Articles on satellite tracking, orbital mechanics, and the technology behind Call a Satellite.
Every object in orbit is monitored by a global network of radar stations and telescopes. The U.S. Space Surveillance Network tracks over 27,000 objects, assigning each a unique NORAD catalog number. Ground stations observe each pass, measure position and velocity, and publish updated orbital elements so anyone can predict where a satellite will be at any moment.
A Two-Line Element set (TLE) is a compact, standardized format that describes a satellite's orbit using six Keplerian elements plus drag and timing information. Published by CelesTrak and the 18th Space Defense Squadron, TLEs are the foundation of satellite tracking — they tell propagation algorithms exactly how to compute a spacecraft's future position.
SGP4 (Simplified General Perturbations 4) is the standard algorithm for predicting satellite positions from TLE data. It accounts for Earth's oblateness, atmospheric drag, and gravitational perturbations to compute latitude, longitude, altitude, and velocity at any given time. Call a Satellite uses SGP4 via the satellite.js library to track spacecraft in real time.
Space debris — spent rocket stages, defunct satellites, and collision fragments — poses a growing risk to operational spacecraft. Tracking networks monitor debris as small as 10 cm in low Earth orbit, publishing TLE data so operators can plan collision-avoidance maneuvers. Understanding debris tracking is essential to keeping space sustainable.