Greg Roberts' Request About Differential Orbit Correction (Re: Seesat-l Digest, Vol 4, Issue 24)

From: Charles D Phillips via Seesat-l <>
Date: Tue, 24 Jun 2014 12:17:04 -0500 (CDT)
Greg -

Certainly many people will suggest that you go out and purchase a license for a
commercial product - FreeFlyer, STK, etc.

Perhaps a part of your "fun" is getting some code to run? I would suggest you
look up some code made available by Dr David Vallado in his very amazing book -
he has code for many tasks. It is available in Fortran, Pascal, and C - with
Matlab and other extensions.

You could get a copy of this and pick your preferred application to run it on.

If you just wanted to be able to independently predict time to observe you could
get a program like GPredict. That is what I use here on my Macs but it is
available for various platforms.

Good luck!!


> Message: 4
> Date: Tue, 24 Jun 2014 11:18:54 +0200
> From: Greg Roberts via Seesat-l <>
> To: <>
> Subject: Fw: Differential Orbit Correction
> Message-ID: <D4485189B31043B7A9458EDE539E8868_at_ASTROCOM>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=response
> Morning all
> With my continual cloud and rain at the moment chances of optical observing
> are
> rare so Im playing around with some computer software.
> Some of the old timers may recall the Satellite Orbits group that operated
> from
> the Royal Aircraft Establishment at Farnborough and issued a regular
> rhoneographed publication called SATELLITE OBSERVING NOTES and from time to
> time
> had articles contributed by observers in the OBSERVERS FORUM. One such article
> in April 1979 was by David Hopkins who was the first amateur to observe and
> maintain orbits on classified earth satellites.
> His article contained a program listing of the program DOC. The original
> computer listing appears to have been retyped onto a wax stencil by someone
> and
> in the process introduced several errors etc with sometimes the script running
> out of page, and sometimes rather illegible.
> I tried tackling this program in 1988 and gave up with the comment on the
> original script "Impossible to debug - too full of errors"! In a moment of
> weakness a few days ago I decided to tackle this problem again and have now
> corrected etc about 90% of the original script but have now hit a serious bug
> and, for the moment, it looks like Im doomed.
> The program basically forms 7 pairs for RA and Dec for each of the 7 elements
> of the orbit which may be changed - time is kept as a constant. This data is
> used to form 7 simultaneous equations in the seven unknowns needed to match
> the
> residuals between computed and observed positions and the equations are solved
> using a matrix inversion.
> The original program was written in BBC Basic (?) and occupied about 2K and
> mostly used single letter variables - sometimes using a particular variable to
> mean something else from what it was originally. It was also written
> specifically for Davids station at Bournemouth so there were a lot of
> constants
> in the program . I have managed to identify all constants used and rewrite the
> program for multi-station use.
> As I said earlier Ive got the program to succesfuly run through about 90% of
> the
> rewritten code but have reached a point where it appears a matrix ends up by
> being zero and is used a short while later to be a divisor and of course
> anything divided by the value zero causes the program to crash.
> So my query now is -
> (1) did anyone else try and use /rewrite this program
> (2) were any program corrections issued in Satellite Observing Notes
> subsequent
> to the listing that appeared in SATELLITE OBSERVING NOTES 725 of 1979 ? I
> unfortunately no longer have these issues.
> I last heard from David Hopkins about ten years ago at which point he had
> given
> up satellite tracking and taken up terrestial bird watching instead.
> Any help/comments would be greately appreciated and yes, I know Im reinventing
> the wheel but I enjoy programming and hopefully prevents me from going senile
> too
> soon :-))
> Cheers
> Greg
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Received on Tue Jun 24 2014 - 12:17:42 UTC

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