A new global weather observatory for the U.S. armed forces was lofted into orbit aboard its Atlas 5 booster rocket from California on Thursday to provide tactical forecasts to military operations.

Read our full launch story.

T+plus 18 minutes, 50 seconds. SPACECRAFT SEPARATION! The Defense Meteorological Satellite Program F19 spacecraft has been released from the United Launch Alliance Atlas 5 rocket, completing today's ascent from Vandenberg Air Force Base in California.

The Lockheed Martin-built craft carries a sophisticated suite of weather instruments to observe virtually the entire planet twice daily. Data from DMSP satellites is used to create global weather forecasts that military commanders and strategic planners rely upon.

The satellites can track weather systems by visible and infrared cloud-cover imagery, day or night, plus monitor ice and snow coverage, pollution and fires.

T+plus 16 minutes. Confirmation has been received that the Centaur main engine cutoff occurred following its burn to inject the DMSP F19 spacecraft into polar orbit.

T+plus 10 minutes, 30 seconds. About five minutes remain in this burn of Centaur's single Pratt & Whitney Rocketdyne RL10 engine.

T+plus 8 minutes. The RL10 is burning liquid hydrogen and liquid oxygen propellants.

T+plus 6 minutes. Centaur engine readings look normal as this 11-minute burn continues.

T+plus 4 minutes, 50 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the spacecraft have separated.

T+plus 4 minutes, 45 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust.

T+plus 4 minutes, 40 seconds. The Atlas 5's Common Core Booster first stage has been jettisoned, and the Centaur upper stage's liquid hydrogen and liquid oxygen systems are being readied for engine start.

T+plus 4 minutes, 30 seconds. BECO. Booster Engine Cutoff is confirmed as the RD-180 powerplant on the first stage completes its burn. Standing by to fire the retro thrusters and separate the spent stage.

T+plus 3 minutes, 55 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.

T+plus 3 minutes, 20 seconds. The engine has throttled down to 92 percent as planned.

T+plus 3 minutes. RD-180 is performing well as the rocket climbs away from the planet.

T+plus 2 minutes, 25 seconds. The rocket now weighs half of what it did at liftoff.

T+plus 2 minutes. Atlas is flying due south from Vandenberg and looking good.

T+plus 85 seconds. Mach 1 as the main engine fires at full throttle.

T+plus 60 seconds. One minute into the ascent. It will take 18 minutes for the two-stage rocket to deploy the satellite into the planned orbit.

T+plus 60 seconds. One minute into the ascent. It will take 18 minutes for the two-stage rocket to deploy the satellite into the planned orbit.

T+plus 30 seconds. Pitch, yaw and roll maneuvers have been performed, putting Atlas 5 on the proper heading. The rocket is riding atop 860,000 pounds of thrust from the RD-180 main engine.

T+plus 15 seconds. The launcher is maneuvering to its southerly trajectory to deliver the DMSP observatory into orbit.

LIFTOFF! Liftoff of the Atlas 5 rocket with the DMSP 19 spacecraft, observing the world's weather for the warfighter.

T-minus 20 seconds. "Go Atlas" and "Go Centaur" was just called by launch team during a final status check.

T-minus 40 seconds. Centaur's liquid oxygen and liquid hydrogen tanks are stable at flight pressures.

T-minus 1 minute until the launch.

T-minus 90 seconds. The safety system has been armed.

T-minus 1 minute, 50 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.

T-minus 1 minute, 55 seconds. The launch sequencer has been commanded to start.

T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching from ground power to internal batteries.

T-minus 2 minutes, 30 seconds. The first stage RP-1 kerosene fuel tank and the liquid oxygen have stepped up to proper flight pressure levels.

T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for launch.

T-minus 3 minutes, 50 seconds. The ground pyrotechnics have been enabled.

T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket carrying the DMSP satellite. Liftoff is set to occur at 7:46 a.m. local.

A direct link to text updates.

The payload is confirmed on internal power for flight.

Countdown clocks will resume in one minute.

