"The United Launch Alliance team is proud to serve alongside our mission partners and privileged that the Air Force has entrusted the ULA team to deliver the critical national security capabilities provided by AEHF 3 to orbit for our soldiers, sailors, airman and Marines around the world," said Jim Sponnick, ULA vice president of Atlas and Delta programs, in a statement.

The launch marked the 75th mission conducted by ULA since it started operations in December 2006.

"Today's successful launch was the 75th since ULA was formed nearly seven years ago, the 40th Atlas 5 mission, and the fourth ULA launch in the last two months," Sponnick said. "The ULA team and our many mission partners emphasize a one-launch-at-a-time focus on mission success along with a strong commitment to continuous improvement - these elements together are the keys to launching our customer's missions successfully at this unprecedented tempo in a reliable and cost-effective manner."

The eyes of the space world now turn to Virginia, where an Orbital Sciences Antares rocket is set for launch in five-and-a-half hours on a demonstration mission to the International Space Station.

Standing by to pick up the countdown at T-minus 4 minutes.

• The 622nd launch for Atlas program since 1957
• The 332nd Atlas to occur from Cape Canaveral
• The 211th mission for the Centaur upper stage
• The 188th use of Centaur by an Atlas rocket
• The 440th production RL10 engine to be launched
• The 46th flight of the RD-180 main engine
• The 40th launch of an Atlas 5 since 2002
• The 18th Atlas 5 launch with solid boosters
• The 64th Evolved Expendable Launch Vehicle flight
• The 15th Atlas 5 dedicated to the Defense Department
• The 34th Atlas 5 to occur from the Cape
• The 7th nighttime Atlas 5 launch from the Cape
• The 75th United Launch Alliance flight overall
• The 9th ULA launch of the year
• The 32nd Atlas 5 under United Launch Alliance
• The 14th 500-series flight of the Atlas 5
• The 3rd Atlas 5 to fly in the 531 configuration
• The 3rd AEHF satellite
• The 3rd Atlas launch for AEHF
• The 6th Atlas launch of 2013

The cumulus cloud rule is now "go" and a new flight profile with upgraded upper level wind data has been loaded into the Atlas 5's flight computer and verified.

Meanwhile, computers are now processing upper level wind data as the launch team works to overcome an earlier computer problem.

Meanwhile, forecasters expect the cumulus cloud rule to be cleared in a few minutes.

The AEHF 3 satellite is now confirmed on internal power.

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Constructed around Lockheed Martin's A2100 satellite model with a 14-year design life, the AEHF satellites like the one being launched today feature power-generating solar panels stretching 89 feet tip-to-tip and two antenna-laden deployable wings.

The satellites are designed with autonomy to resolve on-board problems without guidance from the ground.

They are built to follow the military's aging Milstar satellite series that provide the preeminent communications with top-level protection.

While all the Milstars remain in use, the emerging AEHF fleet will fly alongside to offer their faster data speeds and expand the capacity for secure communications across the world.

Following separation from the launch vehicle nearly 51 minutes after liftoff today, ground controllers will begin maneuvering AEHF 3 into geosynchronous orbit with four burns of a liquid-fueled apogee engine and pulses with the satellite's electric propulsion system. Then engineers will extend the craft's solar arrays and antennas before beginning in-orbit testing.

"United Launch Alliance is honored to be supporting the U.S. Air Force in the launch of the AEHF 3 satellite," said Mark Dowhan, ULA's vice president of launch operations. "The ULA team is focused on attaining perfect product delivery for the AEHF 3 mission, which includes a focus on mission success and excellence on meeting all the needs of our customers. That singular focus is paramount as we launch critical capabilites for the thousands of men and women protecting our freedoms around the world. We are proud to serve with our mission partners in the preparation and launch of this important mission for the U.S. Air Force."

This launch continues a string of five national security launches the Air Force is peforming with ULA in a three-month span from July through October, using both Atlas 5 and Delta 4 rockets from the Cape and Vandenberg Air Force Base in California. The surge began with the July 19 launch of an Atlas 5 rocket with the Navy's second Mobile User Objective System communications satellite, followed by the launch of the Air Force's sixth Wideband Global SATCOM satellite Aug. 7 on a Delta 4 rocket.

