Hi there,
I am sorry to make that little noise again, but I got again that issue with tracking the ISS, and this time, I can be a bit clearer, while not yet enough to nail the issue I guess.
First or all, the issue is not showing up all the time, for instance, soon after orbit insertion, everything is fine, it seems that I am encountering the problem when I am around ~200km from ISS
It has nothing to do with the star tracker, let's assume it is tracking stars, but we just have RDV NAV ENA (ITEM 1) in SPEC 33. In OPS 201, when tracking ID 1 (ITEM
with the -Z body axis (ITEM 14 +3) with Omicron vanishing (ITEM 17 +0), the Shuttle never manages to reduce the errors on Roll and Yaw, they actually oscillate while growing. There seems to be an instability, the REQD value for Roll reads +180.0 while the actual R reading seems to go further apart from +180.0, especially when trying to reduce the one on Yaw, and conversely.
From that unstable state, if I switch back ITEM 14 +1 to the X body axis, the pointing is fine, no issue. Back to ITEM 14 +3, pointing impossible. Then, I have tried to enter a value of Omicron ITEM 17 +0.01, and here we go, the pointing was fine along the -Z axis!
Edit: this is happening on a regular basis between 100km/200kmish from ISS, it looks like the Shuttle gets locked into that position, exactly as if it was locked into an Euler singularity in the error angles!??
Cheers,
Chris.