Monday @ 10:37 a.m. EDT (1437 UTC)
The Atlas V rocket is headed to the launch pad. Photo by United Launch Alliance

Monday @ 10:46 a.m. EDT (1446 UTC)
The Atlas V rocket is headed to the launch pad. Photo by United Launch Alliance

Monday @ 10:50 a.m. EDT (1450 UTC)
This launch will mark the 50th mission that United Launch Alliance has performed for the U.S. Air Force, launching communications, navigation and missile warning satellites, weather observatories and more since 2007.
More than half of the missions have used the Atlas V rocket, while others flew on Delta II and Delta IV, including the first operational Delta IV Heavy.
All but two originated from Cape Canaveral in Florida, with a pair of polar-orbiting weather craft launching from Vandenberg Air Force Base in California.
A wide range of orbits were achieved during the 49 Air Force launches so far, extending from low Earth orbit, to medium Earth orbit for the GPS constellation, transfer orbits and even direct insertion into geosynchronous orbit 22,300 miles up.
Monday @ 11:10 a.m. EDT (1510 UTC)
The Atlas V rocket has completed the first 1,800 feet on its journey into space, traveling by rail from the Vertical Integration Facility to the Space Launch Complex 41 pad for Tuesday night’s countdown to liftoff of AEHF-4, a protected communications relay station in space for the U.S. military and allies.
Over the next few hours, umbilical connections will be made with launch pad systems, the environmental control system feeding conditioned air to the rocket and payload will be switched to facility supplies to allow the portable trailers used during rollout to be unplugged and moved away, and the first stage will be loaded with 25,000 gallons of RP-1 fuel, a highly refined kerosene.
The launch countdown will begin Tuesday at 5:25 p.m. EDT (2125 UTC), leading to a liftoff nearly seven hours later at 12:15 a.m. EDT (0415 UTC) on Wednesday.
Our live countdown updates will begin on this page on Tuesday at 5:15 p.m. EDT.
The live ULA webcast of the launch begins Tuesday at 11:55 p.m. EDT and will be viewable on this page.
Photo by United Launch Alliance

Monday @ 1:30 p.m. PDT (1730 UTC)
See our Flickr page for a collection of beautiful photos of the Atlas V rocket taken by United Launch Alliance during rollout to the pad today.
Photo by United Launch Alliance

