FRIDAY, JUNE 24, 2016
RECAP STORY: And then there were five.

The constellation-building Atlas 5 rocket from United Launch Alliance successfully deployed the fifth communications spacecraft for the Navy's Mobile User Objective System today to form a new rugged smartphone network for the U.S. military.

Read our launch story.

1818 GMT (2:18 p.m. EDT)
"The launch of MUOS 5 is a major milestone. MUOS will be a game changer in communications for our service men and women on the front lines around the world," said Mark Woempner, director of Narrowband Communications Systems at Lockheed Martin.

"Now that the Navy's constellation is complete, we will continue to work with our government and industry teammates to further refine MUOS based on user feedback. We are committed to bringing all of MUOS' advanced capabilities to our warfighters."

1753 GMT (1:53 p.m. EDT)
"We are honored to deliver the final satellite in the MUOS constellation for the U.S. Navy," said Laura Maginnis, ULA vice president, Custom Services.

"I am so proud of the team for all their hard work and commitment to 100 percent mission success," Maginnis said. "It is amazing to deliver our second national security payload from the Cape in just two weeks. I know this success is due to our amazing people who make the remarkable look routine."

1740 GMT (1:40 p.m. EDT)
This was the 134th successful Atlas program launch in a row spanning more than two decades and the 63rd for an Atlas 5.
1725 GMT (1:25 p.m. EDT)
The next Atlas 5 rocket launch from Cape Canaveral, a 421-configured vehicle with two solid-fuel boosters, is planned for July 28 on the NROL-61 mission for the National Reconnaissance Office. Liftoff will occur some time during a four-hour, unclassified launch period extending from 8 am to 12 noon EDT (1200-1600 GMT).
1723 GMT (1:23 p.m. EDT)
T+plus 2 hours, 53 minutes. SPACECRAFT SEPARATION! The Centaur upper stage has deployed the U.S. Navy's fifth Mobile User Objective System satellite, dubbed MUOS 5, for a 15-year mission to provide communications to U.S. military forces. It will be parked over the Indian Ocean.

Just a few minutes before separation, the Centaur completed its third burn of the day to put the MUOS spacecraft into a high-perigee geosynchronous transfer orbit as planned.

1720 GMT (1:20 p.m. EDT)
T+plus 2 hours, 50 minutes. MECO 3. Centaur has completed its third burn of the day to raise the orbit's low point and reduce orbital inclination for the MUOS spacecraft. It was a planned minute-long firing by the Centaur's single Aerojet Rocketdyne RL10C engine.
1719 GMT (1:19 p.m. EDT)
T+plus 2 hours, 49 minutes. Ignition! The RL10C-1 engine running again for its third firing during this launch.
1714 GMT (1:14 p.m. EDT)
T+plus 2 hours, 44 minutes. Five minutes away from the burn. Centaur is reorienting to the proper position for the next engine firing.
1605 GMT (12:05 p.m. EDT)
A video replay of tooday's launch is posted here.
1507 GMT (11:07 a.m. EDT)
We will pause our live updates at this time. Check back around 1:20 p.m. EDT for confirmation of the third Centaur burn and deploy of the MUOS 5 satellite to complete today's mission.
1505 GMT (11:05 a.m. EDT)
T+plus 35 minutes. A typical Atlas 5 ascent to geosynchronous transfer orbit, the standard dropoff point for communications satellites, uses just two firings by the Centaur to achieve the highly elliptical, egg-shaped orbit to deploy the payloads. From there, the satellites use their own engines in the subsequent days to fly into the operational locations 22,300 miles above the equator.

But the sizable MUOS, at nearly 15,000 pounds, drove planners to create a three-burn launch profile for the hefty payload to use all of the available performance from the Atlas-Centaur that in turns saves the satellite's precious onboard fuel supply for maneuvering over its 15-year life.

The three burns provides 1,000 pounds greater lift capability than a conventional 2-burn geosynchronous transfer orbit.