The ULA launch director and Air Force mission director have given their approval to press onward with the countdown.

All systems are reported "go" to continue with the countdown for liftoff at 7:46 a.m. The clocks will resume from this hold at 7:42 a.m.

Standing by for the final readiness check to be conducted. The launch team will be polled for a "go" or "no go" to proceed with the count.

The spacecraft payload is switching to internal power.

The current observed weather conditions are clear skies, winds of just 4 knots and a temperature of 42 degrees.

Here's a look at some stats about today's mission. This will be:

• The 626th launch for Atlas program since 1957
• The 292nd Atlas launch from Vandenberg AFB since 1959
• The 41st Atlas to use Space Launch Complex 3
• The 8th Atlas 5 launch from Vandenberg AFB since 2008
• The 215th mission for the Centaur upper stage
• The 192nd use of Centaur by an Atlas rocket
• The 445th production RL10 engine to be launched
• The 50th flight of the RD-180 main engine
• The 44th launch of an Atlas 5 since 2002
• The 69th Evolved Expendable Launch Vehicle flight
• The 29th 400-series flight of the Atlas 5
• The 21st Atlas 5 to fly in the 401 configuration
• The 16th Department of Defense launch of Atlas 5
• The 80th United Launch Alliance flight overall
• The 36th Atlas 5 under United Launch Alli
• The 2nd Atlas launch of 2014

T-minus 4 minutes and holding. The countdown has entered the planned hold to give the launch team a chance to review all systems before pressing ahead with liftoff. Today's launch time is aimed for 7:46:30 a.m. local (10:46:30 a.m. EDT; 1446:30 GMT).

T-minus 5 minutes and counting. Standing by to go into the final built-in hold that will last for 10 minutes.

The fuel-fill sequence for the first stage main engine has been completed.

Thirty minutes from liftoff now. The countdown clocks are heading to the T-minus 4 minute mark where a planned 20-minute, 30-second hold will occur. Launch of Atlas 5 remains scheduled for 7:46:30 a.m. local.

The workhorse Centaur upper stage has flown in various configurations for decades and will be making its 215th mission with Landsat. For this launch, the stage will use one Pratt & Whitney-built RL10A-4-2 liquid oxygen/liquid hydrogen engine that develops a thrust of about 22,300 pounds.

The stage is 41.5 feet in length and 10 feet it diameter. It also houses the navigation unit that serves as the rocket's guidance brain.

The Atlas 5 rocket's rigid body first stage is known as the Common Core Booster. The CCB replaced the "balloon" pressure-stabilized stage used by previous Atlas vehicles.

It is equipped with the RD-180 liquid-fueled main engine. This liquid oxygen/kerosene powerplant is a two-thrust chamber, two-nozzle engine.

As the CCB's name suggests, the stage is common and is used in all the various configurations of the Atlas 5 family. The booster stage is 106.6 feet long and 12.5 feet diameter.

Centaur liquid hydrogen has reached flight level.

This flight builds on the legacy of the Atlas vehicle's 401 configuration, which has flown over 20 times in the past decade with the combination of a four-meter payload fairing, no solid rocket boosters and a single-engine Centaur upper stage.

Depending on a payload's weight and desired orbit, mission planners add strap-on solid boosters to the United Launch Alliance-made rocket to incrementally increase the vehicle's performance.

But this cargo, the 2,700-pound DMSP spacecraft headed for polar orbit is satisfied with the lifting power of the basic Atlas 5 design.

The vehicle will fly southward away from Vandenberg headed south. Without using an solid motors, however, the rocket won't produce a smokey contrail off the pad.

The Russian RD-180 first stage main engine will ignite at T-minus 2.7 seconds, roaring to full power while undergoing a check to ensure its vital signs are healthy.

Rising off the pad in a slow, majestic fashion, the 19-story Atlas vehicle will deliver nearly a million pounds of ground-shaking thrust for the mid-morning departure.

