Re: Started A "Macintosh Software" Site

From: Gavin Eadie via Seesat-l <>
Date: Thu, 5 Mar 2020 15:23:23 -0500
Jumping back two and a half years .. the "SGP4 propagator that I migrated
to Swift" is now available at:

The TLE parsing and SGP4 propagation code usage is described in the file.  The library contains various other astronomical functions
for which the documentation is not (yet) fleshed out.  Testing the
SatelliteKit library against the sample TLE results in the "Revisiting
Spacetrack Report #3" generates identical output to machine accuracy.  Some
of that paper's TLEs are pathological, in the sense that they are intended
to fail; SatelliteKit fails with those too, though not always in ways I
understand (the Orekit library, on which this work was based, does not test
those pathological TLEs).

Like many things, this is a work in progress, but I feel it is time to put
it out there so it can stand, fall or be ignored on its merits.  The "in
progress" parts relate to applying more scaffolding around the core
propagation function (related to obtaining and caching file/Internet TLE
files, observer azimuth/elevation visibility, eclipse depth, etc) and do
not impact the purpose of SGP4, the computation of position and velocity

On Sat, Jul 22, 2017 at 12:33 AM Gavin Eadie <> wrote:

> The Orekit library, written in Java, at also
> contains a SGP4 propagator that I migrated to Swift.  This is a work in
> progress but, if I ever update my simple iOS ISS tracker it will be based
> on that code.  There’ll be more to say about this work when it gets a
> little more mature and is published.
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Received on Thu Mar 05 2020 - 14:24:59 UTC

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