BY JUSTIN RAY

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

Additional coverage for subscribers:
VIDEO: DELTA 2 ROCKET LAUNCHES DAWN PLAY
VIDEO: LAUNCH AS SEEN FROM JETTY PARK PIER PLAY
VIDEO: DAWN'S DEPLOYMENT FROM ROCKET ANNOUNCED PLAY
VIDEO: POST-FLIGHT COMMENTS FROM LAUNCH MANAGER PLAY
VIDEO: PAD'S MOBILE GANTRY ROLLED BACK FOR LAUNCH PLAY
VIDEO: THE PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: OVERVIEW OF DAWN'S SCIENCE MISSION PLAY
VIDEO: NARRATED HIGHLIGHTS OF DAWN'S LAUNCH PREPS PLAY
VIDEO: NARRATED HIGHLIGHTS OF DELTA 2 ROCKET PREPS PLAY

MORE: FULL VIDEO COVERAGE OF DAWN MISSION PLAY
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THURSDAY, SEPTEMBER 27, 2007

Seeking to explore the uncharted worlds of Vesta and Ceres in the heart of the asteroid belt, NASA's Dawn space probe rocketed off planet Earth at sunrise Thursday to begin the three-billion-mile adventure that is counting on the craft's exotic ion engines to drive the eight-year trek.

Read our launch story.

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

Photos from this morning's launch are posted here.

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

"With the launch of Dawn, ULA is continuing to show its dedication to providing safe, cost-effective, reliable access to space for U.S. government missions," said Mark Wilkins, vice president of Delta Programs at United Launch Alliance. "ULA has brought together the most talented professionals in the launch industry and we are honored to launch spacecraft, such as Dawn, supporting NASA's critical national mission to explore the universe."

1250 GMT (8:50 a.m. EDT)

"The Delta 2-Heavy has performed well. We're exactly where we want to be," NASA launch manager Omar Baez says. "The first stage, the second stage and the third stage were all nominal - nothing funny in the data so far. And from what see in the orbits we're right on the money."

This is the 76th consecutive successful Delta 2 rocket launch dating back to May 1997. The Delta 2's overall history since debuting in 1989 has achieved 129 successes in 131 flights.

Three more Delta 2 launches are planned this year beginning with a Global Positioning System satellite deployment mission for the Air Force on October 17 from Cape Canaveral. The launch of an Italian radar Earth-imaging craft for civilian and military uses is set for December 5 from Vandenberg Air Force Base, California. Another GPS satellite launch is targeted for December 20 from the Cape.

1240 GMT (8:40 a.m. EDT)

Spaceflight Now Plus subscribers can watch a movie of this morning's launch here.

To learn more about this service, click here.

1235 GMT (8:35 a.m. EDT)

T+plus 61 minutes, 58 seconds. SPACECRAFT SEPARATION! NASA's Dawn asteroid explorer has been released from the Delta 2 rocket's third stage, completing today's launch!

The probe will encounter Mars in 2009 to use the Red Planet's gravity in a sling-shot maneuver for the trek into the asteroid belt for reconnaissance of the massive asteroid Vesta in 2011 and "dwarf planet" Ceres in 2015.

Scientists want up-close studies of Vesta and Ceres to learn more about the processes and conditions during the solar system's formation four-and-a-half-billion years ago. The spacecraft will orbit at increasingly lower altitudes above the two diverse objects during multi-month visits to determine the composition, internal structure and evolutionary history of the bodies.

"Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Dawn principal investigator Christopher Russell of the University of California, Los Angeles. "One is rocky and is representative of the building blocks that constructed the planets of the inner solar system. The other may very well be icy and represents the outer planets. Yet, these two very diverse bodies reside in essentially the same neighborhood. It is one of the mysteries Dawn hopes to solve."

Vesta is believed to be solid rock. The oval-shaped object has an average diameter of approximately 320 miles. But Ceres could harbor water or ice beneath its rocky crust. The "baby planet" has an average diameter of about 600 miles.

1232 GMT (8:32 a.m. EDT)

T+plus 58 minutes. The rocket is flying northeastward across Australia. Release of the Dawn spacecraft is about four minutes away.

