I've seen a few different answers given, so I want to specifically address the nit-picky pieces.

First, when calculating the relative position of two objects in the UVW/RIC frame, should the differential ECI coordinate be $R_{pri} - R_{sec}$ or $R_{sec} - R_{pri}$? my gut says $R_{sec} - R_{pri}$. That way, the secondary being ahead and above is positive.

Editing to remove the second question, which I have been able to answer myself. Given position R and velocity V, the rotation matrix to uvw should be defined by |R|, |R x V|, and |w x R|. Order matters, so |w x R| produces a vector towards the direction of motion, while |R x w| will be in the opposite direction.



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