Satellite arcs
It seems the last probable position (the two arcs) are based on data received via Inmarsat geostationary IOR satellite (aka Inmarsat 3 F1, position 64.5 east). I don't know the exact service used, but it's probably something using a low gain antenna, presumably the "Aero L" 600/1200 b/s service or something similar, using X.25-alike packet switching technology. The ability to provide estimate distance from the satellite means the service probably uses some sort of point-to-multipoint Time-Division Multiplexing (TDM/TDMA) which requires synchronizing multiple transmitters so the satellite receives all data packets in their assigned time frames. This is typically done using "Timing advance", calculated each time a connection is established. This calculation may be very precise, but the satellite may only get/use the most significant portion of the value, thus greatly reducing the precision.
I don't really think the satellite adjusts its antennas to accommodate the next expected connection![Smile](https://forums.jetphotos.com/core/images/smilies/icon_smile.gif)
The reason the previous distances (arcs) are not available may be as simple as this: they (Inmarsat) possibly don't log each TA, but only store "current" (last) value in a record describing an active terminal. On the other hand, previous connections (attempts) are logged (without TA) for billing purposes.
K.
It seems the last probable position (the two arcs) are based on data received via Inmarsat geostationary IOR satellite (aka Inmarsat 3 F1, position 64.5 east). I don't know the exact service used, but it's probably something using a low gain antenna, presumably the "Aero L" 600/1200 b/s service or something similar, using X.25-alike packet switching technology. The ability to provide estimate distance from the satellite means the service probably uses some sort of point-to-multipoint Time-Division Multiplexing (TDM/TDMA) which requires synchronizing multiple transmitters so the satellite receives all data packets in their assigned time frames. This is typically done using "Timing advance", calculated each time a connection is established. This calculation may be very precise, but the satellite may only get/use the most significant portion of the value, thus greatly reducing the precision.
I don't really think the satellite adjusts its antennas to accommodate the next expected connection
![Smile](https://forums.jetphotos.com/core/images/smilies/icon_smile.gif)
The reason the previous distances (arcs) are not available may be as simple as this: they (Inmarsat) possibly don't log each TA, but only store "current" (last) value in a record describing an active terminal. On the other hand, previous connections (attempts) are logged (without TA) for billing purposes.
K.
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