1231 GMT (8:31 a.m. EDT)

T+plus 57 minutes, 19 seconds. The Star 48B third stage has burned out of its solid fuel, ending the Delta 2 rocket's powered flight for the launch of dawn.

1230 GMT (8:30 a.m. EDT)

T+plus 56 minutes, 20 seconds. Good chamber pressure reported from the third stage.

1229 GMT (8:29 a.m. EDT)

T+plus 55 minutes, 58 seconds. Third stage ignition! The upper stage motor has been lit to propel Dawn out of Earth orbit.

1229 GMT (8:29 a.m. EDT)

T+plus 55 minutes, 30 seconds. Stage separation confirmed.

1228 GMT (8:28 a.m. EDT)

T+plus 54 minutes, 25 seconds. SECO 2. The second stage has completed its second burn of this launch. In the next minute, tiny thrusters on the side of the rocket will be fired to spin up the vehicle in preparation for release of the third stage.

1226 GMT (8:26 a.m. EDT)

T+plus 52 minutes, 30 seconds. Good chamber pressure reported from the second stage engine. Also, good flow rates of the fuel and oxidizer.

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

T+plus 51 minutes, 43 seconds. The second stage engine has ignited to resume the powered flight of this morning's Dawn launch.

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

T+plus 51 minutes, 34 seconds. Second stage hydraulics have been activated.

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

T+plus 51 minutes, 20 seconds. Dongara has picked up the rocket's signal as it flies over the Indian Ocean off the west coast of Australia.

1215 GMT (8:15 a.m. EDT)

T+plus 41 minutes. The next firing by the Delta rocket's second stage is coming up in 10 minutes. The Dongara tracking station in Australia should acquire the rocket about a minute before ignition. The site will relay the rocket's signal back to the Cape to provide confirmation of the second stage burn.

1209 GMT (8:09 a.m. EDT)

T+plus 35 minutes. As the rocket coasts in this parking orbit, it performs a "BBQ roll" maneuver to keep the thermal conditions on the vehicle equal. This maneuver was scheduled to start at about T+plus 15 minutes and conclude at T+plus 49 minutes.

1204 GMT (8:04 a.m. EDT)

T+plus 30 minutes. Delta is crossing Africa now. A map of the rocket's planned flight path is available here.

1154 GMT (7:54 a.m. EDT)

T+plus 20 minutes. The official liftoff time this morning was 7:34:00.372 a.m.

1146 GMT (7:46 a.m. EDT)

T+plus 12 minutes. The rocket has flown out of range from the Antigua tracking station. The next communications will come when Delta approaches the west coast of Australia.

1145 GMT (7:45 a.m. EDT)

T+plus 11 minutes. The rocket has successfully achieved a parking orbit with an apogee of 100.6 miles, perigee of 99.99 miles and inclination of 28.6 degrees. That is right on the pre-planned orbit parameters.

"Can't get better than that," says launch telemetry commentator Marc Lavigne.

1143 GMT (7:43 a.m. EDT)

T+plus 9 minutes, 4 seconds. SECO 1. The second stage engine cutoff has occurred, completing the motor's first firing of the day. The Delta 2 rocket and Dawn have arrived in a preliminary orbit around Earth following launch this morning from Cape Canaveral. The vehicle will coast for more than 40 minutes before the second stage is re-ignited.

1142 GMT (7:42 a.m. EDT)

T+plus 8 minutes. The second stage engine is consuming a hydrazine propellant mixture and nitrogen tetroxide oxidizer. This burn is needed to achieve a parking orbit around Earth.

1141 GMT (7:41 a.m. EDT)

T+plus 7 minutes, 40 seconds. Good chamber pressure reported on the second stage engine.

1141 GMT (7:41 a.m. EDT)

T+plus 7 minutes, 15 seconds. Delta is 97 miles in altitude, 908 miles downrange from the launch pad and traveling at 15,500 mph.

1140 GMT (7:40 a.m. EDT)

T+plus 6 minutes, 45 seconds. The Air Force's downrange tracking station on Antigua Island has acquired the rocket's signal.

