An Open-Source, Hybrid Communication System Twin and Tool for CubeSat Applications

This paper presents a digital replica of a satellite communication system. To correctly depict end-to-end connectivity, a rudimentary flight software package around an imaging payload is built using NASA JPL’s F Prime framework. For radio communication, a custom implementation of the AX.25 protocol is built in Python and implemented into a GNU Radio block. In GNU Radio, an appropriate signal processing chain for up and downlink is set up. The resulting flow graph can be used fully digitally, for simulation or be connected to software defined radios for true, over-the-air communication. The Python implementation performs sufficiently well for a low data rate, real time, duplex connection. Through two USRP devices and two laptops, acting as satellite and ground station respectively, reliable end-to-end communication is achieved. All software tools used for this work are open source, resulting in an affordable and accessible package and versatile starting point for testing, prototyping and educational purposes.