BY JUSTIN RAY

Follow the countdown and launch of the Boeing Delta 2 rocket with the CALIPSO and CloudSat environmental research spacecraft. Reload this page for the very latest on the mission.

THURSDAY, APRIL 27, 2006
2005 GMT (4:05 p.m. EDT)

NASA has issued a further statement on the sensor issue that delayed today's launch attempt:

"On Wednesday, engineers and mission managers assessed a suspect temperature sensor on the Boeing Delta 2 rocket's second stage. Following a thorough data analysis, they concluded the unusual temperature sensor readings observed during the previous two launch attempts were primarily the result of higher temperature pressurization rates and are not indicative of any defect in the sensor. The sensor does not require replacement and can fly as is."

1620 GMT (12:20 p.m. EDT)

The Delta 2 rocket has been cleared for another launch attempt on Friday.

The issue with the second stage temperature sensor was resolved. Engineers had been concerned about the sensor's bonding and whether repairs were needed, a Boeing spokesperson said. Managers met to discuss the situation and concluded no action was necessary.

The weather forecast calls for acceptable conditions at the 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT) launch time. But viewing is expected to be hampered for spectators due to fog and low visibility.

"An upper level ridge moves into the central coast and Vandenberg area bringing stable weather conditions," the launch weather officer reported today. "Marine layer stratus will develop and move into Vandenberg Friday morning. Winds will remain Northwesterly at 12 - 18 knots for tower roll and decrease to 4 - 8 knots by T-0. Visibility will decrease to 1 mile in fog. Max upper level winds will be from the North at 40 knots at 35,000 feet."

The layer of stratus clouds is predicted at 300 feet with full-sky coverage and tops at 1,500 feet. The temperature will be between 52 and 57 degrees F.

The forecast for Saturday morning, should the launch be delayed for some reason, calls for similar conditions.

0310 GMT (11:10 p.m. EDT Wed.)

A suspect nitrogen temperature sensor on the Boeing Delta 2 rocket's second stage is the reason for the scrub. The sensor may need replacing, NASA says. Engineers are analyzing the situation.

Launch will occur no earlier than Friday morning, pending resolution of the issue.

0257 GMT (10:57 p.m. EDT Wed.)

Air Force officials at Vandenberg say the launch is being rescheduled for 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT) on Friday. The Range's press release is attributing this delay from Thursday to Friday due to "maintenance issues."

0201 GMT (10:01 p.m. EDT Wed.)

SCRUB! The Thursday morning launch has been scrubbed due to a technical problem with the Delta 2 rocket, NASA says. Details on the problem and how long the delay will last have not been confirmed.

WEDNESDAY, APRIL 26, 2006

The weather has remained gloomy at Vandenberg all day. Skies have been gray and overcast. Rain has fallen from time to time. Launch officials are hoping conditions will improve this evening and allow better weather for the Delta 2 rocket to fly early Thursday.

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

A bleak weather outlook forced cancellation of today's opportunity to launch the CALIPSO and CloudSat spacecraft aboard a Boeing Delta 2 rocket from Vandenberg Air Force Base, California. The sixth launch attempt will be made Thursday.

The decision came about 100 minutes before the planned 1002:19 GMT (3:02:19 a.m. PDT; 6:02:19 a.m. EDT) launch time. Loading of liquid oxygen into the rocket's first stage was supposed to be underway when the scrub was called. But officials had delayed the start of that fueling operation while the dismal weather situation was reviewed.

"That is just something we deal with in this business. We have to have good weather and if it's not good we will not launch," NASA spokesman Bruce Buckingham said. "We needed good weather and we're just not going to get it this morning."

Air Force meteorologists were predicting a high chance of violating several launch weather rules today due to thick cloud cover and rain. Conditions were observed "no go" and expected to remain that way, Buckingham said.

This was the fifth scrub in six days for the mission. Another try will be made tomorrow. The weather system impacting Vandenberg is forecast to move out and leave greatly improved conditions for a 1002 GMT launch attempt.

"We anticipate we'll have a much better shot at getting off the ground, as far as weather is concerned," Buckingham said.

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

Weather is expected to improve dramatically over the next 24 hours. The Air Force launch weather officer says there's an 80 percent chance of good conditions tomorrow.

0823 GMT (4:23 a.m. EDT)

SCRUB! Unfavorable weather at Vandenberg Air Force Base has scrubbed today's launch attempt. Liftoff will be rescheduled for 1002 GMT tomorrow.

0822 GMT (4:22 a.m. EDT)

Another weather update has been briefed to management. But the outlook has not improved. The liquid oxygen loading is being delayed while officials discuss the situation.

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

Second stage propellant tank pressurization has been accomplished.

0818 GMT (4:18 a.m. EDT)

The liquid oxygen tanking is on hold at the moment.

0810 GMT (4:10 a.m. EDT)

Mission managers will be getting another weather update before giving a final "go" to start loading liquid oxygen into the Delta 2 rocket's first stage. There's also a countdown clock synchronization problem under discussion, NASA spokesman Bruce Buckingham says.

0805 GMT (4:05 a.m. EDT)

The rocket's guidance system has been turned on.

0804 GMT (4:04 a.m. EDT)

The latest update from meteorologists indicates an 80 percent chance of weather criteria violation this morning due to thick clouds, winds and rain.

0802 GMT (4:02 a.m. EDT)

Launch time now two hours away. Coming up on first stage liquid oxygen loading, weather permitting.