1500 GMT (11:00 a.m. EDT)
T+plus 30 minutes. Centaur now begins a quiet two-and-a-half-hour coast through space, moving higher and away from the planet before the third and final burn occurs nearly 2 hours and 49 minutes into flight. Deployment of MUOS 5 from the rocket to complete the launch is expected 2 hours, 53 minutes after launch.
1458 GMT (10:58 a.m. EDT)
T+plus 28 minutes. The second burn by Centaur inserted the rocket into another precise orbit as targeted.
1456 GMT (10:56 a.m. EDT)
T+plus 26 minutes, 17 seconds. MECO 2. Main engine cutoff confirmed. Centaur has completed its second burn of the day, this one taking the next step upwards to substantially increase the altitude from the previous parking to nearly geosynchronous height.
1455 GMT (10:55 a.m. EDT)
T+plus 25 minutes, 30 seconds. Engine performance remains normal.
1454 GMT (10:54 a.m. EDT)
T+plus 24 minutes, 30 seconds. About two minutes are left in the burn to reach the next orbit. Everything continues to look nominal.
1453 GMT (10:53 a.m. EDT)
T+plus 23 minutes. Continued good engine operation is being delivered by the RL10C, no problems reported.
1452 GMT (10:52 a.m. EDT)
T+plus 22 minutes. The engine is burning well. This is a planned six-minute firing by the Centaur's single Aerojet Rocketdyne RL10C engine.
1450 GMT (10:50 a.m. EDT)
T+plus 20 minutes, 31 seconds. Ignition! The Centaur's single RL10C engine has re-ignited to climb into a highly elliptical intermediate orbit on the way to the final perch later today.
1450 GMT (10:50 a.m. EDT)
T+plus 20 minutes, 26 seconds. Liquid hydrogen and liquid oxygen system prestarts are underway.
1450 GMT (10:50 a.m. EDT)
T+plus 20 minutes. Centaur getting into its pressurization sequence.
1449 GMT (10:49 a.m. EDT)
T+plus 19 minutes. The flight path is taking the vehicle over the equatorial Atlantic Ocean, soon to near the western coast of Africa where the next Centaur burn will occur. It will soar away from the Indian Ocean over the course of the next couple hours before the RL10C restarts for a final time to accelerate MUOS into the geosynchronous transfer orbit and separating the payload.
1448 GMT (10:48 a.m. EDT)
T+plus 18 minutes. Centaur is half-way through this coast period. It is completing a slow roll to keep thermal heating even across the rocket's surfaces.
1444 GMT (10:44 a.m. EDT)
T+plus 14 minutes. That first burn by Centaur inserted the rocket into the precise target orbit as planned.
1442 GMT (10:42 a.m. EDT)
T+plus 12 minutes, 28 seconds. MECO 1. Centaur's main engine has shut down following its first burn today, achieving a preliminary orbit around Earth. The rocket will coast in this orbit for about 8 minutes before the RL10C engine re-ignites for the next burn.
1442 GMT (10:42 a.m. EDT)
T+plus 12 minutes, 2 seconds. Centaur is now orbital.
1441 GMT (10:41 a.m. EDT)
T+plus 11 minutes, 30 seconds. About one minute are left in this burn of Centaur.
1440 GMT (10:40 a.m. EDT)
T+plus 10 minutes. All systems reported stable as the Centaur fires to reach an initial Earth orbit.
1439 GMT (10:39 a.m. EDT)
T+plus 9 minutes. The RL10C continues to perform well, burning liquid hydrogen and liquid oxygen propellants.
1438 GMT (10:38 a.m. EDT)
T+plus 8 minutes, 20 seconds. Vehicle traveling at 15,087 mph.
1437 GMT (10:37 a.m. EDT)
T+plus 7 minutes, 15 seconds. The rocket has performed a planned roll to improve antenna links with NASA's orbiting Tracking and Data Relay Satellite System.
1436 GMT (10:36 a.m. EDT)
T+plus 6 minutes, 55 seconds. A look at first stage performance numbers show a nominal burn by the booster.
1436 GMT (10:36 a.m. EDT)
T+plus 6 minutes. RL10C performing well.
1435 GMT (10:35 a.m. EDT)
T+plus 5 minutes. Centaur engine readings look good as this burn gets underway.
1434 GMT (10:34 a.m. EDT)
T+plus 4 minutes, 46 seconds. Centaur has ignited! The RL10C engine is up and running at full thrust for its first of three firings today to reach the intended geosynchronous transfer orbit.
1434 GMT (10:34 a.m. EDT)
T+plus 4 minutes, 37 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.
1434 GMT (10:34 a.m. EDT)
T+plus 4 minutes, 33 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.
1433 GMT (10:33 a.m. EDT)
T+plus 3 minutes, 40 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the MUOS spacecraft have separated, exposed the satellite to space. Also jettisoned was the Forward Load Reactor, a two-piece deck that rings the Centaur stage to support the bulbous fairing during launch.
1433 GMT (10:33 a.m. EDT)
T+plus 3 minutes, 30 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.
1433 GMT (10:33 a.m. EDT)
