NUTS Backplane Revision - Improving Reliability and Modularity of the NTNU Test Satellite

Abstract

The NTNU Test Satellite is double CubeSat being built at NTNU. The main payload of the satellite is a camera for earth observations. The satellite is based on a modular design with a "motherboard" style backplane where modules are placed in slots. In the current revisions of the backplane, lack of documentation and partially incomplete schematics combined with an increase in complexity over several iterations has made the task of realizing the backplane within an acceptable time-frame difficult. For data transfer the current backplane makes use of two parallel \ac{I2C} buses for redundancy and a custom made arbitration bus for arbitration between the two OBCs (On-board Controllers) in the satellite. This results in a complex arbitration scheme having to be implemented in software with the potential of fault propagation over the arbitration bus between modules. A new design is proposed using CAN bus with built in arbitration with priority based on message address. Due to the robust nature of the CAN bus a single bus is considered able to replace the two \ac{I2C} buses. In the current design control signals for the backplane are sent using a single wire custom serial bus implementation based on shift-registers. The proposed new design connects the control of utility functions and housekeeping on the backplane, such as module power management, to the CAN bus. A new schematic design for the backplane is presented and test methodology suggested. The design is partially assembled on breadboard and tested. Lastly a partial hardware test and verification is presented before a conclusion is reached on the reduced complexity and future ease of implementation when it comes to board layout and production.