Re: Finding geosat passes in Heavens Above

From: Ed Cannon (
Date: Thu Apr 06 2006 - 02:55:48 EDT

  • Next message: Peter Wakelin: "SATOBS 2006 April 05-06"

    It looks like CalSky may give you current positions for geosats,
    but it may not be quite that simple.  I noticed that in the list 
    that I got, it included an AKM, and IUS, and an SL-nn R/B(2).  
    All of those are of course upper stages, not payloads.  Plus, I 
    don't know if it will indicate which ones are operational as 
    opposed to those which aren't.  (BTW, I noticed that CalSky 
    seems to have Molniyas listed -- a very different type of high 
    So CalSky may work for what you want, but I'll say that I've 
    been using Mike McCants' Highfly for years, and it gives all of 
    the predictions I want.  It gives altitude/elevation and azimuth, 
    RA and Dec (1950 or 2000), height (the orbital height, from the 
    satellite to the subsatellite point) and range (distance from 
    observer to the satellite, with both height and range in either 
    miles or kilometers).  You can set a step size.  I usually use 
    one hour intervals, but you can use one minute if you like.  
    (For eccentric orbits, it adjusts the step size for perigee 
    passes -- or something like that.)  You can set a magnitude 
    limit, etc.  And this is freeware!  Yes it's DOS, but that's 
    really not so bad.  It's a quick download, a small and fast and 
    flexible program.  It's available on Mike's website, on this 
    Highfly will generate predictions for objects with mean motion
    less than 9 revolutions per day; Quicksat gives predictions
    for objects with MM greater than 4 revs.  So there are a fair
    number of objects for which both programs will give you 
    predictions.  In that case you can choose which format you 
    prefer to use on a given night. 
    So, the main things with Highfly are getting it set up and
    then getting orbital elements and maintaining your intrinsic
    magnitudes file.  Once you've used it just a few times, it's
    very straightforward and useful.
    If you want graphical predictions, Rob Matson's SkyMap will
    give you those.  
    Oh, I just remembered an important footnote about flashing
    geosynchs.  They're really "near geosynchs"; almost all of 
    them are drifting, and at various different rates.  Also, 
    almost all of them have non-zero inclinations, so they move 
    north and south through the night.  So they're not nearly as 
    simple as operational geosats, almost all of which are right 
    on the equator and maintain their longitude.  With the 
    operational ones with zero inclination, all you need to know 
    is altitude and azimuth, or very straightforward RA positions, 
    all on the same declination through the entire night.
    The thing is that the tumbling flashing ones can flash very 
    brightly, and, when flashing, the maxima are many magnitudes
    brighter than the normal very faint magnitudes of operational
    Ed Cannon - Austin, Texas, USA
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