position change in ECEF EoM

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MTA
MTA 2015-4-30
评论： Saif Awwad 2015-5-16
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

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回答（1 个）

Saif Awwad
Saif Awwad 2015-5-8
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.
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MTA
MTA 2015-5-13
Hi Saif
Sure, you can personal message it if it is not contributing to the thread directly.
Saif Awwad
Saif Awwad 2015-5-16
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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