Two-Line Element Sets and SGP-4

class satkit.TLE

Two-Line Element Set (TLE) representing a satellite ephemeris

Stucture representing a Two-Line Element Set (TLE), a satellite ephemeris format from the 1970s that is still somehow in use today and can be used to calculate satellite position and velcocity in the “TEME” frame (not-quite GCRF) using the “Simplified General Perturbations-4” (SGP-4) mathemematical model that is also included in this package.

For details, see: https://en.wikipedia.org/wiki/Two-line_element_set

The TLE format is still commonly used to represent satellite ephemerides, and satellite ephemerides catalogs in this format are publicly availalble at www.space-track.org (registration required)

TLEs sometimes have a “line 0” that includes the name of the satellite

property arg_of_perigee: time: Argument of Perigee, in degrees

property bstar: str

Drag of the satellite

should be rho0 * Cd * A / 2 / m

Units (which are strange) is multiples of 1 / Earth radius

property eccen: float: Satellite eccentricity, in range [0,1]

property epoch: time: TLE epoch

static from_file(filename: str) → list[TLE] | TLE

Load TLEs from input text file Return a list of TLES loaded from input text file.

If the file contains lines only represent a single TLE, the TLE will be output, rather than a list with a single TLE element

Parameters:: filename (str) – name of textfile lines for TLE(s) to load
Returns:: a list of TLE objects or a single TLE of lines for only 1 are passed in
Return type:: list[TLE] | TLE

static from_lines(lines: list[str]) → list[TLE] | TLE

Return a list of TLES loaded from input list of lines

If the file contains lines only represent a single TLE, the TLE will be output, rather than a list with a single TLE element

Parameters:: lines (list[str]) – list of strings with lines for TLE(s) to load
Returns:: a list of TLE objects or a single TLE of lines for only 1 are passed in
Return type:: list[TLE] | TLE

property inclination: float: Inclination, in degrees

property mean_anomaly: float: Mean anomaly in degrees

property mean_motion: float: Mean motion in revs / day

property mean_motion_dot: float: 1/2 of first derivative of mean motion, in revs/day^2

Note

the “1/2” is because that is how number is stored in the TLE

property mean_motion_dot_dot: float: 1/6 of 2nd derivative of mean motion, in revs/day^3

Note

The “1/6” is because that is how number is stored in the TLE

property name: str: The name of the satellite

property satnum: int: Satellite number, or equivalently the NORAD ID

class satkit.sgp4_opsmode

Ops Mode for SGP4 Propagation

property afspc: int: afspc (Air Force Space Command), the default

property improved: int: Improved

class satkit.sgp4_gravconst

Gravity constant to use for SGP4 propagation

property wgs72: int: WGS-72

property wgs72old: int: WGS-72 Old

property wgs84: int: WGS-84

satkit.sgp4(tle: TLE | list[TLE], tm: time | list[time] | numpy.typing.ArrayLike[time], **kwargs) → tuple[numpy.typing.ArrayLike[numpy.float64], numpy.typing.ArrayLike[numpy.float64]]

SGP-4 propagator for TLE

Note

Run Simplified General Perturbations (SGP)-4 propagator on Two-Line Element Set to output satellite position and velocity at given time in the “TEME” coordinate system

A detailed description is at: https://celestrak.org/publications/AIAA/2008-6770/AIAA-2008-6770.pdf

Parameters:

tle (TLE | list[TLE]) – TLE (or list of TLES) on which to operate
tm (time | list[time] | npt.ArrayLike[time]) – time(s) at which to compute position and velocity

Keyword Arguments:

gravconst (satkit.sgp4_gravconst) – gravity constant to use. Default is gravconst.wgs72
opsmode (satkit.sgp4_opsmode) – opsmode.afspc (Air Force Space Command) or opsmode.improved. Default is opsmode.afspc
errflag (bool) – whether or not to output error conditions for each TLE and time output. Default is False

Returns:

position and velocity in meters and meters/second, respectively, in the TEME frame at each of the “Ntime” input times and each of the “Ntle” tles

Return type:

tuple[npt.ArrayLike[np.float64], npt.ArrayLike[np.float64]]

Example

>>> lines = [
>>>        "0 INTELSAT 902",
>>>     "1 26900U 01039A   06106.74503247  .00000045  00000-0  10000-3 0  8290",
>>>     "2 26900   0.0164 266.5378 0003319  86.1794 182.2590  1.00273847 16981   9300."
>>> ]
>>>
>>> tle = satkit.TLE.single_from_lines(lines)
>>>
>>> # Compute TEME position & velocity at epoch
>>> pteme, vteme = satkit.sgp4(tle, tle.epoch)
>>>
>>> # Rotate to ITRF frame
>>> q = satkit.frametransform.qteme2itrf(tm)
>>> pitrf = q * pteme
>>> vitrf = q * vteme - np.cross(np.array([0, 0, satkit.univ.omega_earth]), pitrf)
>>>
>>> # convert to ITRF coordinate object
>>> coord = satkit.itrfcoord.from_vector(pitrf)
>>>
>>> # Print ITRF coordinate object location
>>> print(coord)
ITRFCoord(lat:  -0.0363 deg, lon:  -2.2438 deg, hae: 35799.51 km)