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.

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.