0724 GMT (3:24 a.m. EDT)

The first stage helium and nitrogen system pressurization has been completed.

0706 GMT (3:06 a.m. EDT)

Activation of the rocket's guidance control system is starting.

0702:19 GMT (3:02:19 a.m. EDT)

T-minus 150 minutes and counting! The Terminal Countdown has started for today's launch. Liftoff from Vandenberg Air Force Base in California is targeted for precisely 1002:19 GMT. The launch window is open for just one second.

The countdown currently stands at T-minus 150 minutes. However, there are two holds -- totaling 30 minutes in duration -- planned at T-minus 20 minutes and T-minus 4 minutes.

The SLC-2W pad area has been cleared of workers. However, a warning horn is being sounded at the complex as a precaution to alert any remaining personnel in the vicinity that they should leave immediately.

The pad clearing allows the start of hazardous operations such as the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

0653 GMT (2:53 a.m. EDT)

Each launch team member polled has reported a "ready" status to enter Terminal Count.

0647 GMT (2:47 a.m. EDT)

"Man stations for Terminal Count."

0602 GMT (2:02 a.m. EDT)

T-minus 150 minutes and holding. The countdown has entered a planned 60-minute built-in hold. Clocks will be stopped two more times this morning -- at T-minus 20 minutes and T-minus 4 minutes -- leading to liftoff at 1002:19 GMT (3:02:19 a.m. PDT; 6:02:19 a.m. EDT).

0530 GMT (1:30 a.m. EDT)

Activities are continuing to move forward at Vandenberg for this morning's planned launch.

0200 GMT (10:00 p.m. EDT Tues.)

Officials received a weather briefing a couple of hours ago and decided to proceed with the countdown.

Launch of a Boeing Delta 2 rocket carrying two cloud-studying satellites for NASA is scheduled for 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT) from Vandenberg Air Force Base, California. This will be the fifth try in six days to launch the mission.

TUESDAY, APRIL 25, 2006
1120 GMT (7:20 a.m. EDT)

A smooth countdown unraveled about five minutes before launch time this morning, forcing a fourth delay in five days for the Boeing Delta 2 rocket and two environmental satellites.

Launch team members had reported they were "go" for the precise 1002:40 GMT (3:02:40 a.m. PDT; 6:02:40 a.m. EDT) liftoff from California's Vandenberg Air Force Base. Countdown clocks were about to resume from the planned T-minus 4 minute hold mark. And then engineers suddenly announced high-altitude winds had become unfavorable for the vehicle to ascend through.

"We are 'no go' for upper air winds," a launch official radioed the team.

"Copy that, do not come out of the hold," a team member replied.

"(Launch conductor), let's do our scrub turnaround please."

"Yes, sir."

Weather balloons were deployed throughout the countdown to gauge the speed and direction of upper level winds. NASA spokesman Bruce Buckingham said the data from the last balloon revealed that winds in the region where the Delta 2 rocket flies through maximum aerodynamic pressure were unsafe for a launch today.

"The winds must be in limits at that point to not risk damage to the vehicle during its most fragile point in the flight," said Buckingham.

This launch has one second to lift off each day, which leaves no margin to deal with last-minute issues. That instant in time is dictated by the orbital mechanics of delivering CALIPSO and CloudSat into the proper position for joining NASA's "A-Train" of Earth-observing satellites.

Officials are planning to try again Wednesday. The launch is still targeted for 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT).

But tomorrow's weather outlook is not perfect. Air Force meteorologists say there's a 60 percent chance that cloudy conditions brought by a low pressure system from the Pacific will violate launch rules.

This $515 million mission has endured three previous scrubbed shots at launch. Friday's countdown was less than a minute to blastoff when the phone communications links were lost between officials in Vandenberg's Mission Directors Center and the CALIPSO operations site in Toulouse, France. NASA initially implied these were communication lines involving the spacecraft, but it was more simple than that. CALIPSO was built in Europe under a joint project between the U.S. and France space agencies.

Opportunities on Saturday and Sunday had to be passed up because of problems scheduling an aerial refueling tanker plane to support the downrange launch telemetry relay aircraft.

1006 GMT (6:06 a.m. EDT)

"We have scrubbed our launch attempt for today," NASA spokesman Bruce Buckingham says. "The reason being upper level winds went out of constraints. They were trending a little bit toward the red and in fact approached and passed the red-line limit as we made our last evaluation prior to launch."

1002 GMT (6:02 a.m. EDT)

The launch team is setting up for another countdown tomorrow. Liftoff time remains 1002 GMT. But an approaching weather system makes the forecast somewhat iffy due to possible thick clouds, rain and gusty winds.

1001 GMT (6:01 a.m. EDT)

NASA spokesman Bruce Buckingham says the latest weather balloon data revealed high-altitude winds in the region where the Delta 2 rocket flies through maximum aerodynamic pressure were not safe for the launch today.

0958 GMT (5:58 a.m. EDT)

SCRUB! The upper level winds have been deemed unacceptable for liftoff today. This will force the mission to be scrubbed because the launch window extends only one second.

0957 GMT (5:57 a.m. EDT)

NO GO!

0956 GMT (5:56 a.m. EDT)

Just two minutes are remaining before the countdown resumes.

0954 GMT (5:54 a.m. EDT)

The launch team's final readiness poll just occurred. Everyone said they were ready to proceed with the countdown.