Four minutes into the flight, staging will occur as the Centaur ignites and the nose cone is jettisoned. The Centaur will burn for about 11 minutes, achieving a circular orbit 530 miles high.

Deployment of the payload to complete the launch sequence is expected 18 minutes and 28 seconds.

The weather forecast has been update and currently shows a 100 percent chance of favorable conditions for launch.

Now 60 minutes from launch. All activities are proceeding smoothly toward a liftoff at 7:46 a.m. Pacific Time.

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

And check out Spaceflight Now's Facebook page!

The liquid hydrogen tank in the Centaur upper stage just reached the 97 percent level. Topping is now beginning.

Fast-filling of the first stage liquid oxygen has been completed at the tank's 97.5 percent mark. Topping mode is now underway.

The Centaur liquid hydrogen tank is 60 percent loaded so far. The cryogenic propellant will be consumed with liquid oxygen by the stage's Pratt & Whitney-made RL10 engine.

Liquid oxygen on Centaur has reached flight level.

Now beyond the three-quarters level of liquid oxygen on the first stage.

Chilldown of the liquid hydrogen system is now complete, allowing the super-cold rocket fuel to begin filling the Centaur upper stage.

First stage liquid oxygen tank is passing the half-full mark. Chilled to Minus-298 degrees F, the liquid oxygen will be used with RP-1 kerosene by the RD-180 main engine on the first stage during the initial minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket earlier.

Now 90 minutes from liftoff. There are no reports of technical troubles from the launch team and the weather is beautiful for today's countdown. Fueling operations remain in work for the launch time of 7:46 a.m. local.

The Centaur liquid oxygen tank reached the 96 percent level and the topping off process is starting.

The first stage liquid oxygen loading is switching from slow-fill to fast-fill mode as planned.

The Centaur liquid oxygen tank is 75 percent full now.

And the chilldown conditioning of liquid hydrogen propellant lines is starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 13,000 gallons of the cryogenic propellant.

Half of the Centaur liquid oxygen tank has been filled so far.

NEW LAUNCH TIME. The target liftoff time has been tweaked by 30 seconds to 7:46:30 a.m. local.

The Centaur liquid oxygen tank is nearing one-quarter full already.

The conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin flowing supercold liquid oxygen into the Atlas 5's first stage.

The Common Core Booster stage's liquid oxygen tank is the largest tank to be filled today. It holds about 50,000 gallons of cryogenic oxidizer for the RD-180 main engine.

Filling of the Centaur upper stage with about 4,300 gallons of liquid oxygen is beginning at Vandenberg's Space Launch Complex 3 following the thermal conditioning of the transfer pipes.

The liquid oxygen -- chilled to Minus-298 degrees F -- will be consumed during the launch by the Centaur's single RL10 engine along with liquid hydrogen to be loaded into the stage a little later in the countdown.

The Centaur liquid oxygen system's pad storage area has been prepped. The next step is conditioning the transfer lines, which is now beginning to prepare the plumbing for flowing the cryogenic oxidizer.

T-minus 120 minutes and counting! The launch countdown has resumed for today's flight of the Atlas 5 rocket following the planned half-hour built-in hold.

Clocks have one more hold scheduled at T-minus 4 minutes. That pause will last 20 minutes during which time the final "go" for launch will be given.

All remains targeted for liftoff at 7:46 a.m. local time (1446 GMT) from Vandenberg Air Force Base, California.

The launch team and all systems are "ready" to proceed with the countdown and begin fueling the Atlas 5 rocket this afternoon as planned.

Loading of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.

The Atlas launch conductor is briefing his team on procedures before entering into the final two hours of the countdown. A readiness check of the team members is next.

Atlas 5 represents the culmination of evolution stretching back several decades to America's first intercontinental ballistic missile. At the dawn of the space age, boosters named Atlas launched men into orbit during Project Mercury and became a frequent vehicle of choice to haul civil, military and commercial spacecraft to orbit.