A massive spy satellite for the National Reconnaissance Office launched Aug. 28 on a Delta 4-Heavy rocket from Vandenberg, and today's AEHF 3 mission is the fourth in the series of five launches.

Another Delta 4 rocket is on the launch pad at Cape Canaveral being prepared for an Oct. 17 launch of a new GPS navigation satellite.

If you are heading out to the beach or Port Canaveral to watch the launch, sign up for our Twitter feed to get occasional countdown 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.)

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

Launch remains scheduled for 3:04 a.m. EDT (0704 GMT), but the launch team has a two-hour window to wait out inclement weather.

Engineers have convened an anomaly team to discuss a "talkback" signal loss from a vent valve on the Atlas 5's first stage, but the issue is not keeping the launch team from continuing fueling operations this morning.

The Common Core Booster stage's liquid oxygen tank is the largest tank to be filled today. It holds 48,750 gallons of cryogenic oxidizer for the RD-180 main engine.

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 pumped into the stage a little later in the countdown. The Centaur will perform two firings to propel the AEHF satellite into its intended orbit today.

Clocks have one more built-in hold planned at T-minus 4 minutes. That pause will last 10 minutes during which time the final "go" for launch will be given. All remains targeted for liftoff at 3:04 a.m. EDT (0704 GMT) from Cape Canaveral's Complex 41.

In the next couple of minutes, chilldown thermal conditioning of the mobile launch platform upon which the rocket stands will begin. This is meant to ease the shock on equipment when supercold cryogenic propellants start flowing into the rocket.

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

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This initial pause was designed to give the team some margin in the countdown timeline to deal with technical issues or any work that could fall behind schedule before fueling starts. But all is going smoothly today, with officials not reporting any troubles in the count.

The final hold will occur at T-minus 4 minutes.

The outlook calls for scattered clouds at 2,500 feet, broken clouds at 14,000 and 30,000 feet, east winds gusting to 20 knots, and a temperature of about 77 degrees Fahrenheit. The primary concerns are with violating the thick cloud and cumulus cloud rules.

At this time, all weather constraints are "go" for launch.

The C-band and S-band systems have also been tested in the countdown. They are used for vehicle tracking and telemetry relay, respectively. The countdown continues for launch at 3:04 a.m. EDT (0704 GMT).

Clocks are picking up the seven-hour sequence of work that will prepare the booser, payload and ground systems for blastoff at 3:04 a.m. EDT (0704 GMT).

Soon the launch team will begin powering up the rocket to commence standard pre-flight tests. Over the subsequent few hours, final preps for the Centaur's liquid oxygen and liquid hydrogen systems will be performed, along with a test of the rocket's guidance system and the first stage propulsion and hydraulic preps, internal battery checks and testing of the C-band system used to track the rocket as it flies downrange, plus a test of the S-band telemetry relay system. The Complex 41 site will be cleared of all personnel at 12:09 a.m. EDT (0409 GMT).

A planned half-hour hold begins at 12:24 a.m. EDT (0424 GMT) when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled at 12:51 a.m. EDT (0451 GMT) to verify all is in readiness to start fueling the rocket for launch. Supercold liquid oxygen begins flowing into the Centaur upper stage around 1:11 a.m. EDT (0511 GMT), followed by the first stage filling around 1:24 a.m. EDT (0524 GMT). Liquid hydrogen fuel loading for Centaur will be completed a short time later. A final hold is scheduled at the T-minus 4 minute mark starting at 2:50 a.m. EDT (0650 GMT). That 10-minute pause will give everyone 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.

The launch window extends from 3:04 to 5:04 a.m. EDT (0704-0904 GMT).

Read our full story. Check out photos of the Atlas 5's rollout.

The voyage resumes Wednesday at 3:04 a.m. EDT (0704 GMT) with liftoff of the two-stage Atlas 5 rocket. Wednesday's launch window extends for two hours.

The countdown will begin at 8:04 p.m. EDT Tuesday (0004 GMT Wednesday), leading to activation of the rocket, final testing and system preps. Fueling operations start at 1:11 a.m. EDT (0511 GMT).

"My thanks to the entire team for its dedication in bringing AEHF 3 to launch and to the Air Force for trusting ULA to deliver this critical national security capability to orbit," said Jim Sponnick, ULA's vice president of Atlas and Delta programs.

The weather forecast from the Air Force's 45th Weather Squardon calls for 60 percent chance of violating launch constraints.

