A United Launch Atlas 5 rocket is set to launch the U.S. Air Force’s fifth Advanced Extremely High Frequency communications satellite from Cape Canaveral. This timeline shows the major mission events planned over a nearly six-hour flight to an optimized geostationary transfer orbit.
The 197-foot-tall (60-meter) rocket, propelled by an RD-180 main engine and five solid rocket boosters, is set for liftoff during a two-hour launch window Thursday, Aug. 8, that opens at 5:44 a.m. EDT (0944 GMT).
The AEHF 5 mission will be the 80th flight of an Atlas 5 rocket, and the first Atlas 5 launch of 2019.
Built by Lockheed Martin, the AEHF 5 satellite joins four previous satellites in the AEHF constellation launched by Atlas 5 rockets in 2010, 2012, 2013 and 2018. The first four AEHF satellites in orbit allowed the Air Force’s new generation of secure, nuclear-hardened voice, video and data relay spacecraft to span the globe, and the addition of a fifth AEHF geostationary relay satellite will grow the network’s capacity and resiliency.
The Atlas 5 launch sequence will last 5 hours, 40 minutes, from liftoff until deployment of the AEHF 5 spacecraft. On this mission, ULA added extra hardware and maneuvering fuel to the Centaur upper stage, enabling the launcher to deliver the AEHF 5 satellite closer to its final orbit more than 22,000 miles (nearly 36,000 kilometers) above the equator.
“We’re launching with the Centaur geosynchronous orbit kit,” said Col. Shane Clark, AEHF 5 mission director from the Launch Enterprise Systems Directorate at the Air Force’s Space and Missile Systems Center. “The GSO kit enables an orbital insertion much closer to the final orbit than a traditional geosynchronous transfer orbit, maximizing on-orbit capability of the AEHF 5 space vehicle.”
The extra performance provided by the GSO kit will allow the Centaur upper stage to coast an additional two hours before its third firing. Spacecraft separation is scheduled for T+plus 5 hours, 40 minutes, more than two hours later than the time of deployment on the most recent Atlas 5 launch with an AEHF satellite.
Thanks to the mission profile change, the AEHF 5 satellite will separate in an orbit with a perigee, or low point, several thousand miles higher than achieved on the AEHF 4 launch last October. That means AEHF 5 will need to consume less of its own finite propellant supply to circularize its orbit, leading to a longer operating lifetime for the mission.
According to an Atlas 5 user’s guide published by ULA, the GSO kit includes additional battery power, a full load of hydrazine to control the upper stage’s orientation in space, and additional shielding over sensitive components, including the Centaur’ hydrogen and oxygen tanks.
An overview of the Atlas 5/AEHF 5 launch sequence and a ground track map illustrating the rocket’s path after liftoff are are posted below.
T+0:00:34.4: Mach 1
T+0:01:45.8: Jettison SRBs
T+0:03:23.3: Payload Fairing Jettison
T+0:04:26.2: Main Engine Cutoff
T+0:04:32.2: Stage Separation
T+0:04:42.2: Centaur Ignition 1
T+0:11:41.5: Centaur Cutoff 1
T+0:22:49.9: Centaur Ignition 2
T+0:28:53.3: Centaur Cutoff 2
T+5:36:00.0: Centaur Ignition 3
T+5:37:46.6: Centaur Cutoff 3
T+5:40:35.7: AEHF 5 Separation
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