Topped with the high-energy Centaur upper stage, Atlas rockets have been used since the 1960s to dispatch ground-breaking missions for NASA, including the Surveyors to the Moon, Mariner flights to Mars, Venus and Mercury, and the Pioneers that were the first to visit Jupiter and beyond.

n its newest era, the Atlas 5 rocket sent the Mars Reconnaissance Orbiter to the red planet in 2005, propelled the New Horizons probe toward Pluto and the solar system's outer fringes in 2006, doubled up with the dual Lunar Reconnaissance Orbiter and LCROSS impactor to the Moon in 2009, hurled Juno to Jupiter in August 2011 and dispatched the car-sized Curiosity rover on the Mars Science Lab mission in November 2012 and the Mars-bound MAVEN orbiter this past November.

The rocket launching DMSP F19 was born of the Air Force's commercial competition to develop next-generation Evolved Expendable Launch Vehicles. It has flown 43 times since debuting in 2002, carrying out 15 flights dedicated to the Defense Department, 11 missions for NASA, nine flights with commercial payloads, and eight with spy satellites for the National Reconnaissance Office.

T-minus 2 hours and holding. The countdown just entered the first of the planned holds over the course of the morning that will lead to the 7:46 a.m. PDT launch of the Atlas-Centaur rocket.

This initial pause lasts 30 minutes, giving the team some margin in the countdown timeline to deal with technical issues or any work that is running behind. The final hold is scheduled to occur at T-minus 4 minutes.

With all the hands-on work now finished at the pad, technicians are clearing Space Launch Complex 3 for the remainder of the countdown.

And 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.)

Testing of the vehicle's guidance system is complete.

Completed in the countdown over the past few minutes, engineers conducted checks of the vehicle's internal batteries and finished final preps to the Atlas hydraulics and propulsion systems. Also, the C-band tracking and S-band telemetry system testing have been accomplished.

The pad crew reports the gantry is parked, closed up and ready for launch.

The 8-million-pound mobile service tower has been retracted from around the Atlas 5 rocket, revealing the 19-story-tall vehicle for liftoff at 7:46 a.m. PST today.

The ground crews are getting the gantry's doors closed, plus finishing the final buttoning up of pad equipment over before all workers clear the pad for the remainder of the countdown.

Today's launch will be the eighth Atlas 5 rocket to fly from Vandenberg's Space Launch Complex 3-East pad. The site underwent an extensive overhaul, with construction occurring in 2004 and 2005, to accommodate the larger and more powerful Atlas 5 family of rockets. Some of the major modifications included:

• 30-foot extension to mobile service tower
• 20-foot exhaust duct depth increase
• 250-ton Fixed Launch Platform installed
• Significant ambient and cryogenic fluid ground system modifications
• Complete replacement of the Ground Command/Control/Communication system
• New and refurbished Launch Control/Mission Support Centers

This is the 41st Atlas overall to fly from SLC 3 throughout Vandenberg history.

Internal battery checks are now underway.

The gantry is clear of the vehicle. Meanwhile, the S-band system used for data-relay during launch is being tested. The C-band tracking system will be checked out shortly.

Rollback of the launch pad's service gantry is underway! This is a major milestone in today's countdown, getting the mobile tower retracted to uncover the Atlas 5 rocket.

The structure's internal crane was instrumental in bringing the rocket stages and payload together. And now the fully assembled Atlas 5 has been unveiled for its 44th launch, the eighth to originate from Vandenberg.

A readiness poll of the team has verified all systems are GO for retraction of the gantry.

Clocks begin ticking now for today's flight by the Atlas 5 rocket from America's western spaceport to deploy the DMSP F19 military weather observatory into space.

"Through the continued dedication, detailed preparation and hard work of our combined government-contractor team, DMSP-19 is ready to launch," said Col. Scott Larrimore, head of the Space and Missile Systems Center's Defense Weather Systems Directorate.

"For more than five decades, DMSP has been providing reliable, timely and dependable environmental information essential to the warfighter. DMSP-19 will extend this proud tradition well into the next decade."

As the countdown gets started, the launch team will power up the rocket to conduct standard pre-flight tests and ready the vehicle.