1140 GMT (7:40 a.m. EDT)

T+plus 6 minutes. The vehicle continues to accelerate on the power provided by the second stage engine.

1139 GMT (7:39 a.m. EDT)

T+plus 5 minutes, 30 seconds. Delta is 80 miles in altitude, 538 miles downrange from the launch pad and traveling at nearly 14,500 mph.

1138 GMT (7:38 a.m. EDT)

T+plus 4 minutes, 48 seconds. The rocket's 9.5-foot diameter nose cone enclosing the spacecraft has been jettisoned.

1138 GMT (7:38 a.m. EDT)

T+plus 4 minutes, 40 seconds. The Delta's second stage engine has ignited following jettison of the spent first stage.

1138 GMT (7:38 a.m. EDT)

T+plus 4 minutes, 32 seconds. MECO. Main engine cutoff is confirmed. The first stage has completed its firing.

1138 GMT (7:38 a.m. EDT)

T+plus 4 minutes, 12 seconds. First stage systems continue to look good. The chamber pressures in the main engine and the twin vernier steering thrusters are normal.

1137 GMT (7:37 a.m. EDT)

T+plus 3 minutes, 40 seconds. Delta is 52 miles in altitude, 207 miles downrange from the launch pad and traveling at nearly 9,700 mph.

1136 GMT (7:36 a.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.

1135 GMT (7:35 a.m. EDT)

T+plus 1 minute, 55 seconds. The air-lit boosters continue to burn along with the main engine. The vehicle is 19 miles in altitude, 44 miles downrange, traveling at 4,000 mph.

1135 GMT (7:35 a.m. EDT)

T+plus 1 minute, 23 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.

1135 GMT (7:35 a.m. EDT)

T+plus 60 seconds. One minute into the flight.

1134 GMT (7:34 a.m. EDT)

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

1134 GMT (7:34 a.m. EDT)

T+plus 35 seconds. Delta has broken the sound barrier. The first stage main engine and six strap-on solid motors are burning well.

1134 GMT (7:34 a.m. EDT)

T+plus 20 seconds. Dawn is rising aboard the 12-story Delta rocket on a spectacular sunrise ascent from Cape Canaveral.

1134 GMT (7:34 a.m. EDT)

LIFTOFF! Liftoff the Delta 2-Heavy rocket launching the Dawn spacecraft on a three-billion-mile trek to the uncharted worlds of Vesta and Ceres in the heart of the asteroid belt.

1133 GMT (7:33 a.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.

1133 GMT (7:33 a.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.

1132 GMT (7:32 a.m. EDT)

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

1132 GMT (7:32 a.m. EDT)

T-minus 90 seconds. Topping of the liquid oxygen tank to the 100 percent level is underway.

1132 GMT (7:32 a.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.

1131 GMT (7:31 a.m. EDT)

T-minus 2 minutes, 15 seconds. The Dawn spacecraft has been declared "go" for launch.

1131 GMT (7:31 a.m. EDT)

T-minus 3 minutes and counting. The rocket's third stage safe and arm devices are being armed. The third stage will boost Dawn out of Earth orbit for the voyage to the asteroid belt.

1130 GMT (7:30 a.m. EDT)

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

1130 GMT (7:30 a.m. EDT)

T-minus 4 minutes and counting! Clocks are running again for the final minutes to liftoff of the United Launch Alliance Delta 2 rocket that will propel NASA's Dawn spacecraft on its eight-year mission. Launch will occur at 7:34 a.m. from pad 17B at Cape Canaveral Air Force Station in Florida.

1129 GMT (7:29 a.m. EDT)

One minute away from picking up the countdown.

1127 GMT (7:27 a.m. EDT)

The ship has cleared the hazard zone.

1125 GMT (7:25 a.m. EDT)

The countdown will come out of this hold at 7:30 a.m. for launch at 7:34 a.m.

1121 GMT (7:21 a.m. EDT)

NEW LAUNCH TIME. Liftoff has been reset for 7:34 a.m. EDT.

1118 GMT (7:18 a.m. EDT)

The Dawn spacecraft is going back to external power during this extra wait.

