BY JUSTIN RAY

Follow the countdown and launch of the ULA Delta 2 rocket with NASA's GLAST observatory. Reload this page for the very latest on the mission.

Additional coverage for subscribers:
VIDEO: THE DELTA 2-HEAVY ROCKET BLASTS OFF WITH GLAST PLAY
VIDEO: LAUNCH REPLAY: PAD 17B WIDE-SCREEN CAMERA PLAY
VIDEO: LAUNCH REPLAY: PAD 17A LOOKING SOUTHWARD PLAY
VIDEO: LAUNCH REPLAY: THE UCS-23 WEST TRACKER PLAY
VIDEO: LAUNCH REPLAY: TRIDENT BLUFF LOCATION PLAY
VIDEO: LAUNCH REPLAY: CCAFS INDUSTRIAL AREA PLAY
VIDEO: ROLLBACK OF PAD'S MOBILE SERVICE TOWER PLAY
VIDEO: PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: DELTA 2'S PRE-LAUNCH CAMPAIGN HIGHLIGHTS PLAY
VIDEO: GLAST'S PRE-LAUNCH CAMPAIGN HIGHLIGHTS PLAY
NEW!: HIGH DEFINITION VIDEO
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WEDNESDAY, JUNE 11, 2008

A Delta 2 rocket roared to life and successfully boosted a $690 million space telescope into orbit today, the most sophisticated observatory ever built to study the tell-tale high energy gamma rays generated by the most violent explosions and processes in the known universe.

Read our full story.

1815 GMT (2:15 p.m. EDT)

"The entire GLAST Team is elated the observatory is now on-orbit and all systems continue to operate as planned," said GLAST program manager Kevin Grady of NASA's Goddard Space Flight Center in Greenbelt, Md.

"After a 60-day checkout and initial calibration period, we'll begin science operations," said Steven Ritz, GLAST project scientist at Goddard. "GLAST soon will be telling scientists about many new objects to study, and this information will be available on the internet for the world to see."

1747 GMT (1:47 p.m. EDT)

This was the 81st consecutive successful Delta 2 rocket launch dating back to May 1997. The Delta 2's overall history since debuting in 1989 has achieved 134 successes in 136 flights.

The next Delta 2 rocket launch is just a week away. Liftoff from Vandenberg Air Force Base in California is scheduled for 12:46 a.m. local time (3:46 a.m. EDT; 0746 GMT) on June 20 to deliver into orbit the Jason 2 spacecraft, a joint U.S. and European project to measure sea surface height. NASA calls it the Ocean Surface Topography Mission.

For Cape Canaveral, the next Delta 2 launch from here is not expected until sometime this fall when the another GPS satellite goes up.

1742 GMT (1:42 p.m. EDT)

"They are telling us it was a beautiful launch, at least all the preliminary data look that way. The spacecraft has separated from the second stage. The two solar arrays have deployed. Everything just looks nominal. We couldn't be happier," say Steven Ritz, the mission's project scientist.

"We have about two weeks of checking out the spacecraft itself, that supports the instruments. And then about two weeks from now we will be turning on the instruments, checking them out, doing basic checks, calibrations, initial configurations. Then we begin the process of calibrations and preliminary science observations."

The science mission is scheduled to start 60 days after launch.

1739 GMT (1:39 p.m. EDT)

Both power-generating solar arrays on the GLAST observatory had been deployed.

"We couldn't be happier," says Steven Ritz, the mission's project scientist.

1738 GMT (1:38 p.m. EDT)

"The 1st Space Launch Squadron is proud to be a part of the NASA GLAST team," said Maj. Timothy Spies, Delta 2 operations controller with the Air Force's 1st Space Launch Squadron. "Throughout buildup of the Delta 2 rocket and launch sequence processing the entire NASA, ULA, and AF team worked very well together to ensure a safe and successful ride for the GLAST spacecraft."

"The GLAST launch represents the true spirit of space exploration and we look forward to partnering with NASA on similar endeavors in the future," said Brig. Gen. Susan Helms, 45th Space Wing commander.