Now, the team members are receiving countdown procedure instructions.

0952:40 GMT (5:52:40 a.m. EDT)

Now 10 minutes until this night-owl rocket launch from Vandenberg Air Force Base, California.

0952 GMT (5:52 a.m. EDT)

NASA Launch Manager Chuck Dovale just conducted his pre-launch poll. Everyone reported a ready status. "Roger that, team is ready for launch."

0949 GMT (5:49 a.m. EDT)

The CALIPSO and CloudSat spacecraft are undergoing their final re-configuration for launch.

0948:40 GMT (5:48:40 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, final polls will be conducted to ensure everything is set for liftoff.

0946 GMT (5:46 a.m. EDT)

The launch weather officer confirms that all conditions remain favorable for flight.

0943 GMT (5:43 a.m. EDT)

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

0942:40 GMT (5:42:40 a.m. EDT)

T-minus 10 minutes. The Range Safety test has been performed.

0938 GMT (5:38 a.m. EDT)

Inhibited checks are now beginning for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course or malfunction during the launch.

0932:40 GMT (5:32:40 a.m. EDT)

T-minus 20 minutes and counting. Clocks are ticking again after the planned 20-minute hold. The countdown will proceed to T-minus 4 minutes where the final hold is scheduled.

0928 GMT (5:28 a.m. EDT)

The Boeing launch team was just polled to confirm everyone is "ready" to continue the countdown. Again, nothing is amiss.

0925 GMT (5:25 a.m. EDT)

NASA Launch Manager Chuck Dovale has polled the space agency's management team for a "go" to proceed on with the countdown. No constraints were reported.

0922 GMT (5:22 a.m. EDT)

Now half-way through this built-in hold at T-minus 20 minutes. Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.

0912 GMT (5:12 a.m. EDT)

T-minus 20 minutes and holding. The countdown has just gone into a planned 20-minute built-in hold. These holds are designed to give the launch team a chance to work any problems or catch up on activities running behind schedule. And engineers will have time to examine all the data from the just-completed steering tests.

Launch remains targeted for the exact moment of 1002:40 GMT from Vandenberg Air Force Base, California.

0909 GMT (5:09 a.m. EDT)

The first stage engine steering checks are complete.

0907 GMT (5:07 a.m. EDT)

T-minus 25 minutes and counting. The countdown is nearing a planned 20-minute built-in hold at the T-minus 20 minute mark. Another hold is scheduled at T-minus 4 minutes. Launch is still set to occur at 1002 GMT this morning.

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

The second stage engine slews are complete. First stage tests have begun.

0903 GMT (5:03 a.m. EDT)

The launch team is 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.

0902 GMT (5:02 a.m. EDT)

There's one hour remaining in the countdown to liftoff. Everything appears to be progressing very smoothly this morning. No significant worries or glitches are being discussed. And the launch weather officer has given a 100 percent chance of acceptable conditions for the 1002 GMT liftoff time.

0852 GMT (4:52 a.m. EDT)

The next event in the countdown comes up in 10 minutes -- the engine steering checks.

0843 GMT (4:43 a.m. EDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank was completed at 0842:59 GMT. The operation took 23 minutes and 54 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel last night. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels last week. The four strap-on booster rockets are solid-propellant.

0839 GMT (4:39 a.m. EDT)

Now 20 minutes into the liquid oxygen loading. Once the first stage tank is 95 percent full, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the rocket.

0832 GMT (4:32 a.m. EDT)

The countdown is entering the final 90 minutes to liftoff.

0829 GMT (4:29 a.m. EDT)

The outer skin of the first stage is icing over as the liquid oxygen tanking operation passes the 10-minute point. It will take about 25 minutes to fill the rocket.

0824 GMT (4:24 a.m. EDT)

Liquid oxygen loading has passed the five-minute mark.

0819 GMT (4:19 a.m. EDT)

Supercold liquid oxygen is starting to flow into the first stage of the Boeing Delta 2 rocket as the countdown continues for today's 1002 GMT launch.

The liquid oxygen, chilled to Minus-298 degrees F, is being pumped from a launch pad storage tank, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel -- loaded aboard the vehicle a few hours ago -- will be consumed by the first stage main engine.

0814 GMT (4:14 a.m. EDT)

The launch team has been given a "go" to start the preparations for loading the rocket's first stage liquid oxygen tank.

0812 GMT (4:12 a.m. EDT)

Roadblocks around the pad are established and the flight hazard area is cleared of all personnel, safety officials report. These steps are confirmed before the hazardous operation of liquid oyxgen loading starts.

0807 GMT (4:07 a.m. EDT)

Second stage propellant tank pressurization has been accomplished.

0803 GMT (4:03 a.m. EDT)

Work to turn on the rocket's guidance system just finished.

0802 GMT (4:02 a.m. EDT)

Now two hours from launch of the Delta rocket. Weather continues to look good and there are no technical problems being reported with the booster or spacecraft.

0733 GMT (3:33 a.m. EDT)

The second stage helium and nitrogen system pressurization is reported complete.

0725 GMT (3:25 a.m. EDT)

The first stage helium and nitrogen system pressurization has been completed.

0706 GMT (3:06 a.m. EDT)

Activation of the rocket's guidance control system is starting.