1117 GMT (7:17 a.m. EDT)

The constraint to launch is a ship in the restricted waters of the Atlantic where the solid rocket boosters fall. The Coast Guard is making contact with the vessel to get it cleared from the hazard zone.

1115 GMT (7:15 a.m. EDT)

HOLD EXTENDED. The countdown will not resume as planned. The Range has gone to a "no go" status.

1114 GMT (7:14 a.m. EDT)

Two minutes remain in the built-in hold.

1111 GMT (7:11 a.m. EDT)

All systems are reported "ready" by the launch team. There are no technical problems standing in the way of liftoff at 7:20 a.m. EDT.

1111 GMT (7:11 a.m. EDT)

The final pre-flight poll of the launch team is underway.

1110 GMT (7:10 a.m. EDT)

Now 10 minutes from launch.

1109 GMT (7:09 a.m. EDT)

NASA launch manager Omar Baez just polled his agency team and gave a "go" to proceed with the count.

1107 GMT (7:07 a.m. EDT)

The Dawn spacecraft atop the Delta 2 rocket is switching to internal power for launch.

1106 GMT (7:06 a.m. EDT)

T-minus 4 minutes and holding. The countdown has entered the final planned built-in hold. This is a scheduled 10-minute pause leading to today's liftoff at 7:20 a.m. for the Delta 2 rocket and Dawn spacecraft.

During the hold, officials will poll the various team members in the "soft blockhouse," Range Operations Control Center and Mission Directors Center.

1104 GMT (7:04 a.m. EDT)

The launch weather officer reports conditions are "go" for liftoff.

1101 GMT (7:01 a.m. EDT)

Now 19 minutes from liftoff. The first stage kerosene fuel tank is being pressurized.

1055 GMT (6:55 a.m. EDT)

T-minus 15 minutes and counting. The countdown has resumed following the planned hold. Clocks will tick down to T-minus 4 minutes where the final hold is scheduled. Liftoff of the Delta rocket from Cape Canaveral is slated to occur at 7:20 a.m. EDT this morning.

1051 GMT (6:51 a.m. EDT)

A launch team poll for a "ready" status to resume the countdown reported no constraints to continuing onward this morning.

1050 GMT (6:50 a.m. EDT)

Now 30 minutes to launch.

1045 GMT (6:45 a.m. EDT)

Now half-way through this built-in hold at T-minus 15 minutes. Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned. Activitites are going smoothly for this morning's 7:20 a.m. liftoff of the Delta 2-Heavy rocket with the Dawn spacecraft.

Today's launch will be:

• The 327th Delta rocket launch since 1960
• The 131st Delta 2 rocket mission since 1989
• The 5th of 2007

1035 GMT (6:35 a.m. EDT)

T-minus 15 minutes and holding. The countdown has entered a planned 20-minute built-in hold. The pause is designed to give the launch team a chance to work any problems or catch up on activities that might be running behind schedule. Engineers will also have time to examine all the data from the just-completed steering tests.

1030 GMT (6:30 a.m. EDT)

The first stage steering checks just finished, completing these slew tests for today's countdown.

1026 GMT (6:26 a.m. EDT)

Slews of the second stage engine are complete.

1025 GMT (6:25 a.m. EDT)

Technicians are starting 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.

1022 GMT (6:22 a.m. EDT)

The official weather forecast has improved to an 80 percent chance of good conditions this morning. The revised outlook calls for just a few clouds at 3,000 feet, good visibility and northerly winds. The isolated rain showers in the area are staying to the southeast.

1020 GMT (6:20 a.m. EDT)

Sixty minutes from the start of the eight-year, three-billion-mile mission of the Dawn spacecraft.

1016 GMT (6:16 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.

1004 GMT (6:04 a.m. EDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank just concluded. 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 at 7:20 a.m. 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 this week. The nine strap-on booster rockets and third stage use solid propellants.

1002 GMT (6:02 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.

0950 GMT (5:50 a.m. EDT)

Now 90 minutes to launch. All systems are "go" for liftoff at 7:20 a.m. EDT this morning from Cape Canaveral.

0946 GMT (5:46 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.

0936 GMT (5:36 a.m. EDT)

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 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.

