Decoding packets from AALTO-1 ( 42775)

Regarding Observation 2007321
AALTO-1 using modulation and TI CC1125 packet protocol same as Reaktor Hello World.


The framing for both satellites follow the IEEE 802.15.4. Synchronization words however are different. Until we fix the schema on the DB that will allow that kind of parameterization, I will add a work around flowgraph or something similar.

It’s not correct , syncword 0x35, 0x2E, 0x35, 0x2E same for both, perhaps preamble different number of bytes (but data succesfully decoded, see observation).
Снимок экрана 2020-04-13 в 11.31.59
Снимок экрана 2020-04-13 в 11.31.22

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Oh you are right. I was looking on the S-Band sync word.

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Thanks @uy0ll your suggestion has been approved. Hopefully we will start to see decoded data from AALTO-1.


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).



Thanks for the info, I’ve just approved @uy0ll suggestion in so now the transmitter has the right frequency which means that we will see more decoded frames. Also I have noticed @BOCTOK-1 to give priority on the GFSK transmitter over the CW one when scheduling AALTO-1.

With these info maybe we can start building a decoder (cc’ing @DL4PD but anyone else is also welcome) in order to create a dashboard at even if it doesn’t make so much sense, if I understand correctly the format, it would be nice to visualize whatever we can.

@petrinm as soon as you have more info on Foresail-1 please let us know with a thread here or by opening issues on related SatNOGS repositories (here for decoder and here for adding the satellite in DB) so we can prepare and test any implementation before launch.

much better ( observation #2049855 ) , thank you @petrinm and @fredy.

P.S. Why I can’t find received data in ?

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Telemetry data decoded by script reaktor_hello_world_fsk9600_decoder.grc succesfully uploaded to for 43743 - Reaktor Hello World ( observation #2108420 ), but still not for 42775 - AALTO-1 ( observation #2108418 ).
What is the reason?

We don’t sync data by default from Network to DB for all the satellites/transmitters. I’ve just enabled the sync for the frames of AALTO-1 from now on. For the older ones as it is more complicated I’ve added a task at Thanks for point it out.

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