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- Jan 2023
Most satellite communications make use of big satellites which orbit up at 36,000km. Perched at such a height a satellite seems to sit still in the sky, and that vantage allows it to serve users spread across very large areas. But even if such a satellite is big, the amount of bandwidth it can allocate to each user is often quite limited. The orbits used by Starlink’s much smaller satellites are far lower: around 550km. This means that the time between a given satellite rising above the horizon and setting again is just minutes. To make sure coverage is continuous thus requires a great many satellites, which is a hassle. But because each satellite is serving only a small area the bandwidth per user can be high. And the system’s latency—the time taken for signals to get up to a satellite and back down to Earth—is much lower than for high-flying satellites. High latencies can prevent software from working as it should, says Iain Muirhead, a space researcher at the University of Manchester. With software, rather than just voice links, increasingly used for tasks like controlling artillery fire, avoiding glitches caused by high latency is a big advantage.
Useful explanation of why Starlink (and LEO for that mater) is superior to high-orbit conventional satellites:
- it is closer to the Earth thus having much smaller latency (commercial tests say 20-40ms in practice at user end, comparing to cca 0.5s for GeoStationary Orbit satellites)
- because it's so many satellites rather than a single or few, one LEO satellite can serve less people and thus provides bigger bandwidth, at level of 'broadband' (commercial tests say 50-200Mbps/10-20Mbps) It's advantage is thus primarily in number of satelites which are in tens of thousands; previously, each GSO was under a particular point on Earth and serving only those people all time.
- Since LEO orbit around Earth very fast (completing a full earth orbit in under one hour), they can possibly provide connectivity everywhere, even the poles