Design and Validation of an Innovative Data Bus Architecture for CubeSats

Since the first successful CubeSat missions in the early 2000s, payloads for this form factor have emerged and have increased in technical performance level. This trend is likely to continue in the near future. However, despite the subsequent increase in data load and the increasing modularity of components, there are no clear trends for a new electro-mechanical interface standard. The only widely adopted data bus in CubeSats, I2C, is limited in terms of data rate and reliability. Custom solutions overcoming these limitations are generally not well documented, and especially implementation results in CubeSats are lacking. Therefore, there exists a need to increase the performance and reliability of the CubeSat bus platform. This paper proposes an innovative CubeSat data bus architecture, including performance and reliability tests. The first need is to increase the feasible data rates to be compatible with future large-data payloads. Secondly, the system’s reliability must be increased compared to the current I2C standard, as many launched CubeSats using this data bus experience severe problems such as bus lockups and even a few catastrophic failures. The concept proposed in this paper is to separate the main bus used for telemetry and command from the data bus used for payload data, which provides room for optimising the performance of both buses. The selected bus technology standards used to drive the hardware were found through a survey and subsequent trade-off of available serial bus standards. For the main bus, this trade-off results in either a CAN bus or RS485 bus to both increase the robustness of the internal network and potential data throughput. For the payload bus, a USB-based bus is selected to provide a high data rate with increased reliability compared to often-used standards. The combination of both options optimises performance while keeping electrical power consumption at a minimum. Making use of the common modular designs of CubeSats and recent developments in the respective data bus technologies, a flexible, robust and high performance data bus architecture is devised. A practical setup simulating a CubeSat with multiple realistic subsystems generating pseudo data is used to validate the operations of such a data bus. To find the maximum capacity of the network, multiple subsystems are connected with varying high and low data rates, thereby simulating current typical CubeSat subsystems and potential future payloads requiring high capacity data networks. Furthermore, methodologies are developed for implementation and qualification of the proposed bus in future CubeSat missions.