1735 GMT (1:35 p.m. EDT)

"Today's launch was the culmination of tremendous teamwork by NASA, ULA and the Air Force to ensure that GLAST received a safe and accurate ride to orbit," said Jim Sponnick, United Launch Alliance vice president, Delta Product Line.

"ULA has a long history of providing reliable launch services for NASA's space exploration missions and we are honored to have played a vital role in supporting this critical mission that will help to unlock the mysteries our universe."

1731 GMT (1:31 p.m. EDT)

"We have had a pretty good launch. The satellite's where it needs to be," says NASA Launch Manager Omar Baez. "We had a nominal separation from what we can tell. The satellite has been communicating through the TDRSS network since a little while after the fairing came off. So they have been getting data for quite a bit. We had confirmation from the launch vehicle that we separated, and also from the spacecraft. All they are waiting for now is for their solar arrays to deploy."

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

Deployment of the solar arrays on the GLAST spacecraft is underway.

1721 GMT (1:21 p.m. EDT)

T+plus 76 minutes. Just after the satellite was released, the second stage used its helium system to perform a retro maneuver and gently back away from the observatory.

1720 GMT (1:20 p.m. EDT)

T+plus 75 minutes, 9 seconds. SPACECRAFT SEPARATION! NASA's Gamma-ray Large Area Space Telescope has been deployed from the Delta 2 rocket's second stage to complete today's launch from Cape Canaveral.

GLAST promises to provide a far sharper insight into universe's most extreme and powerful objects like monstrous black holes, spinning neutron stars and gamma ray bursts.

"It's really like the human race is getting a new pair of glasses to see the universe in gamma rays," said Steven Ritz, the mission's project scientist.

"It is a new kind of telescope that will show us new things about the universe."

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

T+plus 74 minutes, 45 seconds. Deploy sequence has begun.

1718 GMT (1:18 p.m. EDT)

T+plus 73 minutes, 30 seconds. The second stage's roll, pitch and yaw rates have stopped in preparation for GLAST separation.

1716 GMT (1:16 p.m. EDT)

T+plus 71 minutes, 30 seconds. The second stage burn appears to have been nominal, NASA says.

1714 GMT (1:14 p.m. EDT)

T+plus 69 minutes, 21 seconds. SECO 2. The second stage has completed its second burn of this launch of the GLAST spacecraft. The rocket will release the satellite in a little more than five minutes.

1713 GMT (1:13 p.m. EDT)

T+plus 68 minutes, 40 seconds. Good chamber pressure reported on the second stage.

1713 GMT (1:13 p.m. EDT)

T+plus 68 minutes, 17 seconds. Ignition! The Delta 2 rocket's second stage is firing again. This burn will boost the vehicle from its current elliptical orbit into the desired 300-nautical-mile circular orbit.

1712 GMT (1:12 p.m. EDT)

T+plus 67 minutes, 20 seconds. Kwajalein has acquired the rocket's signal.

1710 GMT (1:10 p.m. EDT)

T+plus 65 minutes. The Delta 2 rocket should be coming within the Kwajalein tracking site's coverage zone in the next couple of minutes. The station, located in the Marshall Islands, will receive telemetry from the second stage and route the information back to Cape Canaveral.

1655 GMT (12:55 p.m. EDT)

T+plus 50 minutes. Restart of second stage engine is expected at about T+plus 68 minutes. The stage will fire for approximately 65 seconds to circularize the orbit. Deployment of the payload to complete the launch is expected around T+plus 75 minutes.

1645 GMT (12:45 p.m. EDT)

T+plus 40 minutes. As this coast phase of the launch continues, you can see a map of the rocket's planned track here.

1630 GMT (12:30 p.m. EDT)

T+plus 25 minutes. The official liftoff time was 12:05:00.521 p.m. EDT (1605 GMT).

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

T+plus 14 minutes. All of the planned launch events have occurred as planned and the Delta is quietly coasting in its parking orbit, NASA says.

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

T+plus 12 minutes, 15 seconds. The rocket has flown out of range from the Antigua tracking station. The next site to acquire signal will be Kwajalein facility in about 55 minutes.

1616 GMT (12:16 p.m. EDT)

T+plus 11 minutes. The vehicle is 107 miles in altitude, 1,711 miles downrange from the launch pad and traveling at 17,193 mph.

