m. EST.

2053 GMT (3:53 p.m. EST)

The launch pad swing arm retraction system pins are being pulled. The three arms will be rotated away from the Delta 4 rocket at liftoff.

Also, the RS-68 engine spin start pressurization operation is starting.

2051 GMT (3:51 p.m. EST)

The three Common Booster Core main engines slew tests are now finished. There were no problems reported in any of the checks, which confirm the rocket will be able to steer itself properly during ascent.

2046 GMT (3:46 p.m. EST)

Now 45 minutes away from launch. Weather is absolutely beautiful at Cape Canaveral.

2044 GMT (3:44 p.m. EST)

The upper stage RL10 engine steering checks have been completed. The Common Booster Core tests are next.

2038 GMT (3:38 p.m. EST)

The engine steering tests have begun.

2037 GMT (3:37 p.m. EST)

Liquid oxygen tank topping is starting. This means all eight cryogenic tanks in the Delta 4-Heavy rocket have been filled today. The replenishment topping continues through the final minutes of the countdown to replace the supplies that naturally boil away.

2035 GMT (3:35 p.m. EST)

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

2032 GMT (3:32 p.m. EST)

The Range Safety checks have been completed without any problems reported. Upper stage liquid oxygen loading has reached the 90 percent point.

2020 GMT (3:20 p.m. EST)

The Air Force-controlled Eastern Range is preparing to run inhibited command destruct receiver checks. This ensures safety personnel can destroy the Delta 4 rocket if it veers off course or experiences a problem during launch.

2004 GMT (3:04 p.m. EST)

Upper stage liquid hydrogen loading has just completed. Checks will performed before topping begins. Liquid oxygen tank filling continues.

2000 GMT (3:00 p.m. EST)

Filling of the upper stage liquid oxygen and liquid hydrogen tanks is still underway. The cryogenic tanks on the three Common Booster Cores are in topping mode.

1950 GMT (2:50 p.m. EST)

After performing vent and relief checks on the CBC liquid hydrogen tanks, topping is now starting.

1931 GMT (2:31 p.m. EST)

Liftoff of the Boeing Delta 4-Heavy rocket's maiden flight is two hours away. The rocket is being fueled at Cape Canaveral's pad 37B as the countdown targets launch at 4:31 p.m. EST (2131 GMT). The available launch window extends one hour beyond the newly established T-0.

1926 GMT (2:26 p.m. EST)

The upper stage liquid hydrogen tank is 10 percent full.

1918 GMT (2:18 p.m. EST)

NEW LAUNCH TIME! Liftoff has been officially rescheduled to 4:31 p.m. EST (2131 GMT).

1916 GMT (2:16 p.m. EST)

T-minus 5 minutes and holding. The countdown has just entered a planned hold point. Clocks will remain here for at least two hours while the launch team plays catchup on fueling and other activities delayed by ground support equipment problems this morning. Liftoff is not expected before 4:25 p.m. EST (2125 GMT). The launch window extends to 5:31 p.m. EST (2231 GMT). Weather continues to look good.

Boeing says problems with the main engine water cooling system, then a liquid oxygen pump were to blame for the delays this morning. It was initially believed that the countdown sequencer was involved in the second issue.

The three Common Booster Cores that will fire to lift the rocket off the Cape Canaveral launch pad are now filled with their supplies of liquid oxygen and liquid hydrogen. Loading of the upper stage is in the early phases.

1907 GMT (2:07 p.m. EST)

The CBC liquid hydrogen filling is complete.

Thermal conditioning of the upper stage liquid oxygen and liquid hydrogen systems is finishing. The loading of those tanks will begin shortly.

1851 GMT (1:51 p.m. EST)

The launch team is preparing to start chilldown thermal conditioning of the upper stage liquid oxygen system. The hydrogen side of the upper stage is already in chilldown.

1846 GMT (1:46 p.m. EST)

T-minus 35 minutes and counting. Depite the holdups in today's countdown by technical issues, the clocks have continued to tick on schedule. Once the countdown reaches T-minus 5 minutes at 2:16 p.m., the clocks will enter an extended hold for a couple of hours while fueling of the rocket is completed. Officials say liftoff will not happen before 4:25 p.m. EST.

1843 GMT (1:43 p.m. EST)

The liquid hydrogen filling of the three Common Booster Cores is passing the 60 percent level.

Read our earlier status center coverage.



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