Re: Unidentified Satellites

From: Gavin Eadie (gavin@umich.edu)
Date: Wed May 08 2013 - 03:21:45 UTC

  • Next message: Scott Tilley: "ST OBS May 6 & 7th, 2013"

    On May 7, 2013, at 9:02 PM, Mark McCarron <mark.mccarron@live.co.uk> wrote:
    
    > When looking at the sky, assuming that the field of view is around 140 degrees wide (and the view is unobstructed), how far away could a satellite be from the observer in both a straight line and in reference to the ground?
    > 
    > Some are crossing the horizon in under 30 secs and others are taking a few minutes.
    
    
    .. When you say ".. crossing the horizon in under 30 secs and others are taking a few minutes" are you seeing objects rise, cross the sky and set in that time?  If that happens in a few minutes, and the object is a satellite, it's not very high up.  The ISS (410Km up) crosses the sky, 10 degree elevation horizon to horizon, through the zenith, covering about 3000Km of ground track in about seven minutes; anything doing it faster, is very likely to be in a lower orbit.
    
    .. And I assume you've seen ISS hundreds of times if you've been watching satellites for years.  How do the objects you're talking about compare?  Do they ever pass north of you (ISS doesn't)?  Do you see them all night, or just before dawn and after dusk? Do they come or go from a favored point of the compass -- polar orbits are easy to identify.  Do they stay visible all the way across the sky?  As I was writing this, Frank Reed replied and his suggestion is an excellent one -- get some data like he describes to SatSat-L, and the list'll get you back an identification if the object is in orbit round the earth!
    
    > How accurate is Kepler data and data pushed out by USSTRATCOM?  How far could satellites deviate from this plotted location?
    
    .. It's really pretty accurate, though that accuracy fades with time -- I'd guess fresh orbital data should be good to 3-10Kms down-track and a ~100m cross-track.  The lower the orbit, the faster the accuracy erodes, and the faster the elements are refreshed.
    
    Gavin Eadie
    Ann Arbor, MI
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