https://www.um.edu.mt/library/oar/handle/123456789/129100 2026-06-12T09:24:19Z https://www.um.edu.mt/library/oar/handle/123456789/147102 Title: The PQ8 architecture : deploying picosatellite constellations from a single launch Abstract: Over the past decade, demand for nano- and pico-class satellites has surged, driving up costs and competition for launch opportunities. CubeSat launches, once easily accessible, have become prohibitively expensive for small institutions, especially when considering constellation deployment. Although the PocketQube standard offers a lower cost alternative, its adoption has been limited and its cost benefits modest, primarily due to launch integration limitations, debris mitigation and trackability concerns. To address these challenges, this work proposes the PQ8 Architecture: a novel deployment model for pico-scale satellite constellations that reduces launch costs by up to 87 %, simplifies integration, and enables the simultaneous deployment of multiple satellites. The research is divided into three key components. First, the structural design is developed to accommodate eight PocketQube-sized satellites within a 1U CubeSat frame, while remaining scalable. The design is evaluated using finite element analysis and mechanical testing, including modal analysis, vibration, shock, and static load tests, all in accordance with ECSS launch qualification guidelines.. Second, constellation dispersal is addressed through tailored differential drag control algorithms. This approach calculates separation velocities and timing to achieve in-plane phasing, accounting for the operational parameters introduced by the PQ8 form factor. Two case studies with orbital simulations validate the method’s effectiveness and scalability. Third, a novel disengagement mechanism is presented, in which magnetorquer coils are reconfigured to act as synchronized electromagnetic actuators. The circuitry is validated through simulation and bench-top testing, and actuator forces are confirmed via finite element analysis. Overall separation dynamics are then demonstrated using a pendulum testbed to emulate near-free-body translational and rotational disengagement behaviour. Together, these contributions, structural innovation, coordinated dispersal, and integrated separation, form a robust and cost-effective platform for small-satellite constellations. The PQ8 Architecture significantly lowers the barriers to entry and enables missions that would otherwise be financially or logistically infeasible. Description: Ph.D.(Melit.) 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145633 Title: Surface engineering of wire arc additively manufactured AZ80 magnesium alloy Abstract: This study investigates the surface engineering of wire arc additively manufactured (WAAM) AZ80 magnesium alloy, focusing on the combined effects of process parameters, heat treatment, and shot peening on its microstructure and mechanical performance. WAAM AZ80 was produced using two processing conditions: one producing materials with higher defect content (P1) and the other yielding a densified, near-defect-free condition (P2). Specimens were extracted along both parallel and perpendicular to the build direction to assess anisotropy, and benchmarked against wrought EN AW-6082 aluminium alloy in the T6 condition. The findings showed that process-induced defects strongly influenced tensile anisotropy, whereas T6 heat treatment improved ductility, hardness, and tensile strength, reducing orientation-dependent disparity and bringing the mechanical properties closer to EN AW-6082. Compression strength exhibited limited sensitivity to defect content. Shot peening further enhanced the surface integrity by inducing grain refinement, work hardening, and CRS, though at the expense of increased roughness. The surface hardness increased by up to 45% in WAAM AZ80 and by 14% in EN AW-6082, while peak CRS reached ~110 MPa in WAAM AZ80 and ~280 MPa in EN AW-6082. Fatigue life improvements were most pronounced in WAAM AZ80, with shot peening extending life by up to 160%, depending on the printing and associated defect orientation, and enabling run-outs beyond 106 cycles in P2 samples through delayed crack initiation and reduced surface-connected porosity. Although EN AW-6082 retained higher absolute fatigue strength, the results demonstrate that refined process control, T6 heat treatment, and shot peening can collectively transform WAAM AZ80 into a competitive lightweight alternative for aerospace and satellite applications, particularly under cyclic loading conditions. Attempts to improve electrical performance through gold coatings highlighted the challenges of plating reactive magnesium alloys. While electroplating failed to achieve uniform coverage, sputtered coating produced more continuous films but did not significantly enhance conductivity, underscoring the need for tailored pretreatments and interlayers for functional integration. Description: M.Sc.(Melit.) 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/144767 Title: A ‘prosthesis life-cycle ontology’-based service system framework to cater for amputees’ evolving needs Abstract: Lower-limb prostheses remain essential to restoring mobility and independence for amputees, yet their design and aftercare continue to be fragmented, reactive, and inefficient. Current practices are characterised by siloed stakeholder input, tacit rather than structured knowledge, and limited methods for adapting to the evolving needs of both amputees and prosthesis sub-systems. This thesis addresses these systemic inefficiencies by developing the Adaptive Prosthesis Life-Cycle Service System Framework (adProLiSS), an ontology-based, consequence-aware framework that reconceptualises prosthesis management as an integrated product–service system (PSS). The research aim was to improve amputees’ overall prosthesis experience, measured in terms of time efficiency, cost efficiency, functionality, user