RE: Crunching Numbers

From: McConahy, Ralph (
Date: Wed Feb 02 2000 - 15:12:30 PST

  • Next message: Dale Ireland: "Re: Decay watch: 2000 Feb 2 19:30 UTC"

    > wrote:
    >>When I joined this list, I figured it was all about 'just' 
    >>watching the satellites. But I frequently get these emails 
    >>from all of you with "elsets" or "OBS". 
    >>And the letters contain all numbers with + and - marks.
    >>Could someone help me out here?! What do they mean, and 
    >>how do I interpret them? 
    "Elsets" are element sets, also known as two-line elements or simply TLE.
    Here's an example:
    Mir Complex
    1 16609U 86017A   00032.55381491  .00040933  11633-4  16578-3 0  3075
    2 16609  51.6516 240.6892 0016841 293.2056  66.7169 15.86997725797610
    For info on what the numbers mean see:
    Also see the home page of the first one above for much more about visual
    satellite observing:
    "OBS" stands for Observation. Some of the OBS emails you see are timings
    where each line indicates a satellite's position at a given point in time.
    These are in interactive orbit determination format (or IOD format). See for an explanation.
    Other emails you may see could be flash timings for tumbling satellites in
    PPAS format (photometric periods of artificial satellites). See sections 5 &
    6 of
    The OBS in IOD format probably won't help you much, they are mostly used to
    create or update TLEs. The TLEs themselves, however, can be helpful (in
    fact, are necessary) if you want to make your own satellite predictions. You
    can obtain software allowing you to make your own predictions from 
    Depending on the satellite orbit TLEs are only good for a few days to a
    couple weeks so you need to constantly obtain updated TLEs. A good place to
    get TLEs is from and download the file (contains TLEs for about 1500 satellites). Or, for a
    smaller list (about 120 satellites), go to and download the file.
    >>Also- Some [brighter?] satellites you follow, such as
    >>USA 129 or ETS-6: Where do you get the info for these? 
    Not sure what info you are looking for, but some info about the actual
    spacecraft can be found at and most (unclassified)
    missions have their own web pages.
    The above mentioned links in no way exhausts the amount of data available on
    the web about these topics. Many other valuable resources are maintained by
    members of the SeeSat-L list and are often referenced at the bottom of their
      Ralph McConahy
      34.8829N  117.0064W  670m
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