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Data Files

The satkit package relies upon a number of data files for certain calculations:

  • leap-seconds.list — A list of the UTC leap seconds since 1972. This is a common file on *nix platforms and is used to keep track of the number of seconds (currently 37) that UTC lags TAI.

  • linux_p1550p2650.440 — File containing the precise ephemerides of the planets and 400 large asteroids between the years 1550 and 2650, as modelled by the Jet Propulsion Laboratory (JPL). Note: this file is large (~100 MB) and may take a long time to download.

  • tab5.2a.txt, tab5.2b.txt, tab5.2d.txt — Tables from IERS Conventions Technical Note 36, containing coefficients used in the precise rotation between the inertial International Celestial Reference Frame and the Earth-fixed International Terrestrial Reference Frame.

  • EGM96.gfc, JGM2.gfc, JGM3.gfc, ITU-GRACE16.gfc — Files containing gravity coefficients for various gravity models. These are used to compute the precise acceleration due to Earth gravity as a function of position in the Earth-fixed ITRF frame.

  • SW-All.csv — Space Weather. The solar flux at \(\lambda = 10.7\text{cm}\) (2800 MHz) is an indication of solar activity, which in turn is an important predictor of air density at altitudes relevant for low-Earth orbits. This file is updated at celestrak.org every 3 hours with the most-recent space weather information.

  • EOP-All.csv — Earth orientation parameters. This includes \(\Delta UT1\), the difference between \(UT1\) and \(UTC\), as well as \(x_p\) and \(y_p\), the polar "wander" of the Earth rotation axis. This file is updated daily with most-recent values at celestrak.org.

Acquiring the Data Files

The data files are included with the satkit-data package, a dependency of satkit.

The data files can also be manually downloaded with the following command:

satkit.utils.update_datafiles()

If the files already exist, they will not be downloaded, with the exception of the space weather and earth orientation parameters files, as these are regularly updated.

Download Location

The data files are all downloaded into a common directory. This directory can be queried via Python:

satkit.utils.datadir()

The satkit package will search for the data files in the following locations, in order, stopping when the files are found:

  • data subdirectory of the satkit-data package, if installed (which it should be, as it is a prerequisite)
  • Directory pointed to by the SATKIT_DATA environment variable
  • $HOME/.satkit-data
  • $DYLIB_PATH/share/satkit-data where $DYLIB_PATH is the location of the satkit shared library called by Python
  • macOS only: $HOME/Library/Application Support/satkit-data
  • $HOME/satkit-data
  • $HOME
  • /usr/share/satkit-data
  • macOS only: /Library/Application Support/satkit-data

If no files are found, the satkit package will go through the above list of directories in order, stopping when a directory either exists and is writable, or can be created and is writable. The files will then be downloaded to that location.