La Marca, Tobia Armando (2025) Guidance and Control of Small Platforms for Earth Orbiting, Re-Entry and Space Exploration Applications. [Tesi di dottorato]

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Abstract

This PhD thesis develops guidance, navigation, and control algorithms for space systems across diverse scenarios, ranging from drag-based controlled de-orbiting on the Earth to Mars atmosphericaided orbit insertion. Two guiding lines run through the thesis: (i) a distance-based progression of operational scenarios moving sequentially farther from Earth, and (ii) a dual treatment of aerodynamic force (and induced torque), either exploited as an actuation mechanism for guidance and control, or, conversely, rigorously modeled and mitigated as a disturbance, to meet both fine and coarse pointing mission requirements, or to keep trajectory-tracking error low. Based on that, the thesis centers on four focus areas, summarized below in the order in which they appear in the dissertation. First, a drag-based de-orbiting tracking controller is developed for small platform equipped with deployable heat-shield, using incremental model predictive control. By modulating the exposed cross-section, the ballistic coefficient is tuned in-flight to dissipate orbital energy through aerodynamic drag and to track prescribed descent profiles under control hardware and operational constraints. The predictive controller adapts to strong plant variations across the whole flight envelope and adopts an offset-free formulation in the attempt to remove steady-state error without external disturbance observers or estimators. Second, for Earth-observation missions in very low Earth orbit (VLEO), an attitude-control architecture with reaction wheels momentum management is designed to regulate stored momentum about a non-zero reference value and to limit reaction wheels duty cycles, while preserving pointing performance under strong aerodynamic torques. Attitude stabilization uses a modified quaternion feedback regulator. During attitude-hold phases, that is, when no reorientation maneuvers are required, a dead-band control logic suppresses the control torque within a predefined angular threshold, thereby reducing reaction wheel duty cycles. The momentum-management module employs a proportional–integral–derivative law that commands a fraction of the total control torque in the null space of the four reaction wheels allocation matrix. The control architecture is evaluated both in maneuvering scenarios, via execution of forward motion compensation maneuvers, and in prolonged nadir-keeping phases. The overall control architecture is based solely on reaction wheels, avoiding hybrid solutions with auxiliary actuators (e.g., magnetorquers). Third, the performance of the same quaternion feedback regulator is validated for visionbased target pointing in proximity operations. Its robustness is quantified via μ-analysis on a linear fractional transformation model with structured and unstructured uncertainties in sensors, actuators, plant-model parameters, and environmental disturbances. The controller is integrated with a relative-attitude guidance law that exploits vision-based navigation to align the LiDAR boresight of a chaser spacecraft with a designated target in Low Earth Orbit, ensuring accurate line-of-sight pointing under realistic sensing and operational conditions. To reduce actuator usage, the scheme incorporates the previously introduced dead-band logic, implemented as a keep-in conical region with a half-angle of 1.5◦ about the line of sight; when the boresight remains within this cone, the control torque is suppressed, thereby lowering reaction wheel duty cycles without degrading pointing performance and while keeping the target within the LiDAR field of view. Fourth, the feasibility and mission-level characterization of aerocapture at Mars for small spacecraft with a deployable heat shield are assessed, identifying viable orbit-insertion opportunities and post-aerocapture orbits that meet prospective science objectives while satisfying thermal and structural platform limits. Additionally, a sensitivity analysis performed on a scenario of interest, provides information about the aerocapture success rates on the basis of the post aerocapture orbit parameters obtained under environmental and system-level uncertainties. These analyses are enabled by a simulation environment that balances computational efficiency with the minimum model fidelity required to achieve kilometer-level propagation accuracy across the considered operational scenarios. Results indicate that, across the first three studies, the designed algorithms are computationally efficient and achieve the required positioning and pointing accuracy in high-disturbance aerodynamic regimes or during proximity operations. On the other hand, from a space-exploration perspective, the Mars aerocapture analysis indicates generous capture margins and provides a streamlined methodology that serves as a reference baseline for rapid feasibility analysis of aerocapture concepts.

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