On-Board Computer
April 1, 2025
Author: Sydney Macdonald VA7SPF
We have completed the first revision of a new subsystem based on old heritage for MARMOTSat - the On-Board Computer (OBC)! The OBC is the system that manages the status of the satellite, executes commands received from the ground, and collects telemetry data from the other subsystems on the satellite. The OBC is built on a TMS570 microcontroller and uses FreeRTOS, a real-time operating system, to schedule and execute commands based on their priority. This allows the spacecraft to operate autonomously while out of range of the ground station.
The assembled OBC board
MARMOTSat’s OBC was designed in-house by our team, and is based on the design used on ORCASat with some updates and new features to fit the new mission. The biggest update from ORCASat is that the OBC board has a new layout. This layout incorporates some new features for MARMOTSat, including a Controller Area Network (CAN) bus and a UART Multiplexer (Mux). These changes were made to accommodate the satellite’s new stack-up.
A CAN bus is a differential signaling protocol which allows different electrical devices to send messages to each other efficiently and reliably, allowing the OBC to talk to the other subsystems. The UART Mux works as a back up communication system for the ADCS and GNSS subsystems. The Global Navigation Satellite System (GNSS), an OEM719 receiver, obtains the time and position of the satellite, ensuring the OBC has accurate time data. Below you can see the OBC with the GNSS receiver (and the battery pack!) connected.
