TechnicalTLE
Two-Line Element Set
A standardized data format for describing the orbital elements of Earth-orbiting objects, enabling position prediction.
Two-Line Element Sets (TLEs) are the standard format for distributing orbital data for space objects. Despite limitations in accuracy, TLEs remain widely used for space operations.
Format Structure TLEs consist of two 69-character lines containing:
- Satellite catalog number
- Classification
- International designator
- Epoch (date and time)
- Mean motion derivatives
- BSTAR drag term
- Inclination
- Right ascension of ascending node
- Eccentricity
- Argument of perigee
- Mean anomaly
- Mean motion (revolutions per day)
Propagation TLEs use SGP4/SDP4 propagators:
- SGP4: Near-Earth objects (period < 225 minutes)
- SDP4: Deep-space objects (period > 225 minutes)
Accuracy Limitations
- Position errors grow over time
- ~1-3 km accuracy at epoch
- ~10+ km after several days
- Better data available (but often restricted)
Sources
- Space-Track.org (US Space Force)
- Celestrak (aggregator)
- EU SST (European data)
- Commercial providers