Optomechanical design and analysis of a calibration unit for the ELT multi-conjugate adaptive optics system (MAORY)

This thesis, inserted in the frame of a technical effort which will be relevant for the advancement in Astronomy, Astrophysics and Space Science, reports the main activities concerning the preliminary design and analysis of the MAORY Calibration Unit. This subsystem will enable MAORY, the MCAO system of ELT (the biggest telescope ever built), to run calibration templates as well as verification and test procedures, independently from other activities carried at the telescope. Its design reveals very challenging, for both optical and mechanical reasons: the high focus and pupil quality, joined with the tight mass and volume budgets, as well as the large number of sources of different wavelengths and fluxes, make the Calibration Unit an innovative and rather complex instrument. The present work is organized in five chapters. Chapter 1 gives an overview of Adaptive Optics, with particular attention to Multi-Conjugate Adaptive Optics. After an historical background, the main atmospheric parameters affecting the observations are presented. The AO groundwork is then described, with its main actors, followed by an overview of the AO current technologies. Finally, various scientific applications of AO are presented. Chapter 2 gives an overview on the main calibrations in Adaptive Optics, in order to highlight their crucial role to obtain an optimal functioning and push over and over the performances of present and future AO systems. Chapter 3 is focused on the description of MAORY, the MCAO system of the ELT telescope. This innovative instrument represents a great technological challenge and is being designed and built by a consortium of partners in Italy (INAF is the lead Institute), France (IPAG) and Ireland (NUIG), together with ESO. MAORY is here described in its AO architecture, its subsystems and in terms of expected performances. Chapters 4 and 5 represent the core of this dissertation, summarizing my effort and my contribution to the project. Chapter 4 gives a full description of the Calibration Unit of MAORY, at the current level of development (Preliminary Design Review). Starting from the rationale and the requirements definition, the architecture of the instrument is presented, with subsequent detailed description of both optical and mechanical design and of the various subsystems. The definition of the requirements, that has taken quite a long time (the process is still ongoing) and required a joined effort of MAORY/ESO Calibration Team, MAORY System Engineers and Calibration Unit Team, was necessary to select the best ideas and turn them into a conceptual design. Two optical designs have been developed in parallel: a fully-refractive concept, carried on by myself with the support of other INAF researchers, and a catadioptric solution, carried on by an optical designer of NUIG with my support and chosen as baseline design after a preliminary trade-off. The mechanical design, sewn around the optical relay, is carried on by myself in collaboration with a mechanical designer of INAF-OAAb and the supervision of the rest of the Team. Chapter 5 is the natural extension of the previous chapter and shows all the analyses carried out on the Calibration Unit, necessary to validate the solutions chosen, as well as to understand their pro and cons. All the analyses have been carried on by myself, with the supervision of the rest of the Team.