A second stage battery low voltage reading is what stopped the countdown about 50 seconds before liftoff tonight, rocket-maker United Launch Alliance says.

Given the three consecutive days of trying to launch, officials will give the team a chance to catch its breath tomorrow and set the next attempt for Thursday evening at 7:20 p.m. PDT (10:20 p.m. EDT).

"During the terminal launch countdown on Tuesday, at approximately one minute before launch, mission managers noted a low second stage battery voltage reading. This battery is used to power the electrical systems on the Delta 2 second stage during flight," ULA's press statement reads.

"To allow for crew rest after three straight days of launch attempts and engineers the time required to correct this issue, the next launch attempt is scheduled for Nov. 4."

We'll pass along further information about the technical details behind the scrub and launch rescheduling plans as they become available.

The weather forecast for tomorrow, should the launch be rescheduled for then, calls for another night of beautiful conditions at Vandenberg.

Draining of the supercold liquid oxygen from the first stage is getting underway. And the rocket's pressure vessels are being vented down from flight levels.

It is too early to know when the next launch attempt will be made. Another try could be made tomorrow night at 7:20 p.m. PDT.

The launch team is working through the post-hold checklist to safe the Delta 2 rocket and ground equipment, ultimately placing systems back into the configuration they were in at T-minus 4 minutes and holding.

This automatically cancels tonight's launch attempt because the available liftoff opportunity lasts only a split second. There's no time left to resolve the issue and still fly this evening.

The launch team detected two alarms about a minute before liftoff and had to stop the countdown clocks.

HOLD! The countdown has been halted.

T-minus 80 seconds. First stage liquid oxygen topping to 100 percent is underway.

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

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.

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

T-minus 3 minutes and counting down to the fourth Delta rocket launch dedicated to deploying the COSMO-SkyMed quartet.

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.

T-minus 4 minutes and counting! Clocks are ticking down the final moments for liftoff of Delta 350 with the COSMO-SkyMed 4 spacecraft. Launch is set for 7:20:05 p.m. local time from California's Central Coast.

Now five minutes from launch! The "go" has been given for release of the hold in one minute.

This evening's instantaneous launch opportunity occurs at 7:20:05 p.m. local (10:20:05 p.m. EDT; 0220:05 GMT). The launch is precisely timed to put the payload into the proper orbital plane for the COSMO-SkyMed satellite constellation. That means there's just a split second available for the rocket to lift off.

At the time of launch, the COSMO 1 satellite will be 389 statute miles over the Middle East, COSMO 2 above the South Pacific at 395 statute miles and COSMO 3 passing over Antartica at 405 statute miles altitude.

COSMO 4 has been configured for launch.

A second flight program is being loaded into the rocket based on the winds aloft.

No problems were reported in that poll.

The final pre-flight poll of the launch team now underway to confirm systems are "ready" for liftoff of the Delta 2 rocket and COSMO 4 spacecraft.

Now 10 minutes from launch. This will be:

• The 350th Delta rocket launch since 1960
• The third Delta of 2010
• The 148th Delta 2 rocket mission since 1989
• The 39th Delta 2 rocket launch from Vandenberg AFB
• The 46th commercial mission for Delta 2
• The 20th commercial Delta 2 from Vandenberg
• ULA's 7th commercial Delta 2 conducted for Boeing
• The fourth of four COSMO-SkyMed satellites

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 time of 7:20:05 p.m. local (10:20:05 p.m. EDT; 0220:05 GMT) for the Delta 2 rocket with COSMO 4.

The COSMO 4 spacecraft is undergoing final configuring for launch.

The launch weather officer confirms all conditions are "go" for liftoff.

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

The upper level wind conditions have been loaded into the Delta 2 rocket's flight computer for launch.

Twenty minutes to go. The Delta rocket will be flying in its configuration known as the 7420-10 vehicle. The two-stage launcher is fitted with four strap-on solid-propellant motors and a 10-foot diameter composite nose cone.

