Hi Alexander,
Nice to see some properly decoded telemetry packets from Aalto-1 in a SatNOGS observation. Usually there are just Morse and AX.25 beacon packets. I’m one of the Aalto-1’s operators and builders, so I could open up a bit more the frames you have received.
The first frame in you observation starts:
10 42 4A 07 0D 03 F5 83 7D C9 B3 A2 81 AD
These bytes have following meanings:
0x10: Telemetry packet ID
0x424A: Telemetry packet sequence number
0x07: Service type (7 = File Transfer)
0x0D: Service subtype (13 = Downlink Transmit TM)
0x03F5: File block ID (1013)
83 7D C9 B3 A2 81 AD...: A block of file data.
The first 8 frames in the observation (File block IDs from 0x03F5 to 0x04BB) are from black calibration spectral image taken 14.2.2020 09:17:37 UTC. The total file is 282kBytes. On the next 8 frames, the file block ID has reset back to beginning (0x000F - 0x00D5) because the ground station started to downlink next file on the list which is another spectral image taken 09:39:17 UTC on the same day.
The way how file downlinking works on Aalto-1 is that ground station initializes the transfer by sending a filename to the satellite and waiting for ACK. After this ground station starts requesting the satellite to send bursts of file blocks based on its file transfer status log file. The burst can contain 20 consecutive file blocks or 5 arbitrary blocks indicated by request which ground station hasn’t received properly. After a single burst the ground station checks what is got and sends request for next burst.
Unfortunately ~4kHz frequency offset in the observation breaks most of the frames. Aalto-1’s center frequency should be pretty accurately 437.220 MHz but for some reason SatNOGS’ transmitters info defines it to be 437.216 MHz for GFSK9k6 mode. With correct center frequency and that good SNR, you should be able to decode much more frames.
Unfortunately with Aalto-1, we don’t have any nice method to push these file blocks received by others to our mission control software so we cannot benefit much of these packets. ATM, we are finishing the building of our new satellite, Foresail-1, which will hopefully have a much better mission control and file transfer system for SatNOGS assisted operations (all the features related to this haven’t been finished yet).
BR,
Petri