comfort, emotional well-being, and aftercare quality, through the design, implementation, and evaluation of a prosthesis life-cycle framework that supports adaptive, knowledge-based decision-making. To test this aim, seven research questions (RQ1–RQ7) were formulated, spanning the identification of life-cycle activities, stakeholder roles, tools and methods, critical constraints, specifications of a prosthesis PSS, and its applicability and evaluability across prosthesis types. Conceptually, the thesis advances the state of the art by introducing the Prosthesis Life-Cycle Consequence Knowledge Modelling Frame (PLCCKMF), a domain-specific ontology that formalises heterogeneous consequence knowledge, including intended and unintended, interacting and non-interacting outcomes, across physical, functional, emotional, systemic, and semantic domains. Methodologically, the work contributes a closed-loop life-cycle methodology, digital tool support through the Patient–Prosthesis Management System (PPMS) and the Consequence-Driven Co-Design Support Tool (CD-CST), and a scenario-based evaluation strategy combining physical demonstrators, digital platforms, and stakeholder engagement. Practically, these contributions were validated through prototype demonstrations addressing ulcer detection, weight distribution monitoring, fall risk, maintenance alerts, and daily logging. Evaluation findings indicate that adProLiSS delivers measurable improvements across the six evaluation criteria, enhances stakeholder collaboration, and enables decision traceability in ways not achieved by conventional approaches. The framework was shown to reframe amputees from passive recipients to active contributors of consequence knowledge, support clinicians in preventive and evidence-based aftercare, and allow engineers to anticipate design consequences before physical prototyping. The findings carry implications for service providers and policymakers, particularly in highlighting how consequence awareness and interoperability standards such as HL7/FHIR could guide future procurement practices and rehabilitation service models. The research is not without limitations. The scope was bounded to lower-limb prostheses, early-stage digital and physical prototypes, and a geographically localised but scientifically justified stakeholder sample. Nonetheless, the framework establishes a demonstrable foundation that can be extended to upper-limb prostheses, scaled through multi-centre evaluations, and advanced via ontology governance methods and higher-TRL digital systems. Future work also envisions adProLiSS as an educational simulator and as a bi-directional communication platform for real-time patient–clinician interaction. In conclusion, this thesis contributes to engineering design knowledge by embedding consequence awareness and ontology-driven reasoning into the prosthesis life-cycle, demonstrating how structured knowledge representation and adaptive service-system integration can improve both design and aftercare. The adProLiSS framework thus stands as a novel paradigm for prosthesis life-cycle management, bridging conceptual, methodological, and practical advances, and as a commitment to enhancing the lived experiences of amputees through more collaborative, knowledge-based, and adaptive healthcare systems. Description: Ph.D.(Melit.) 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/144766 Title: Graphene oxide on porous polyurethane substrates : synthesis, deposition, and characterisation Abstract: Graphene oxide (GO) is a chemically functionalised, two-dimensional nanomaterial with broad applicability in areas such as water purification, sensing, coating and membrane fabrication. Its abundant oxygen-containing functional groups enable strong interactions with various polymers, making it a suitable candidate for forming multifunctional hybrid materials. Traditional GO synthesis methods involve corrosive acids, strong oxidising agents, and elevated temperatures, which pose safety risks due to the release of toxic fumes and the potential of forming explosive by-products. This doctoral study proposes a simplified, room temperature method using only concentrated H2SO4 and KMnO4, eliminating the need for heating and reducing hazardous emissions. Characterisation confirmed the effective oxidation and exfoliation of graphite with an average lateral flake size of 15.06 ± 1.87 μm and 87 layers, into GO sheets with resultant lateral sheet size of 10.22 ± 0.62 μm and ~ 10 layers. X-ray Photoelectron Spectroscopy (XPS) analysis showed that in-house synthesised GO had a comparable oxygen content and functional group distribution to commercial GO, with epoxy (C–O) as the dominant group. X-ray induced Auger spectroscopy revealed a reduction in sp2-hybridised carbon from 80.21% in graphite to 45.52% in GO, confirming effective oxidation. The second phase of this study focused on the deposition of the synthesised GO on the top surface of a modified porous polyurethane (PU) support. Due to the inherent chemical inertness of PU, surface modification was carried out using chromic acid etching followed by polydopamine (PDA) deposition at a fixed concentration and varied deposition times (6, 12, and 24 hours). Characterisation showed that chromic acid altered the PU surface both physically and chemically, increasing hydrophilicity. PDA further modified the surface, introducing functional groups such as COOH/N-C=O, C-O-C=O, and C=O, thus enhanced the compatibility with GO. GO was then deposited at two concentrations (1 g/L and 10 g/L) and three different deposition times (6, 12, and 24 hours). Only the higher concentration resulted in uniform coverage. Characterisation confirmed the successful chemical anchoring of GO to the PDA-modified PU, facilitated by reactions between the oxygen functionalities in GO (acid anhydride and epoxy groups) and the amine groups in the PDA layer. Description: Ph.D.(Melit.) 2025-01-01T00:00:00Z