0931 GMT (5:31 a.m. EDT)

The official "go" has been given by the launch director to start filling the rocket's first stage with liquid oxygen.

0930 GMT (5:30 a.m. EDT)

Preps for liquid oxygen loading are starting.

0924 GMT (5:24 a.m. EDT)

NASA launch manager Omar Baez just polled the agency's management team to verify there are no constraints with proceeding into liquid oxygen loading. No technical issues with rocket systems, the spacecraft or Range are being worked and weather is acceptable right now. There had been one Range issue under discussion but that has been resolved.

0919 GMT (5:19 a.m. EDT)

The launch weather officer says none of the weather rules are being violated right now. He says the odds of favorable weather this morning could be increased from the current 60 percent chance once the weather reconnaissance aircraft gets airborne to survey the clouds and showers around the Cape this morning.

0914 GMT (5:14 a.m. EDT)

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

0905 GMT (5:05 a.m. EDT)

The launch time weather forecast continues to predict scattered clouds at 3,000 and 10,000 feet, isolated rain showers in the area, northerly winds and a temperature around 77 degrees F. There is a 60 percent chance that weather will be acceptable for liftoff this morning. The cloud cover and showers are the concerns.

Should the launch be delayed to Friday for any reason, tomorrow's weather outlook calls for an 80 percent chance of good conditions.

0904 GMT (5:04 a.m. EDT)

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's launch. The tank was filled with a highly refined kerosene, called RP-1, during a 19-minute, 18-second process that concluded at 5:04:22 a.m. local time.

The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage starting in about 30 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.

0901 GMT (5:01 a.m. EDT)

Rapid-loading of the RP-1 tank has concluded with 9,750 gallons already aboard the rocket. Fine load is continuing to finish filling the tank.

0857 GMT (4:57 a.m. EDT)

The launch team has computed that today's full load for the first stage fuel tank is 9,947 gallons.

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

0853 GMT (4:53 a.m. EDT)

The first stage tank is half full, with 5,000 gallons aboard now.

0850 GMT (4:50 a.m. EDT)

Launch of the Delta rocket with the Dawn asteroid orbiter is two-and-a-half hours away.

0845 GMT (4:45 a.m. EDT)

Fueling just commenced. About 10,000 gallons of the kerosene propellant 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.

0840 GMT (4:40 a.m. EDT)

Preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank are starting. 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.

0825 GMT (4:25 a.m. EDT)

The launch team is starting pressurization steps for the first and second stage helium and nitrogen systems and second stage fuel tanks. And activation of the rocket's Redundant Inertial Flight Control Assembly guidance computer is beginning now.

0820 GMT (4:20 a.m. EDT)

BEGIN COUNT. The Terminal Countdown has been initiated for today's launch of the Dawn spacecraft aboard the Delta 2 rocket. No technical concerns have been reported by the launch team and activities are progressing on schedule. The odds of acceptable weather is 60 percent.

The next three hours will be spent fueling the rocket, activating systems and performing final testing before liftoff at 7:20 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. Two planned holds -- at the T-minus 15 minute and the T-minus 4 minute points -- will give the launch team some time to catch up on any work running behind. The first hold will last 20 minutes in duration, the second extends 10 minutes.

0811 GMT (4:11 a.m. EDT)

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

Liftoff of the Delta 2 rocket remains targeted to occur ontime at 7:20 a.m. local time.

0750 GMT (3:50 a.m. EDT)

Now 30 minutes through this scheduled hour-long hold in the countdown.

The Delta rocket today will be flying in its configuration known as the 7925-Heavy vehicle. The three-stage launcher is fitted with nine strap-on solid-propellant motors that are slightly larger than ones normally flown on Delta 2 rockets, giving the vehicle added power.

0720 GMT (3:20 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.

0335 GMT (11:35 p.m. EDT Wed.)

Tower rollback to the launch position is being completed. Now, workers will turn their attention to configuring the pad and putting the final touches on equipment and the rocket before clearing Complex 17 overnight. The three-hour Terminal Countdown will begin at 4:20 a.m.

