How it works
A geostationary satellite sits 35,786 km above the equator and turns with the Earth, so it stays at one point in your sky.9 The box takes your latitude and longitude and the satellite's longitude, and works out the compass bearing from true north (azimuth), the angle above the horizon (elevation) and the distance. It treats the Earth as a sphere of 6,378 km radius, which is within a fraction of a degree for pointing. A magnetic compass differs from true north by the local declination.
Handheld satellite phones and push-to-talk terminals on Inmarsat use the Inmarsat-4 and Inmarsat-6 satellites and Alphasat;12 Thuraya serves Europe, Africa, the Middle East and Central Asia from 44° E.34 The satellite must be above the horizon with a clear view of the sky: below about 10° buildings, trees and hills block it.
Low-orbit networks need no pointing: Iridium's 66 satellites fly about 780 km up and cover the whole planet, poles included, which is what Iridium PTT runs on.56 Globalstar flies at 1,414 km7 and Starlink's licensed shells at 540–570 km.8 The delay table shows radio waves alone, at the speed of light; coding, buffering and the network add to it.
How satellite push-to-talk works and what it costs: satellite push-to-talk explained.
