8 ms·

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 sate

by roshanj 10y ago

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/ https://spire.com/products/sense/ )

espadrine 10y ago
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?
- roshanj 10y ago
  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#Nanosatellites 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.

8 ms·

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 sate

by roshanj 10y ago

espadrine 10y ago
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?
- roshanj 10y ago
  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#Nanosatellites 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.