Oct. 16, 2018 @ 8:30 a.m. (1230 UTC)
Join us this evening for live reports throughout the Atlas V countdown to the AEHF-4 satellite launch. Our updates from the Atlas Spaceflight Operations Center will begin on this page at 5:15 p.m. EDT (2115 UTC), just prior to initiating the countdown.
Liftoff of the Atlas V rocket from Cape Canaveral Air Force Station in Florida is scheduled for 12:15 a.m. EDT (0415 UTC).
The official launch weather forecast from the 45th Weather Squadron continues to predict an 80 percent chance of favorable conditions at liftoff time. The outlook includes some scattered clouds, the chance of an isolated coastal shower, good visibility, southeasterly winds of 10 knots and a temperature near 80 degrees F.
See our Flickr page for nighttime photos of the Atlas V rocket on the launch pad at Cape Canaveral taken last evening by United Launch Alliance.
5:15 p.m. EDT (2115 UTC)
From the Atlas Spaceflight Operations Center at Cape Canaveral Air Force Station in Florida, this is Atlas Launch Control at T-minus 6 hours, 20 minutes and holding.
We are just seven hours away from liftoff of the United Launch Alliance Atlas V rocket with the U.S. Air Force’s Advanced Extremely High Frequency-4 spacecraft, a protected communications satellite to operate in geosynchronous orbit.
Activities are on schedule for liftoff from Space Launch Complex 41 at 12:15 a.m. EDT (0415 UTC). The launch window extends to 2:15 a.m. EDT (0615 UTC), a duration of exactly two hours.
We will be starting the countdown at 5:25 p.m.
5:25 p.m. EDT (2125 UTC) -- Countdown begins
This is Atlas Launch Control at T-minus 6 hours, 20 minutes (L-6 hours, 50 minutes) and counting.
Countdown clocks are ticking for our liftoff just after midnight tonight. There are two pre-planned, built-in holds, each lasting 15 minutes, scheduled in the count. One pause is reserved prior to fueling at T-minus 2 hours, the other occurs prior to the terminal count at T-minus 4 minutes.
The Atlas V rocket, designated AV-073, will launch AEHF-4 into a high-perigee, low-inclination elliptical geosynchronous transfer orbit. This orbit benefits the satellite by requiring less fuel to reach its final circular geosynchronous altitude 22,300 miles above the Earth, as explained in a tweet by ULA CEO Tory Bruno earlier today.
”Interesting trajectory tonight. All our orbits are customized. This is a GTO, but we will coast for several hours out to apogee and then do a major lift of the perigee. This will leave the spacecraft with only a small amount of remaining energy to add in order to circularize,” Bruno said.
It will take three hours and 33 minutes to perform this Atlas V mission, from liftoff until deployment of the AEHF-4 spacecraft, and the Centaur upper stage will perform three burns to haul the heavy payload to the optimized orbit.
Our rocket variant being flown tonight is the Atlas V 551 configuration that is distinguished by the five-meter-wide composite payload fairing, five solid rocket boosters that are side-mounted to the first stage and a single RL10C-1 engine on the Centaur upper stage. It stands 197 feet tall.
5:40 p.m. EDT (2140 UTC)
This is Atlas Launch Control and T-minus 6 hours, 5 minutes (L-6 hours, 35 minutes) and counting.
The application of power to the Atlas and Centaur stages is underway at the start of today's countdown procedures. The stages are being powered up to begin launch day testing and final preparations for fueling operations.
Over the next few hours, final preps for the 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.
5:55 p.m. EDT (2155 UTC)
The launch team is controlling the countdown from the Atlas Spaceflight Operations Center, or ASOC, located about four miles from the launch pad, in conjunction with a team of personnel performing hands-on tasks at the Space Launch Complex 41 pad. They are being supported by customer staff stationed at Cape Canaveral’s Hangar AE, Range controllers at the Morell Operations Center and teams of engineers monitoring from ULA’s Denver Operations Support Center.
We are progressing on schedule this evening. An initial weather briefing from the Air Force launch weather officer is coming up in about an hour.
6:06 p.m. EDT (2206 UTC)
Power up of the Atlas-Centaur rocket for today's AEHF-4 launch has been accomplished. Guidance system testing is the next major milestone in the countdown as we continue tracking on schedule for liftoff at 12:15 a.m. EDT (0415 UTC). At T-minus 5 hours 39 minutes (L-6 hours, 9 minutes) and counting, this is Atlas Launch Control.
6:37 p.m. EDT (2237 UTC)
The guidance system test is beginning.
6:42 p.m. EDT (2242 UTC)
We are working no issues in the countdown. Liftoff remains scheduled for 12:15 a.m. EDT (0415 UTC).
6:54 p.m. EDT (2254 UTC) – Weather 90% GO
This is Atlas Launch Control at T-minus 4 hours, 51 minutes (L-5 hours, 21 minutes) and counting. Launch Weather Officer Jessica Williams from the Air Force's 45th Weather Squadron reports that conditions at Cape Canaveral are looking favorable for the flight of Atlas V and AEHF-4 tonight, forecasting a 90 percent chance of acceptable conditions at liftoff time.
The outlook calls for some scattered clouds, a chance of a coastal rain shower, good visibility, southeasterly winds of 10 to 12 knots and a temperature of 81 to 82 degrees F.
The only slight concern will be cumulus clouds causing a launch rule violation.
7:00 p.m. EDT (2300 UTC)
A photo of the Atlas V rocket taken a short time ago. Credit: United Launch Alliance.