T+plus 3 minutes. The vehicle weighs just a quarter of what it did at liftoff.
1432 GMT (10:32 a.m. EDT)
T+plus 2 minutes, 50 seconds. Reaction control system has been activated.
1432 GMT (10:32 a.m. EDT)
T+plus 2 minutes, 40 seconds. Everything still looking good on the first stage as the rocket powers downrange on the thrust being produced by the main engine.
1432 GMT (10:32 a.m. EDT)
T+plus 2 minutes, 30 seconds. Vehicle is right on course.
1431 GMT (10:31 a.m. EDT)
T+plus 1 minute, 53 seconds. All five of the Aerojet Rocketdyne-made solid rocket motors have successfully separated from the Atlas 5, having completed their job of adding a powerful kick at liftoff.
1431 GMT (10:31 a.m. EDT)
T+plus 93 seconds. Solid rocket booster burnout has occurred. But the spent motors will remain attached to the first stage for a few seconds, until the Atlas 5 reaches a point where the airborne dynamic pressure reduces to an allowable level for a safe jettison.
1431 GMT (10:31 a.m. EDT)
T+plus 60 seconds into this complex three-hour mission to deploy the Navy's fifth Mobile User Objective System communications satellite in a high-perigee geosynchronous transfer orbit.
1430 GMT (10:30 a.m. EDT)
T+plus 51 seconds. A period of maximum dynamic pressure is being experienced by the rocket.
1430 GMT (10:30 a.m. EDT)
T+plus 40 seconds. The main engine is throttling down to ease the stresses on the vehicle in the lower atmosphere.
1430 GMT (10:30 a.m. EDT)
T+plus 36 seconds. Mach 1.
1430 GMT (10:30 a.m. EDT)
T+plus 30 seconds. The vehicle is heading due eastward to reach a 28-degree inclination preliminary parking orbit 12 minutes from now.
1430 GMT (10:30 a.m. EDT)
T+plus 15 seconds. Pitch, yaw and roll maneuvers are underway as the Atlas 5 thunders away from Cape Canaveral with its RD-180 engine and five solid rocket boosters burning.
1430 GMT (10:30 a.m. EDT)
LIFTOFF! Liftoff of the Atlas 5 rocket to complete the Navy's mobile communications satellite constellation in the sky!
1429 GMT (10:29 a.m. EDT)
T-minus 20 seconds. "Go Atlas", "Go Centaur" and "Go MUOS 5" was just called by launch team during a final status check.
1429 GMT (10:29 a.m. EDT)
T-minus 40 seconds. Centaur's liquid oxygen and liquid hydrogen tanks are stable at flight pressures.
1429 GMT (10:29 a.m. EDT)
T-minus 55 seconds. Range is green.
1429 GMT (10:29 a.m. EDT)
T-minus 1 minute. Now 60 seconds away from launching the fifth Mobile User Objective System communications satellite.
1428 GMT (10:28 a.m. EDT)
T-minus 90 seconds. The rocket's safety system has been armed.
1428 GMT (10:28 a.m. EDT)
T-minus 1 minute, 45 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.
1428 GMT (10:28 a.m. EDT)
T-minus 1 minute, 55 seconds. The launch sequencer has been commanded to start.
1428 GMT (10:28 a.m. EDT)
T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching from ground power to internal batteries.
1427 GMT (10:27 a.m. EDT)
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.
1427 GMT (10:27 a.m. EDT)
T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for launch.
1426 GMT (10:26 a.m. EDT)
T-minus 3 minutes, 50 seconds. The ground pyrotechnics are enabled.
1426 GMT (10:26 a.m. EDT)
T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket with a new mobile communications satellite for the U.S. Navy from Cape Canaveral, Florida.
1425 GMT (10:25 a.m. EDT)
The MUOS 5 satellite is on internal power.
1425 GMT (10:25 a.m. EDT)
Standing by to pick up the count.
1424 GMT (10:24 a.m. EDT)
The ULA launch director and the Air Force mission director have given their respective final approvals to resume the countdown.
1423 GMT (10:23 a.m. EDT)
Polling of the team by Atlas launch conductor just occurred. All systems are reported GO for flight.
1420 GMT (10:20 a.m. EDT)
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.
1418 GMT (10:18 a.m. EDT)
The Atlas 5 rocket stands 206 feet tall and weighs 1.3 million pounds at launch.
1415 GMT (10:15 a.m. EDT)
Here's a look at some stats about today's mission. This will be:
1414 GMT (10:14 a.m. EDT)
The vehicle's three cryogenic tanks are at flight level.
1412 GMT (10:12 a.m. EDT)
The MUOS 5 satellite is switching to internal power for launch.
1411 GMT (10:11 a.m. EDT)
T-minus 4 minutes and holding. The countdown has entered the planned 15-minute hold to give the launch team a chance to review all systems before pressing ahead with liftoff.
1410 GMT (10:10 a.m. EDT)
T-minus 5 minutes. Standing by to go into the final built-in hold.
1401 GMT (10:01 a.m. EDT)
Weather is observed GO for liftoff based on the current conditions and forecast to stay favorable for a 10:30 a.m. EDT (1430 GMT) launch today.

