Warning: This code is experimental; please see the LICENSE.

An SGP4 implementation based on github.com/aholinch/sgp4/tree/master/src/c, which ultimately originated with David Vallado.

    This file contains the sgp4 procedures for analytical propagation
    of a satellite. the code was originally released in the 1980 and
    1986 spacetrack papers. a detailed discussion of the theory and
    history may be found in the 2006 aiaa paper by vallado, crawford,
    hujsak, and kelso.

                           companion code for
              fundamentals of astrodynamics and applications
                                   2013
                             by david vallado
     (w) 719-573-2600, email [email protected], [email protected]

This implementation is a hand-edited transpilation of C sources to Go by c2go (version v0.25.9 Dubnium 2018-12-30), and the emitted code was edited by hand. The original C implementation test suite was included in this process.

The substantive edits (of Go sources emitted by the transpiler) were the use of 64-bit integers to address at least one 32-bit overflow and using floating point constants instead of naked integer constants when the entire expression consisted of the latter with some division. Example: var x2o3 float64 = 2 / 3 was edited to be var x2o3 float64 = 2.0 / 3.0.

With those changes, the original (transpiled and hand-edited) tests almost all pass. The one exception is for NORAD ID 20413 at mins=1844335, where 1e-07 < rdist < 1e-06. The tests have been edited to tolerate rdist < 1e-06 rather than demand rdist < 1e-07.

The main constructor is NewTLE(), and the primary method is Prop(). See ExampleProp() in surface_test.go.

See the documentation for details.

The example command-line program sgp4go reads TLEs from stdin and writes propagation data to stdout. See test.sh for an example invocation.

Some sgp4go executables are available here.

1. SGP4 in AIAA-2006-6753-Rev2.

2. Fundamentals of Astrodynamics and Applications (also at Amazon).

3. space-trace.org's SGP4 binaries and example code.

4. C source code for this implementation.