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
Argument of Perigee, in degrees
- property bstar
Drag of the satellite
should be rho0 * Cd * A / 2 / m
Units (which are strange) is multiples of 1 / Earth radius
- property eccen
Satellite eccentricity, in range [0,1]
- property epoch
TLE epoch
- static from_file(filename: str)
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
- static from_lines(lines: list[str])
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
- property inclination
Inclination, in degrees
- property mean_anomaly
Mean anomaly in degrees
- property mean_motion
Mean motion in revs / day
- property mean_motion_dot
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
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
The name of the satellite
- property satnum
Satellite number, or equivalently the NORAD ID
- class satkit.sgp4_opsmode
Ops Mode for SGP4 Propagation
- property afspc
afspc (Air Force Space Command), the default
- property improved
Improved
- class satkit.sgp4_gravconst
Gravity constant to use for SGP4 propagation
- property wgs72
WGS-72
- property wgs72old
WGS-72 Old
- property wgs84
WGS-84
- satkit.sgp4(tle: TLE | list[TLE], tm: time | list[time] | numpy.typing.ArrayLike[time], **kwargs)
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:
- 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)