1615 GMT (12:15 p.m. EDT)

T+plus 10 minutes, 31 seconds. SECO 1. The second stage engine cutoff has occurred, completing the motor's first firing of the day. The Delta 2 rocket with GLAST has arrived in a preliminary orbit around Earth following launch today from Cape Canaveral. The vehicle will coast for about an hour before the second stage is re-ignited.

1614 GMT (12:14 p.m. EDT)

T+plus 9 minutes, 20 seconds. The vehicle is 107.5 miles in altitude, 1,318 miles downrange from the launch pad and traveling at 16,247 mph.

1613 GMT (12:13 p.m. EDT)

T+plus 8 minutes, 20 seconds. The vehicle is 104.4 miles in altitude, 1,080 miles downrange from the launch pad and traveling at 15,429 mph.

1613 GMT (12:13 p.m. EDT)

T+plus 8 minutes. Second stage engine chamber pressure continues to look good.

1612 GMT (12:12 p.m. EDT)

T+plus 7 minutes, 15 seconds. The Air Force's downrange tracking station on Antigua Island has acquired the rocket's signal, relaying telemetry from the rocket back to the Cape.

1611 GMT (12:11 p.m. EDT)

T+plus 6 minutes, 10 seconds. The vehicle is 89 miles in altitude, more than 600 miles downrange from the launch pad and traveling over 14,000 mph.

1611 GMT (12:11 p.m. EDT)

T+plus 6 minutes. The second stage engine is firing well, consuming a hydrazine propellant mixture and nitrogen tetroxide oxidizer. This burn is needed to achieve a parking orbit around Earth.

1609 GMT (12:09 p.m. EDT)

T+plus 4 minutes, 45 seconds. The spent first stage has been jettisoned and the Delta's second stage engine has ignited!

1609 GMT (12:09 p.m. EDT)

T+plus 4 minutes, 28 seconds. MECO. The first stage main engine cutoff is confirmed.

1609 GMT (12:09 p.m. EDT)

T+plus 4 minutes. A half-minute remaining in the first stage burn. Everything is reported normal aboard the vehicle.

1608 GMT (12:08 p.m. EDT)

T+plus 3 minutes, 45 seconds. The vehicle is 48.2 nautical miles in altitude, 217.8 miles downrange from the launch pad, traveling at 9,874 mph.

1608 GMT (12:08 p.m. EDT)

T+plus 3 minutes, 15 seconds. The main engine is still firing normally, burning a mixture of highly refined kerosene fuel and supercold liquid oxygen.

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

T+plus 2 minutes, 55 seconds. The vehicle is 35.6 nautical miles in altitude, 124 miles downrange from the launch pad, traveling at 7,330 mph.

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

T+plus 2 minutes, 41 seconds. The three air-ignited solid rocket boosters have burned out and separated. The rocket is now flying solely on the power generated by the liquid-fueled first stage main engine.

1606 GMT (12:06 p.m. EDT)

T+plus 1 minutes, 35 seconds. The vehicle is 13.6 nautical miles in altitude, 33.6 miles downrange from the launch pad, traveling at 3,075 mph.

1606 GMT (12:06 p.m. EDT)

T+plus 1 minute, 17 seconds. All six ground-start solid rocket boosters have burned out of propellant and separated from the Delta 2's first stage. A moment before the jettison occurred, the three remaining motors strapped to rocket ignited to continue assisting the rocket's RS-27A main engine on the push to space.

1606 GMT (12:06 p.m. EDT)

T+plus 60 seconds. One minute into the flight. The Gamma-ray Large Area Space Telescope is thundering away from Cape Canaveral on its easterly path, en route to orbit to observe some of the most dynamic and powerful forces in the cosmos.

1605 GMT (12:05 p.m. EDT)

T+plus 50 seconds. The rocket has flown through the area of maximum aerodynamic pressure in the lower atmosphere.

1605 GMT (12:05 p.m. EDT)

T+plus 35 seconds. Delta has broken the sound barrier.

1605 GMT (12:05 p.m. EDT)

LIFTOFF! Liftoff of the Delta 2-Heavy rocket with NASA's new gamma ray observatory, seeking out the extreme objects in the universe!