Skies are clear, radar is clear and winds are 4 knots.

1400 GMT (10:00 a.m. EDT)
Just 30 minutes until liftoff time. Today's launch is the fifth for the Navy's new Mobile User Objective System satellite constellation to provide mobile communications to U.S. military forces.

In its launch configuration atop the Atlas rocket with the two power-generating solar arrays stowed on the sides and the umbrella reflectors folded up, MUOS stands 22 feet tall, 12 feet wide and 6 feet deep. The craft was built on Lockheed Martin's A2100 satellite design used by dozens of previous communications spacecraft.

Following separation from the launch vehicle nearly three hours after liftoff today, ground controllers will begin maneuvering MUOS 5 into geosynchronous orbit, deploying its power-generating solar arrays to span more than 90 feet, unfurling a pair of umbrella-like antenna reflectors on boom assemblies and fully checking out the onboard communications equipment.

Eight orbital raising burns are expected over the next 8-9 days, followed by the antenna reflector deploys, then a test program that Lockheed Martin will perform. The military will take control of the satellite in a few months to conduct its own acceptance evaluation before the craft enters UHF service.

1359 GMT (9:59 a.m. EDT)
The fuel-fill sequence for the first stage main engine is starting.
1352 GMT (9:52 a.m. EDT)
This is the fifth and final planned launch of a Mobile User Objective System spacecraft by the Navy.

MUOS No. 1 was launched Feb. 24, 2012 aboard an Atlas 5 and serves as the Pacific Ocean satellite.

MUOS No. 2 launched July 19, 2013 aboard another Atlas 5 and serves as the continental U.S. satellite.

MUOS No. 3 went up atop an Atlas 5 on Jan. 20, 2015 to cover the Atlantic Ocean region.

An Atlas 5 launched MUOS No. 4 on Sept. 2, 2015 to serve the Indian Ocean region.

1349 GMT (9:49 a.m. EDT)
Weather odds have improved to 90 percent GO for launch today.
1345 GMT (9:45 a.m. EDT)
Now 45 minutes from liftoff. Today marks the 63rd flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 62 missions since debuting in August 2002, the Atlas 5 has flown 24 flights dedicated to the Defense Department, 14 commercial missions, 12 for NASA and 12 with spy satellites for the National Reconnaissance Office.
1341 GMT (9:41 a.m. EDT)
The Atlas 5 rocket now stands fully fueled with its cryogenic liquid oxygen and liquid hydrogen as the countdown continues on schedule for a liftoff at 10:30 a.m. EDT (1430 GMT).
1339 GMT (9:39 a.m. EDT)
The liquid hydrogen tank in the Centaur upper stage just reached the 96 percent level. Topping is beginning.
1334 GMT (9:34 a.m. EDT)
Fast-filling of the first stage liquid oxygen tank has been completed. Topping mode is now underway.
1332 GMT (9:32 a.m. EDT)
Centaur's liquid hydrogen tank is 50 percent full. The cryogenic propellant will be consumed with liquid oxygen by the stage's Aerojet Rocketdyne-made RL10C engine.
1331 GMT (9:31 a.m. EDT)
First stage liquid oxygen tank is 90 percent full thus far. 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 four minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket after rollout.
1330 GMT (9:30 a.m. EDT)
Now 60 minutes from liftoff.

