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In the recent ULA video by Tory Bruno Tory Talk // Atlas V Lucy: RAAN Steering (linked below) he gave some short hints about RAAN steering.

  • What is RAAN (Right Ascension of Ascending Node) steering?

  • He mentioned the Atlas V rocket achieves precise orbital insertion with the help of RAAN steering even with some delay. How is this possible? (A diagram is much appreciated)

  • Do Space X and other Launch Service providers (LSP) use a similar kind of technology?

Although this technology is a secret sauce, at least the second and third answers should be answerable IMO. Thank you.

Video is only 2 minutes long, but currently there are no closed captions:

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  • $\begingroup$ Can you visualize launch to a 0 deg inclination geostationary orbit from a latitude other than equator ? The rocket can steer away from the natural inclination arising from the latitude of the launch site to the zero degree inclination orbit. AFAIK, RAAN is the same thing as inclination but measured against the prime meridian* instead of the equator. $\endgroup$
    – AJN
    Oct 22, 2021 at 10:54

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Partial answer:

I don't think it's quite as mysterious as it first seems.

Bruno explains that the launch site on Earth only passes through the orbital plane of its first intercept target for a moment, and suggests that that launch window is only 1 second long, otherwise "you can't get there from here" anymore.

In reality there are going to be trajectory correction maneuvers along the way so a 1 second launch window is not imposed by orbital mechanics, it's pretty much theatrics.

However, he explains that the Right Ascension of Ascending Node steering is a name for a way to calculate a good way to "fly into the plane" or "get back to the plane" correct plane when launching either side of the moment of intersection.

For a 75 minute long window, they know how to calculate the best way to adjust the trajectory in real time, so that whenever the launch takes place the flight software in the rocket will already be able to execute the calculation and optimized trajectory.

They don't need to recalculate it and upload it depending on the exact deviation from optimum time.

I don't recall what this dynamic recalculation technique is called but this is not the first time that Bruno has talked about how they can "recalculate launch trajectories on the fly".

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  • $\begingroup$ It is essentially a trade-off of "How much does it cost you to recycle a launch if you miss the window" vs. "How much does it cost to develop the control software, and to carry the extra propellant, and how much does that extra propellant reduce your payload mass to orbit". $\endgroup$
    – Jörg W Mittag
    Oct 22, 2021 at 6:38
  • $\begingroup$ @uhoh so how other LSP is doing orbital insertion? Does that mean they also estimate the time and do orbital insertion & are you suggesting the launch window can be greater than 1 sec generally? $\endgroup$
    – Auberron
    Oct 22, 2021 at 12:12
  • $\begingroup$ @Auberron mostly I'm just interpreting what Bruno is saying. I guess I did say that a 1 second launch window was "theatrics" and in fact I might be wrong. It could be that in the past, or for some current provider with a legacy system, they have to have a 1 second window for certain orbits. I think that aspect can be explored with a new question! $\endgroup$
    – uhoh
    Oct 22, 2021 at 13:23
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    $\begingroup$ @Auberron You can link to these for background: Why was TESS' launch window open for only 40 seconds per day? and Why would a mission to Sun-Earth L1 have an instantaneous launch window? $\endgroup$
    – uhoh
    Oct 22, 2021 at 13:23

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