Flightgear forums12/11/2022 ![]() So the state vectors of Shuttle and target propagated by the navigation system have errors, and that leads to errors in relative quantities - range, proximity coordinates. We don't know precisely where a rendezvous target is either for the same reason. So that mandates periodic state vector updates. We don't know precisely where the Shuttle is because the intertial navigation always drifts a little. I think I finally got the rel nav filters under control (after some confusion what is what and updates what and what is displayed where.) So this is for fans of Shuttle avionics intricacies only. In practice, the effect of the combiner is that if you're not at the optimal view point, the pattern will appear partially shifted outside the glass, as the pattern center will stay locked on the same point of the observed object (parallax correction for head movement for the distance to ISS shown here is negligibly small).īut now the angular scale can be used regardless of where the head is.Īnd it's all properly integrated into systems, it powers off when the circuit breaker is pulled, when the power switches are flicked or when the bus voltage drops below operating value. Which is not hard conceptually, but of course the offset and scale gains for each axis have to be set correctly, and to measure that out is a bit tedious and took me the better part of two hours (part of the work was to make sure the COAS pattern in FWD position is exactly aligned with the boresight of the HUD, and the pattern in AFT position upward is aligned with the off-axis values reported by the Z star tracker - so we want the target in the pattern center when the star tracker reports zero offset angles.) Which of course makes it useless if the user dares to move the view - so in order to make it useful, the parallax correction has to be re-computed for every movement of the viewpoint. It's surprisingly tedious to make the device actually useful - since (like a HUD), it is a combiner and hence a projection from infinity - so just painting the pattern onto the glass is not enough, because then the axis center and the apparent angular scale depends on where the viewpoint is. ![]()
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