Focal Plane Assembly Design for Multiband Electro-Optical Payloads for Monitoring Terrestrial and Planetary Environments

This PhD thesis focuses on the design of a Focal Plane Multi-Channel Assembly (MCA) for a space mission, aimed at improving the understanding of climate processes and of the complex interactions between the atmosphere, land surface and oceans. The work has been developed within the framework of the LUCE mission, formerly CALIGOLA, a next-generation spaceborne multi-wavelength Raman LIDAR conceived to provide advanced observations of atmospheric, oceanic, terrestrial and cryospheric phenomena. Within the LUCE instrument architecture, the MCA represents the core element of the receiver chain, being responsible for the spectral separation, optical conditioning and detection of the optical signals collected by the receiving telescope. This work presents the preliminary design and engineering development of the MCA conducted during the Phase A and early Phase B1 activities of the LUCE programme. The work follows the engineering methodology prescribed by the European Cooperation for Space Standardization (ECSS), encompassing requirements engineering, trade-off analyses, preliminary design activities and multidisciplinary engineering assessments. Starting from the mission scientific objectives and instrument-level requirements, a structured requirements allocation process was performed to derive the functional, optical, mechanical, thermal and accommodation requirements governing the subsystem development. These requirements were subsequently used to drive a series of trade-off analyses aimed at identifying the most suitable architectural solutions capable of satisfying the demanding performance objectives of the mission while maintaining compatibility with mass, envelope, manufacturability and programmatic constraints. Particular emphasis was devoted to the thermo-mechanical design of the MCA. Since optical performance is strongly dependent on dimensional stability and alignment preservation, the development process focused on minimizing thermo-elastic deformations through an integrated thermal and structural design approach. Several accommodation concepts optical configurations, materials and thermal-control architectures were assessed and compared. The trade-off campaign ultimately converged towards a modular architecture based on a dedicated optical bench mechanically separated from the receiver telescope, providing improved integration flexibility and reduced Assembly, Integration and Test (AIT) complexity. The selected MCA configuration implements an eight-detector architecture covering ultraviolet, visible and infrared spectral channels. The optical layout employs a cascade of dichroic beam splitters to perform spectral separation, while a dedicated rhomboidal architecture was selected for the ultraviolet section to maximize optical robustness and spectral discrimination efficiency. To optimize packaging efficiency and minimize the overall envelope, a folded dual-face accommodation concept was adopted, distributing the optical channels on both sides of the optical bench. From the structural perspective, a dedicated trade-off was performed to identify the most suitable optical bench architecture. The final solution consists of an aluminium honeycomb sandwich panel supported through three titanium Isostatic Mount Devices (IMDs). This configuration provides an effective compromise between stiffness-to-mass ratio, manufacturability, thermal compatibility, structural integrity and integration robustness. The titanium bipods simultaneously provide controlled mechanical compliance and thermal isolation, significantly reducing the transmission of thermo-elastic disturbances from the hosting structure. The thermal-control architecture was designed to address the heat dissipation associated with the detector assemblies while preserving optical stability. A solution based on localized heat extraction, pyrolytic graphite thermal straps, a common cold plate and conventional heat-pipe technology was selected. Dedicated thermal shielding and Multi-Layer Insulation (MLI) were additionally introduced to reduce environmental radiative disturbances and improve thermal stability. To support the design process, dedicated thermal and structural mathematical models were developed. The thermal behaviour of the MCA was investigated through an ESATAN-TMS Lumped Parameter Thermal Model, while the structural response was evaluated through a Nastran-based Finite Element Model. These models enabled the assessment of thermal distributions, heat-transfer paths, structural integrity, modal be haviour and thermo-elastic performance under representative operational and environmental conditions. The analyses demonstrated that the selected architecture satisfies the preliminary requirements allocated to the subsystem. The thermal assessments confirmed the effect tiveness of the thermal-control concept and highlighted the importance of minimizing thermal gradients to preserve optical alignment. The structural analyses showed adequate stiffness levels, satisfactory load-transfer characteristics and acceptable thermos-elastic behaviour, while the verification activities confirmed the numerical robustness and physical representativeness of the developed models. The results obtained throughout this work establish a technically coherent and analytically supported baseline for the MCA development. More generally, the thesis demonstrates the importance of adopting an integrated multidisciplinary approach in the design of modern spaceborne optical instruments, where optical, thermal and structural disciplines are strongly coupled and must be addressed simultaneously to achieve the required scientific performance. The developed architecture and associated engineering methodology provide a solid foundation for the subsequent phases of the LUCE programme and contribute to the realization of a new generation of space LIDAR instruments dedicated to the observation of the coupled atmosphere–ocean–land system.