After quickly climbing away from its coastal pad, the rocket will soar southward over the Pacific Ocean. The four solid boosters burn out and separate less than 90 seconds into the flight about 15 nautical miles up, leaving the kerosene-powered main engine to continue pushing the rocket to an altitude of 60 miles. The spent stage then jettisons to let the hydrazine-fueled second stage ignite.

Within 12 minutes, the vehicle settles into an initial 100 x 348 nautical mile parking orbit along a trajectory the cruises above the South Pacific before crossing Antarctica and then proceeding northbound toward Africa. The second stage reignites its engine for 12 seconds over Madagascar to reach a near-circular polar orbit of 335 x 341 nautical miles (385 x 392 statute miles) above the planet.

The 4,200-pound payload is expected to be released from the rocket 58 minutes after blastoff.

T-minus 15 minutes and counting. Countdown clocks are running again following the planned 20-minute hold. The count will continue to the T-minus 4 minute mark where another planned hold is scheduled. Launch remains set to occur at 7:20:05 p.m. local (10:20:05 p.m. EDT; 0220:05 GMT).

A poll of the launch team confirms everyone is ready to press ahead with the countdown after this pre-planned 20-minute hold.

Now just 30 minutes away from blastoff. The purpose of tonight's launch is hauling the COSMO-SkyMed 4 satellite into its desired orbital perch, joining three sister-craft deployed by previous Delta 2 rockets in 2007 and 2008.

Each of these spacecraft in the Constellation of Small Satellites for Mediterranean basin Observation (COSMO) can produce 450 images per day.

The satellites have proved themselves beneficial to humanitarian organizations responding to natural disasters, such as hurricanes and earthquakes.

The constellation of four satellites enables any specific region of the planet to be observed by COSMO-SkyMed every six hours. That allow authorities to assess and begin responding when a crisis strikes.

The picture-collecting time between civil and military uses is proportional to the financial contributions made during development of the system. The Italian Space Agency funded about 70 percent and the Ministry of Defence provided about 30 percent.

Imagery released for civilian purposes have a resolution of 1 meter, meaning objects as small as that size can be seen. The military capability is even sharper, though its exact resolution is classified.

The second stage's fuel and oxidizer tanks, which were filled with storable propellants earlier this week, are being pressurized for launch.

T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final portion of the Terminal Countdown. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

Now moving into data link checks to verify good telemetry connections.

The first stage engine steering checks are complete.

The second stage engine slews just finished. First stage tests are starting.

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.

Another absolutely gorgeous sunset at America's western spaceport, as seen in the live webcast. The Delta rocket will be blasting off just after nightfall.

Sixty minutes to launch of the fourth COSMO-SkyMed satellite -- Italy's home-grown Earth observing system that is the country's largest space project.

Developed by Thales Alenia Space Italia for the Italian Space Agency and the Italian Ministry of Defence, COSMO-SkyMed is a constellation of radar-imaging spacecraft for civil and military reconnaissance.

Each satellite is equipped with an X-Band Synthetic Aperture Radar instrument for environmental monitoring, resource management and territorial security surveillance. They are capable of seeing the ground in daylight or darkness, with clear skies or cloudy ones.

Checks of the rocket's safety system have been accomplished in the past few minutes of the countdown.

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The process took 26 minutes and 25 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

And now the Delta 2 rocket stands fully fueled its launch of the COSMO-SkyMed spacecraft at 7:20 p.m. local (10:20 p.m. EDT; 0220 GMT). The vehicle's first stage was successfully loaded with RP-1 kerosene fuel earlier today. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels a few days ago. And the four strap-on booster rockets are solid-propellant.

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.

Liftoff is just 90 minutes away. Everything is looking good for tonight's launch of the 350th flight for the Delta rocket program.

Ten minutes into the flow. LOX loading is an approximate 25-minute process to fill the first stage liquid oxygen tank.

