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I want to allign my satellite with the orbital angular momentum vector. Thus, I've computed this vector in a Fixed Coordinate System using the cross product (r x v) between position vector and velocity vector (also in Fixed Coordinate System) provided by STK report.

However, the Matlab computed angular momentum vector doesn't match with the one provided by STK (also expressed in Fixed Coordinate System).

Can anyone help me to figure out why this happens and in which way to compute the correct Orbital Angular Momentum considered by STK?

EDIT: The vector considered in STK is Orbit_AngMomentum in Vectors(Fixed)

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    $\begingroup$ I would recommend you do NOT used a fixed coordinate frame. The fixed frame in STK is attached to the rotating earth. That makes it evil for a number of reasons: It is not inertial, it relies on computations of earth's orbit precession and nutation, it requires knowledge of the UT-UT1 offset and polar motion. Unless you have a strong need to express vectors in fixed, I recommend using an inertial frame. $\endgroup$ Commented Oct 7, 2022 at 22:18
  • $\begingroup$ Hi Carlos, thanks for your answer. You're right about using an inertial frame rather than a fixed one. However, as you suggested, I've a strong need to express vectors in fixed. Therefore, I want to figure out why this discrepancy happens just becaus i'm using the same STK's vectors which already includes the dut1, precession and nutation, etc. corrections $\endgroup$ Commented Oct 10, 2022 at 9:21
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    $\begingroup$ I think your problem is arising because the V vector in the fixed frame has built into it a component of the earth's rotation. So I don't think you can simply cross it with R to get a true angular momentum representation in the fixed frame. Fixed is non inerial so things become very non-intuitive as to what they mean. If you display Orbit_AngMomentum both Fixed and Inertial in STK 3D window, you will see that they don't coincide. I'd have to dig in to rotation matrices to see exactly what STK calls Orbit_AngMomentum in fixed frame. $\endgroup$ Commented Oct 14, 2022 at 17:04
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    $\begingroup$ Provided you have the STK Analysis Workbench license you can also try to construct your cross vector product that way and see how it compares against how you are doing it in Matlab. $\endgroup$ Commented Oct 14, 2022 at 17:10
  • $\begingroup$ Yeah, I've already done that but the STK's cross product did not match with mine. Despite this, your suggestion to use an inertial frame works, thus I'm thinking to move on this path. $\endgroup$ Commented Oct 17, 2022 at 6:51

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