0702:40 GMT (3:02:40 a.m. EDT)

T-minus 150 minutes and counting! The Terminal Countdown is now underway for today's launch the Boeing Delta 2 rocket with the CALIPSO and CloudSat spacecraft. Liftoff from Vandenberg Air Force Base in California is targeted for precisely 1002:40 GMT. The launch window is open for just one second.

The countdown currently stands at T-minus 150 minutes. However, there are two holds -- totaling 30 minutes in duration -- planned at T-minus 20 minutes and T-minus 4 minutes.

The SLC-2W pad area has been cleared of workers. However, a warning horn is being sounded at the complex as a precaution to alert any remaining personnel in the vicinity that they should leave immediately.

The pad clearing allows the start of hazardous operations such as the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

0653 GMT (2:53 a.m. EDT)

Each launch team member polled has reported a "ready" status to enter Terminal Count.

0647 GMT (2:47 a.m. EDT)

"Man stations for Terminal Count." The launch team members have been instructed to take positions at their consoles. A readiness poll will be performed in a few minutes to verify everyone is prepared to resume the countdown at the end of this scheduled hold at 0702:40 GMT.

0632 GMT (2:32 a.m. EDT)

The launch complex has been cleared of all workers. The Terminal Countdown begins in 30 minutes.

0602 GMT (2:02 a.m. EDT)

T-minus 150 minutes and holding. The countdown has entered a planned 60-minute built-in hold. Clocks will be stopped two more times this morning -- at T-minus 20 minutes and T-minus 4 minutes -- leading to liftoff at 1002:40 GMT (3:02:40 a.m. PDT; 6:02:40 a.m. EDT).

0557 GMT (1:57 a.m. EDT)

The downrange telemetry relay aircraft, known as Big Crow, and the aerial refueling tanker are both airborne now, the launch team says. Problems getting the tanker scheduled to support the launch caused the Saturday and Sunday countdown attempts to be scrubbed.

Big Crow will serve as the mobile telemetry station to relay data from the Delta 2 rocket's second stage during its firing to reach an initial orbit around Earth this morning. The burn ends about 11 minutes into flight, which is after the rocket has flown out of range from the Vandenberg ground tracking site.

0430 GMT (12:30 a.m. EDT)

Mission managers and launch team members are arriving at Vandenberg for the final hours of this morning's countdown. At the Space Launch Complex 2 pad, the mobile service tower has been rolled back to reveal the 12-story Delta 2 rocket. Pad crews are moving equipment, configuring systems and completing their checklists to prepare the seaside complex for today's liftoff.

0100 GMT (9:00 p.m. EDT Mon.)

The Boeing Delta 2 rocket's first stage has been filled with its kerosene propellant for the overnight blastoff. The vehicle took on 10,000 gallons of fuel while still shrouded inside the launch pad's mobile service gantry. That tower is being moved back tonight, and early activities will culminate with the start of the Terminal Countdown at 0702 GMT (12:02 a.m. local; 3:02 a.m. EDT).

SUNDAY, APRIL 23, 2006
1730 GMT (1:30 p.m. EDT)

The Boeing launch team hopes to try again Tuesday morning to deliver two cloud-studying satellites into orbit for NASA using a Delta 2 rocket. Attempts on Saturday and Sunday were thwarted when a refueling tanker aircraft needed to support the downrange launch tracking plane was unavailable.

That tracking plane -- called the "Big Crow" -- will receive live telemetry from the Delta 2 during the initial firing of the second stage that puts the rocket into a parking orbit around Earth. The rocket will fly beyond the coverage zone of the Vandenberg Air Force Base tracking station during the engine burn, prompting the need for an aircraft to serve as a relay to collect the Delta 2 telemetry and then transmit it to engineers at the launch site.

The ground track map illustrates the Big Crow's coverage circle over the Pacific Ocean. The area is marked as MT, or mobile telemetry.

A Tuesday launch, however, still hinges on support being arranged with the refueling plane.

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

NASA says the launch could happen on Monday but the Air Force-controlled Western Range at Vandenberg says liftoff has been delayed to Tuesday at the earliest.

Air Force meteorologists have issued a weather forecast for Tuesday, which predicts a 90 percent chance of acceptable conditions. Winds early in the countdown during tower rollback and thick clouds at launch time are the only areas for concern.

"An upper level ridge will move east of Vandenberg as a low pressure system moves into the Eastern Pacific with a frontal system extending to the south. Weather associated with the system will remain west of Vandenberg," the launch weather officer said of Tuesday morning's outlook.

At the 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT) launch time, meteorologists expect stratus clouds hanging over the pad at 400 feet and cirrus at 18,000 feet, visibility of 2 miles and fog, winds from the north at 5 to 10 knots and a temperature of 53 to 58 degrees F. Maximum upper level winds will be 45 knots from the southwest at 40,000 feet.

0612 GMT (2:12 a.m. EDT)

Today's scrub was caused by more problems with a refueling aircraft required by a downrange launch tracking plane, a NASA spokesman now confirms. Discussions are underway to determine a new launch date.

0515 GMT (1:15 a.m. EDT)

SCRUB! Today's launch attempt has been scrubbed because a downrange tracking asset needed to support the mission is unavailable. Technicians at Vandenberg have been instructed to secure the countdown operation for the night.

0402 GMT (12:02 a.m. EDT)

A second countdown is underway for the Delta 2 rocket launch of CALIPSO and CloudSat. The mobile service tower has been returned to the launch position. Terminal Count will begin at 0702 GMT.