Pressurization of the first stage helium and nitrogen systems has been completed as the countdown continues to launch of the COSMO-SkyMed 4 satellite.

Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from a 28,000-gallon storage tank at Space Launch Complex 2, through plumbing and into the bottom of the 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.

The launch team is performing the preparatory steps for filling the liquid oxygen tank.

The official "go" has been given to start first stage liquid oxygen loading right on time.

The rocket's guidance and control system has been brought online.

Now two hours from launch.

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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 time of 7:20:06 p.m. local (10:20:06 p.m. EDT; 0220:06 GMT) for the Delta 2 rocket with COSMO 4.

The COSMO 4 spacecraft is undergoing final configuring for launch.

The launch weather officer confirms all conditions are "go" for liftoff.

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

The upper level wind conditions are being loaded into the Delta 2 rocket's flight computer for launch.

T-minus 15 minutes and counting. Countdown clocks are running again following the planned 20-minute hold. The count will continue to the T-minus 4 minute mark where another planned hold is scheduled. Launch remains set to occur at 7:20:06 p.m. local (10:20:06 p.m. EDT; 0220:06 GMT).

Approval has been given restart the countdown as scheduled. A poll of the launch team verified all systems were ready to go.

Now just 30 minutes from launch. Tonight's mission marks the 350th flight in the Delta rocket family dating back 50 years, a history that spans America's space program.

"It's special, 350 is special. We've been working really hard to make sure all of the missions (are successful). We treat each one of them unique and make sure everything goes smoothly, and hopefully our customer will be happy with it," says Hieu Lam, Boeing's mission director.

"I started with Delta 178, so it's been 172 Delta's that I've been involved with in one way or another. I've been an engineer, mission manager or program manager. I've seen everything from the first Delta 2 to Delta 3 to Delta 4, and I'm very, very happy to have a career here with Delta."

United Launch Alliance says no problems are being worked in the countdown

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T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final portion of the Terminal Countdown. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

The first stage engine steering checks just finished.

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

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.

Sixty minutes to launch. The Delta rocket will be flying in its configuration known as the 7420-10 vehicle. The two-stage launcher is fitted with four strap-on solid-propellant motors and a 10-foot diameter composite nose cone.

After quickly climbing away from its coastal pad, the rocket will soar southward over the Pacific Ocean. The four solid boosters burn out and separate less than 90 seconds into the flight about 15 nautical miles up, leaving the kerosene-powered main engine to continue pushing the rocket to an altitude of 60 miles. The spent stage then jettisons to let the hydrazine-fueled second stage ignite.

Within 12 minutes, the vehicle settles into an initial 100 x 348 nautical mile parking orbit along a trajectory the cruises above the South Pacific before crossing Antarctica and then proceeding northbound toward Africa. The second stage reignites its engine for 12 seconds over Madagascar to reach a near-circular polar orbit of 335 x 341 nautical miles (385 x 392 statute miles) above the planet.

The 4,200-pound payload is expected to be released from the rocket 58 minutes after blastoff.

It's a spectacular autumn sunset along California's Central Coast at Vandenberg Air Force Base, America's western spaceport.

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The process took 26 minutes and 30 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

And now the Delta 2 rocket stands fully fueled its launch of the COSMO-SkyMed spacecraft at 7:20 p.m. local (10:20 p.m. EDT; 0220 GMT). The vehicle's first stage was successfully loaded with RP-1 kerosene fuel earlier this evening. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels a few days ago. And the four strap-on booster rockets are solid-propellant.

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.

Liftoff time is just 90 minutes away.

Ten minutes into the flow. LOX loading is an approximate 25-minute process to fill the first stage liquid oxygen tank.

It's a really beautiful evening out there at the launch pad, as you can see in the live streaming video.

Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from a 28,000-gallon storage tank at Space Launch Complex 2, through plumbing and into the bottom of the 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.

