TLE (Two-Line Element set)

The orbital elements every tracker consumes. Fixed-column text, one satellite per two lines (three with a name line).

Source: https://celestrak.org/NORAD/documentation/tle-fmt.php
Access: Public. Produced by US Space Force, redistributed by CelesTrak.
Format: Fixed-width text

Schema

Field	Type	Note
Line 1, col 3–7	int	NORAD catalog number
Line 1, col 8	char	Classification (U)
Line 1, col 10–17	string	International designator YYNNNPPP
Line 1, col 19–32	float	Epoch: 2-digit year + fractional day of year
Line 1, col 34–43	float	First derivative of mean motion / 2
Line 1, col 54–61	float	B* drag term (implied decimal + exponent)
Line 1, col 65–68	int	Element set number
Line 2, col 9–16	deg	Inclination
Line 2, col 18–25	deg	Right ascension of ascending node
Line 2, col 27–33	float	Eccentricity (implied leading decimal)
Line 2, col 35–42	deg	Argument of perigee
Line 2, col 44–51	deg	Mean anomaly
Line 2, col 53–63	rev/day	Mean motion. 15.5 ≈ ISS, 12.8 ≈ RS-44, 1.0 = GEO
Line 2, col 64–68	int	Revolution number at epoch
col 69 (both lines)	int	Modulo-10 checksum

Example

ISS (ZARYA)
1 25544U 98067A   26262.51782528  .00016717  00000+0  10270-3 0  9993
2 25544  51.6416 247.4627 0006703 130.5360 325.0288 15.49640963 12345

Gotchas

Only valid with the SGP4 propagator. Feeding TLEs to a Keplerian propagator gives km-scale errors.
LEO elements go stale in days. ISS after a reboost: within hours.
Epoch year is two digits. 57–99 → 1957–1999, 00–56 → 2000–2056.