position change in ECEF EoM

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MTA
MTA on 30 Apr 2015
Commented: Saif Awwad on 16 May 2015
Hi
I might have some rust on my mechanics, but I couldn't understand why both the ECEF and the LLA position changes with time under a zero body forces and moments.
It is easy to test, an ECEF quaternion EoM block with zero inputs and arbitrary initial position (not at a pole) and zero initial body translational and rotational velocities and a WGS84 planet.
I know that the position change is due to the transport term (specifically the centripetal acceleration) emerging from solving eom in a rotating frame. However, these transport terms will affect the inertial position (ECI position) not the ECEF and LLA positions. Thus a stationary point on a rotating planet will have a constant ECEF and LLA position, but its ECI position will be changing with time.
Would anyone kindly explain what am I missing? or is the block doing something it shouldn't?
Kind regards,
Mohamad

Answers (1)

Saif Awwad
Saif Awwad on 8 May 2015
I faced a somehow similar problem some time ago, which I could not answer until today. Please let me know if you find an answer.
Thanks.
  4 Comments
MTA
MTA on 13 May 2015
Hi Saif
Sure, you can personal message it if it is not contributing to the thread directly.
Saif Awwad
Saif Awwad on 16 May 2015
With a body of zero forces and moments, is the change in both of ECEF and LLA positions analogical? As you said, only ECI should be changing with time. So I am doubting some sort of a bug in the code converting ECEF to LLA or vise versa.
I will be messaging about further topics outside the scope of this thread.

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