0246 GMT (10:46 p.m. EDT Wed.)

The pad 17B mobile service gantry has started slowly rolling away from the Delta 2-Heavy rocket.

0050 GMT (8:50 p.m. EDT Wed.)

Launch pad technicians are busy at work tonight preparing the mobile service tower for its rollback to reveal the Delta 2-Heavy rocket at Complex 17. The gantry is expected to be retracted before midnight.

The tower was used to stack the multi-stage vehicle atop the pad's launch mount, attach the nine strap-on solid motors and hoist the payload aboard the rocket. This cocoon-like structure wraps around the Delta to offer weather protection and full access for workers during the pre-launch campaign.

Liftoff remains on schedule for 7:20 a.m. EDT Thursday morning from Cape Canaveral's pad 17B.

WEDNESDAY, SEPTEMBER 26, 2007

NASA is poised to launch an innovative spacecraft Thursday that will use ultra-efficient ion engines to reach and orbit the two largest members of the asteroid belt between Mars and Jupiter. The unprecedented mission is, quite literally, a "blue light special" in the realm of interplanetary exploration.

Read our preview story.

TUESDAY, SEPTEMBER 25, 2007

With the final touches now complete on the Dawn spacecraft, the future asteroid orbiter is counting down the remaining hours to blastoff at sunrise Thursday from Cape Canaveral, Florida.

The beefed up United Launch Alliance Delta 2-Heavy rocket, equipped with larger solid-fuel boosters, is scheduled to thunder from pad 17B at 7:20 a.m. EDT (1120 GMT). The morning's available launch window will extend to 7:49 a.m., giving a 29-minute period for the liftoff to occur.

Weather forecasters are predicting a 60 percent chance of acceptable conditions. Coastal rain showers and cumulus clouds over the launch area will be the chief worries.

The launch readiness review was conducted Tuesday morning. All systems were reported "go" except for one remaining technical concern about the clearance between the satellite's high-gain antenna and the acoustic blankets inside the rocket's nose cone during launch. Engineers completed their analysis and managers ruled Tuesday afternoon that there was no problem for flight.

Launch countdown operations will commence Wednesday evening. Retraction of the mobile service tower from around the 12-story rocket should be completed before midnight.

Thursday's three-hour Terminal Countdown picks up at 4:20 a.m. EDT. The early-morning count includes fueling of the first stage with highly refined kerosene and supercold liquid oxygen propellants.

A standard pause 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 Dawn'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 39 nautical miles up.

"If you live in the Bahamas, this is one time you can tell your neighbor, with a straight face, that Dawn will rise in the west," said Dawn Project Manager Keyur Patel of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Weather permitting, we are go for launch Thursday morning, a little after dawn."

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, 31 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 Dawn during the trek through the atmosphere is shed just seconds after the second stage comes to life.

Nine minutes into the ascent, the second stage completes its initial firing. The Delta settles into a 100-nautical mile parking orbit along a trajectory that cruises above the central Atlantic before crossing Africa and the Indian Ocean. The second stage reignites its engine off the west coast of Australia at T+plus 51 minutes. The burn will last more than two-and-a-half-minutes as the rocket begins a northeasterly trek over Australia.

The solid-fueled kick motor that serves as the Delta's third stage then spins up and pops free of the second stage to ignite for an 85-second firing to propel Dawn out of Earth orbit.

Dawn should be released from the rocket at 8:22 a.m. EDT, some 62 minutes after an on-time blastoff, while flying northeast of Australia near the Solomon Islands.

"After separation, the spacecraft will go through an automatic activating sequence, including stabilizing the spacecraft, activating flight systems and deploying Dawn's two massive solar arrays," said Patel. "Then and only then will the spacecraft energize its transmitter and contact Earth. We expect acquisition of signal to occur anywhere from one-and-a-half hours to three-and-a-half hours after launch."

Watch this page for live play-by-play countdown and launch reports.

MONDAY, SEPTEMBER 24, 2007
1630 GMT (12:30 p.m. EDT)

Filling of the Delta 2 rocket's second stage with storable fuel is being completed at pad 17B today as preparations proceed for the Thursday's sunrise liftoff on NASA's Dawn asteroid orbiter.

