FindNextAboveToBelowCrossingPoint fails to find the crossing

[VE3NEA]

Under certain circumstances the elevation angle of a satellite gets stuck at some positive value, and FindNextAboveToBelowCrossingPoint finds the crossing only a few years in the future. This code reproduces the problem:

    public void ReproduceError()
    {
      var myLocation = new GeodeticCoordinate(Angle.FromDegrees(44), Angle.FromDegrees(-79), 270);
      var groundStation = new GroundStation(myLocation);

      string tle0 = "0 GOES 18";
      string tle1 = "1 51850U 22021A   24184.52757794  .00000099  00000-0  00000+0 0  9998";
      string tle2 = "2 51850   0.0386 165.9928 0000260 341.7596 186.2013  1.00270475  8635";

      var satellite = new Satellite(tle0, tle1, tle2);
      var start = DateTime.Parse("2024-07-02 21:57:20Z");
      var end = start.AddMinutes(60);

      var passes = groundStation.Observe(satellite, start, end, TimeSpan.FromSeconds(15));
      if (passes.Count > 0) Debug.WriteLine($"Pass end: {passes[0].End}");
    }

This code runs for about a minute and then prints:

Pass end: 2035-01-12 03:26:30

[parzivail]

Interesting, thanks for reporting it. I'll take a look.

[parzivail]

I did not fix the root cause of this issue (finding AOS/LOS for geostationary satellites), but I did introduce a new method in 1.4.0 on Satellite called IsGeostationary which is recommended to be checked before attempting to observe the satellite. Simply, a geostationary satellite can just have the current elevation checked, and likely will not have AOS/LOS events.