On-board Software Development & Mission Testing for the EIRSAT-1 Satellite and Prospects for Future Astrophysics Missions

The field of transient gamma-ray astronomy has witnessed many exciting developments over the past 50 years, starting with the serendipitous detection of gamma-ray bursts (GRBs), the most luminous electromagnetic (EM) events in the Universe, and extending to the recently established role of EM transients in multi-messenger astrophysics. These developments can largely be attributed to the launch of advanced space-based observatories, which are required for observations in this energy range. Currently, however, most satellites tasked with observing the gamma-ray sky are doing so well beyond their nominal mission lifetime. This thesis concerns the development of future observatories capable of enabling gamma-ray research. The work presented is focused on the development of flight software for the Educational Irish Research Satellite (EIRSAT-1). EIRSAT-1 is a 2U CubeSat with objectives spanning education, technology demonstration and science, that are to be realised by three novel payloads: 'EMOD', a thermal materials experiment; 'WBC', a software-based attitude control test-bed; and 'GMOD', a miniaturised gamma-ray detector developed for the detection of GRBs. The growing popularity of CubeSats is driven by their compact, standardised form factor, based on units (U) of 10cm×10cm×10cm, which reduces traditional barriers to entry, such as cost and development time. For transient gamma-ray astronomy, where events are typically short-lived and unpredictable, the unique potential for constellations of CubeSats hosting technologies, like GMOD, to provide all-sky coverage also motivates this work. A key challenge addressed throughout this thesis relates to the historically high failure rate of CubeSats, which ultimately impacts their use as tools for astronomical research. More specifically, this work discusses in detail the design-to-testing methods used to produce reliable CubeSat software for EIRSAT-1. Finally, the expected performance of EIRSAT-1 to observe an interesting class of gamma-ray transient, known as magnetar giant flares (GFs), will be reviewed through simulations, along with another future gamma-ray mission concept, known as the Transient High-Energy Sky and Early Universe Surveyor (THESEUS).