The formal "go" has been given for liquid oxygen loading. The earlier heater trouble has been resolved, officials report.

Work to turn on and configure the Delta's onboard guidance computer has been completed.

The launch team is beginning preparations for filling the rocket's first stage liquid oxygen tank.

Pressurization of the first stage helium and nitrogen systems has been completed as the countdown continues to launch of the COSMO-SkyMed 4 satellite.

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's planned launch. The tank was filled with a highly refined kerosene, called RP-1, during a 20-minute, 29-second process.

The next major task in the count will be loading supercold cryogenic liquid oxygen into the first stage.

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.

Rapid-loading of the RP-1 tank has concluded with 9,800 gallons already aboard the rocket. Fine load is continuing to finish filling the tank.

Current weather conditions at the launch pad include clear skies, unrestricted visibility and northwesterly winds of 18 knots.

The weather outlook continues to be perfect for launch. There's a zero percent chance of clouds or ground winds violating the weather rules tonight.

The launch team has computed that today's full load for the first stage fuel tank is 9,948 gallons.

Once the tank is filled to 98 percent or 9,800 gallons, the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

About ten minutes into the fueling process. The rocket's kerosene tank has been filled with 5,000 gallons so far.

Fueling begins. About 10,000 gallons of the kerosene propellant are pumping into the base of the rocket from storage tanks at the pad as fueling of the Delta 2's first stage begins for tonight's launch.

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First stage fueling preparations are in work. After verifying valves, sensors, flow meters and equipment are ready, a highly-refined kerosene fuel will begin flowing into the vehicle a few minutes from now.

Vehicle pressurizations are getting started and approval has been given to start loading the first stage with its kerosene fuel supply.

The last members of the pad crew are departing the restricted area around Space Launch Complex 2, clearing the way for full countdown activities to get underway.

Hazardous operations, such as pressurizing the first and second stage helium and nitrogen systems and the second stage fuel and oxidizer tanks, won't begin until after the launch pad is cleared of all workers.

The rocket's guidance computer is being turned on to activate the control system for flight.

Countdown begins! The three-hour Terminal Countdown sequence has been initiated for today's launch of the Delta 2 rocket from Vandenberg Air Force Base in California.

Technicians are still at the launch pad working on the heater issue that prompted last night's scrub. But the countdown has started in hopes of being able to launch this evening at 7:20:06 p.m. local (10:20:06 p.m. EDT; 0220:06 GMT). Today's available launch window is open for just one second.

The launch team has been polled to verify all consoles are manned and ready to begin the Terminal Countdown when this hold ends at 4:20 p.m.

The call to "man stations for Terminal Count" just went out to the launch team.

T-minus 150 minutes and holding. The countdown has gone into the pre-planned 60-minute built-in hold. The Terminal Countdown begins once the hold concludes, leading to launch at 7:20:06 p.m. local (10:20:06 p.m. EDT; 0220:06 GMT) from Vandenberg Air Force Base in California.

The launch pad is getting configured, team members are arriving on console in the control center and clocks are ticking toward tonight's liftoff. The exact launch time being targeted is 7:20:06 p.m. PDT, one second earlier than last night.

Launch preparations are underway for tonight's second shot at flying the Delta 2 rocket with the COSMO-SkyMed 4 satellite. The mobile service gantry is beginning to retract away from the launcher right now, rolling back on rail tracks to uncover the 12-story space booster.

The tower had been moved around the Delta after last night's scrub as part of standard procedures. The rocket was drained of its first stage fuels and put back into a safe configuration following the postponement.

The great weather enjoyed last night will continue for tonight's launch opportunity, Air Force meteorologists say.

With high pressure dominating the weather pattern at Vandenberg Air Force Base, the forecast calls for a 100 percent chance of conditions within the Delta 2 rocket's launch criteria.

The launch time outlook includes just a couple high cirrus clouds around 30,000 feet, visibility of seven miles, northwesterly winds of 15 to 20 knots and a temperature between 62 and 67 degrees F.

