Re: Extracting Long/Lat from TLE's

From: Anthony Ayiomamitis (anthony@perseus.gr)
Date: Mon May 28 2001 - 08:26:35 PDT

  • Next message: Anthony Ayiomamitis: "Re: Re: Extracting Long/Lat from TLE's"

    > Date: Sun, 27 May 2001 16:36:50 -0400
    > From: Bruno Tilgner <Bruno_Tilgner@compuserve.com>
    > To: SEESAT-D <SeeSat-D@blackadder.lmsal.com>
    >
    > Anthony Ayiomamitis wrote:
    >
    > >      How would one go about extracting a satellite's longitude and
    > >latitude from the TLE's? I realize that this will be a function of time
    > >but my question is restricted to geosats and, therefore, time as a
    > >confounding variable should be immaterial. I realize that geosats
    > >experience very small perturbations in their orbits but this is
    > >something I can live with (for now).
    >
    > Don't underestimate the motion of so-called "geostationaries". If they
    > are not exactly at the right orbital altitude they will drift more or
    > or less quickly eastward or westward. However this is not the case for
    > operational satellites. However, many operational satellites have
    > significant orbital inclinations, so they will perform small loops
    > accordingly. You either have to filter these satellites out or you must
    > take time into account so as not to be off-target by several degrees.
    
    Hi Bruno,
    
         I did not mean to underestimate the impact of perturbations in the supposedly
    static orbits. This was simply another aspect of my mini-project to be pursued at a
    later stage. Nevertheless, thank for the information as it confirms my desire to
    pursue this aspect later.
    
    > >      I am interested in writing some software to basically parse a
    > >geosat TLE file and produce a list of corresponding longitudes and
    > >latitudes. I would like to produce results, if possible, accurate to
    > >within one and, preferably, two decimal places.
    >
    > This software exists already and is almost exclusively based on the
    > NORAD SGP4/SDP4 algorithms. Whilst the SGP4 algorithm, applicable
    > to LEO objects, yields very accurate results, SDP4 is flawed. It
    > cannot predict accurately the daily loops. But in general it is
    > capable of predicting the location of a geosat so that it can be
    > found with a telescope.
    
    In that case, this will have to suffice. I was hoping for much more accuracy but
    that's life ...
    
    > >      I am setting the stage for a mini-project involving the
    > >photography of geosat constellations and would like to be able to
    > >generate the above-mentioned results at a whim's notice so as to plan my
    > >photo sessions and photo composition/framing.
    >
    > If I interpret your e-mail address correctly, you are located in Greece.
    
    Yes, I am.
    
    > You will be able to see two ASTRA and one HOTBIRD constellation.
    
    These two constellations were to be my initial step into the geosat exercise with a
    few other items to be pursued shortly thereafter.
    
    > For your project you are not so much interested in longitude/latitude
    > but in azimuth/elevation. If you want to get an impression of what can
    > be done photographing geosats with a CCD camera through a telescope,
    > I suggest you have a look at http://www.astroinfo.ch/aida/sposetti.
    > I have made all the calculations necessary to obtain these photos and
    > to interpret them.
    
    For starters, the above site is most impressive. It also contains and addresses some
    of the items I wanted to pursue. With respect to azimuth/elevation vs
    longitude/latitude, some of the things I want to pursue will have to be done "in the
    field" an hour or so away from Athens which means I will have to rely on the most
    tangible coordinate system possible which, if possible, should be independent of time
    as I have no idea what time during a given night I will be in a position while out in
    the field to pursue my photography work.
    
    Another reason I would like to know the relative positions of the satellites is to be
    able to interpolate pixel by pixel the coordinates on the scanned image and map them
    to established and precise coordinates of the satellites themselves so as to indentify
    each and every imaged satellite.
    
    Anthony.
    
    > Bruno Tilgner
    > Saint-Cloud, France
    > bruno_tilgner@compuserve.com
    >
    >
    >   ------------------------------------------------------------------------
    >
    > Subject: Re: Extracting Long/Lat from TLE's
    > Date: Sun, 27 May 2001 16:30:00 -0500
    > From: "Allen Thomson" <thomsona@flash.net>
    > To: "SeeSat" <SeeSat-L@blackadder.lmsal.com>
    >
    > Bruno_Tilgner@compuserve.com said,
    >
    > [much snippage]
    >
    > > If you want to get an impression of what can be done photographing
    > > geosats with a CCD camera through a telescope, I suggest you have
    > > a look at http://www.astroinfo.ch/aida/sposetti.   I have made all the
    > calculations
    > > necessary to obtain these photos and to interpret them.
    >
    > Very nice!
    >
    > I was especially impressed by
    > http://aida.astroinfo.org/sposetti/fireworks.jpg.html , which probably
    > deserves to get into the orbital mechanics textbooks.
    >
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    >   ------------------------------------------------------------------------
    >
    > Subject: Re: Extracting Long/Lat from TLE's
    > Date: Mon, 28 May 2001 00:17:00 -0400
    > From: JAY RESPLER <jrespler@superlink.net>
    > To: SeeSat-L <SeeSat-L@blackadder.lmsal.com>
    >
    > Anthony Ayiomamitis wrote:
    > >       How would one go about extracting a satellite's longitude and
    > > latitude from the TLE's?
    >
    > I used to use MrOrbit. That has a function giving lat/long.
    >
    > >       I am interested in writing some software to basically parse a
    > > geosat TLE file and produce a list of corresponding longitudes and
    > > latitudes. I would like to produce results, if possible, accurate to
    > > within one and, preferably, two decimal places.
    >
    > Unless you just want the exercise, software already exists.
    >
    > >       I am setting the stage for a mini-project involving the
    > > photography of geosat constellations and would like to be able to
    > > generate the above-mentioned results at a whim's notice so as to plan my
    > > photo sessions and photo composition/framing.
    >
    > As mentioned before, you don't need lat/long. You do want azimuth/
    > elevation. The best way to do that is use a prediction program
    > like HIGHFLY. You may then make predictions at a moment's notice.
    >
    > --
    > Jay Respler
    > --
    >           JRespler@superlink.net
    > SKY VIEWS: http://mars.superlink.net/jrespler/skyviews.htm
    >    Satellite Tracker * Early Typewriter Collector
    >            Freehold, New Jersey
    >
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