A satellite is only useful when someone is listening
A LEO satellite sees any given ground station for a few minutes at a time, a few times a day. The rest of the orbit it is storing data and waiting. How much data you get down per day is therefore a scheduling problem as much as a link-budget one, and it drives the choice of ground network.
How long is a pass?
At 500 km altitude the orbital period is about 94.6 minutes and a pass directly overhead lasts roughly 8–10 minutes horizon-to-horizon; most passes are lower in the sky and shorter, and usable time above a 10° elevation mask is often 5–7 minutes. A single mid-latitude station sees a polar-orbiting satellite on roughly 4–6 passes per day, clustered into two groups. Polar stations (Svalbard, Inuvik, Troll) see almost every orbit — which is why every Earth-observation operator wants time on them.
Ground Station as a Service (GSaaS)
Ten years ago you built or leased dishes. Today you rent antenna minutes from networks — AWS Ground Station, KSAT, SSC, Leaf Space, Viasat RTE, ATLAS — and pay per pass or per minute. The trades: coverage (how many sites, how polar), supported bands (X and Ka downlink are the differentiators), scheduling flexibility, and whether your data lands in your cloud account or on a disk in Norway.
Data relay: skip the ground
If passes are the bottleneck, talk to a satellite that is always in view instead. NASA's TDRSS relays did this for the Shuttle and ISS; commercial LEO relay constellations and optical inter-satellite links do it now. Starlink's laser mesh means a Starlink-equipped satellite is always connected. The cost is a second radio, and being a customer of another constellation.
Latency: the speed of light is a hard constraint
Radio travels at 299,792 km/s. One-way time to a satellite directly overhead is just altitude ÷ c:
| Orbit | Altitude | One-way (zenith) | Round trip (bent pipe, user→sat→gateway→sat→user) |
|---|---|---|---|
| LEO (Starlink) | ~550 km | ~1.8 ms | ~7–8 ms + processing; real-world 25–50 ms |
| MEO (O3b) | ~8,000 km | ~27 ms | ~110 ms; real-world ~150 ms |
| GEO | 35,786 km | ~119 ms | ~480 ms; real-world 550–650 ms |
| Moon | ~384,400 km | ~1.3 s | ~2.6 s |
| Mars (closest) | ~55 million km | ~3 min | ~6 min |
| Mars (farthest) | ~400 million km | ~22 min | ~44 min |
The GEO number is why voice calls over old satellite phones felt awkward and why video-game latency from GEO broadband is unfixable. LEO constellations exist largely to delete those 500 ms. For the Moon, 2.6 seconds means rovers can be teleoperated — carefully. For Mars, they cannot; every rover is autonomous by necessity.
Try it
Enter an altitude and see the orbital period, how many times a day it circles Earth, and the light-time. Then go watch the real thing: /satellite-tracker shows live positions, and /whats-overhead tells you when the ISS passes your house. In Space Tycoon, the same physics sets how long your ships take to reach the Belt — see /space-tycoon.