SATURDAY, APRIL 22, 2006
1720 GMT (1:20 p.m. EDT)

The weather forecast for Sunday calls for acceptable conditions to launch the Boeing Delta 2 rocket from Vandenberg Air Force Base, California.

At the 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT) launch time, meteorologists expect stratocumulus clouds at 2,000 feet and altocumulus at 10,000 feet, visibility of 7 miles, winds from the southwest at 5 to 10 knots and a temperature of 50 to 55 degrees F.

0403 GMT (12:03 a.m. EDT)

Launch of the Boeing Delta 2 rocket carrying the CALIPSO and CloudSat spacecraft for NASA has been reset for Sunday at 1002 GMT (3:02 a.m. PDT; 6:02 a.m. EDT) from Vandenberg Air Force Base in California.

Friday's countdown was aborted less than a minute before liftoff when the communications link between CALIPSO and its French ground facilities was lost.

Officials had hoped to reattempt the launch early Saturday. But NASA spokeswoman Erica Hupp said a refueling aircraft required to support a launch tracking plane was unavailable for the new date.

So liftoff of the $515 million mission to examine clouds and particles in the atmosphere has been pushed back to Sunday.

FRIDAY, APRIL 21, 2006

Launch managers are keeping open the possibility of flying the Delta 2 rocket at 3:02 a.m. PDT (1002 GMT; 6:02 a.m. EDT) on Sunday. NASA spokespeople at Vandenberg Air Force Base still cannot confirm what problem led to the further delay.

The weather forecast for Sunday is favorable. The upper level low pressure system that has influenced the Vandenberg weather over the past couple of days will slowly move to the northeast and leave a stable atmosphere in its wake, the launch weather officer says.

2233 GMT (6:33 p.m. EDT)

DELAY. Saturday's launch opportunity has been scrubbed. Details on the reason for the further postponement and when the launch will be rescheduled are expected later tonight.

2150 GMT (5:50 p.m. EDT)

Air Force meteorologists are predicting a 70 percent chance of favorable weather for Saturday morning's liftoff of the Boeing Delta 2 rocket.

"Vandenberg is currently under the influence of an upper level low located west of the central coast. As the low moves across central California, isolated areas of precipitation and cumulus clouds will develop," the launch weather officer reported earlier today.

"Winds at the surface will increase throughout the morning and afternoon hours and be from the West-northwest at 15 - 20 knots gusting to 25 knots by tower roll, but will subside through the evening to 12 - 18 knots by T-0. Upper level winds will be Southwesterly with the max wind at 30,000 feet at 50 knots."

The weather team says there's a 30 percent chance that winds will be too strong for rollback of the mobile service tower from around the rocket this evening.

For launch time, the forecast calls for stratocumulus clouds at 1,500 feet, cumulus clouds at 2,000 feet and altocumulus at 10,000 feet, visibility of 7 miles, light rain in the vicinity and a temperature of 52 to 57 degrees F.

Worries for launch will be cloud thickness and precipitation.

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

This morning's launch of two cloud-studying environmental satellites aboard a Boeing Delta 2 rocket was scrubbed due to a last-minute communications glitch.

Countdown clocks were entering the final 60 seconds before the planned 1002 GMT liftoff from Vandenberg Air Force Base in California when the abort was called.

"Hold, hold, hold," a launch team member commanded.

The primary and backup communications links between the CALIPSO spacecraft and its ground support network in France were lost simultaneously, NASA spokesman Bruce Buckingham said. Controllers required the communications path, forcing the launch to be stopped.

CALIPSO, or the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, is a joint project between the U.S. and France that will generate a global picture of aerosol particles suspended in the atmosphere. The craft is French-built.

Faced with only a split second to launch CALIPSO and its co-passenger aboard the Delta 2 rocket, NASA's CloudSat spacecraft, the mission was automatically scrubbed when the hold was called. Officials are planning to make another launch try tomorrow, if the communications snag can be fixed.

"We anticipate the comm link will be resolved. In fact, the word coming in right now is that they have reestablished communications," Buckingham said a short time ago.

"There will be some discussions throughout the morning to understand exactly how the communications links went down and to assure that will not be the case tomorrow."

1009 GMT (6:09 a.m. EDT)

Tomorrow's one-second launch opportunity will be 1002:26 GMT (6:02:26 a.m. EDT; 3:02:26 a.m. PDT).

1006 GMT (6:06 a.m. EDT)

Officials are tentatively posturing themselves for another launch attempt tomorrow.

1005 GMT (6:05 a.m. EDT)

The launch team is working through rocket safing procedures following the countdown abort.

1005 GMT (6:05 a.m. EDT)

Both the primary and backup communications links between CALIPSO and its support center in France went down simultaneously, violating the launch requirements, NASA says. The satellite is a joint U.S. and French project.

1003 GMT (6:03 a.m. EDT)

The CALIPSO spacecraft lost communications lock with its ground systems. That prompted the mission team to call a hold.

1002 GMT (6:02 a.m. EDT)

The countdown was halted just inside T-minus 1 minute due to a problem. This effectively scrubs the liftoff for today. The available launch window was just one-second long, leaving no margin for any delays.

1001 GMT (6:01 a.m. EDT)

HOLD! Countdown has been stopped.

1001 GMT (6:01 a.m. EDT)

T-minus 1 minute. The Range has given its final clear-to-launch.

