Daniel Estévez

Voyager 1 is the furthest spacecraft and the first ever to exit the solar system. Fueled by its radioisotope generators, after more than 40 years of flight it is still sending us data about the interstellar medium using its 3.7 metre dish antenna and 8.4 GHz transmitter. In this talk we report two adventures regarding the reception of the Voyager 1 signal.

In the first part, we show the successful detection of the Voyager 1 signal using one of the 6.1 metre dishes at the Allen Telescope Array in November 2020. Calculations show that using stable frequency references and accurate Doppler correction, this feat might also be possible for amateurs with smaller dishes if they integrate several hours of data to pull out the very weak signal from the noise. In the second part, we use some recordings done by the 100 metre Green Bank Telescope in 2015 and 2020 to decode the data transmitted by Voyager 1. The spacecraft predates the modern CCSDS standards, so its data has some interesting aspects.

All this work has been done using GNU Radio, Python, and other open source tools. The data and results are publicly available.

gr-satellites is a GNU Radio OOT module that contains a collection of telemetry decoders for Amateur satellites. At FOSDEM20 we presented an on-going large refactor to improve modularity and usabilty. The new version was finally released in June and includes a command line tool to run the decoders, GNU Radio blocks of both high and low level to allow customized designs, and comprehensive user documentation. Moreover, gr-satellites now has cross-platform support through Conda, has been included in Debian and has an Ubuntu PPA.

In this talk we will look at the main features of the new gr-satellites releases and the important things that have happened this year surrounding the development of gr-satellites.

gr-satellites is a GNU Radio out-of-tree module with the goal of decoding every Amateur satellite. Currently it supports more than 80 different satellites. After GNU Radio 3.8 was released last summer, gr-satellites is seeing a lot of development and important changes. A refactored version, which will be released as gr-satellites 3.0 is on the works. This version brings more modularity to avoid code duplication, more flexibility in the input and output that the user can employ, and the idea to improve its integrability with other tools. Satellites are defined using a YAML file and the GNU Radio flowgraph is constructed on the fly by a Python script by connecting so called "component" blocks. Advanced users can also use the components directly in their own flowgraphs. This talk gives an overview of the gr-satellites 3.0 development progress.

Outernet is a company whose goal is to ease worldwide access to internet contents by broadcasting files through geostationary satellites. Most of the software used for Outernet is open source, but the key parts of their receiver are closed source and the protocols and specifications of the signal used are secret. I have been able to reverse engineer most of the protocols, and a functional open source receiver is now available.

Outernet is a company whose goal is to ease worldwide access to internet contents by broadcasting files through geostationary satellites. Currently, they broadcast an L-band signal from 3 Inmarsat satellites, giving them almost worldwide coverage. The bitrate of the signal is 2kbps (or 20MB of content per day), and they use the signal to broadcast Wikipedia pages, weather information and other information of public interest. Most of the software used for Outernet is open source, but the key parts of their receiver are closed source and the protocols and specifications of the signal used are secret. I think this is contrary to the goal of providing free worldwide access to internet contents. Therefore, I have worked to reverse engineer the protocols and build an open source receiver. I have been able to reverse engineer most of the protocols, and a functional open source receiver is now available. In this talk, I'll explain which modulation, coding and framing is used for the Outernet L-band signal, what are the ad-hoc network and transport layer used, how the file broadcasting system works, and some of the tools and techniques I have used to do reverse engineering.