Rollback of the mobile service tower from around the rocket is expected in about three hours. Once the gantry is removed, crews at the pad will make preparations to systems and equipment before the site is cleared of all personnel for fueling.

A planned 30-minute hold begins when the count reaches T-minus 120 minutes at 4:56 a.m. local time. With a few minutes remaining in the hold, the team will be polled to verify all is in readiness to start loading propellant into the rocket for launch.

Supercold liquid oxygen begins flowing into the Centaur upper stage around 5:43 a.m. local, followed by the Atlas first stage. Liquid hydrogen fuel loading for Centaur will be completed a short time later.

A final hold is scheduled at 7:22 a.m. when clocks hit the T-minus 4 minute mark. That will give the team a chance to finish any late work and assess the status of the rocket, payload, Range and weather before proceeding into the last moments of the countdown.

Liftoff remains targeted for 7:46 a.m. local time (10:46 a.m. EDT; 1446 GMT).

The Launch Review Review was completed today as mission managers cleared the Atlas 5 rocket to launch the DMSP Flight 19 weather satellite on Thursday morning from California.

At the end of today's meeting, the launch team was given approval to begin the countdown Thursday at midnight local (3:00 a.m. EDT; 0700 GMT). The mobile service gantry will be retracted to unveil the 19-story-tall rocket at 3 a.m. local, followed by the start of fueling operations just after 5:45 a.m.

Liftoff is scheduled for 7:46 a.m. local (10:46 a.m. EDT; 1446 GMT) from Space Launch Complex 3-East at Vandenberg Air Force Base, California.

The morning's launch window will extend for 10 minutes.

The weather forecast for Thursday's launch appears to be excellent, with good visibility and no fog hampering the view at Vandenberg Air Force Base. There is a 90 percent chance of acceptable conditions.

The outlook includes some high cirrus clouds, visibility of 7 miles, northwesterly winds at 12 gust 18 knots and a temperature around 50 degrees F.

The only slight concern is for cloud thickness lingering in the region from a passing cold front.

A $518 million military weather satellite that has been waiting 15 years to shine will be launched into orbit Thursday atop an Atlas 5 rocket from the western spaceport in California.

Read our full story.

After the Range outage that postponed two Cape Canaveral launches indefinitely in Florida, focus now turns to California and the planned launching next Thursday of an Atlas 5 rocket with a military weather satellite.

"It really has been remarkably smooth," said Lt. Col. James Bodnar, commander of the 4th Space Launch Squadron at Vandenberg. "Right now, everything is on schedule for a 3 April launch."

Liftoff of the United Launch Alliance vehicle is slated for 7:46 a.m. PDT (10:46 a.m. EDT; 1446 GMT) next Thursday from Space Launch Complex 3-East on South Base.

"The biggest milestone in the past couple of weeks was stacking the satellite on top of the booster, which ULA did on the 19th. Now we have a fully built rocket, with satellite, a completed assembly, sitting on the launch pad. There are some minor processing that still needs to be done, but all of the parts are there for the launch," Bodnar said.

This is the first time the 4th Space Launch Squadron has overseen both the rocket and satellite launch campaigns, picking up additional duties surrounding the DMSP F19 satellite processing.

"We are rocket people. Our entire squadron is built around knowing every detail there is to know about the Atlas 5 and Delta 4 rocket systems. So this was a unique challenge for us," Bodnar said.

It will be the 44th Atlas 5 rocket launch, the 8th from Vandenberg and the program's 16th with an Air Force payload. It is ULA's 80th launch and third this year.

This week's Range outage on the East Coast delayed both an Atlas 5 launch for the National Reconnaissance Office and a Falcon 9 cargo delivery run to the International Space Station. New launch dates for both are pending.

Check out a gallery of last week's payload delivery to the launch pad here.

A new global weather observatory for the U.S. military was hoisted aboard its Atlas 5 rocket booster in California on Wednesday, two weeks before it is shot into space to track the world's storms.

Read our full story.