Flight of the Delta 2 has been rescheduled for Monday evening, rocket-maker United Launch Alliance says, after tonight's scrub was called for a heater problem.

"During the terminal launch countdown Sunday, an engine section heater did not operate properly. The heater is designed to keep the Delta 2's engine components warm during the fueling of the rocket prior to flight," ULA's press statement reads.

"To allow engineers the time required to correct this issue, the scheduled Sunday launch attempt was delayed 24 hours. Updates to the COSMO-SkyMed 4 mission status will be issued as new information becomes available."

To recap, the Delta 2 rocket was fueled up and counting down to blastoff tonight from Vandenberg Air Force Base, California. Activities were going smoothly and no problems had been announced. However, engineers were monitoring a potential concern and the management team ultimately determined it was prudent to delay the launch for further analysis. We'll pass along further information about the problem as it becomes available.

For now, launch could be rescheduled for Monday night at 7:20 p.m. PDT carrying the Italian COSMO-SkyMed 4 radar-imaging satellite.

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The launch team will prepare for another countdown tomorrow night for liftoff at 7:20 p.m. PDT (10:20 p.m. EDT), assuming the issue can be resolved in time.

A worry has popped up and officials have decided to postpone the launch until tomorrow night. There's not enough time to sort through the situation and get the rocket off the ground in tonight's one-second liftoff opportunity.

SCRUB. Tonight's launch attempt is being called off due to a technical concern that has arisen.

Now just 30 minutes away from this 350th flight of the Delta rocket.

"I'm personally just very proud to be part of this team. When you look back at the accomplishments of Delta 1, Delta 2 and now Delta 4, it's amazing," says Kris Walsh, ULA's commercial program manager. "It's a milestone, but every one is just a unique launch and making sure that everything is ready."

T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final portion of the Terminal Countdown. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

But United Launch Alliance says everything is proceeding smoothly with no problems to report on this night.

The first stage engine steering checks just finished.

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

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.

Sixty minutes to launch. A large crowd of VIPs representing the the Italian Space Agency and the Italian Ministry of Defence will be on hand at Vandenberg to cheer the Delta 2 rocket and COSMO 4 into orbit tonight.

"Each one of these COSMO launches has been special for us and for our customer as well. This is probably the biggest satellite program they have in their country. So it is a major event for them. They invite a lot of dignitaries and very high-level government officials," Hieu Lam, the mission director.

It's a beautiful night at the launch pad. The sun is setting and rocket is poised for its nighttime blastoff.

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The process took 26 minutes and 30 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

And now the Delta 2 rocket stands fully fueled its launch of the COSMO-SkyMed spacecraft at 7:20 p.m. local (10:20 p.m. EDT; 0220 GMT). The vehicle's first stage was successfully loaded with RP-1 kerosene fuel earlier today. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels a few days ago. And the four strap-on booster rockets are solid-propellant.

Liftoff is just 90 minutes away. The second stage's fuel and oxidizer tanks, which were filled with storable propellants earlier this week, are being pressurized for launch.

Ten minutes into the flow. LOX loading is an approximate 25-minute process to fill the first stage liquid oxygen tank.

Live streaming video of the Delta 2 rocket being fueled is airing in the right-hand side of this page. Hit reload on your browser to get the player running.

Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from a 28,000-gallon storage tank at Space Launch Complex 2, through plumbing and into the bottom of the 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.

Right on schedule, the launch team is beginning preparations for filling the rocket's first stage liquid oxygen tank.

A reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text message updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

The rocket's guidance and control system has been brought online.

Now two hours from launch. Tonight's mission marks the 350th flight in the Delta rocket family dating back 50 years, a history that spans America's space program.

"It's special, 350 is special. We've been working really hard to make sure all of the missions (are successful). We treat each one of them unique and make sure everything goes smoothly, and hopefully our customer will be happy with it," says Hieu Lam, Boeing's mission director.

