
Obtaining New Elements
======================

   Most satellites being actively operated are occasionally required to perform
orbit correcting manoeuvres. This is particularly true of the sun-synchronous
satellites. Also, the orbit perturbations included in these (or any) orbit
models are approximations only, and so eventually predictions from these
elements will not be very accurate. This means that although I have included a
recent large set of elements with this distribution, you will eventually need
to update them. Generally speaking, elements that are less than a week old will
give you a prediction error of up to a few seconds, which is adequate for most
people.

   There are several places where you can get hold of regular elements updates,
and the sources I am currently aware of are listed below. If you hear of any
other sources of elements, please let me know as I would like to keep this list
as complete as possible as an aid to users of !Spotter.

   Anonymous FTP
   -------------

      This is available to anyone on the Internet, or to anyone who can access
   any of the numerous FTP Email servers. FTP to archive.afit.af.mil
   (129.92.1.66), and change to directory pub/space. An update of the list
   provided in this distribution is held in file 'tle.new', but several subsets
   of this file exist, and some of these are:

             tle.vis  - Visible satellites only
             tle.gps  - GPS satellites
             tle.sts  - Most recent shuttle elements only (only updated when
                        a shuttle mission is in progress)
             tle.met  - Meteorological satellites

      These files are updated weekly.

   NETNEWS
   -------

      The file tle.vis is posted weekly to NETNEWS groups sci.space.news and
   rec.radio.amateur.misc, usually on a Friday afternoon. Shuttle elements,
   are usually posted seperately prior to and during a shuttle mission.

   BBS
   ---

      The most recent NORAD two line elements are updated several times weekly
   on the Celestial BBS, and so this is the place to go if you really need the
   latest data. The number is +1 513 427-0674, and may be accessed 24 hours/day
   at 300, 1200, 2400, 4800, or 9600 bps using 8 data bits, 1 stop bit, no
   parity. This is in the US, and so can work out expensive for regular updates.


Stuart Martin, 3rd April 1993.
