Source code for m4opt.observer._tle

from typing import override

from astropy import units as u
from astropy.coordinates import TEME, SkyCoord
from satellite_tle import fetch_tle_from_celestrak
from sgp4.api import SGP4_ERRORS, Satrec

from ._core import ObserverLocation




class TleObserverLocation(ObserverLocation):
    """An Earth satellite whose orbit is specified by its `two-line element (TLE) <https://www.space-track.org/documentation#tle>`_.

    Notes
    -----
    The orbit propagation is based on the example code at
    :ref:`astropy-coordinates-satellites`.

    Examples
    --------

    Here is an example TLE for BurstCube (NORAD ID 59562):

    >>> from astropy.time import Time
    >>> from astropy import units as u
    >>> import numpy as np
    >>> from m4opt.observer import TleObserverLocation
    >>> line1 = '1 59562U 98067WM  24220.55604657  .00200610  00000+0  13802-2 0  9999'
    >>> line2 = '2 59562  51.6321  52.1851 0005233 205.4266 154.6476 15.73479335 17375'
    >>> orbit = TleObserverLocation(line1, line2)

    Evaluate the position and velocity of the satellite at one specific time:

    >>> time = Time('2024-08-08 01:10:41')
    >>> orbit(time)
    <EarthLocation (4172.83539674, -514.29983197, -5254.79814474) km>

    Or evaluate at an array of times:

    >>> times = time + np.linspace(0 * u.min, 2 * u.min, 50)
    >>> orbit(times).shape
    (50,)

    If any orbit propagation errors occur, then a :class:`RuntimeError` is
    raised:

    >>> time = Time('2025-01-01 00:00:00')
    >>> orbit(time)
    Traceback (most recent call last):
      ...
    RuntimeError: mrt is less than 1.0 which indicates the satellite has decayed

    """  # noqa: E501

    def __init__(self, line1: str, line2: str):
        """Create a TLE from the text of its two lines."""
        self._tle = Satrec.twoline2rv(line1, line2)



    @classmethod
    def from_id(cls, norad_id: int) -> "TleObserverLocation":
        """Get the latest TLE for a satellite from Celestrak.

        Examples
        --------

        Look up the latest TLE for the Fermi Gamma-Ray Space Telescope.

        >>> from m4opt.observer import TleObserverLocation
        >>> tle = TleObserverLocation.from_id(33053)
        """
        *_, line1, line2 = fetch_tle_from_celestrak(norad_id)
        return cls(line1, line2)




    @override
    def __call__(self, time):
        shape = time.shape
        time = time.ravel()

        time = time.utc
        e, xyz, vxyz = self._tle.sgp4_array(time.jd1, time.jd2)
        x, y, z = xyz.T
        vx, vy, vz = vxyz.T

        # If any errors occurred, only raise for the first error
        e = e[e != 0]
        if e.size > 0:
            raise RuntimeError(SGP4_ERRORS[e[0]])

        coord = SkyCoord(
            x=x * u.km,
            v_x=vx * u.km / u.s,
            y=y * u.km,
            v_y=vy * u.km / u.s,
            z=z * u.km,
            v_z=vz * u.km / u.s,
            frame=TEME(obstime=time),
        ).itrs.earth_location
        if shape:
            coord = coord.reshape(shape)
        else:
            coord = coord[0]
        return coord