GEO: one far relay
Where no cable or fibre reaches, the internet can arrive by radio. A dish on your roof talks to a satellite, and a modem inside turns that radio link into your ordinary home network.
A geostationary (GEO) satellite circles 35,786 km above the equator, once every 23 h 56 min: exactly as fast as Earth turns. So it seems to hang still in the sky, and your dish stays pointed at one spot.
You open a page. The request leaves the dish as radio waves at the speed of light, about 300,000 km per second. Even at the shortest distance, 35,786 km takes 119 ms.
The satellite is only a relay. It beams the request back down to a ground station, called a gateway, which is wired to the internet. After two trips the request has spent 239 ms in the air.
The website's reply comes back to the gateway over fibre, and the gateway beams it up to the same satellite: a third trip of 35,786 km. That makes 358 ms of radio travel so far.
A fourth trip brings the reply home: 4 × 35,786 = 143,144 km, about 477 ms at the speed of light. Add processing and queues, and real GEO round trips are usually 550 to 700 ms.
LEO: many close satellites
Low Earth orbit (LEO) satellites fly far lower: Starlink's are about 550 km up. One lap takes about 96 minutes, so each one crosses your sky in a few minutes, and thousands are needed to cover Earth.
Your request now climbs only about 550 km to a satellite overhead. That takes about 1.8 ms, roughly 65 times less than the trip to a GEO satellite.
The satellite relays it to a gateway, and the reply returns the same way. All four trips add up to about 2,200 km: just 7.3 ms of radio travel. Real Starlink round trips are usually 25 to 60 ms.
Satellites keep moving, so the link hands over to the next one before the first one sets. The flat dish is a phased array: many tiny antennas, each timed slightly differently, so their waves add up in one steerable direction.
Weather
Satellite internet uses radio at about 10 to 30 GHz, waves only 1 to 3 cm long. Raindrops absorb and scatter them, so heavy rain weakens the signal: GEO and LEO links both slow down or briefly drop.
The numbers, step by step
;; step 1/11 · dish · local ;; at your house home network 192.168.1.0/24 (Wi-Fi and cables, as before) satellite modem turns packets into radio signals and back dish sends and receives a narrow radio beam website 203.0.113.10 (somewhere on the internet)
Light times use c = 299,792.458 km/s and the shortest legs, with the satellite straight overhead; real slant paths are longer. Measured round trips add processing, scheduling, queues and the route beyond the gateway: GEO usually 550–700 ms, Starlink usually 25–60 ms.