A United Launch Atlas 5 rocket is set to launch the U.S. Air Force’s sixth and final 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, March 26, that opens at 2:57 p.m. EDT (1857 GMT).
The AEHF 5 mission will be the 83rd flight of an Atlas 5 rocket, and the second Atlas 5 launch of 2020.
Built by Lockheed Martin, the AEHF 6 satellite joins five previous satellites in the AEHF constellation launched by Atlas 5 rockets in 2010, 2012, 2013, 2018 and 2019. 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 two more 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 6 spacecraft. On this mission, ULA added extra hardware and maneuvering fuel to the Centaur upper stage, enabling the launcher to deliver the AEHF 6 satellite closer to its final orbit more than 22,000 miles (nearly 36,000 kilometers) above the equator.
The GSO kit was added to the Atlas 5 rocket on the fifth AEHF launch last August, after the first four AEHF missions did not employ the additional capability.
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.
Thanks to the mission profile change, the AEHF 6 satellite will separate in an orbit with a perigee, or low point, several thousand miles higher than would be possible without the GSO kit. That means AEHF 6 — like AEHF 5 last year — 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 6 launch sequence and a ground track map illustrating the rocket’s path after liftoff are are posted below.