AEHF-4 - Atlas V 551 (AV-073) - CCAFS SLC-41 - 17.10.2018, 04:15 UTC

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7:30 p.m. EDT (2330 UTC)

The sun has set at Cape Canaveral as our countdown continues smoothly for launch of the Atlas V rocket. Credit: United Launch Alliance.

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7:45 p.m. EDT (2345 UTC)

An open-loop test of the S-band system used to relay telemetry from the launch vehicle during flight is underway. Also, the GPS Metric Tracking Antenna used to follow the vehicle's progress downrange is being checked.

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Maxar Technologies‏ @MaxarTech 19 мин. назад

.@DigitalGlobe's #WV3 caught an #Atlas5 rocket on the pad in Cape Canaveral just a few hours ago. The rocket is scheduled to launch tonight (Oct. 16) at 12:15 AM EDT for a @usairforce comms satellite.

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8:06 p.m. EDT (0006 UTC)

Internal battery checks are beginning now.

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10/17/2018 03:16 Stephen Clark

The first of several weather balloons have been launched at Cape Canaveral to measure high-altitude winds as the Atlas 5 countdown proceeds toward liftoff at 12:15 a.m. EDT (0415 GMT).

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8:47 p.m. EDT (0047 UTC)

This is Atlas Launch Control at T-minus 2 hours, 58 minutes (L-3 hours, 28 minutes) and counting. The initiation of gaseous nitrogen flow to the launch vehicle has started. This changes the environmental control system to supply nitrogen gas rather than conditioned air to the internal compartments of the Atlas first stage, Centaur upper stage and the payload fairing in preparation for fueling and launch.

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9:15 p.m. EDT (0115 UTC)

This is Atlas Launch Control at T-minus 2 hours, 30 minutes (L-3 hours) and counting. Countdown activities continue on schedule at the Space Launch Complex 41 pad and inside the Atlas Spaceflight Operations Center for tonight's Atlas V satellite-delivery mission. In the past few minutes, first stage propulsion and hydraulic preps were reported complete. The propulsion preps configured the ground liquid oxygen transfer system and ground pneumatic supply systems for filling the Atlas first stage LOX tank and pressurizing the Atlas helium bottles for launch. The hydraulic preps configured the ground hydraulic pressure unit to provide for first stage main engine pre-launch hydraulic control.

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9:27 p.m. EDT (0127 UTC) – Weather remains 90% GO

In the pre-fueling weather briefing to mission management, Air Force Launch Weather Officer Jessica Williams reports that conditions remain favorable at Cape Canaveral for a rocket countdown this evening. There are no weather constraints against proceeding into Atlas V fueling operations as scheduled.

The launch time forecast remains 90 percent favorable.

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ULA‏Подлинная учетная запись @ulalaunch 2 мин. назад

Did you know? The #AtlasV 551 with #AEHF4Road2Launch has a 5-m fairing, 1 RD-180 main engine, 5 solid rocket boosters and 1 RL10A Centaur upper stage engine

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10/17/2018 04:39 Stephen Clark

With the final hands-on work accomplished, technicians are departing the Complex 41 launch pad and heading to a fall-back position a safe distance away. This evacuation is a key step before the Atlas 5 is filled with cryogenic propellants.

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9:45 p.m. EDT (0145 UTC) -- Countdown holding

This is Atlas Launch Control at T-minus 2 hours and holding. The countdown has entered the first of two planned, built-in holds that are scheduled in today's timeline. These are 15-minute blocks of time that gives the countdown some margin to resolve issues or catch up work that could be running late. This particular hold provides an opportunity to ensure all is ready before fueling operations begin. The final hold occurs at T-minus 4 minutes.

At the present time, however, all activities are on schedule and no problems are being addressed by the launch team.

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9:58 p.m. EDT (0158 UTC) — Go for fueling

A readiness poll of the launch team by Launch Conductor Ed Kitta, with concurrence of ULA Launch Director Bill Cullen, has approved cryogenic tanking operations to begin once the countdown resumes tonight. The Atlas V rocket will be loaded with approximately 66,000 gallons of liquid oxygen and liquid hydrogen over the next hour or so.

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10/17/2018 05:00 Stephen Clark

T-minus 2 hours and counting. The countdown clock is ticking again, as the ULA launch team marches toward liftoff of an Atlas 5 rocket at 12:15 a.m. EDT (0415 GMT) with the U.S. Air Force's fourth Advanced Extremely High Frequency communications satellite.

There is one more built-in hold in today's countdown, expected at T-minus 4 minutes.

A thermal conditioning procedure known as chilldown will begin shortly to prepare the plumbing on the Atlas 5's mobile launch platform for the transfer of super-cold cryogenic propellants into the rocket.

Once cryogenic tanking begins, nearly 66,000 gallons of liquid hydrogen and liquid oxygen will be loaded into the two-stage Atlas 5 rocket.

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:!:  

ULA‏Подлинная учетная запись @ulalaunch 4 мин. назад

We understand YouTube is down and we are working on alternate solutions for launch streaming. #AtlasV #AEHF4Road2Launch

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10/17/2018 05:10 Stephen Clark

Liquid oxygen is now flowing into the Atlas 5's Centaur upper stage at Cape Canaveral's Complex 41 launch pad. About 4,150 gallons of the cryogenic propellant, chilled to minus 298 degrees Fahrenheit, will be burned by the Centaur's single Aerojet Rocketdyne RL10 engine along with the liquid hydrogen to be loaded aboard later in the countdown.

Three burns by the Centaur's RL10 engine over a nearly three-and-a-half hour span are planned on tonight's mission to inject the AEHF 4 military communications satellite into an elliptical geostationary transfer orbit with an apogee, or high point, of 21,933 miles (35,299 kilometers), a perigee, or low point, of 5,539 miles (8,914 kilometers), and an inclination of 12.8 degrees.

The AEHF 4 satellite, built by Lockheed Martin, will use its on-board engine to circularize its orbit over the equator at an altitude of more than 22,000 miles.

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William Harwood‏ @cbs_spacenews 2 мин. назад

A5/AEHF4: The AEHF relay stations, built by Lockheed Martin, are designed to provide jam-proof, secure communications around the world 10 times faster than earlier Milstar comsats; two more AEHF satellites are expected to launch in 2019 and 2020.

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10/17/2018 05:30 Stephen Clark

Chilldown of the liquid hydrogen transfer lines at Complex 41 is getting started now. This is a step in preparation for loading the super-cold fuel, stored at minus 423 degrees Fahrenheit, into the Centaur upper stage.

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10:30 p.m. EDT (0230 UTC)

Filling of the Atlas V rocket's largest tank has begun. About 48,800 gallons of super-cold oxidizer for the main engine is flowing into the liquid oxygen tank on common core booster first stage.

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ULA‏Подлинная учетная запись @ulalaunch 3 мин. назад

#AEHF4Road2Launch will launch on an #AtlasV 551 rocket. Here's an expanded view of the rocket.

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