The Delta 2 rocket's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

1000 GMT (6:00 a.m. EDT)

T-minus 80 seconds. LOX topping to 100 percent is underway.

1000 GMT (6:00 a.m. EDT)

T-minus 1 minute, 45 seconds. The launch pad water suppression system is being activated.

1000 GMT (6:00 a.m. EDT)

T-minus 2 minutes. The first stage liquid oxygen vents are now being closed so the LOX tank can be pressurized for launch. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

0959 GMT (5:59 a.m. EDT)

T-minus 2 minutes, 30 seconds. The payloads have been declared "go" for launch.

0959 GMT (5:59 a.m. EDT)

T-minus 2 minutes, 45 seconds. Vehicle ordnance is being armed.

0959 GMT (5:59 a.m. EDT)

T-minus 3 minutes.

0958 GMT (5:58 a.m. EDT)

T-minus 3 minutes, 45 seconds and counting. The Delta 2 rocket's systems are now transferring to internal power for launch. And the launch pad water system is being enabled.

0958 GMT (5:58 a.m. EDT)

T-minus 4 minutes and counting! Clocks are ticking down the final moments for liftoff of Delta 314 with the CALIPSO and CloudSat spacecraft. Launch is set for 1002:08 from Vandenberg Air Force Base, California.

0957 GMT (5:57 a.m. EDT)

The "go" has been given to restart the countdown clock in one minute.

0956 GMT (5:56 a.m. EDT)

Just two minutes are remaining before the countdown resumes.

0954 GMT (5:54 a.m. EDT)

The team members are now receiving final instructions on countdown procedures.

0954 GMT (5:54 a.m. EDT)

The launch team's final readiness poll just occurred. Everyone said they were ready to proceed with the countdown.

0952 GMT (5:52 a.m. EDT)

The launch team is looking at a technical issue.

0948 GMT (5:48 a.m. EDT)

The CALIPSO and CloudSat spacecraft are undergoing their final re-configuration for launch.

0948:08 GMT (5:48:08 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, final polls will be conducted to ensure everything is set for liftoff.

0946 GMT (5:46 a.m. EDT)

The launch weather officer has announced that all conditions are within limits for flight.

0943 GMT (5:43 a.m. EDT)

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

0942 GMT (5:42 a.m. EDT)

T-minus 10 minutes.

0938 GMT (5:38 a.m. EDT)

Inhibited checks are now beginning for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course or malfunction during the launch.

0932 GMT (5:32 a.m. EDT)

T-minus 20 minutes and counting. Clocks are ticking again after the planned 20-minute hold. The countdown will proceed to T-minus 4 minutes where the final hold is scheduled.

0928 GMT (5:28 a.m. EDT)

The Boeing launch team was just polled to confirm everyone is "ready" to continue the countdown.

0925 GMT (5:25 a.m. EDT)

NASA Launch Manager Chuck Dovale says the Delta 2 rocket, both payloads, the Range, downrange tracking assets, weather and upper level winds all remain "go" for liftoff.

0922 GMT (5:22 a.m. EDT)

Data link checks have been completed.

0922 GMT (5:22 a.m. EDT)

Now half-way through this built-in hold at T-minus 20 minutes. Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.

0915 GMT (5:15 a.m. EDT)

The first stage engine steering checks are complete.

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

The launch weather officer says all conditions are "go" for liftoff at this time.

0912 GMT (5:12 a.m. EDT)

T-minus 20 minutes and holding. A 20-minute built-in hold in the countdown has started. These holds are 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.

Launch remains targeted for the precise moment of 1002:08 GMT from Vandenberg Air Force Base, California.

0911 GMT (5:11 a.m. EDT)

The second stage engine slews are complete. First stage tests have begun.

0909 GMT (5:09 a.m. EDT)

The launch team is 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.

0907 GMT (5:07 a.m. EDT)

T-minus 25 minutes and counting. The countdown is nearing a planned 20-minute built-in hold at the T-minus 20 minute mark. Another hold is scheduled at T-minus 4 minutes. Launch is still set to occur at 1002 GMT this morning.

0906 GMT (5:06 a.m. EDT)

The steering checks are running a few minutes behind schedule.

0902 GMT (5:02 a.m. EDT)

There's one hour remaining in the countdown to liftoff.

0852 GMT (4:52 a.m. EDT)

Next up in the countdown will be engine steering checks starting about 10 minutes from now.

0843 GMT (4:43 a.m. EDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank was completed at 0842:47 GMT. The operation took 23 minutes and 52 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel last night. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels earlier this week. The four strap-on booster rockets are solid-propellant.

0839 GMT (4:39 a.m. EDT)

Now 20 minutes into the liquid oxygen loading. Once the first stage tank is 95 percent full, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the rocket.

0832 GMT (4:32 a.m. EDT)

The countdown is entering the final 90 minutes to liftoff. All continues to go well today.

0829 GMT (4:29 a.m. EDT)

The outer skin of the first stage is icing over as the liquid oxygen tanking operation passes the 10-minute point. It will take about 25 minutes to fill the rocket.

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

Upper level winds were a concern earlier tonight. However, data from weather balloons indicates conditions aloft are improving.

0824 GMT (4:24 a.m. EDT)

Liquid oxygen loading has passed the five-minute mark.

0819 GMT (4:19 a.m. EDT)

Supercold liquid oxygen is starting to flow into the first stage of the Boeing Delta 2 rocket as the countdown continues for today's 1002 GMT launch.