Crews pumped nitrogen tetroxide into the stage on Sunday, but inclement weather precluded the technicians from beginning the Aerozine 50 fuel loading. That hydrazine propellant is being placed aboard the rocket today.

The storable hypergolic fuels power the second stage's Aerojet AJ118-K engine. The stage fires twice during the launch to boost Dawn toward its Earth departure trajectory.

Thursday's launch window will extend from 7:20 to 7:49 a.m. EDT. The weather outlook for the launch opportunity predicts a 70 percent chance of favorable conditions.

Mission managers will gather Tuesday morning for the Launch Readiness Review to assess the progress of pre-flight preparations and any lingering technical issues. If all aspects are deemed "go" for launch, the meeting will conclude with officials giving approval to enter into the countdown on Wednesday night.

SUNDAY, SEPTEMBER 23, 2007
2030 GMT (4:30 p.m. EDT)

Stormy weather at Cape Canaveral prevented technicians from completing work to load storable hypergolic propellants into the Delta 2 rocket at launch pad 17B today, prompting a one-day postponement for this week's liftoff of the Dawn asteroid orbiter.

Launch had been planned for Wednesday. But this slip in the pad schedule means the liftoff will be delayed to Thursday morning at 7:20 a.m. EDT.

TUESDAY, SEPTEMBER 11, 2007

The long-awaited voyage of NASA's Dawn space probe to rendezvous with a pair of small worlds in the asteroid belt has returned to the launching pad for departure from Earth in two week's time.

Read our full story.

SATURDAY, JULY 7, 2007

The scientist leading NASA's Dawn spacecraft to fly the first reconnaissance mission to explore a massive asteroid and a "dwarf planet" believed to harbor water has been designing the project for more than a decade. Liftoff was supposed to happen this weekend, yet troubles interfered. And officials Saturday ordered another delay -- all the way to September.

Read our full story.

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

Launch has been put off until September, NASA decided today. Check back shortly for a full story.

FRIDAY, JULY 6, 2007
2355 GMT (7:55 p.m. EDT)

ANOTHER DELAY. The Dawn asteroid exploration mission won't be launching before Sunday, July 15, NASA officials announced Friday evening after extensive discussions about the availability of downrange tracking assets and the overall readiness to go fly.

The United Launch Alliance Delta 2-Heavy rocket stands fully assembled with Dawn nestled inside the vehicle's nose cone at Cape Canaveral's pad 17B.

But this is the third delay in the past two days for the launch. Stormy weather prevented the Delta 2 rocket's second stage from being fueled on Thursday, forcing the liftoff to be delayed from Saturday to Sunday. NASA decided early Friday morning to slip the launch another 24 hours - to Monday - because of troubles with a telemetry-relay aircraft.

Problems with the tracking plane and delays getting a substitute ship into the Atlantic Ocean region has been a source of headaches for the launch officials. Either the aircraft or the instrumented ship is required to receive telemetry from the rocket during the second and third stage firings off the west-central coast of Africa. Without a mobile tracking asset in place, engineers would have no insight or data while those critical events of the launch occur.

NASA is racing against the calendar because Dawn's current launch opportunity closes July 19, giving just a few days left to get the spacecraft on the required trajectory to fly past Mars for a sling-shot maneuver and then into the asteroid belt for its rendezvous with Vesta and Ceres over the next eight years.

If this period is missed, another one opens in September and extends through late October.

What impact, if any, this latest delay could have to the planned August 3 launch of the Mars lander Phoenix aboard another Delta 2 rocket from the neighboring pad is not immediately clear. The alignment of the planets dictates a tight August 3 to August 24 window for the Phoenix liftoff to happen.

The start of Dawn's mission to examine up close two of the solar system's largest asteroids has been hit by a number of setbacks, including outright cancellation of the project in March 2006. After a heated controversy, NASA restarted the mission less than a month later.

Plans called for the launch to happen June 20, but that date was scrapped because more time was needed to prepare the Delta rocket before on-pad assembly could start. Then a targeted June 30 launch day was doomed when the pad's crane developed a problem last month, causing a hiatus in attaching the solid-fuel boosters.

