If you've ever opened a satellite-tracking site and glanced at the raw data behind it, you've probably seen something like this: two lines of closely packed numbers and letters, seemingly unreadable. That format is a TLE, and it's been the backbone of satellite tracking since the 1970s.
What a TLE actually contains
A TLE is a compact snapshot of a satellite's orbit at a specific moment in time. Rather than storing a full trajectory, it stores a small set of orbital parameters — things like inclination (the tilt of the orbit relative to the equator), eccentricity (how circular or stretched the orbit is), and mean motion (how many times the satellite circles Earth per day). From those handful of numbers, well-established physics can reconstruct where the satellite will be at any future moment, at least for a while.
- Epoch — the exact reference time the orbital data was measured.
- Inclination — the angle between the orbit and Earth's equator.
- Eccentricity — how elliptical the orbit is.
- Mean motion — orbits completed per day.
Where the data comes from
OrbitMap sources its TLEs from CelesTrak, a long-running, free, public catalog of orbital data for active satellites. CelesTrak refreshes its data regularly using tracking measurements, and publishes it openly so that developers, hobbyists, and researchers can build tools like this one without needing their own ground-station network.
From two lines of text to a moving dot
Turning a TLE into an actual position requires an orbital propagation model — software that takes those parameters and calculates latitude, longitude, and altitude for any requested moment in time. OrbitMap uses the industry-standard SGP4/SDP4 model, the same family of algorithms used across the satellite-tracking world, to do this calculation directly in your browser as time passes.
This is also why satellite positions on any tracker — including OrbitMap — are technically estimates. A TLE becomes gradually less accurate the further you get from its epoch, which is why fresh data matters and why long-range predictions (like exact pass times weeks from now) carry more uncertainty than “where is it right now.”
Why this matters if you're watching the sky
Understanding that satellite positions come from a model — not a live GPS feed off the satellite itself — helps set the right expectations. It's part of why we're upfront in our Terms of Service that OrbitMap is built for learning and curiosity, not for navigation or safety-critical use.
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