How the tracker works
Every satellite's orbit is described by a set of numbers called a two-line element set (TLE), published openly from US Space Force tracking data. This page downloads the current sets from CelesTrak and works out every position in your browser with the SGP4 model, the same method used by professional tracking software. Nothing is streamed from the satellites themselves: it's pure orbital maths, accurate to within a few kilometres.
Reading the map
The ground track is the path of the point directly beneath the satellite. Because Earth turns underneath, each orbit crosses further west than the last, so the ISS passes over a different part of the world on every 90-minute lap. The footprint is the area from which the satellite is above the horizon. For the ISS at about 420 km it's roughly 4,500 km across, which is why a radio contact via the station can span a whole continent. The higher the satellite, the bigger its footprint: GPS satellites at 20,000 km can see almost half the Earth.
The satellite groups
- Space stations: the ISS, China's Tiangong and the spacecraft visiting them.
- Amateur radio satellites: the FM and linear transponder satellites you can work with a handheld. See the amateur satellite pass predictor.
- Weather satellites: including the Meteor-M satellites, whose 137 MHz pictures you can receive. See the weather satellite page.
- Navigation satellites: GPS, Galileo, GLONASS and BeiDou. See the GNSS sky view.
- Brightest satellites: ones you can see with your own eyes. See the visible pass times.
Questions
Where is the ISS right now?
The map shows its position live, updated every two seconds, with its path for the next 95 minutes.
How fast does the ISS travel?
About 27,600 km/h, going round the Earth once every 92 minutes or so.
How high is the ISS?
About 400 to 420 km. Its height slowly falls between engine burns that raise it again.
Is this tracking legal?
Yes. The orbit data is published openly, and the positions are worked out with maths. It doesn't receive or decode any signals.