Creating a highly flexible and autonomous stratospheric observatory: the essential elements of the European Stratospheric Balloon Observatory payload control software

Balloon-based astronomical missions offer a potential for cost-effective large and complex astronomical infrastructure in between ground and space-based observatories. Balloons are particularly suitable for UV and IR observations. Even though stratospheric observations have a long history, they have been up to recently they have been one-shot missions. The design of balloon platforms is usually formed around one or more specific instruments and their requirements. Not surprisingly, flight and ground software architecture in these missions may often seem like a second thought, with very limited flexibility intended. The relatively limited budget and short operations time of these platforms to some extent justifies the decision to not invest in a flexible flight or ground software. The same applies to the onboard autonomy of these scientific systems, including autonomous scheduling, data processing, and Fault Detection, Isolation and Recovery methods implemented onboard. The implemented autonomy is relatively limited and only answers the expected circumstances of one mission. Autonomy is usually implemented in the form of separated scripts miming automatically in parallel with some communications in between them, but not as autonomous adaptive operations. However, the progress in development of super-pressure balloons, would provide access to longer balloon missions, and safe landing technologies would help to reuse these platforms and launch them several times. The European Stratospheric Balloon Observatory infrastructure (ESBO) is an on-going effort to improve the way scientific balloons have been used up to now, by creating an autonomous, highly flexible, and reusable platform, capable of integrating different instruments, long autonomous flights, and frequent launches. The promise of reusability and exchangeability of the instruments at the core of ESBO requires a flexible design both at hardware and software levels. The goal of this paper is to describe the flexible and autonomous payload control software developed for ESBO's first prototype, STUDIO, and its various elements. The essential elements covered are the instrument independent telescope stabilization system based on COTS elements, the autonomous and highly flexible science data downlink manager, the onboard scheduler, mode-based telescope operations and finally, the fault detection, isolation, and recovery routines onboard. The software is developed based on an open-source flight software framework for space systems and is open-source to benefit the community working on similar missions. In addition to the flight software, the paper briefly describes the flexible autonomous science pipeline on ground, designed to perform arbitrary chain of processing steps based on specific type of data received, and the pointing monitoring software. Both these web-based elements use web-based tools to enhance remote operations in the future.