Explanation of the space-fixed heading angle

caningo

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Hello fellow orbinauts! :salute:

Today I was going through some of the old Apollo mission reports and come across this term which I can't seem to grasp its meaning:

Space-fixed heading angle:

Angle of the projection of the inertial velocity vector onto the local body-centered, horizontal plane, measured positive eastward from north, deg
My question is, if I'm looking down onto this plane that they are defining, what is north? It's obvious this plane is not aligned with the Earth Z+ axis which is geographic north, right?

Any help clearing this confusion would be greatly appreciated. :thumbup:
 

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caningo

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Seems like this one was a toughie since no one was able to provide an answer. :lol:

Anyways, after searching around for like a week or so I finally came upon the solution. :bananadance:

A picture is worth a thousand words or so they say...

sfhedangle.jpg


The heading angle is σ in the figure.

I hope this helps anyone who happens to have the same question later in the future.

Peace! :thumbup:
 
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