Every ship within range of an AIS receiving station. There are deadspots far out and see and behind obstructions.

Yep, terrestrial AIS receivers can only receive messages from ships that are less than ~50 nautical miles off the coast. Further out than that and you need satellite-based AIS data.

(I'm an engineer at Spire, we've launched a constellation of nanosatellites that does exactly that: https://spire.com/products/sense/ )

The website is extremely clear. I am wondering a few further things.

What network design is used to communicate between the satellites? I presume that they don't all go at the same speed in the same direction, so the network layout must be flexible, right?

Also, what is their size? You called them nanosatellites, can they really be a hundred nanometers big? How are they powered, and how are they put out of commission?

Correct, our constellation uses several different types of orbits to achieve global coverage. The satellites don't communicate directly with one another but rather through a globally distributed network of groundstations. When a satellite passes within view of one of our groundstations we are able to downlink the AIS data which then gets processed and delivered to customers.

Ah yes! I think the term "nanosatellites" is a bit confusing--it refers to satellites between 1 and 10 kg (https://en.wikipedia.org/wiki/Miniaturized_satellite#Nanosat...). Ours are 3U cubesats so they are about 30cm long. Much bigger than a hundred nanometers!

They have solar panels which are used to charge batteries, and since they are in low-earth-orbit they will eventually de-orbit and burn up on reentry after several years. The FCC actually requires that cubesats re-enter the atmosphere within 25 years.

There is AIS sat or something(, we used to refer to it by that name.)

It scans the entire (?) globe every few hours. I think accrss to those observations is one of the benefits of a paid AIS subscription.

There are many satellites doing AIS these days. Some commercial and some operating for governments. It has a huge impact on coast guard activities as you can imagine. All vessels over a certain size is required to transmit an AIS beacon, and traditionally reception was from land-based stations with limited range. Coast guard can now correlate the information in the AIS beacon with satellite imagery and verify them, and can focus on vessels that does not emit the beacon or is falsifying it. It can also be used to find the culprit of oil-slicks.

Probably not taking subscriptions from Somalia...

This is endlessly fascinating, thank you. I'm sure there's fun work being done by commodities traders using this type of data - sure enough there's a pricing section for API calls to their service. I would be curious to see how well it can predict performance for manufactured goods though - for large-scale consumers like Wal-Mart it might be possible to say that rising imports to the US (more container ships incoming) point to increased demand by consumers, therefore invest in Wal-Mart.