"I started with Delta 178, so it's been 172 Delta's that I've been involved with in one way or another. I've been an engineer, mission manager or program manager. I've seen everything from the first Delta 2 to Delta 3 to Delta 4, and I'm very, very happy to have a career here with Delta."

The forecast for launch time includes a few low stratus clouds at 100 feet, some high cirrus at 25,000 feet, six miles of visibility with haze, northwesterly winds of 10-15 knots and a temperature between 58 and 63 degrees F.

The weather outlook continues to be perfect for launch. There's a zero percent chance of clouds or ground winds violating the weather rules tonight.

Pressurization of the first stage helium and nitrogen systems has been completed as the countdown continues to launch of the COSMO-SkyMed 4 satellite.

Although the launch countdown affords time at this point in the operation to fuel the Delta 2 rocket's first stage, those 10,000 gallons of highly refined kerosene propellant were loaded earlier this morning prior to retraction of the mobile service tower.

The early fuel loading was performed to give the rocket added weight and stability while the Delta is exposed to the weather.

The kerosene, called RP-1, will be consumed along with liquid oxygen by the first stage RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

Filling of the stage with cryogenic liquid oxygen will begin about an hour from now.

The rocket's control system and guidance computer are being turned on. And the launch team is starting the steps to pressurize the first and second stage helium and nitrogen systems and the second stage fuel and oxidizer tanks.

Countdown begins! The three-hour Terminal Countdown sequence has been initiated for today's launch of the Delta 2 rocket from Vandenberg Air Force Base in California. The booster will carry into orbit COSMO 4, completing the radar-imaging satellite quartet for Italy.

Liftoff from the Space Launch Complex 2 pad is scheduled for 7:20:07 p.m. local (10:20:07 p.m. EDT; 0220:07 GMT). Today's available launch window is open for just one second.

Between now and the launch time, the rocket's guidance system will be activated, onboard helium and nitrogen tanks brought up to pressure, the liquid oxygen supply loaded into the first stage, checks performed on the safety system and steering tests conducted on the engines.

This is a standard countdown for the Delta 2, a typical timeline to ready the vehicle for flight. Pre-planned holds are built into the countdown at the T-minus 15 and T-minus 4 minute points. The first will last 20 minutes; the second will be 10 minutes in length. Those pauses are designed to give the launch team the opportunity to work problems or catch up on items perhaps running behind schedule.

Polls of the various launch team members and managers occur during that T-minus 4 minute hold to ensure everything is ready to proceed into the busy final minutes that see the rocket put on internal power, pressurized and armed for liftoff from California's Central Coast.

"It is a very normal Delta 2 rocket countdown. The only thing is it's a one-second window. But we've done that many, many times for NASA missions as well as previous COSMO missions too," says Hieu Lam, Boeing's mission director.

"Man stations for Terminal Count." The launch team has been polled to verify all members and the systems they oversee are ready to enter into the countdown.

The Delta rocket will be flying in its configuration known as the 7420-10 vehicle. The two-stage launcher is fitted with four strap-on solid-propellant motors and a 10-foot diameter composite nose cone.

After quickly climbing away from its coastal pad, the rocket will soar southward over the Pacific Ocean. The four solid boosters burn out and separate less than 90 seconds into the flight about 15 nautical miles up, leaving the kerosene-powered main engine to continue pushing the rocket to an altitude of 60 miles. The spent stage then jettisons to let the hydrazine-fueled second stage ignite.

Within 12 minutes, the vehicle settles into an initial 100 x 348 nautical mile parking orbit along a trajectory the cruises above the South Pacific before crossing Antarctica and then proceeding northbound toward Africa. The second stage reignites its engine for 12 seconds over Madagascar to reach a near-circular polar orbit of 335 x 341 nautical miles (385 x 392 statute miles) above the planet.

