CelesTrak: orbital element sets for Starlink, OneWeb, Kuiper and every constellation

What it is

CelesTrak is the oldest public source of orbital data on the internet, maintained by Dr. T.S. Kelso since the 1980s and still updated round the clock (the elements page shows its refresh time to the second). It redistributes the general perturbation (GP) element sets of the US Space Force's public catalogue and adds its own groupings, tools and supplemental data. Everything is free and needs no account, which is why nearly every tracking app, including satellitemap.space, and every research framework, including Hypatia, reads from it.

What you can do with it

• Download a constellation in one request: groups exist for Starlink, OneWeb, Kuiper (Amazon Leo), Qianfan and Hulianwang Digui among the mega-constellations; Iridium NEXT, Orbcomm, Globalstar, Intelsat, SES, Eutelsat and Telesat among communications operators; GPS, GLONASS, Galileo and BeiDou for navigation.
• Choose a format: classic two-line elements (TLE, 2LE, 3LE) or the CCSDS Orbit Mean-Elements Message as XML, KVN, JSON or CSV. The query pattern is gp.php?GROUP=starlink&FORMAT=csv.
• Use supplemental GP data: for some operators CelesTrak publishes ephemerides derived from the operator's own tracking rather than radar, which is more accurate for satellites that manoeuvre often.
• Count what is in orbit: the number of rows in the Starlink group is the number of catalogued Starlink objects on that day, a figure to set against the operator's own claims and against Jonathan McDowell's statistics.

Who it is for

Developers and analysts. An integrator sizing a maritime or aviation deployment can compute pass geometry and elevation angles for a route from these elements; a journalist or consultant can verify a launch count; a ground station operator schedules contacts from them. It is not a tool for choosing a provider, but it is the data behind every honest statement about constellation size and altitude in our LEO providers listings.

How to use it

1. Pick the group on the elements page (for example Starlink) and the format; copy the URL.
2. Fetch it from your script no more than a few times a day: CelesTrak asks users to cache, and the elements only change when the catalogue updates.
3. Propagate with SGP4 (Python sgp4, or Skyfield, which handles the OMM formats) to get positions at a given time; compute look angles from your site.
4. For long-term analysis, keep a daily snapshot: the catalogue is a live view, not an archive.

Limits

GP elements are mean elements for the SGP4 model with kilometre-level accuracy, not precise ephemerides; they are unsuitable for conjunction analysis, which is what commercial services such as LeoLabs exist for. Objects appear in the catalogue days after launch, and classified payloads are absent. Respect the site's usage guidance: it is run as a public service.

Related

Definitions: orbital inclination, orbital period, elevation angle, satellite constellation. Directories: Starlink providers, OneWeb providers.