AEHF-6 | Atlas V 551

Lift Off Time
(Subject to change)
March 26, 2020 – 18:57:00 UTC | 14:57:00 EDT 
Mission Name and what it is
AEHF-6, the sixth launch of an Advanced Extremely High Frequency satellite 
Launch Provider
(What rocket company is launching it?)
United Launch Alliance (ULA)
U.S. Space Force Space and Missile Systems Center
Atlas V 551
Launch Location

Space Launch Complex (SLC) -41, Cape Canaveral AFS, Florida, USA

Payload mass
6,128 kg (13,510 pounds)
Where are the satellites going?
Geostationary Earth Orbit (GEO) (Initially geostationary transfer orbit, GTO)
Will they be attempting to recover the first stage?
No this is not a capability of United Launch Alliance 
Where will the first stage land?
It will crash into the Atlantic ocean approximately 600 km off shore 
Will they be attempting to recover the fairings?
No this is not a capability of United Launch Alliance 
Are these fairings new?
This will be the:
  • 83rd flight for an Atlas V rocket
  • Sixth AEHF satellite
Where to watch
Livestream link

Maybe even more fun you can watch with Tim Dodd, the Everyday Astronaut, starting at T minus 30! Come ask questions and join the conversation live!

Graphic by Geoff Barrett Rocket by Stanley Creative

What’s all this mean?

With the AEHF-6 mission, we get to experience another spectacular Atlas V launch! Atlas V is built and launched by United Launch Alliance (ULA). For this mission an Atlas V 551 configuration will launch an Advanced Extreme High Frequency-6 (AEHF-6) satellite to Geostationary Earth Orbit for the United States military. It will aid them in fast and secure communication.

The Atlas V Rocket

The Atlas V Common Cores are manufactured near Decatur, Alabama and then transported via the Mississippi river and the Gulf of Mexico to either California or Florida.

What does 551 Mean?

The configuration of the Atlas V for the AEHF-6 mission  is 551.  But wait, what does “551” mean, anyway? The last three numbers or letters in the Atlas V’s name denote the configuration of the rocket. The first number/letter shows the fairing diameter size (in meters, of course) of ‘N’ for no fairing. The number 5 obviously means a 5 meter fairing.

The second number determines the number of strap on solid rocket boosters (SRBs). It can range from 0 to 5, and in this case, there are five on various sides of the center common core. The third and final number refers to the number of engines on the Centaur Upper Stage, which can be either one or two. In this case there will be one engine. The only time that there have been two engines (while on an Atlas V) was on Starliner’s OFT-1. So to review, for the AEHF-6 mission, this rocket has a five-meter fairing, five solid rocket boosters, and one engine on the Centaur Upper Stage.

rocket fire steam water vapor rocket atlas v 551 united launch alliance launch pad florida night
The “flamey-end” of an Atlas V 551 rocket. Notice the 5 SRBs on each side split into a group of two and a group of three.

Why are the SRBs positioned this way?

It is unique to the Atlas rocket to have their solid rocket boosters (SRBs) positioned in this way, but why is that? When, like in this case, 5 SRBs are used, they are positioned with two on one side and three directly opposite of them. If you notice carefully in the image below, there are long and somewhat flat pipes “running” down the side of the first core stage. These are called raceways and carry fuel from the tanks down to the engines and some carry gases back up to the tanks to pressurize them so the fuel stays flowing out the pipes. When Atlas was designed, these raceways were placed in their positions without the thought of SRB placement. So when more SRBs were needed, they were placed in the most convenient spot.

engine atlas v ula raceway piple rocket fuel
Notice the cylindrical and flatter pipes that run down the sides of the booster. Those prohibit SRB placement in those areas.

But you might ask, won’t that offset the thrust and make it fly in the wrong direction? Well, the answer is no. Because the engines on the core stage can gimbal, they counteract that offset of thrust by vectoring their thrust which is known as thrust vector control, or TVC. The SRBs, and most of them for that matter, do not have TVC abilities.

rocket white srb atlas v fairing fuel engine
A diagram of the entire Atlas V family with the SRB placement for each number shown.

So what about the payload?

The sixth Advanced Extreme High Frequency-6 (AEHF-6) which is built by Lockheed Martin (power or bus) and Northrop Grumman. Its main goal is to provide a fast, highly reliable and secure connection for United States soldiers in all levels of conflict. The backbone of the Department of Defense communication are these satellites. Once they are in orbit they will be integrated into the Milstar (Military Strategic & Tactical Relay) constellation of military satellites.

satellite AEHF earth rocket northrop grumman
Illustration of an AEHF satellite in Geostationary orbit.

AEHF-6’s Instruments

What might you find on an AEHF satellite? For power, it has two expandable five segment solar arrays that will use solar energy and convert it into electrical energy for the satellite to use. That conversion happens in the “bus” or the main power unit. Various types of antennas with different capabilities to produce the fastest and most secure communications and data transfer for the United States military.

  1. great coverage and info, you make understanding these complex systems easier to understand. Your coverage is what NASA and SpaceXNow don’t give you! Keep up the good work!
    Thank you

  2. It says “Cape Canaveral AIR Force Station” as launch site, but shouldn’t it now be the SPACE Force Station?

    Other than that, great coverage, thank’s a lot!

  3. As a newcomer to this kind of stuff about rockets and space, I have a suggestion. Some of the terms are difficult to understand and it would be really helpful if we could hover over the word and it gives us a brief definition of what it is. Just a suggestion but otherwise I love the article!

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