Re: significantly different predictions by different programs

From: AleksGT (AleksGT@mail.ru)
Date: Tue Oct 31 2006 - 15:14:30 EST

  • Next message: Bruce MacDonald: "Re: re:Sat.program predictions"

    Hi!
    
    >Ed Cannon wrote
    >It has come to my attention that among the programs being used for
    >predictions, there are some significantly differing results for
    >at least some objects.  A specific case is ETS 6 (94-56A, 23230).
    >Orbitron and Heavensat gave predictions that were something like
    >one hour of RA different from what Highfly predicted...
    
    To try to find where error can be, may i ask you more detailed information about your coordinates, time zone,
    used satellites tles, and all corresponding data?
    
    >Mike McCants wrote:
    >When I ran Heavensat and asked it to find a passage near a star
    >during this 20 minute interval, it produced a prediction that the
    >satellite would pass about 1/10 of a degree from the star SAO 192166
    >at 02:00:51.  The altitude was 27.5 and the azimuth was 152.0.
    >When I changed the field of view to 2 degrees, the mag 6 star was
    >just above the plotted satellite trajectory.
    >When I ran Heavensat in the "passes prediction" mode, the output
    >was the entire 14 hours that ETS 6 was above my horizon (even though
    >the duration was set to 20 minutes).  The [***] was around the maximum
    >altitude of the pass - alt 62, azi 153, time 12:22.  So this was 10
    >hours after the 20 minute "duration" of the prediction.  I could
    >zoom in on the 02:00 part of the trajectory and the alt/azi was
    >correct, but the 6th magnitude star did not appear.  It seems that
    >the stars are in their proper places for 12:22 UT, not 02:00 UT.
    >There are no RA and Dec labels on this display.  This is confusing.
    >So I can see how you could select a part of the trajectory that
    >was one or more hours off of the time of prediction and the stars
    >would not be in the right place for that part of the trajectory.
    
    Shortly - there is no bug.
    
    I will try to explain:
    The logic of mode "passes prediction" is to give prediction of
    satellite pass for whole trajectory from rise to set if duration interval
    lays in borders or intersects of full pass time. After passes
    prediction, program always shows satellite in its maximum altitude and draws stars of course for the
    same time. Satellite trajectory cannot be selected, it is just shows
    related information. So it is normal when Mike not saw the wanted
    star in the position for 02:00:51 part of track. This star was at place
    at time of satellite maximum altitude (12:22). All objects in program
    are always drawn at the time which displays on left-top HUD or right-bottom status field.
    To avoid this confusion i will add a function on the right click on
    track to set corresponding time, but now i only may recommend to
    change time for the sky.
    
    
    Best regards,
    Aleks
    
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