Launch on July 15 would be possible during a window stretching from 3:22 to 3:54 p.m. EDT.

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

Launch has been pushed back to Monday during an opportunity that will extend from 3:56 to 4:25 p.m. EDT (1956-2025 GMT). A NASA spokesperson says this delay from Sunday to Monday was caused by a problem with the downrange tracking aircraft needed to support telemetry relay during the launch.

Fueling of the second stage with the storable propellants will be rescheduled for tomorrow.

Weather forecasters put the odds of acceptable conditions on Monday at 60 percent. Clouds and thunderstorms within 10 miles of the rocket's flight path will be the concerns to watch.

1235 GMT (8:35 a.m. EDT)

It appears that launch preparations, including the second stage fuel loading and a countdown dress rehearsal planned for today, are being delayed an additional 24 hours. We're awaiting official word from NASA on the reasons and confirmation of a launch date.

THURSDAY, JULY 5, 2007

DELAY. Launch of NASA's Dawn spacecraft has been postponed 24 hours -- to Sunday afternoon -- due to unexpected delays in fueling the Delta 2 rocket's second stage today.

A mismatch between temperatures inside the rocket's nose cone and the second stage caused the vehicle to be a bit too warm for the fueling process to begin at launch pad 17B this morning, a NASA spokesperson explained. The temperatures are being adjusted today in hopes of starting the oxidizer filling later this afternoon.

Complicating the situation further is the stormy weather over Cape Canaveral. A lightning advisory covering the launch area would have prevented the fueling from starting even if the rocket temperature problem hadn't cropped up, the spokesperson said.

If the lightning threat clears later this afternoon, pad crews hope to perform the oxidizer portion of the fueling sequence. That would lead to the hydrazine propellant load occurring tomorrow. But if the weather remains uncooperative today, both oxidizer and fuel would be pumped into the vehicle tomorrow.

The second stage uses storable nitrogen tetroxide and a hydrazine blend called Aerozine 50 to power its Aerojet AJ118-K engine. The stage fires twice during the launch to boost Dawn toward its Earth departure trajectory.

Sunday's launch window will extend from 4:04 to 4:33 p.m. EDT. The weather outlook for the launch opportunity predicts a 60 percent chance of thunderstorms and associated clouds violating the weather rules.

The updated forecast is posted here.

NASA has Sunday and Monday to get the Dawn mission launched or else face a standdown until July 15. The reason is arranging downrange tracking assets to receive telemetry from the rocket during the second and third stage firings, a firm requirement for the launch.

A tracking ship positioned in the Atlantic Ocean off the west-central coast of Africa was expected to be used for the launch. But problems getting the vessel in place forced a late switch to the "Big Crow" instrumented tracking aircraft. NASA says the plane has another job it must support next week, making Saturday, Sunday and Monday the only days that the space agency could reserve the aircraft's services in the near-term.

Hitting Dawn's trajectory to the asteroid belt and the upcoming Mars lander launch from the neighboring Delta rocket pad at Complex 17 makes any liftoff possibilities after July 19 problematic. So mission officials literally have their fingers crossed that Dawn will fly either Sunday or Monday. If not, they say the launch would have its next shot between July 15 and 19. Should they be unlucky and still not have Dawn off the ground by the end of that period, the next chance wouldn't come until September or October, depending on a number of factors.

1230 GMT (8:30 a.m. EDT)

The second stage of the United Launch Alliance Delta 2-Heavy rocket that will loft NASA's Dawn asteroid explorer this weekend is scheduled to be loaded with its supply of storable propellants at Cape Canaveral's pad 17B today.

The decision to proceed with the fueling was made Wednesday after lengthy discussions about the availability of downrange tracking assets and the overall readiness to launch the mission.

Liftoff is planned for Saturday during a window extending from 4:09 to 4:36 p.m. EDT.

Weather forecasters are predicting a 60 percent chance that thunderstorms will prevent the launch on Saturday as well as the backup opportunity on Sunday. See the latest forecast here.

Watch this page for complete live coverage of Saturday's countdown and flight of the Delta rocket.