> As far as I know, their satellites are not capable of steering beams, and rely purely on the placement directly down from where they are
This is wrong. From their FCC filing(1), they use AESA phased array antennaes, and each satellite is capable of simultaneously maintaining "many" (unspecified) steered beams that are <2.5 degree wide.
Also, the receiver is capable of distinguishing between multiple beams covering it so long as there is more than 10 degrees of angular separation between them from it's point of view. If I understood it correctly, this will allow nearly every visible satellite at the same orbital height (less the ones very nearest to horizon) to communicate with targets that are geographically very near to each other at full bandwidth. After the very first phase has been launched, they can provide a total of ~500 Gbps of downlink bandwidth to any spot target that lies between 40 and 60 degrees latitude. The later additions at high orbits help with total capacity and especially with targeting multiple targets relatively near each other, but do not help provide more bandwidth per city, as that is limited by the 10 degree angular separation requirement.
The VLEO (330km-ish) constellation will help with that by reducing the size of each spot.
one noteworthy item from the filing is that they intend to build 200 Gateway earth stations just within the continental United States, which means that the vast majority of satellites will be functioning as Bent pipe repeaters. I don't think that there will be a lot of traffic traveling satellite to satellite in a multiple hop arrangement. 200 sites for their ka band trunk links from satellite to earth station means that a CPE terminal in, for example rural NW Montana might have a 25-30ms latency to a gateway in Spokane, and from there the latency to internet destinations will be all fiber based, same as any existing ISP.
if I had to guess on the earth station siting, they are picking locations which are medium-sized cities with decent terrestrial fiber connectivity, which will be within the same satellite view footprint as adjacent rural areas. Such as an earth station in Boise may serve mountainous remote areas of ID.
This 200 Earth station figure also lends me to believe that the first manufacturing run of satellites may not have any satellite to satellite trunk link ability at all, but that they will ALL be bent pipe architecture. this means that if SpaceX wants to serve a particular area, they need to have an earth station on terrestrial fiber in the same region, which is simultaneously visible to satellites and end users.
I think that's a very good observation, especially given the recent news that as part of musk firing some of the leadership on the project, he wants the satellites to be significantly simpler.
If that's the case then the problem becomes exponentially more complex than I was thinking, and the technical challenges are going to be far harder than I'd first thought. Doing frequency reuse and interference mitigation at the rates they need to if they're going to steer the beams is enormously complex.
I'm in agreement about the technical challenge - doing it with "low cost" phased array CPE is challenging. If I had to engineer it I'd design something with a pair of highly shielded, tight focal axis parabolic antennas (basically a miniaturized o3b terminal), like two 60cm size on two-axis tracking motorized mounts. But there's no way that sort of setup with a unique rf chain for each of two dishes would be under $5000.
This is wrong. From their FCC filing(1), they use AESA phased array antennaes, and each satellite is capable of simultaneously maintaining "many" (unspecified) steered beams that are <2.5 degree wide.
Also, the receiver is capable of distinguishing between multiple beams covering it so long as there is more than 10 degrees of angular separation between them from it's point of view. If I understood it correctly, this will allow nearly every visible satellite at the same orbital height (less the ones very nearest to horizon) to communicate with targets that are geographically very near to each other at full bandwidth. After the very first phase has been launched, they can provide a total of ~500 Gbps of downlink bandwidth to any spot target that lies between 40 and 60 degrees latitude. The later additions at high orbits help with total capacity and especially with targeting multiple targets relatively near each other, but do not help provide more bandwidth per city, as that is limited by the 10 degree angular separation requirement.
The VLEO (330km-ish) constellation will help with that by reducing the size of each spot.
(1): https://cdn3.vox-cdn.com/uploads/chorus_asset/file/8174403/S...