Comprehensive Flight Software Design and Validation for the Harvard CubeSat I Mission

Abstract

This thesis analyzes the software architecture, development decisions, and testing procedures of the Harvard Undergraduate CubeSat (HUCSat), a six-year student-led nanosatellite project dedicated to evaluating the economic and practical viability of nitinol shape memory alloys to rotate solar panels. Section 1 provides a contextual background concerning the HUCSat’s overall hardware design and layout of circuit boards. Section 2 dives specifically into the Flight Controller Board (FCB) chip, defending how our team progressed through rapid prototypes to our ultimate settlement on the RP2350 microprocessor. Section 3 presents all the major software files that the FCB employs to schedule and operate all necessary tasks. This includes a main loop file, data processing files, finite-state machine (FSM) files, drivers, managerial classes, and configuration files. Some of this work is novel, developed for this thesis from scratch or re-purposed from open-source development code. Across sections 1-3, I detail the design considerations that had to be considered, justifying the transition from one variation to the next. Finally, Sections 4-5 underscore the testing and experiment procedure to ensure robustness and clarity of the mission, respectively. The primary contributions of this thesis are threefold. First, I present the implementation of new low-level software components, including hardware drivers and device managers abstractions tailored to the RP2350 PROVES Kit open-source flight controller. Second, I defend the development of testing methodologies (covering over 1,100 lines of newly-written test code), operational procedures, and experimental designs used to validate system behavior. Overall, such details will underscore the satellite’s resilience to concerns including radiation-induced faults, Low-Earth Orbit (LOE) temperature fluctuations, and memory constraints. Third, for the FCB, I introduce a novel dynamic, fault-tolerant, and non-blocking task-scheduling framework to conduct all HUCSat operations. Specifically, this framework integrates a system-wide finite state machine and data processing class with asynchronous task execution and command-data handling extensions to enable adaptive-decision making based on individual component health and telecommand data. In addition, its usage of a radiation-tolerant watchdog timer and non-volatile reboot and counter registers that have access to backup power systems ensure dynamic fault-tolerance. In sum, these contributions aim to provide a concrete reference to future generations constructing CubeSat flight software. To the best of knowledge, this is Harvard College’s first ever nanosatellite launch supported by NASA’s CubeSat Launch Initiative (CSLI) initiative.