Re:Satellite program predictions

From: Greg Roberts (
Date: Tue Oct 31 2006 - 15:39:38 EST

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    Evening all
    I forwarded some of the SeeSat reports about
    the program HEAVENSAT to its author and
    queried whether a bug or not. I attach his reply
    just received which clarifies operation of his
    Hope this helps.
    ----- Original Message ----- 
    From: "HeavenSat" <>
    To: "Greg Roberts" <>
    Sent: Tuesday, October 31, 2006 8:23 PM
    Subject: Re: Bug?
    > Hi!
    >>>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...
    > I will take a little time for me to examine the problem.
    >>I have installed and tested Heavensat and I believe that its
    >>computations are correct, but I found that one of its displays
    >>could be misleading.
    >>In particular, I tested a case where ETS 6 was low in my south
    >>rising towards apogee:
    >>30.3N 97.8W BCRC 2006 Oct 28 Times are UT 23230 ETS 6 94 56A
    >>Hrs Min Alt Azi Hgt Range R A Dec (2000)
    >>2 0 27.8 152.6 9643 11298 23 41.36 -26.48
    >>2 10 26.6 148.0 10447 12190 0 10.02 -25.53
    >>The SeeSat program and Ted's ObsReduce produced very similar answers.
    >>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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