Re Rate of SPACECOM elsets Phillip Clark & Allen Thomson

John W. Gardner, Jr. (gardjw@juno.com)
Sat, 22 Aug 1998 18:08:08 EDT

Gentlemen,

I was captivated by your responses. Being that I'm a hopeless TLE
junkie, I will undertake to learn the specifics.

Though I knew epochs were determined at time of equator crossing, I
had always assumed that there was only one site, or cluster of sites
within a given area to track satellites.  I had no idea that this was
a world wide endeavor!  This expands my appreciation to those who
brings us data so I/we may say "Hmmmm...satellite is early.".

I thought I knew enough about TLE's to get into trouble. And here was
the realization I didn't even know what trouble was.


Many Thanks!  


Request/question by John Gardner,Jr <gardjw@juno.com> 8/21/98

>How many element sets can SPACECOM ( tracking system ) generate per
>second?  The data below suggests at least 578 per second.
>
>
>MOLNIYA 1-77 PKM (D)
>1 20586U 90039D   98218.02957138  .00000042  00000-0  10000-3 0  3225
>2 20586  65.0091 168.8065 6957126 258.0501  22.4981  1.96438197 59395
>
>MOLNIYA 1-77 PKM (D)
>1 20586U 90039D   98218.02957140 +.00000815 +00000-0 +10000-3 0 03237
>2 20586 065.0257 168.8034 6958959 258.0387 022.5029 01.96433589059396



Response from: Phillip Clark <psclark@dircon.co.uk> 8/22/98

I do not have a direct answer to this question, but using differences 
between orbital epochs does not suggest an answer.

The orbital epochs which are given in the TLEs are normally projected 
back in time to give the northbound equator-crossing time for that 
particular circuit of the Earth, and therefore do not reflect the time 
interval between orbital measurements.   The example given simply shows 
that two TLEs were generated within one orbital period for this 
particular object, and thus we have slightly different orbits.



Response from: "Allen Thomson" <thomsona@dzn.com> 8/22/98

As Phillip Clark has explained, the epochs are not indicative, as they
are
the result of processing the raw observations.

>From http://www.spacecom.af.mil/usspace/space.htm :

"Combined, these types of sensors make up to 80,000 satellite
observations
each day. This enormous amount of data comes from SSN sites such as Maui,
Hawaii; Eglin, Florida; Thule, Greenland; and Diego Garcia, Indian Ocean.
The data is transmitted directly to USSPACECOM's Space Control Center
(SCC)
via satellite, ground wire, microwave and phone. "

I.E.,  about one observation a second on a global average.  IIRC, there
are
about 150 - 200 MB of new elements per year, which indicates that
approximately 1 to 2 million separate orbital elements are generated by
the
system, about one or two per minute or, again on a global average,
something
like 100 per tracked object per year. It also implies that a few tens of
observations go into each new element set.

Tom Kelso is probably the person to get the real details from.



Reply from: Phillip Clark <psclark@dircon.co.uk> 8/22/98

>On Sat, 22 Aug 1998, Allen Thomson wrote:
>I.E.,  about one observation a second on a global average.  IIRC, there
are
>about 150 - 200 MB of new elements per year

The monthly files which I generate using all of the unclassified element 
sets made available by Goddard come to ~550 Mb a year.




Follow up from: "Allen Thomson" <thomsona@dzn.com> 8/22/98

>Phillip Clark said:
>
>On Sat, 22 Aug 1998, Allen Thomson wrote:
> I.E.,  about one observation a second on a global average.  IIRC, there
>are
> about  150 - 200 MB of new elements per year

>The monthly files which I generate using all of the unclassified element
>sets made available by Goddard come to ~550 Mb a year.

Oops -- I was probably thinking of the compressed size. So at ~140
uncompressed bytes per  elset, that's 4 million a year, about one every
eight seconds, > 10,000 a day.




John Gardner,Jr
gardjw@juno.com

76.98569 W  39.00195 N   62.484m  ASL











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