Satellite Pass Predictor Calculator

This calculator applies Kepler's third law, T = 2π√(a³/μ), to your satellite's orbital altitude to find its orbital period, where a is the orbital radius (Earth's radius plus altitude) and μ is Earth's standard gravitational parameter, 398,600.4418 km³/s². From the period it derives orbital velocity and the ground-track velocity (how fast the satellite's subpoint sweeps across the Earth's surface, scaled down from orbital velocity by the ratio of Earth's radius to orbital radius). The satellite's visibility footprint — how much ground it can theoretically be seen from at zero elevation — comes from the geometric half-angle where a line from your ground station is tangent to the horizon at satellite altitude; that footprint radius, combined with ground-track velocity, sets the maximum theoretical pass duration.

A separate, more realistic "usable" pass duration subtracts out the portion of the pass below your specified minimum elevation angle, since low-elevation signals suffer more atmospheric attenuation, multipath, and terrain blockage. Orbits per day comes straight from dividing a full day by the orbital period, and passes-per-day is a rough rule-of-thumb (roughly 40% of orbits produce a usable pass at mid-latitudes) rather than a precise ground-track/inclination calculation — this tool does not model orbital inclination or your specific latitude in the pass-timing math, so actual visible-pass counts and exact elevation profiles will vary. Doppler shift is calculated at 146 MHz for the maximum closing-velocity case, which is the shift you'd need to tune out as the satellite approaches then recedes during a pass.