Satellite Pass Duration Calculator
The longest a satellite in a circular orbit stays in view from the ground — above a minimum elevation — with its orbital period, the radius of the ground it can see and the slant range at the horizon.
From the ground a satellite is usable only above some elevation, typically 5–10° to clear buildings and thick atmosphere.
How the satellite pass duration calculator works
From the ground a satellite is usable only above some elevation, typically 5–10° to clear buildings and thick atmosphere. Geometry gives the Earth-central angle from the ground station to the satellite at that elevation, and the satellite crosses twice that angle on an overhead pass; divide by its angular rate (from the orbital period) for the duration. Low orbits pass in minutes; the higher the orbit, the longer the pass and the larger the footprint.
Formula: λ = arccos(R cos ε ÷ (R + h)) − ε; T = 2π √((R+h)³ ÷ GM); pass = 2λ ÷ (2π ÷ T)
Worked examples
| Inputs | Maximum pass duration | Note |
|---|---|---|
| 550 km, 10° elevation | 7.94 minutes | about 8 minutes of a 96-minute orbit |
| ISS at 400 km, 5° | 7.9 minutes | about 8 minutes |
| GPS at 20,200 km, 10° | 4.41 hours | over 4 hours |
FAQFrequently asked questions
Why is a low-orbit pass so short?
The satellite crosses its whole visible arc at 7.5 km/s: from 550 km it is above 10° for about eight minutes at best, and most passes are shorter because they are not overhead. That is why low-orbit constellations need hundreds of satellites for continuous coverage.
Why 10° elevation?
Below it the signal path through the atmosphere lengthens and buildings and terrain block the view; 5° is used for open sites, 25° for phased-array user terminals. Higher minimums shorten passes and shrink footprints.
Does Earth’s rotation matter?
Slightly for low orbits (a few percent), more for high ones; the calculator ignores it. At geostationary altitude the satellite never sets, and the formula gives the full orbital period.
How many satellites for continuous coverage?
Roughly the orbit’s circumference divided by the footprint diameter per orbital plane, times enough planes to cover the latitude band — the satellite coverage calculator does that count.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G and the speed of light
- IAU 2015 Resolution B3 — nominal solar and planetary conversion constants — the astronomical unit, solar mass and planetary radii
- NASA — the US space agency
Last checked: September 2026. Constants are CODATA 2018 (G, c) and IAU 2015 nominal values (solar and planetary parameters).