Software – Page 11 – Daniel Estévez

Decoding ESEO

ESEO is an educational satellite project for university students led by ESA. It is a microsatellite based on the S-50 platform by SITAEL and indeed serves as an in-orbit validation of that platform. It carries payloads developed by students in 10 European universities, and also a FUNcube payload from AMSAT-UK. It was launched last Monday in the SSO-A launch.

The satellite transmits 9k6 GFSK telemetry in the 70cm Amateur satellite band (do not confuse this telemetry with the telemetry sent by the FUNcube payload in the 2m Amateur satellite band). Last week I wrote an open letter to the directors of the ESEO program requesting the publication of the complete specifications for this telemetry. The existing documentation is published here as two documents called attachment 1, which describes the coding of the frames, and attachment 2, which describes the structure of the telemetry frames.

The main problem motivating my open letter was that the information in attachment 2 was insufficient to produce a telemetry decoder for ESEO. However, last Tuesday an updated version of this document was published. This new version seems to include all the information we need. Apparently, this new version has been published due to my open letter and the pressure made by some people at ESA surrounding the ESEO project.

I would like to thank all the people that have expressed their opinion about the importance of having well documented protocols in the Amateur radio service, as well as all the people in ESA that have pushed for the publication of the documentation, and understood that this is an important matter.

In this post we look at the coding used by ESEO, that is, everything described in attachment 1, and how the decoder in gr-satellites is implemented.

Uploading PW-Sat2 telemetry with gr-satellites

Yesterday I spoke about decoding the telemetry of PW-Sat2 with gr-satellites. Today I have added to gr-satellites a telemetry submitter block that sends the frames to the PW-Sat2 telemetry server. All users of the PW-Sat2 decoder from gr-satellites are recommended to set this up and submit telemetry to the PW-Sat2 telemetry server, as well as to the SatNOGS database. Here are the instructions to configure the submitter.

Decoding PW-Sat2 with gr-satellites

PW-Sat2 is a students satellite made by the Students Space Association at Warsaw University of Technology, in Poland. The project started in 2013 and was finally launched last Monday in the SSO-A launch. The satellite carries a sail to aid in deorbiting. This will be deployed on the 39th mission day. The deorbit is expected to happen in one year.

The satellite team has made available a lot of open-source software, such as groundstation software for Radio Amateurs, a telemetry server and even the software that runs on the on-board computer. There is also a good amount of design documentation. This is something a bit unusual and admirable for a university satellite.

PW-Sat2 transmits standard G3RUH-scrambled BPSK AX.25 frames in the 70cm Amateur Satellite band. The baudrate can be selected between 1k2, 2k4, 4k8 and 9k6 by the satellite team. The interesting thing is that there are many types of packets besides telemetry. For instance, it can list and transfer on-board files, such as the images taken by the satellite camera. These packets can be decoded by using the FramePayloadDecoder software.

Since the FramePayloadDecoder software is quite complex and it is written in Python, I have decided to make a telemetry parser for gr-satellites that simply loads this software into GNU Radio and passes the frames to the decoder. Here are the instructions to set this up.

Decoding 3CAT-1

A few days ago I spoke about my Reaktor Hello World decoder in gr-satellites. Another of the satellites that were launched with Reaktor Hello World in the November 29 PSLV launch is 3CAT-1, a 1U cubesat from the NanoSat Lab in Universidad Politècnica de Catalunya. It is designed as a technology demonstrator of COTS parts, and integrates four scientific payloads.

The communications system of 3CAT-1 uses a Texas Instrument CC1101 FSK transceiver chip, which is very similar to the CC1125 used in Reaktor Hello World. It transmits a 9k6 FSK telemetry beacon in the 70cm Amateur band. An interesting thing about this beacon is that it is powered by a temperature gradient that generates naturally within the satellite. A Peltier module is used to collect energy from the gradient and power the communications module. This is called “eternal self-powered beacon demonstrator” by the designers of the satellite, since it doesn’t depend on batteries or solar cells.

I have been in contact with Juan Fran Muñoz from NanoSat Lab, who has been kind enough to send me a telemetry recording for 3CAT-1. With this, and following my implementation of the Reaktor Hello World decoder, I have added a decoder for 3CAT-1 to gr-satellites.

Decoding Reaktor Hello World

Reaktor Hello World is a 2U cubesat built by the Finnish company Reaktor Space Lab as a test of their cubesat platform and demonstration of the first miniature infrared hyperspectral imager. It was launched on November 29 by a PSLV from Satish Dhawan Space Centre, together with several other cubesats. It transmits 9k6 GFSK telemetry in the 70cm Amateur satellite band.

The satellite uses a Texas Instruments CC1125 FSK transceiver chip. This is very similar to the CC1101 that I used a few years ago in my 70cm Hamnet experiments, so I already knew the coding and features of this chip quite well. The satellite team has a Github repository with a GNU Radio decoder based on the gr-cc11xx decoder block for the CC11xx series of chips. Since gr-cc11xx doesn’t seem to be maintained anymore, I wanted to implement my own CC11xx decoder in gr-satellites and use it to decode Reaktor Hello World.

