General Question Shuttle Fleet 4.8, launch azimuth for desired heading

andqui

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I'm trying to get a ShuttleFleet 4.8 STS-1 scenario working. Apart from some trouble with AutoFCS not showing bases for which I've asked a seperate question in the Addon Support & Bugs section, the other problem I'm having is that the launch autopilot seems to have trouble maintaining the launch heading.

I want an inclination of 40.3 degrees at a circular 246km orbit corresponds to a launch azimuth of 58.7 degrees, and I've entered that into the scenario file. After launch with the GPC MFD program, I get a roll maneuver which puts me perfectly on that heading as the pitch program starts, no problems so far. However, as the launch progresses, the heading begins to drift south after SRB separation. I end up with a resulting inclination of 48-49 degrees instead as the heading drifts to ~65-70 degrees during the horizontal portion of the ascent. Am I supposed to be able to accurately hit an inclination with the launch autopilot and am doing something wrong, or is something not working right?
 

GLS

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I'm trying to get a ShuttleFleet 4.8 STS-1 scenario working. Apart from some trouble with AutoFCS not showing bases for which I've asked a seperate question in the Addon Support & Bugs section, the other problem I'm having is that the launch autopilot seems to have trouble maintaining the launch heading.

I want an inclination of 40.3 degrees at a circular 246km orbit corresponds to a launch azimuth of 58.7 degrees, and I've entered that into the scenario file. After launch with the GPC MFD program, I get a roll maneuver which puts me perfectly on that heading as the pitch program starts, no problems so far. However, as the launch progresses, the heading begins to drift south after SRB separation. I end up with a resulting inclination of 48-49 degrees instead as the heading drifts to ~65-70 degrees during the horizontal portion of the ascent. Am I supposed to be able to accurately hit an inclination with the launch autopilot and am doing something wrong, or is something not working right?

Hi!
As you move along during ascent, your heading will change because you are no longer at the launch pad latitude. As your latitude increases, the azimuth needed to get to your target orbital inclination will increase. So, as far as the heading slowly changing during launch, it's normal.
 

andqui

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Hi!
As you move along during ascent, your heading will change because you are no longer at the launch pad latitude. As your latitude increases, the azimuth needed to get to your target orbital inclination will increase. So, as far as the heading slowly changing during launch, it's normal.

Thanks. So how do I compensate for it to arrive at the correct inclination that I calculated the launch azimuth for? Or I guess what I'm asking is why then is the autopilot (or me, I don't know) putting me at the wrong inclination when I think I've correctly calculated and rolled to the correct launch azimuth?
 

GLS

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Thanks. So how do I compensate for it to arrive at the correct inclination that I calculated the launch azimuth for? Or I guess what I'm asking is why then is the autopilot (or me, I don't know) putting me at the wrong inclination when I think I've correctly calculated and rolled to the correct launch azimuth?

That I don't know.
BTW: probably a stupid question but, where are you checking the orbital inclination? OrbitMFD? If so, do you have the Frame in Equatorial? Otherwise you will be reading another angle...
 

andqui

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That I don't know.
BTW: probably a stupid question but, where are you checking the orbital inclination? OrbitMFD? If so, do you have the Frame in Equatorial? Otherwise you will be reading another angle...

Oh... I feel stupid now. That explains it. Thank you very much.
 
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