Overview
The Two-Line Element set (TLE) is a compact text format that describes the orbit of an Earth-orbiting object at a specific point in time (the epoch). Developed by NORAD in the 1960s and maintained by the US Space Force's 18th Space Defense Squadron, TLEs are distributed via Space-Track.org and form the basis of most public satellite tracking, including Orbital Radar.
Format
A TLE consists of a title line (optional) followed by exactly two lines of 69 characters each:
ISS (ZARYA) 1 25544U 98067A 26059.50000000 .00016717 00000-0 10270-3 0 9993 2 25544 51.6400 123.0010 0005000 90.0000 270.0000 15.50000000000000
Key Fields
NORAD Catalog Number (25544 for the ISS) — the unique identifier. Epoch — the date/time the orbital parameters are valid. Inclination — the tilt of the orbit relative to the equator. RAAN — right ascension of the ascending node, orienting the orbital plane. Eccentricity — how circular or elliptical the orbit is. Mean Motion — revolutions per day (15.5 for the ISS, meaning ~92 min per orbit).
How Orbital Radar Uses TLEs
Orbital Radar ingests fresh TLEs from Space-Track.org and propagates them forward using the SGP4 algorithm to calculate real-time satellite positions. Because TLEs degrade in accuracy over time (atmospheric drag and other perturbations), they must be regularly refreshed — Orbital Radar updates its catalogue multiple times per day.