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.)

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1320 GMT (9:20 a.m. EDT)
Chilldown of the liquid hydrogen system has been accomplished. The launch team has received the "go" to begin filling the Centaur upper stage with the supercold fuel.
1311 GMT (9:11 a.m. EDT)
The first stage liquid oxygen tank has reached the 50 percent mark.
1308 GMT (9:08 a.m. EDT)
Centaur liquid oxygen tank has reached flight level.
1307 GMT (9:07 a.m. EDT)
The Centaur engine chilldown sequence is being initiated.
1300 GMT (9:00 a.m. EDT)
The Centaur liquid oxygen tank reached the 95 percent level. The topping off process is starting now.
1255 GMT (8:55 a.m. EDT)
The chilldown conditioning of liquid hydrogen propellant lines at Complex 41 is starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 12,300 gallons of the cryogenic propellant.
1253 GMT (8:53 a.m. EDT)
The first stage liquid oxygen loading is transitioning from slow-fill to fast-fill mode.

And the Centaur liquid oxygen tank reached the 95 percent level. The topping off process is starting now.

1249 GMT (8:49 a.m. EDT)
Now half-full on the Centaur upper stage's liquid oxygen tank.
1245 GMT (8:45 a.m. EDT)
The conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin pumping 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 48,800 gallons of cryogenic oxidizer for the RD-180 main engine.

1240 GMT (8:40 a.m. EDT)
Passing the 10 percent level on the Centaur upper stage's liquid oxygen tank.
1234 GMT (8:34 a.m. EDT)
Filling of the Centaur upper stage with about 4,150 gallons of liquid oxygen has begun at Cape Canaveral's Complex 41 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 RL10C engine along with liquid hydrogen to be pumped into the stage a little later in the countdown. The Centaur will perform three firings to propel the MUOS satellite into its intended orbit today.

1227 GMT (8:27 a.m. EDT)
The Centaur liquid oxygen 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.
1215 GMT (8:15 a.m. EDT)
T-minus 120 minutes and counting! The launch countdown has resumed for today's flight of the Atlas 5 rocket on a mission to deploy the U.S. Navy's MUOS 5 mobile communications satellite.

Clocks have one more built-in hold planned at T-minus 4 minutes. During that 15-minute pause, the final "go" for launch will be given. All remains targeted for liftoff at 10:30 a.m. EDT (1430 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.

1212 GMT (8:12 a.m. EDT)
All console operators have reported READY status during the pre-fueling readiness poll. The ULA launch director also voiced his approval for moving forward with the countdown as scheduled today.

The loading of nearly 66,000 gallons of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.

1210 GMT (8:10 a.m. EDT)
The ULA launch conductor at the Atlas Spaceflight Operations Center is briefing his team on procedures before entering into the final two hours of the countdown.
1207 GMT (8:07 a.m. EDT)
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1200 GMT (8:00 a.m. EDT)
T-minus 2 hours and holding. The countdown has just entered the first of two planned, 15-minute holds over the course of the day that will lead to the 10:30 a.m. EDT (1430 GMT) launch of the Atlas rocket. The holds give 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.
1158 GMT (7:58 a.m. EDT)
The danger area has been cleared of all personel.
1145 GMT (7:45 a.m. EDT)
The final hands-on work has wrapped up at the launch pad and technicians are departing the complex. Safety officials will confirm that the surrounding danger area has been cleared of all workers for the remainder of the countdown.

Weather conditions remain "GO" at the present time.

1100 GMT (7:00 a.m. EDT)
The early portion of the countdown has been going well. There are no issues being reported in the count, activities are on schedule and the weather is fine.
0835 GMT (4:35 a.m. EDT)
In today's first weather briefing to mission managers, all current conditions are observed GO for launch of the Atlas 5 rocket and odds for the launch window stand at 80 percent favorable.

The only concern that meteorologists will be watching is development of cumulus clouds late in today's launch window.

The outlook predicts good visibility, southerly winds of 8 to 12 knots and a temperature of 84 degrees F.

The Atlas-Centaur rocket has been powered up at Complex 41 and guidance system testing is getting started for today's launch, as the countdown progresses as planned.

0740 GMT (3:40 a.m. EDT)
The countdown is beginning for launch of the Atlas 5 rocket to deploy the Navy's MUOS 5 communications satellite for mobile military users.