1604 GMT (12:04 p.m. EDT)

T-minus 30 seconds. SRB ignitors will be armed at T-minus 11 seconds.

The launch ignition sequence will begin in the final two seconds of the countdown when a ULA engineer pushes the engine start switch. The process begins with ignition of the two vernier engines and first stage main engine start. The six ground-lit solid rocket motors then light at T-0 for liftoff.

1604 GMT (12:04 p.m. EDT)

T-minus 1 minute. Sixty seconds from launch. The vehicle's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

1603 GMT (12:03 p.m. EDT)

T-minus 75 seconds. The Air Force's Eastern Range has given the all-clear to launch.

1603 GMT (12:03 p.m. EDT)

T-minus 100 seconds. First stage LOX topping to 100 percent is underway.

1603 GMT (12:03 p.m. EDT)

T-minus 2 minutes. Pressurization of the first stage liquid oxygen is now beginning. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

1602 GMT (12:02 p.m. EDT)

T-minus 2 minutes, 40 seconds. The Gamma-ray Large Area Space Telescope has been declared "go" for launch.

1602 GMT (12:02 p.m. EDT)

T-minus 3 minutes and counting.

1601 GMT (12:01 p.m. EDT)

T-minus 3 minutes, 45 seconds. The Delta 2 rocket's systems are now transferring to internal power for launch.

1601 GMT (12:01 p.m. EDT)

T-minus 4 minutes and counting! Clocks are counting again for today's launch of the Delta 2-Heavy rocket with the GLAST telescope at 12:05 p.m. EDT from pad 17B at Cape Canaveral Air Force Station in Florida.

1600 GMT (12:00 p.m. EDT)

A final "go" to continue the countdown has been given to the launch team.

1559 GMT (11:59 a.m. EDT)

Two minutes remain in the built-in hold.

1557 GMT (11:57 a.m. EDT)

The launch team and the launch director are "go."

1556 GMT (11:56 a.m. EDT)

NASA Launch Manager Omar Baez has polled his team again prior to picking up the countdown. The space agency's team is "go."

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

Now 10 minutes from the new launch time.

1553 GMT (11:53 a.m. EDT)

The GLAST spacecraft atop the Delta 2 rocket is going into its proper configuration for launch.

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

NEW LAUNCH TIME. Liftoff is being retargeted for 12:05 p.m. EDT.

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

Weather conditions remain "go" at the moment.

1548 GMT (11:48 a.m. EDT)

The Antigua tracking station is now back online and "go" for launch, a NASA spokesman reports. A new launch time is being coordinated.

Antigua is a critical asset needed to support today's flight by the Delta 2-Heavy rocket. The Air Force site provides coverage during the second stage burn and the vehicle's arrival into the parking orbit.

1545 GMT (11:45 a.m. EDT)

The extended hold in the countdown was called because of a problem with the downrange tracking station on Antigua Island. There is no estimate yet on the length of this hold, NASA says.

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

A new target launch time has not yet been set. Clocks remain holding at T-minus 4 minutes.

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

HOLD EXTENDED. The countdown will not resume as planned. A few more minutes will be added into this hold.

1536 GMT (11:36 a.m. EDT)

Readiness polling of the launch team members is underway.

1535 GMT (11:35 a.m. EDT)

Just 10 minutes remain until liftoff of the United Launch Alliance Delta 2-Heavy rocket carrying NASA's Gamma-ray Large Area Space Telescope.

"GLAST is going to be a great new instrument for looking at the extreme universe, the high-energy sky, in gamma rays. It will open a new window on phenomena throughout the universe, such as super-massive black holes, neutron stars, gamma ray bursts, and what really excites us is the unknown," said Steven Ritz, the mission's project scientist.

"We're really at a unique time in the history of science and of astronomy that we can study the cosmos across the entire electromagnetic spectrum for the first time...GLAST is one of those missions where we are extending our reach significantly," said Jon Morse, director of the astrophysics division at NASA Headquarters.

1534 GMT (11:34 a.m. EDT)

NASA Launch Manager Omar Baez has polled his team for a "go" to proceed with the countdown and no problems were reported.