Batch processing of DSLWP-B Moonbounce: part I

In previous posts I’ve talked about how the DSLWP-B 70cm signal can sometimes be received in the Dwingeloo 25m radiotelescope via a reflection off the Moon’s surface. I’ve studied the geometry of this reflection, the cross-correlation against the direct signal, and even decoded some reflected JT4G.

However, so far the reflection has been detected by hand by looking at the recording waterfalls. We don’t have any statistics about how often it happens or which conditions favour it. I want to make some scripts to process all the Dwingeloo recordings in batch and try to extract some useful conclusions from the data.

Here I show my first script, which computes the power of the direct and reflected signals (if any). The analysis of the results will be done in a future post.

Measuring the stability of a TCXO

Lately, I have been testing the GPSDO that I will use to discipline my Es’hail 2 groundstation. One of the tests I have done is to measure the frequency of the TCXO that I use in my Hermes-Lite 2.0beta2 over a few days. Here I show the details of the measurement process and how to process the data in Python.

Plotting DSLWP-B observations Doppler and geometry

I have made a Python script to plot the Doppler and geometry for a DSLWP-B observation. This can be useful for several things: predicting the downlink and uplink Doppler corrections, checking for the Doppler of the Moonbounce signal, checking the position of DSLWP-B in the sky, and studying Moonbounce geometry.

Keeping track of DSLWP-B images

While writing my previous report, I had to keep track of when each of the images had been taken and when it was downloaded. This can be a bit tricky, since the images do not carry a timestamp. Here I describe the techniques that can bee used to identify and keep track of the images.

Decoding TANUSHA-3

On August 15, during a Russian EVA on the ISS, a total of four Russian nanosatellites were deployed by hand. Although different online sources give incomplete and contradictory information about which satellites were released, it seems that they were SiriusSat 1 and 2, from the Sirius educational centre in Sochi, and Tanusha 3 and 4 from the Southwest State University in Kursk (see also Jonathan McDowell’s space report).

The SiriusSats are using 4k8 FSK AX.25 packet radio at 435.570MHz and 435.670MHz respectively, using callsigns RS13S and RS14S. The Tanushas transmit at 437.050MHz. Tanusha-3 normally transmits 1k2 AFSK AX.25 packet radio using the callsign RS8S, but Mike Rupprecht sent me the other day a recording of a transmission from Tanusha-3 that he could not decode.

It turns out that the packet in this recording uses a very peculiar modulation. The modulation is FM, but the data is carried in audio frequency phase modulation with a deviation of approximately 1 radian. The baudrate is 1200baud and the frequency for the phase modulation carrier is 2400Hz. The coding is AX.25 packet radio.

Why this peculiar mode is used in addition to the standard 1k2 packet radio is a mystery. Mike believes that the satellite is somehow faulty, since the pre-recorded audio messages that it transmits are also garbled (see this recording). If this is the case, it would be very interesting to know which particular failure can turn an AFSK transmitter into a phase modulation transmitter.

I have added support to gr-satellites for decoding the Tanusha-3 phase modulation telemetry. To decode the standard 1k2 AFSK telemetry direwolf can be used. The decoder flowgraph can be seen in the figure below.

The FM demodulated signal comes in from the UDP source. It is first converted down to baseband and then a PLL is used to recover the carrier. The Complex to Arg block recovers the phase, yielding an NRZ signal. This signal is lowpass filtered, and then clock recovery, bit slicing and AX.25 deframing is done. Note that it is also possible to decode this kind of signal differentially, without doing carrier recovery, since the NRZI encoding used by AX.25 is differential. However, the carrier recovery works really well, because there is a lot of residual carrier and this is an audio frequency carrier, so it should be very stable in frequency.

The recording that Mike sent me is in tanusha3_pm.wav. It contains a single AX.25 packet that when analyzed in direwolf yields the following.

RS8S>ALL:This is SWSU satellite TANUSHA-3 from Russia, Kursk<0x0d>
------
U frame UI: p/f=0, No layer 3 protocol implemented., length = 68
 dest    ALL     0 c/r=1 res=3 last=0
 source  RS8S    0 c/r=0 res=3 last=1
  000:  82 98 98 40 40 40 e0 a4 a6 70 a6 40 40 61 03 f0  ...@@@...p.@@a..
  010:  54 68 69 73 20 69 73 20 53 57 53 55 20 73 61 74  This is SWSU sat
  020:  65 6c 6c 69 74 65 20 54 41 4e 55 53 48 41 2d 33  ellite TANUSHA-3
  030:  20 66 72 6f 6d 20 52 75 73 73 69 61 2c 20 4b 75   from Russia, Ku
  040:  72 73 6b 0d                                      rsk.
------

The contents of the packet are a message in ASCII. The message is of the same kind as those transmitted in AFSK.