📘 Definition
SGP4 (Simplified General Perturbations 4) is the standard analytical orbit propagator used to predict satellite positions from Two-Line Element (TLE) data. It models the effects of atmospheric drag, Earth's oblateness (J2 through J4 zonal harmonics), solar and lunar gravitational perturbations (via the SDP4 deep-space extension for periods > 225 minutes), and secular drag effects. TLEs are generated specifically for use with SGP4 — using them with a different propagator will produce incorrect results. Orbital Radar uses SGP4 for the live globe, pass predictions, Doppler correction for ham radio satellites, and the propagation heatmap.
TLE data
Input
Position & velocity (ECI)
Output
1 km (fresh TLE)
Accuracy
SDP4 (period > 225 min)
Deep-Space Variant