1531 GMT (11:31 a.m. EDT)

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for today's launch. During this planned 10-minute hold, officials will poll the various team members in the soft blockhouse, the Range's Morrell Operations Center and the Mission Directors Center. If all systems are "go," the countdown will resume for liftoff at 11:45 a.m. EDT.

1529 GMT (11:29 a.m. EDT)

The launch weather officer reports that all of the rules are "go" for liftoff.

1529 GMT (11:29 a.m. EDT)

The launch pad water tanks are being pressurized.

1526 GMT (11:26 a.m. EDT)

The first stage kerosene fuel tank is being pressurized for flight.

1520 GMT (11:20 a.m. EDT)

T-minus 15 minutes and counting. Clocks are ticking down to T-minus 4 minutes where the final hold is scheduled into the countdown. That hold will last 10 minutes, leading to liftoff at 11:45 a.m. EDT.

1515 GMT (11:15 a.m. EDT)

The first stage engine steering checks have been completed as the countdown continues for today's 11:45 a.m. EDT launch.

1511 GMT (11:11 a.m. EDT)

The second stage engine tests have finished.

1510 GMT (11:10 a.m. EDT)

Technicians are beginning 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.

1505 GMT (11:05 a.m. EDT)

Today's launch will be:

• The 333rd Delta rocket launch since 1960
• The 2nd to fly this year
• The 136th Delta 2 rocket mission since 1989
• The 5th Heavy version of the Delta 2

The earlier Delta 2-Heavy missions all launched NASA spacecraft from Cape Canaveral, including the Mars rover Opportunity and the Spitzer Space Telescope in 2003, the Mercury orbiter MESSENGER in 2004 and the Dawn asteroid spacecraft last year.

1500 GMT (11:00 a.m. EDT)

The countdown is entering the final 45 minutes to liftoff of the GLAST spacecraft aboard the United Launch Alliance Delta 2-Heavy rocket.

1459 GMT (10:59 a.m. EDT)

Range Safety is performing inhibited checks of the command destruct receivers. The CRDs would be used in destroying the Delta rocket should the vehicle veer off course or malfunction during the launch.

1450 GMT (10:50 a.m. EDT)

With the liquid oxygen now aboard the rocket, today's 115-minute launch window has been narrowed to approximately 60 minutes. Here's why:

The Delta rocket's first stage is assembled with its kerosene fuel tank atop the liquid oxygen tank. The plumbing that routes the fuel to the RS-27A main engine runs down through the supercold oxidizer tank. Prolonged exposure to the frigid temperatures of the liquid oxygen naturally causes the kerosene to chill, eventually making it too cold for the launch to proceed.

Now that the oxidizer is aboard the vehicle, a timer automatically limits the amount of time the rocket can sit in the fueled state before the kerosene temperature drops out of an acceptable range for flight today.

"It starts cooling down the (kerosene) to the point where the performance suffers," said Omar Baez, the NASA launch manager.

So today's launch opportunity now extends from 11:45 a.m. until around 12:45 p.m. EDT.

1447 GMT (10:47 a.m. EDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank has concluded. The filling process took 25 minutes and 52 seconds, ending at 10:47:20 a.m. The tank will be replenished through the countdown to replace the supercold liquid oxygen that naturally boils away.

The rocket now stands fully fueled for liftoff. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour-and-a-half. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels earlier over the weekend. The nine strap-on booster rockets use solid propellants.

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

Launch weather officer Joel Tumbiolo says conditions remain acceptable right now. But the early part of today's launch window offer the best chance for cooperation from the weather.

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

The first stage liquid oxygen tank just reached the 95 percent full level. The "rapid load" valve was closed, with the slower "fine load" phase continuing to fill the tank.

1433 GMT (10:33 a.m. EDT)

The launch team has completed work to turn on and configure the Delta's onboard guidance computer.

1431 GMT (10:31 a.m. EDT)

Now 10 minutes into this approximate 25-minute process to fill the first stage liquid oxygen tank. The outer skin of the rocket is beginning to ice over as the supercold oxidizer pumps into the vehicle.

