TLE Tailor

Turn a predicted deployment orbit or supplied ephemeris into a Two-Line Element set (TLE) for SGP4 tracking software.

For a launch-provider orbit, TLE Tailor uses the bundled gmatpy numerical propagator to generate a reference trajectory, then fits an SGP4 model to it. You do not need to build or install GMAT separately.

Get your first TLE

With uv installed, download and unpack the v0.1.0rc1 source archive from the GitHub prerelease, open that project folder and run:

uv run tle-tailor example --output deployment.tle

This offline demonstration uses editable osculating Keplerian elements, a declared UTC epoch and EarthMJ2000Eq frame. It fits a 12,000-second arc, prints position/velocity fit errors, and saves two TLE lines. Existing output files are never overwritten. The demo values are synthetic; use the short quickstart to substitute your provider's inputs.

The supported prerelease target is standard CPython 3.14 on Linux x86_64, with a compatible gmatpy wheel. This is a release candidate; see installation and platform support for the GitHub wheel and source options. TLE Tailor 0.1.0rc1 is distributed through GitHub, not PyPI.

Use your own inputs

• Deployment prediction: check the provider's epoch/time scale, reference frame, units and element/anomaly conventions. See deployment inputs. Osculating elements are not TLE mean elements.
• Already have ephemerides? Fit them directly, without unnecessary propagation.
• Prefer notebooks? Examples separates Python implementations in examples/scripts from notebook companions in examples/notebooks, inside tle_tailor/.
• Optional online comparison: Space-Track uses a hidden password prompt and does not save credentials by default.

A prelaunch TLE describes your supplied prediction and model assumptions. Fit residuals are not a guarantee of the actual or future orbit. Choose an appropriate interval, coordinate placeholder identifiers with your tracking partner, and update the TLE when measured orbit data become available. See fit errors and limitations.

Worked guides: deployment prediction, GPS ephemeris, and optional NovAtel EDIE logs.

More detail

Theory · Measured validation results · Fitting performance · Propagation API and frames · Advanced external GMAT · Changes

The methods build on David Vallado and Paul Crawford's SGP4 Orbit Determination. Project and upstream notices are in LICENSE and NOTICE.