When Orbital Radar shows you a satellite's position, it's not reading a live GPS feed. It's propagating a mathematical model (the TLE) forward in time using a specific algorithm (SGP4).
When Orbital Radar shows you a satellite's position, it's not reading a live GPS feed. It's propagating a mathematical model (the TLE) forward in time using a specific algorithm (SGP4). Understanding the layers of approximation explains why positions can be off — and by how much.
SGP4 (Simplified General Perturbations 4) is the standard algorithm for propagating TLEs. It models the most important forces acting on a satellite to predict future positions.
The position you see on screen has several independent sources of error stacked on top of each other.
Every satellite position on Orbital Radar is a SGP4 propagation from the latest available TLE.
TLE + SGP4 is remarkably effective for its simplicity — kilometre-level accuracy from two lines of text. But it's an approximation, and understanding its limits makes you a better interpreter of what you see on Orbital Radar.