1421 GMT (10:21 a.m. EDT)

LOX LOADING BEGINS. Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from the storage reservoir at Complex 17, through plumbing and into the bottom of the ULA Delta 2-Heavy rocket. The LOX will be consumed by the first stage main engine during the first four-and-a-half minutes of flight along with the 10,000 gallons of RP-1 kerosene already loaded aboard the vehicle.

1418 GMT (10:18 a.m. EDT)

The official "go" has been given by the launch director to start filling the rocket's first stage with liquid oxygen at 10:20 a.m. EDT as planned.

1415 GMT (10:15 a.m. EDT)

Now 90 minutes to launch. Initial preps for liquid oxygen loading are starting.

1410 GMT (10:10 a.m. EDT)

United Launch Alliance Mission Director Rich Murphy has polled his management team in advance of liquid oxygen loading.

1409 GMT (10:09 a.m. EDT)

NASA Launch Manager Omar Baez has polled his team for a "go" to begin loading the first stage liquid oxygen tank of the Delta 2 rocket. No constraints were voiced.

1405 GMT (10:05 a.m. EDT)

Launch weather officer Joel Tumbiolo says "so far, so good." No storms have developed yet and all the rules are "go" for launch right now. He puts the odds of acceptable weather at the 11:45 a.m. EDT launch time at 60 percent. But the odds are expected to worsen into the early afternoon.

1400 GMT (10:00 a.m. EDT)

The launch team is not reporting any significant technical issues with the rocket or spacecraft. The countdown is continuing on schedule.

1355 GMT (9:55 a.m. EDT)

The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage starting in about 25 minutes.

The kerosene and liquid oxygen will be consumed by the stage's Pratt & Whitney Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

1350 GMT (9:50 a.m. EDT)

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's planned 11:45 a.m. EDT launch. The tank was filled with a highly refined kerosene, called RP-1, during a 20-minute, 25-second process that concluded at 9:50:21 a.m.

1347 GMT (9:47 a.m. EDT)

Rapid-loading of the RP-1 tank has concluded as 9,850 gallons have been pumped into the rocket. Fine load is continuing.

1343 GMT (9:43 a.m. EDT)

First stage propellant loading has passed the 8,000-gallon mark. This process to load the kerosene fuel takes about 20 minutes.

1341 GMT (9:41 a.m. EDT)

The launch team has computed that the full load for the first stage fuel tank is 10,085 gallons.

Once the tank is filled to 98 percent or 9,850 gallons, the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

1339 GMT (9:39 a.m. EDT)

Half of the first stage fuel tank has been filled.

1330 GMT (9:30 a.m. EDT)

FUELING BEGINS. About 10,000 gallons of the kerosene propellant, called RP-1, are pumping into the base of the rocket from storage tanks at pad 17B as fueling of the Delta 2's first stage begins for today's launch.

1326 GMT (9:26 a.m. EDT)

Preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank are beginning. After verifying valves, sensors, flow meters and equipment are ready, the highly refined kerosene fuel will start flowing into the vehicle a few minutes from now.

1325 GMT (9:25 a.m. EDT)

First stage helium and nitrogen pressurization is complete. And the "go" has been given for the start of fueling.

1310 GMT (9:10 a.m. EDT)

The launch team has started activation of the rocket's guidance system, as well as the pressurization steps for the first and second stage helium and nitrogen systems and second stage fuel tanks.

1305 GMT (9:05 a.m. EDT)

BEGIN COUNT. The Terminal Countdown has been initiated for today's launch of the Gamma-ray Large Area Space Telescope aboard the Delta 2-Heavy rocket.

The next two hours and 40 minutes will be spent fueling the rocket, activating systems and performing final testing before liftoff at 11:45 a.m. EDT from pad 17B at Cape Canaveral Air Force Station in Florida.

Workers have cleared the Complex 17 area in advance of the hazardous portion in today's launch operation. But a warning horn is now being 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 activities such as pressurizing the helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown clocks currently stand at T-minus 150 minutes and counting. One further planned hold -- at the T-minus 4 minute point lasting for 10 minutes -- will give the launch team a moment to catch up on any work running behind and allow mission managers to conduct final readiness polls before proceeding toward the liftoff.

1300 GMT (9:00 a.m. EDT)

No weather rules are being violated right now. Conditions look favorable at Cape Canaveral for the moment. But the development of storms is expected a little later today, making the odds of acceptable launch weather 60 percent.

