CelesTrak helps professional astronomers and hobbyists alike identify, track, and understand space events.

Space is a dangerous and congested place where there is always something happening. The mission of CelesTrak, operated by Dr. T.S. Kelso, is to help the space community track and understand the numerous events that occur in space on a daily basis.

CelesTrak is more than an authoritative collection of data. It’s an integrated service that helps a great many people — including SSA professionals, policymakers, educators, and enthusiasts — better understand what’s going on in space.

Learn more at CelesTrak.com.

Key Features


SOCRATES, in operation since 2004, was the first online conjunction analysis screening service and is the mainstay of CelesTrak. The tool automatically ingests operator ephemerides for GEO and LEO using an STK-based application.

SOCRATES was the impetus for over a dozen major satellite operators to agree to share data in the interest of safety of flight. This eventually led the way to the formation of the Space Data Association (SDA) and the creation of the Space Data Center (SDC), which today screens almost 800 satellites for 30 operators around the world.

Image from CelesTrak, Socrates

Orbit Visualization

Celestrak's orbit visualization tool uses web-based technologies in Cesium to illustrate a vast catalog of objects in orbit. The tool helps you understand orbital characteristics in an engaging, easy-to-understand interface.

  • Intuitive and interactive.
  • Requires no software installation.
  • Runs on Windows, macOS, Linux, iOS, and Android using any modern web browser. 
  • Uses the appropriate orbital data.
Image from CelesTrak, AGI

Patterns of behavior

CelesTrak uses STK to show patterns of life for satellites. It examines maneuvering GEO satellites to determine whether they are relocating, stationkeeping, or moving to the GEO graveyard.

Image from CelesTrak , Patterns Of Behavior

Supplemental TLEs

CelesTrak fits TLEs to operator ephemeris using the SGP4 model within STK for a variety of data sets

Using Windows applications that link to STK technology, CelesTrak converts TLEs from their native format and appends the appropriate metadata to define the coordinate frame. This helps fill gaps in the current SSA from other providers and helps identify issues like missed maneuvers or cross-tags.

Image from CelesTrak, Supplemental TLEs

Visibility Seasons

There is increasing interest in being able to visually observe things in Earth orbit.

Whether you're an individual wanting to watch an ISS or Starlink pass, or a professional tracking network, it is helpful to be able to see and understand visibility seasons — periods of time when a satellite may or may not be visible from the ground.

Image from CelesTrak, Visibility Seasons


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