PERSEUS, Episode V - The Avionics strikes back: A highly adaptive, COTS-based and value-driven
Creators: name:  M. GOMES 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: SPACE
ADVANCED TECHNOLOGIES
REUSABILITY

description: For the last 17 years, the PERSEUS program of the French space agency (CNES) is a cornerstone of the relationship between future engineers, academic institutions and the space industry. More than 400 students all over France are involved in the design, manufacturing, test and launch of sounding rockets, with the help of major companies and research centers like ArianeGroup or ONERA. Its now undeniable that the space sector is going through disruptive innovations with emergence of new players, that is why PERSEUS aims at raising students awareness of these economic, strategic and scientific dimensions, promoting the research of promising technologies and developing vocation for the new space. After several successful launches of solid-fuel rocket, PERSEUS targets a much higher and ambitious objective through the DREAM ON challenge, a reusable bi-fluid LOX/CH4 propelled rocket with 5km apogee as a first step. In accordance with the Agile principles, the team follows an iterative and incremental workflow in order to gradually integrate crucial core components through several intermediate launchers named ASTREOS. This continuous integration based approach is only possible if all domains related to the launch mission, like ground segment, propulsion system or avionics, are profoundly reshaped to develop a set of modular, flexible and adaptive building blocks. Such process is all the more necessary to conceive avionics systems, since they have to rapidly evolve across ASTREOS successive versions to respond to demanding and changing needs in the context of vehicle recovery strategy like Thrust Vector Control (TVC), Autonomous Flight Termination System (AFTS), parafoil or fin controls, and other complex and sophisticated Guidance, Navigation, and Control (GNC) applications. PERSEUS relies on contributions and inputs from dozens of universities, each with their own teaching, e.g. preferred computing environment or modeling framework, and their specialties depending on whether they are more electronics oriented, software programming focused, or on the contrary rather generic and versatile. In order to achieve an effective collaboration between these partners and a straightforward integration of the produced blocks, while keeping financial investment as low as possible, the best strategy is the extensive use of open-source software and generic mainstream hardware platform. A minimal development of extension cards should only be needed to add specific functionalities like enhanced analog to digital converter, while interface cards could be used to improve electromagnetic compatibility and reach a flight-ready ruggedized system. Taking into account all these aspects, some of which may seem contradictory, is not an easy task but its the challenge that PERSEUS chose to address through the design and manufacturing of a new generation avionics. As we will see in the article, we have first made thorough comparisons of easily available Single Board Computer (SBC) on the market, critical real-time communication protocols, key software libraries, clock synchronization protocols, in order to identify the best match for our specific needs. Unlike old generation avionics which used simultaneously several protocols (USB, RS422, CAN) across mostly homemade microcontroller-based systems, with a clear lack of simplicity and scalability, we are now designing a fully Ethernet-based architecture deployed on a set of Raspberry Pi boards, paired with flexible and easily adaptable ruggedized extension boards.