CubeSat bus interface with Complex Programmable Logic Device

Abstract

A standardized interface for different CubeSat missions is one of the keys to reducing costs and delivery time. A backplane interface approach, proposed by the University of Würzburg in Germany as UWE-3, was implemented in three CubeSat projects at the Kyushu Institute of Technology (Kyutech) to shorten the development and assembly times. The backplane approach also helped to reduce the risk of workmanship errors associated with the harness. However, changes to the proposed standard interface board were necessary in every CubeSat project, to comply with the mission requirements. To obtain more flexibility, especially for data connections, this work introduces a novel idea of a software-configurable bus interface with a backplane board. A Complex Programmable Logic Device (CPLD) was used instead of hardware routing so that we can reconfigure the bus interface by reprogramming the CPLD. The concept was validated by a functional test with a breadboard module. A radiation test verified that the selected CPLD has enough strength to survive total ionization doses of more than 2 years in low Earth orbit. A new backplane board with CPLD has been integrated into the engineering model of the fourth CubeSat project at Kyutech, the BIRDS-3 project, and system level verification has been conducted.