How Satellite Orbits Are Tracked and Predicted

An element set is a compact orbit model

Public catalogs distribute General Perturbations data in formats such as TLE and OMM. The values describe a mean orbit fitted to tracking observations for use with the SGP4 propagation model. They are not a stream of latitude and longitude readings from the spacecraft.

Each record identifies an object, an epoch and parameters such as inclination, eccentricity and mean motion. OMM offers explicit field names and modern date handling, while legacy TLE remains widely used.

Epoch is the anchor time

The epoch states when the element set best represents the fitted orbit. To display the object before or after that moment, software propagates the elements with SGP4. The calculated Earth-relative position also depends on the requested time and Earth rotation. PlanetVexa keeps source epoch and calculation time distinct.

An animation is a sequence of propagated positions. It can be visually smooth while the underlying elements remain one source record.

Predictions lose fidelity as conditions change

All orbit predictions accumulate uncertainty with time. Atmospheric drag is especially variable in low Earth orbit and responds to solar and geomagnetic conditions. Maneuvers, attitude changes and imperfect observations can make an element set obsolete sooner than expected. Fresh elements reduce—but do not eliminate—uncertainty.

A predicted ground track is not an official conjunction assessment, maneuver plan or guarantee that an object will be visible from a particular location.

Object identity must be deduplicated

Names can vary across sources, but the NORAD catalog number provides a stable key for many public objects. PlanetVexa consolidates matching records by catalog ID and shows source age rather than drawing duplicates as separate satellites. Restricted or uncataloged objects cannot be inferred from absence in a public feed.