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

PaulG

New member
Joined
Sep 12, 2008
Messages
159
Reaction score
0
Points
0
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
 
Last edited:

BrianJ

Addon Developer
Addon Developer
Joined
Apr 19, 2008
Messages
1,273
Reaction score
117
Points
63
Location
Code 347
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

New member
Joined
Sep 12, 2008
Messages
159
Reaction score
0
Points
0
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.
 
Top