1256 GMT (8:56 a.m. EDT)

The launch team has been polled to ensure all stations are manned and systems are prepared to move into the countdown. Everyone reported "ready."

Liftoff of the Delta 2-Heavy rocket is still set to occur at 11:45 a.m. EDT.

1245 GMT (8:45 a.m. EDT)

Now three hours from liftoff time. The launch team has gathered in the control center and members are standing by for a readiness poll to be conducted shortly.

1225 GMT (8:25 a.m. EDT)

The weather outlook remains unchanged, Air Force meteorologists reported this morning, with a 60 percent chance of acceptable conditions still predicted for launch today.

"On Wednesday, again expect shower and thunderstorm development over the coastal counties late in the countdown as the sea breeze becomes established and makes slow progress inland. The threat for thunderstorms greatly increases throughout the launch window. Main (launch commit criteria) weather rules of concern will be the Cumulus Cloud Rule and precipitation over the pad and flight path."

The forecast predicts scattered cumulus clouds at 3,000 and 25,000 feet, showers and isolated thunderstorms in the vicinity, northeasterly winds becoming easterly at 10 peaking to 15 knots and a temperature in the low 80s F.

1205 GMT (8:05 a.m. EDT)

T-minus 150 minutes and holding. The countdown has just entered a planned 60-minute built-in hold at Cape Canaveral Air Force Station. The Terminal Countdown will begin once this hold is concluded.

1100 GMT (7:00 a.m. EDT)

A collection of photos of the Delta 2 rocket sitting atop pad 17B following this morning's rollback of the mobile service tower is posted here.

0815 GMT (4:15 a.m. EDT)

Liftoff of the Delta 2-Heavy rocket with the GLAST spacecraft remains targeted for 11:45 a.m. EDT (1545 GMT) today.

Retraction of the pad 17B service gantry from around the rocket was completed overnight. The tower was used to stack the two-stage vehicle atop the pad's launch mount, attach the nine strap-on solid motors and hoist the payload aboard the rocket. The tower also provided the primary weather protection and worker access to the rocket during its stay on the oceanside complex.

Today's Terminal Countdown picks up at 9:05 a.m. EDT. The morning count includes fueling of the first stage with highly refined kerosene and supercold liquid oxygen propellants.

A standard hold at the T-minus 4 minute point will give launch managers the opportunity to survey the status before countdown clocks progress into the quickly paced final minutes that see the vehicle switch to internal power, the liquid oxygen tank pressurized and systems armed.

The main engine and six of the nine strap-on solid rocket motors ignite at liftoff to begin GLAST's ride off the planet. The Delta 2-Heavy features slightly larger solid motors, originally developed for the more-powerful Delta 3 rocket.

Arcing eastward over the Atlantic Ocean, the six solid boosters lit on the ground extinguish 77 seconds into flight as the remaining three motors are ignited moments later. The half-dozen spent boosters are jettisoned at an altitude of 14 nautical miles to fall harmlessly into the sea. The air-lit motors burn out and separate two minutes, 40 seconds after liftoff when the rocket is about 37 nautical miles up.

Once the solids are discarded, the kerosene-powered main engine will continue pushing the rocket above an altitude of 65 nautical miles. The spent stage then jettisons at T+plus 4 minutes, 33 seconds to let the hydrazine-fueled second stage propel the vehicle the rest of the way into space.

The two-piece nose cone that shrouded GLAST during the trek through the atmosphere is shed just seconds after the second stage comes to life 70 miles above the planet.

Ten minutes and 14 seconds into the ascent, the second stage completes its initial firing. The Delta settles into a 100 by 324 nautical mile parking orbit inclined 28.5 degrees, flying along a trajectory that cruises above the central Atlantic before crossing Africa, the Indian Ocean, skirting just north of Australia and out across the western Pacific. The second stage reignites its engine within view of the Kwajalein tracking station in the Marshall Islands at T+plus 68 minutes. The burn will last 65 seconds to put the rocket into a 301 nautical mile circular orbit inclined 25.6 degrees.

GLAST should be released from the rocket at 1 p.m. EDT, some 75 minutes after an on-time blastoff.

