Engineering of flight software architectures for nanosatellite missions presents significant challenges due to constrained on-board computational resources, stringent reliability requirements and complex, mission-specific operational demands. Despite the advancements of the New Space era, architectural designs are seldom available publicly, largely due to intellectual property restrictions. To address this gap, this paper illustrates the flight software architecture for a particular nanosatellite mission as per the 4+1 architectural view model. By deconstructing the on-board software system into its physical, logical, development, process and scenario views, we offer an in-depth analysis of the architectural decisions, trade-offs, and design rationales that guided development. The design presented extends beyond typical reliability and safety to emphasize deployability, integrability, modifiability, and testability design drivers. This experience report intends to advocate rigorous software architecture principles in software engineering for space software, by sharing insights and providing detailed architectural documentation with the overall goal of advancing a novel research agenda within the community.