Advanced Question Longitude of the Ascending Node on the ground vs final orbit

PaulG

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I'm trying to conceptually understand something.


Why is the LAN after achieving orbit drastically different than on the ground just prior to launch? What I can tell, the value is represented by the following "formula", which could very well be wrong, so please, I'd like to understand.


Let G = ascending node on the ground at launch
Let L = latitude of the base (e.g. 28.5)
Let d = directional multiplier, (+1 if going north, -1 if going south)
Let LAN = longitude of the ascending node in orbit. Give or take a little due to the time it takes to get to orbit.

LAN = G+d*(90-L)
So, if my ground latitude is 28.5 and the on ground LAN is 244, the my orbital LAN after launching any direction northward will be around 244+1(90-28.5) = 306.
If going south, it would be 244-1(90-28.5) = 183.


Thanks,
paul
 
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BrianJ

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Hi,
I don't think your formula is correct. This website explains it better than I can:
http://www.braeunig.us/space/orbmech.htm#launch
Equation 4.35 is most relevant. Don't forget that Geocentric Lat. and Long. are not the same as Ecliptic Lat. and Long. (different reference frames).

Cheers,
Brian
 

PaulG

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Thanks. I'm not sure those apply in the instance I'm referring to. What I have observed in terms of the LAN calculated when on the ground versus post orbit is close to what I posted, I just don't understand why.
 
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