The liquid oxygen, chilled to Minus-298 degrees F, is being pumped from a launch pad storage tank, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel -- loaded aboard the vehicle a few hours ago -- will be consumed by the first stage main engine.

0812 GMT (4:12 a.m. EDT)

The launch team has been given a "go" to start the preparations for loading the rocket's first stage liquid oxygen tank.

0812 GMT (4:12 a.m. EDT)

Roadblocks around the pad are established and the flight hazard area is cleared of all personnel, safety officials report. These steps are confirmed before the hazardous operation of liquid oyxgen loading starts.

0810 GMT (4:10 a.m. EDT)

Work to turn on the rocket's guidance system has been completed.

0806 GMT (4:06 a.m. EDT)

NASA Launch Manager Chuck Dovale has polled the space agency's advisory team for a "go" to start loading liquid oxygen. No constraints were reported.

Next, Boeing Mission Director Rich Murphy will do his readiness check before giving the final approval to the launch team.

0802 GMT (4:02 a.m. EDT)

Now two hours from the scheduled launch time. There are no technical concerns being worked with the rocket or payloads. The launch weather officer will be watching cloud thickness as the countdown proceeds. And we're awaiting further word on the upper level wind conditions.

0730 GMT (3:30 a.m. EDT)

Normally during this time in a Delta 2 countdown the first stage is loaded with 10,000 gallons of a highly refined kerosene. However, the propellant was pumped into the rocket several hours ago to weight down the vehicle and gave it more stability in the wind.

0724 GMT (3:24 a.m. EDT)

The first stage helium and nitrogen system pressurization has been completed.

0706 GMT (3:06 a.m. EDT)

Activation of the rocket's guidance control computer is starting.

0702 GMT (3:02 a.m. EDT)

T-minus 150 minutes and counting! The Terminal Countdown is now underway for today's launch the Boeing Delta 2 rocket with the CALIPSO and CloudSat spacecraft. Liftoff from the SLC-2W pad at Vandenberg Air Force Base, California, is still targeted for 1002:08 GMT.

The pad area has been cleared of workers. However, a warning horn is being sounded at the complex as a precaution to alert any remaining personnel in the vicinity that they should leave immediately.

The pad clearing will allow the start of hazardous operations such as the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown currently stands at T-minus 150 minutes. However, there are a pair of holds -- totaling 30 minutes in duration -- planned at T-minus 20 minutes and T-minus 4 minutes.

0653 GMT (2:53 a.m. EDT)

Each launch team member polled has voiced a "ready" status to begin Terminal Count.

0647 GMT (2:47 a.m. EDT)

"Man stations for Terminal Count." The launch team members have been instructed to take positions at their consoles. A readiness poll will be performed in a few minutes to verify everyone is prepared to resume the countdown at the end of this scheduled hold at 0702:08 GMT.

0645 GMT (2:45 a.m. EDT)

Clearing of the launch pad of all workers is underway. Once the area is clear, the hazardous countdown operations can begin.

0615 GMT (2:15 a.m. EDT)

We've posted a collection of photos taken a couple of hours ago when the launch pad mobile service tower was rolled back to reveal the Delta 2 rocket for liftoff. See the gallery here.

0602 GMT (2:02 a.m. EDT)

T-minus 150 minutes and holding. The countdown has entered a planned 60-minute built-in hold. Clocks will be stopped two more times this morning -- at T-minus 20 minutes and T-minus 4 minutes -- leading to liftoff at 1002 GMT.

0550 GMT (1:50 a.m. EDT)

Technicians are busily working around the base of the Delta 2 rocket.

Meanwhile, the full launch team and senior management group are arriving at their consoles. The Terminal Countdown begins in just over an hour.

0520 GMT (1:20 a.m. EDT)

With Thursday's Atlas 5 rocket launch from Florida now in the history books, attention turns to California where a Delta 2 rocket is being prepped for liftoff less than five hours from now. Watch this page for live updates.

0350 GMT (11:50 p.m. EDT Thurs.)

The mobile service tower enclosing the Delta 2 rocket at Space Launch Complex 2-West has just rolled back. The move was delayed for a couple of hours this evening.

WEDNESDAY, APRIL 19, 2006

The Launch Readiness Reviews were held Wednesday and officials gave the "go" to begin the countdown on Thursday afternoon.

"We've held all of our reviews within NASA and we're ready to proceed tomorrow night," NASA launch manager Chuck Dovale said today.

"This vehicle has been on the pad awhile and we're ready to see it fly," Dovale added, noting that on-pad assembly of the rocket began last summer.

Thursday's countdown activities include a weather briefing at 3 p.m. local (6 p.m. EDT) for managers to get an update on the wind conditions for rolling back the service tower from around the Delta vehicle. And the decision will be made whether to load the kerosene fuel into the rocket's stage prior to tower rollback -- to give the Delta more weight and stability once it is exposed -- or keep the fueling operation on the normal schedule during the final three hours of the count.

Moving of the tower into the launch position will occur between 4 and 6 p.m. (7-9 p.m. EDT). The next few hours will be spent configuring the pad and support equipment for launch.

The Terminal Countdown begins at 12:02 a.m. (3:02 a.m. EDT) from the T-minus 150 minute mark. The rocket's guidance computer will be powered up and loading of the first stage will begin if not accomplished earlier.