TUESDAY, JUNE 10, 2008

The GLAST gamma ray telescope, a $690 million successor to one of NASA's original Great Observatories, is scheduled for launch Wednesday from Cape Canaveral.

The Gamma-ray Large Area Space Telescope will ride into orbit aboard a Delta 2-Heavy rocket, a beefed up version of the venerable launcher needed to loft the 9,635-pound spacecraft.

"We have a new observatory with breakthrough capabilities ready to launch," said Steven Ritz, the mission's project scientist. "It is about to open up the universe to us in new and very exciting ways."

Liftoff from pad 17B will occur during a window extending from 11:45 a.m. to 1:40 p.m. EDT (1545-1740 GMT). But that window has two twists to keep in mind during the countdown to launch.

The Delta rocket's first stage is assembled with its kerosene fuel tank atop the liquid oxygen tank. The plumbing that routes the fuel to the RS-27A main engine runs down through the supercold oxidizer tank. Prolonged exposure to the frigid temperatures of the liquid oxygen naturally causes the kerosene to chill, eventually making it too cold for the launch to proceed.

The kerosene is loaded into the rocket first, starting around 9:25 a.m. That will be followed by the liquid oxygen filling operation beginning at 10:20 a.m. Once the oxidizer is aboard the vehicle, a timer will immediately limit the amount of time the rocket can sit in the fueled state before the kerosene temperature drops out of an acceptable range for flight that day.

"It starts cooling down the (kerosene) to the point where the performance suffers," said Omar Baez, the NASA launch manager.

That timer, in effect, shortens the window available launch the rocket to about 60 minutes. If liquid oxygen begins on schedule, the day's launch opportunity then becomes roughly 11:45 a.m. to 12:45 p.m. However, if weather or some technical problem delays the liquid oxygen loading, that 60-minute launch period would shift later in the window.

The other twist is the day's overall 115-minute launch window will be divided into four panes. Each separate block is distinguished by the second stage's planned orientation during the long coast period between engine firings and while releasing the payload 75 minutes after liftoff.

• Block 1 extends from 11:45 a.m. to 12:13 p.m. EDT.
• Block 2 extends from 12:14 to 12:42 p.m. EDT.
• Block 3 extends from 12:43 to 1:11 p.m. EDT.
• Block 4 extends from 1:12 to 1:40 p.m. EDT.

Switching from one block to another will require engineers to change settings in the rocket's flight computer to adjust for the changing sun angles during the launch and optimize the positioning of the GLAST spacecraft upon separation from the booster. It will take 10 to 15 minutes to perform the changes for each block.

Despite the uniqueness of the GLAST window, officials are hopeful of getting the Delta rocket off the ground right on time.

"All we need is that first second," Baez said.

GLAST follows the Compton Gamma Ray Observatory launched by the space shuttle Atlantis in April 1991. This new spacecraft, thanks to advancements in technologies, promises to provide a far sharper insight into universe's most extreme and powerful objects like monstrous black holes, spinning neutron stars and gamma ray bursts.

"GLAST will provide scientists an unprecedented view into the high-energy universe, an opportunity to observe some of the most dynamic and powerful forces in the universe," said Kevin Grady, the project manager from NASA's Goddard Space Flight Center.

"Unlike many telescopes that have a very narrow field of view, the GLAST observatory has a very wide field of view comparable to a person's vision. This will allow the GLAST observatory to view the entire celestial sphere every three hours."

Getting GLAST into its 300-nautical-mile orbit above Earth on Wednesday will depend on good weather at Cape Canaveral. There is a 60 percent chance of acceptable conditions during the window, with cumulus clouds and precipitation over the pad and the rocket's flight path being the main concerns.

The forecast predicts scattered cumulus clouds at 3,000 and 25,000 feet, showers and isolated thunderstorms in the vicinity, westerly winds of 5 peaking to 10 knots becoming southeasterly at 10 peaking to 15 knots and a temperature in the low 80s F.

"Beginning of the launch window will be more favorable than the end," the forecasters said, noting the likely development of afternoon storms.

Watch this page for live reports throughout the countdown and flight of the Delta 2 with GLAST!