Clocks are picking up the seven-hour sequence of work that will prepare the booster, payload and ground systems for blastoff at 10:30 a.m. EDT (1430 GMT).

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 GPS metric tracking system used to follow the rocket as it flies downrange, plus a test of the S-band telemetry relay system.

A planned hold begins when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled to verify all is in readiness to start fueling the rocket for launch.

Supercold liquid oxygen begins flowing into the Centaur upper stage, followed by the first stage filling. 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. That 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 44 minutes to 11:14 a.m. EDT (1514 GMT).

THURSDAY, JUNE 23, 2016
After successfully launching the most powerful Delta rocket two weeks ago, United Launch Alliance rolled the most powerful Atlas from its assembly building to the launch pad today for Friday's military mission.

See today's rollout photo gallery.

ULA operates both families of boosters to launch U.S. national security spacecraft, civil science missions and commercial satellites. Atlas and Delta have logged more than 1,000 launches, evolving from modest beginnings to today's medium- and heavy-lift payload deployers accommodating the entire spectrum of U.S. military spacecraft sizes and orbits needed.

The Atlas 5 rocket, equipped with five strap-on solid-propellant boosters for added performance, will launch the Navy's MUOS 5 mobile communications satellite tomorrow at 10:30 a.m. EDT (1430 GMT). The available launch window extends to 11:14 a.m. EDT.

There is an 80 percent chance of acceptable weather for the launch opportunity. Cumulus clouds will be the only concern.

"Favorable weather continues through launch as high pressure persists over Central Florida," Air Force weather forecasters say.

The launch time outlook calls for scattered low- and high-level clouds, good visibility, southerly winds of 8-12 knots and a temperature of 83 degrees F.

The booster was wheeled out this morning aboard a mobile launcher platform, emerging just after 8 a.m. from the hangar where the rocket's two stages, boosters and payload were integrated over the past few weeks.

The slow drive from the 30-story Vertical Integration Facility to the launch pad used a pair of specially-made “trackmobiles” to carry the rocket’s 1.4-million pound launching platform along rail tracks for the 1,800-foot trip.

The 206-foot-tall rocket will launch the MUOS satellite into a high-perigee geosynchronous transfer orbit. Deployment of the payload occurs nearly three hours into flight.

"With this fifth satellite, MUOS completes the current constellation bringing additional UHF (ultra high frequency) capacity, as well as providing the assurance of an on-orbit spare for the new Wideband Code Division Multiple Access capability," said Capt. Joe Kan, the Navy program manager.

The rocket is flying the 551 vehicle configuration. The version features two stages, five solids and an 18-foot-diameter nose cone. It is powered off the launch pad by an RD AMROSS RD-180 main engine and Aerojet Rocketdyne solids. The Centaur upper stage has an Aerojet Rocketdyne RL10C-1 cryogenic engine.

Countdown clocks begin ticking seven hours before launch, leading to activation of the rocket, final testing and system preps. Fueling will be underway by 8:30 a.m. EDT.

Watch this page for live coverage throughout the countdown and flight of the Atlas-Centaur rocket.

Be sure to 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.)

Playalinda Beach is an ideal public viewing spot for the launch. The location puts you less than five miles from the launch pad to feel the 2.5 million pounds of liftoff thrust! Get directions here.

WEDNESDAY, JUNE 22, 2016
This is the ascent timeline to be followed by the United Launch Alliance Atlas 5 rocket in launching the Mobile User Objective System satellite No. 5 on Friday at 10:30 a.m. EDT.

The Launch Readiness Review was conducted earlier today and gave approval to proceed with the Atlas 5 rocket's rollout tomorrow and flight on Friday.

Weather forecasters continue to predict an 80 percent chance of favorable launch conditions.

TUESDAY, JUNE 21, 2016
PREVIEW: For the fifth time in four years, a massive U.S. Navy satellite will launch atop an Atlas 5 rocket on Friday to finish the military's new $7.7 billion mobile communications framework 22,300 miles in space.

Read our full story.

MONDAY, JUNE 20, 2016
WEATHER: Air Force meteorologists are giving good odds of acceptable weather conditions for the United Launch Alliance Atlas 5 rocket to fly Friday morning from Cape Canaveral to put a Navy mobile communications satellite into orbit.

Read our full story.