20 won't cover the world; Iridium needs 60-70-ish, and they're flying at higher altitudes, so Starlink would need a bit more than that. But also: Capacity. The

20 won't cover the world; Iridium needs 60-70-ish, and they're flying at higher altitudes, so Starlink would need a bit more than that. But also: Capacity. The more satellites you have, the smaller you can make the cells they're projecting to earth, and the higher transmit power levels can be (assuming that the satellites are largely power limited), as well as the better the SNR is going to be as you can focus the same antenna payloads on a smaller area. A beefier satellite with larger solar panels, more antennas, and bigger and reflectors could achieve the same with fewer satellite vehicles, which seems to be the approach ASTS is taking. But Starlink, as far as I understand, is also providing their "regular" beamformed service using the same satellites, and there you can actually increase capacity greatly with more satellites than strictly required for global coverage (since the terminals can also "point", i.e. you and your neighbor can use the same frequency at the same time, but pointed at another satellite, increasing total data rate per Hz).