The outlook predicts scattered and broken cloud decks at 2,500, 14,000 and 30,000 feet with showers and isolated thunderstorm activity. Winds will be out of the east at 15 to 20 knots with a temperature of approximately 77 degrees Fahrenheit.

The primary concerns for Wednesday morning are violating the thick cloud and the cumulus cloud rules.

"On launch day increasing onshore low level flow and persistent tropical moisture will keep probabilities of showers and cloudy conditions high," meteorologists wrote in a forecast synopsis. "Expect showers, cloudy skies, and a chance for an isolated thunderstorm in the vicinity. Breezy onshore easterly winds gusting into the upper teens/low 20s (230 feet) are also expected."

If the launch gets pushed back to Thursday, a drier airmass should take hold over Central Florida. The probability of violating weather constraints Thursday is 40 percent.

Watch this page for live updates throughout the countdown and flight, plus live streaming video.

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This slow, half-hour drive from the 30-story Vertical Integration Facility to Cape Canaveral's Complex 41 pad uses a pair of specially-made "trackmobiles" to carry the rocket's 1.4-million pound mobile launching platform along rail tracks for the 1,800-foot trip.

The 196-foot-tall satellite booster is moving to Cape Canaveral's Complex 41 for the launch of AEHF 3, a jam-resistant satellite built to beam communications between the U.S. military and civilian leadership in the worst scenarios of war.

The two-stage rocket and the AEHF 3 spacecraft were put together inside the assembly building over the past 45 days in preparation for this rollout event. The Atlas 5 is designed to spend minimal time at the launch pad, which does not include a service gantry like other sites.

Rollout is due to begin at 10 a.m. EDT (1400 GMT), with the Atlas 5 rocket riding on rails from the 30-story Vertical Integration Facility to the launch pad at Complex 41. The journey should take about a half-hour to complete.

The rollout begins the final day-and-a-half of launch preparations for the Atlas 5, which is making its 40th flight since debuting in August 2002 with the launch of a commercial communications satellite for Eutelsat. It also marks the 75th rocket flight conducted under the auspices of United Launch Alliance since 2006.

Affixed to this Atlas 5 launcher is the Air Force's third Advanced Extremely High Frequency communications satellite, a 13,600-pound platform to broaden the military's growing constellation of new-generation spacecraft to link the Defense Department's command structure with civilian government leadership.

Wednesday's launch is scheduled for a two-hour window opening at 3:04 a.m. EDT (0704 GMT).

The 196-foot-tall Atlas 5 is flying in the "531" configuration with a five-meter payload fairing built in by RUAG Space in Switzerland, three solid-fueled boosters provided and a single RL10 upper stage engine provided by Aerojet Rocketdyne.

Built by Lockheed Martin Corp., the AEHF 3 satellite is outfitted with communications antennas, transponders and capabilities hardened to operate in a nuclear war. It is also resistant to jamming and beams encrypted voice communications between U.S. military commanders and the president.

In the event of a nuclear catastrophe, the AEHF satellites and the Milstar spacecraft fleet - AEHF's predecessor - would give U.S. forces the edge in the struggle for information and communication, military officials said.

Monday's rollout comes after 45 days of assembly and testing of the Atlas 5 rocket inside the Vertical Integration Facility.

Stacking of the Atlas 5 rocket began with the standing up of the launcher's first stage inside the VIF on Aug. 2. Technicians added three solid rocket boosters before hoisting the rocket's Centaur upper stage into position Aug. 13.

The AEHF 3 satellite, encapsulated inside the Atlas 5's payload fairing, topped off the rocket earlier this month.

Liftoff from Cape Canaveral's Complex 41 has been reset for Sept. 18 at 3:04 a.m. EDT (0704 GMT). The predawn launch window extends exactly two hours.

This year's Atlas manifest has flown five launches so far, all going on their first attempts after smooth countdowns.

The upcoming mission will carry the third Advanced Extremely High Frequency communications spacecraft for the Pentagon's communications network.

The rocket is taking the shape of the 531 configuration in the Atlas 5 family, which will feature a five-meter-diameter nose cone, three strap-on solid fuel boosters and a single-engine Centaur upper stage.

That power will lift the Air Force's Advanced Extremely High Frequency satellite No. 3 into a supersynchronous transfer orbit from the Florida spaceport.

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