SGP4Propagator

class ssapy.propagator.SGP4Propagator(t=None, truncate=False)[source][source]

Bases: Propagator

Propagate using simplified perturbation model SGP4.

Parameters:

  • t (float or astropy.time.Time, optional) –

    Reference time at which to compute the frame transformation between GCRF and TEME. SGP4 calculations occur in the TEME frame, but useful input and output is in the GCRF frame.

    If None (default), the transformation is computed at every output time. This is the correct treatment: the rate of change is small (~0.15 arcsec per day) but not negligible for precise work, and using a single epoch leaves a growing frame error of ~2 m/day at LEO and ~27 m/day at GEO.

    If a time is supplied, a single transformation at that fixed epoch is used for the whole arc (faster, but only approximate). Pass the orbit epoch here to recover the legacy single-transformation behaviour.

    If float, then should correspond to GPS seconds; i.e., seconds since 1980-01-06 00:00:00 UTC

  • truncate (bool, optional) – Truncate elements to precision of TLE ASCII format? This may be required in order to reproduce the results of running sgp4 directly from a TLE.