The 4,200-pound payload is expected to be released from the rocket 58 minutes after blastoff.

The launch complex has been ready for tonight's blastoff and all workers have departed the restricted area for the countdown.

T-minus 150 minutes and holding. At this time, the countdown is entering a planned 60-minute built-in hold. The Terminal Countdown begins once the hold concludes.

Launch remains targeted for 7:20:07 p.m. local (10:20:07 p.m. EDT; 0220:07 GMT) from Vandenberg Air Force Base in California.

Check out this photo collection of the Delta 2 rocket taken during gantry rollback today by Thom Baur for Boeing.

Countdown preparations are underway at Vandenberg Air Force Base's Space Launch Complex 2 for this evening's liftoff of the Delta 2 rocket carrying Italy's COSMO 4 spacecraft.

The 177-foot tall mobile service tower has been retracted from the United Launch Alliance-built rocket. The gantry was used to stack the two-stage vehicle, the four strap-on solid rocket motors and the COSMO payload atop the pad's launch mount. The tower also provided the primary weather protection and worker access to the rocket during its stay at the oceanside complex on North Vandenberg.

Ground teams will spend the next couple of hours getting the pad secured in advance of the Terminal Countdown. Launch remains targeted for exactly 7:20:07 p.m. local (10:20:07 p.m. EDT; 0220:07 GMT).

Making its one and only launch of the year, the venerable Delta 2 rocket awaits a Halloween launch Sunday night from California to complete an orbiting quartet of Italian reconnaissance satellites.

The rocket's launch opportunity is a scant moment in time, meaning liftoff must happen at exactly 7:20:07 p.m. PDT (10:20:07 p.m. EDT) or else wait until another day.

Such a restrictive window is dictated by the satellite mounted atop the 12-story booster. Launching at that specific time ensures optimum insertion of the payload into the desired orbit from the Vandenberg Air Force Base launch pad.

This culminates a series of four launches for Italy's COSMO-SkyMed constellation of radar-imaging spacecraft that observe the Earth's surface for civil and military purposes.

Developed by Thales Alenia Space Italia for the Italian Space Agency and the Italian Ministry of Defence, the COSMO-SkyMed system features X-Band Synthetic Aperture Radar instruments on the satellites for environmental monitoring, resource management and territorial surveillance.

The three earlier satellites in the COSMO program also launched aboard Delta 2 rockets from Vandenberg, successfully lifting off in June and December 2007 and October 2008.

United Launch Alliance is conducting the rocket flight while Boeing manages the commercial contract for the Italian customer. ULA was formed in December 2006 to merge Boeing's Delta and Lockheed Martin's Atlas rocket families under one joint venture to cut the cost for U.S. government space launches. The parent companies have retained the ability to sell the rockets on the commercial marketplace, such as the COSMO flights.

Technicians plan to load highly refined kerosene fuel into the first stage Sunday morning, followed by procedures to retract the mobile service gantry from around the rocket. The tower rollback is anticipated to be finished by 12 noon local time (3 p.m. EDT).

Weather forecasters are predicting winds gusting to 18 knots, well within the limit for removing the tower to reveal the rocket.

The Terminal Countdown will start at 4:20 p.m. local time (7:20 p.m. EDT), beginning the formal three-hour process to bring the rocket to life, load the liquid oxygen for the main engine, conduct extensive final testing and then send it into space.

Mission managers met on Saturday to review the status of pre-launch work and give approval to enter into the countdown operation.

"Things are looking pretty good," said Hieu Lam, mission director and Boeing's Delta commercial program manager. "All systems are green and we'll be ready to support the launch."

The launch time weather outlook says there's a 100 percent chance of acceptable conditions, with just some high, thin cirrus clouds, visibility of five miles, northwesterly winds of 10 to 15 knots and a temperature in the high 50s F.

Watch this page for live updates during the countdown and COSMO 4's trek to orbit aboard the Delta rocket.

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