Performance and Link Quality of an Advanced Satellite Communications Subsystem and Ground Segment in the 70cm Amateur Radio Band

The communications subsystem of an unmanned spacecraft is one of the most important of its subsystems. Ifcommunications fail, it is of no significance whether the rest of the spacecraft is operating correctly or not. With-out communication, no debug of any error at the subsystem level is possible. At present, the commercially avail-able communication interfaces for small satellites like CubeSats do not offer the required reliability.This paper presents lessons learned from more than six years of flight experience of the communication sub-system of the Austrian CubeSat PEGASUS and its ground segment, both developed specifically for this project.New hardware and software concepts were developed, with an emphasis on redundancy and stand-alone opera-tional capability. Major design features include robustness and system flexibility, and the possibility of maintain-ing communications even if the onboard computer and the electrical power subsystem malfunction. In addition,to minimize interference of the space to ground and ground to space link, a new radio transmission protocol wascreated. This package transmission protocol maximizes transmission reliability and usable space for data. Linkquality and performance are also discussed herein, as well as the necessity and efficiency of error detection andcorrection.