A TLE (Two-Line Element set) is a compact, standardized encoding of a satellite's orbit at a moment in time, and SGP4 is the propagation model that turns a TLE into the satellite's position and velocity at any future time.
Pass prediction starts from the most recent TLE for each satellite (published by sources such as Space-Track and CelesTrak) and uses the SGP4 model to propagate the orbit forward. From the propagated positions it computes ground tracks, look angles, and the times a satellite can see an area.
TLE accuracy degrades over days as the real orbit drifts from the modelled one, so fresh TLEs matter: a stale element set produces inaccurate passes. PassPrediction refreshes its catalog on a strict schedule to keep predictions reliable.
A Two-Line Element set is a standardized two-line text encoding of a satellite's orbital elements at a specific epoch, used as the input to orbit-propagation models like SGP4.
The real orbit drifts from the modelled one due to drag and perturbations, so a TLE loses accuracy over days; fresh TLEs keep propagated positions and pass predictions accurate.
Plan a real acquisition over your area on the interactive map, browse the satellite catalog, or read the tasking guides.