Subsystem Description

Functional Architecture

Conceptually, the On-board Computer (OBC) acts as the brain governing the spacecraft, serving as the central component within the overall architecture of this system. It plays a pivotal role in a complex system that accommodates the following five distinct sub-modules: Electrical Power Supply (EPS), Communication System (COMMS), Attitude Determination and Control System (ADCS), and the payload (P/L).

In other words, the main purpose of the subsystem is to perform the housekeeping of the overall satellite. In this regard, performing both data processing and storage in a timely manner while maintaining a low power consumption is crucial so as to guarantee an efficient and robust performance of the PocketQube. In light of this, the Flight Software (FSW) running on the OBC needs then to be carefully designed by the application writter in order to meet the time requirements linked to the varied tasks that the satellite is expected to perform. A common technique used in embedded systems in order to fix this time constraint is implementing Real-Time Operating Systems (RTOS). In the PoCat project, FreeRTOS has been the open-source RTOS selected to manage the on-board FSW.

On the other hand, the OBC hardware needs to accommodate the FSW by providing enough resources for a correct execution. In summary, the breakdown of the OBC from the hardware perspective consists of a low-power but high-performance ARM Cortex M4 microprocessor, volatile and non-volatile memory banks for data storage, interfaces that reach out to peripherals and data buses interconnecting the whole system architecture.

To ensure the desired behaviour of the PocketQube, it is necessary for both software and hardware to converge seamlessly. This will enable the OBC to efficiently manage various tasks that play a critical role in determining the behavior of the picosatellite. In summary, the tasks that are performed by the On-Board Computer for the PoCat space mission are listed below:

• Task scheduling.
• Inter-task communication.
• Power management.
• Telecommand processing.
• Telemetry data handling.
• Payload data acquisition.
• Attitude determination and control.
• Error handling.

Requirements