Another weather briefing is planned for 1:02 a.m. (4:02 a.m. EDT) to brief management on current and forecast conditions before loading supercold liquid oxygen into the first stage. LOX loading is set to get underway at 1:17 a.m.

Steering checks of the rocket's engine nozzles occur at 2:02 a.m. Then the countdown enters a 20-minute planned hold at 2:12 a.m. When the clocks resume ticking, the vehicle's safety-destruct system will be checked by the Range.

The count has a final 10-minute hold at the T-minus 4 minute mark starting at 2:48 a.m. Final polls of the launch team will be conducted to ensure everything is ready to proceed with liftoff.

Launch must occur at exactly 3:02:08 a.m. (6:02:08 a.m. EDT) or else be scrubbed for the day. The launch window is just one-second long.

TUESDAY, APRIL 18, 2006

A pair of environmental satellites seeking new insights into clouds and aerosols will share a launch into space early Friday aboard a Boeing Delta 2 rocket from Vandenberg Air Force Base in California. It will be Boeing's first launch since a contentious labor strike grounded the Delta fleet last fall.

Liftoff is scheduled for 3:02 a.m. local (6:02 a.m. EDT; 1002 GMT). The launch opportunity lasts only a split second to jump into the tracks of NASA's A-Train of Earth-observing satellites.

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat spacecraft are headed for polar orbit where they will fly in formation with NASA's Aqua and Aura satellites.

"This is truly an exciting time. We're entering a new era, sort of a new journey in the observations of the Earth's atmosphere with these new satellite missions," said Graeme Stephens, CloudSat principal investigator from Colorado State University.

CALIPSO is a joint project between the U.S. and France that will generate a global picture of aerosol particles suspended in the atmosphere.

"With the high resolution observation that CALIPSO will provide, we will get a better understanding of aerosol transport and how our climate system works," said David Winker, CALIPSO principal investigator at NASA's Langley Research Center.

NASA's CloudSat will serve as a CAT scan to reveal the inner workings of clouds.

"The new information from CloudSat will answer basic questions about how rain and snow are produced by clouds, how rain and snow are distributed worldwide and how clouds affect the Earth's climate ," Stephens said.

The 12-story Delta 2 rocket will fly from the Space Launch Complex 2-West pad, soaring over the Pacific Ocean and headed southward along the California coast in the predawn darkness. Residents awake just after 3 a.m. could see the fiery contrail of the vehicle streaking to space, if the weather allows.

Meteorologists predict the viewing conditions in the local Vandenberg area, however, will be poor. A complete overcast of low clouds at 400 feet, three miles of visibility and fog is forecast.

But the weather, despite hampering local spectators, is expected to be acceptable for launch. The Air Force launch weather officer says there's an 80 percent chance of meeting the liftoff criteria. The only worry at launch time could be the overhead clouds being too thick for the rocket to safely punch through.

Powering the rocket skyward will be the kerosene-fueled Rocketdyne RS-27A main engine and four solid-fuel boosters. Those Alliant strap-on motors burn out in 65 seconds and then separate about 18 seconds later, leaving the first stage to continue firing through T+plus 4 minutes, 26 seconds.

The second stage then ignites for the first of two burns to deliver CALIPSO and CloudSat into the target orbit. The initial firing lasts six-and-a-half minutes to achieve a parking orbit with a high point of 434 miles, low point of 115 miles and inclination of 98.08 degrees to the equator.

The rocket coasts over the South Pacific, loops around Antarctica and heads northward toward Africa. Then it comes within view of the Malindi tracking station in Kenya as the second stage's Aerojet engine re-starts 60 minutes after liftoff for a short 12-second burn that circularizes the orbit for payload deployment. The orbit resulting from the second burn will have a high point of 436 miles, low point of 427 miles and inclination of 98.2 degrees to the equator.

Release of CALIPSO occurs over Africa at T+plus 62 minutes, 24 seconds, or 4:04 a.m. PDT (7:04 a.m. EDT; 1104 GMT).

The second stage continues on, cruising high above Europe and then the northern-most parts of the globe before crossing over northwestern Canada and back out over the Pacific where the Dual Payload Attach Fitting -- the barrel-like structure that supported CALIPSO during launch and enclosed CloudSat -- is opened up. The top portion of the DPAF is jettisoned at T+plus 95 minutes, 19 seconds to expose CloudSat for its release from the rocket.

CloudSat is deployed over the Pacific at T+plus 96 minutes, 39 seconds, or 4:38 a.m. PDT (7:38 a.m. EDT; 1138 GMT), after nearly completing a full orbit of the Earth.

This Delta 2 mission has been waiting for several months to launch. The payloads were ready to transport from the hangar to the launch pad for liftoff last October. But officials halted the move and the launch because of a looming labor dispute between Boeing and its machinists. That union went on strike in November, grounding the entire Delta program through February.

Technical problems, including concerns with the batteries used in the rockets' flight termination safety-destruct system, added to the delays.

But all of the past issues have been resolved, officials said this week.

"It's good to be back getting ready for a launch," Boeing mission director Rich Murphy said Tuesday.

The Flight Readiness Review was completed Monday with no significant issues left to wrestle. Technicians were spending Tuesday loading the storable propellants into the rocket's second stage. And the final Launch Readiness Reviews to give approval to enter into the countdown will be held on Wednesday.

Watch this page for live updates during the countdown and launch!