What is the difference between the QSW and QSW_INERTIAL frame?
My use case involves the propagation of covariance matrix initially expressed in EME2000.
So, my StateCovarianceMatrixProvider uses the method changeCovarianceFrame() Should I use QSW or QSW_INERTIAL in order to convert the covariance in the QSW(=RTN=RSW) frame, as I propagate the initial state? I don’t understand the difference between the two.
Have a good day!
Manny
P.S. Has the issue discussed in this thread been fixed already or should we wait for Orekit 13.X?
For all the local frames, the “inertial” version is a bit of a weird one. As far as positions are concerned, they will be the same than the non-inertial one. But for velocity and accelerations, no. Basically the rotating part of the transform is ignored, as if \Omega=0. It’s as if you only wanted to change the vector coordinates, ignoring everything about time variation. So to make sense this frame must be redefined at every instant, because the axes are never the same.
I think the main reason for its introduction is that CCSDS defines it (see the registry) and it’s used a lot by some data providers for covariances.
RTN Coordinate Frame: Object-centered quasi-inertial coordinate system as defined and referred to by the RSW_INERTIAL keyword value on the SANA registry’s orbit relative reference frames section (Space Assigned Numbers Authority (SANA)). The Object1-centered RTN coordinate frame: R (Radial) is the unit vector in the radial direction pointed outward from the center of the central body, T (Transverse) is the unit vector perpendicular to the R vector in the direction of the spacecraft velocity, and N (Normal) is the unit vector normal to the satellite’s inertial orbit plane (in the direction of the satellite’s angular momentum) that completes the right-hand coordinate frame (see figure F-1).
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