Mars is universally acknowledged as an exceptionally dusty planet. Its harsh landmass is continuously swept by the action of colossal dust storms that progressively carved Martian surface, producing vast desert plateaus, jagged ridges and hostile landscapes. Furthermore, strongly radiatively active fines injected in atmosphere by aeolian processes interfere with the planetary meteorology, shielding Mars in planet - encircling phenomena influencing globally the climate. Despite understanding dust cycle mechanisms is essential for refining existing models concerning climatology, lithology and geological chronicle of the Red Planet, most of the knowledge has been acquired through remote sensing via orbiters. MicroMED, selected for the ESA’s ExoMars 2020 mission to complete the Dust Suite (Humboldt Payload on board the Kazachok lander), will exert in situ laser scattering technique aimed to characterize size and distribution of aerosol dust at Martian lowest troposphere, target never addressed yet. MicroMED instrument encompasses a selection of space - qualified and designed components and subsystems to perform dust analysis on Mars. The main part of the instrument is the optical bench, whose design and performances have been investigated in previous studies. In this thesis, different design alternatives have been probed in order to cope with modification of the optical group devoted to the generation of the laser beam and its collimation into the optical fibre. The latter group is an off - the - shelf component and is a modified version of the original one, with less mass and size, therefore providing the possibility to improve MicroMED performances, both in terms of mass budget and mechanical stiffness. The design has been performed by means of FE approach, developing different models to fulfil the design requirements in terms of mechanical resistance within expected mechanical and thermal environments and modal behaviour. Firstly, the accommodation of the new optical group has been evaluated on the current optical bench through thermal, modal and quasi - static FE analyses. Then, main activity has been the study of two optimized solutions aiming to improve the dynamic performances and to minimize the mass of the optical bench. Moreover, a comparison between the obtained solutions and outcome from topology optimization has been presented. Finally, in order to verify the feasibility of the new optical group, a testing activity in thermal vacuum environment has been initiated, laying the bases proving the performances of the original optical group. An experimental setup arranged to measure the optical misalignment and the beam power within the operative temperature range has been designed and implemented effectively for measuring the power of a MicroMED optical group mock - up.
Marte è universalmente riconosciuto come un pianeta eccezionalmente polveroso. Le sue terre aspre sono incessantemente spazzate dall'azione di gigantesche tempeste di sabbia, che hanno progressivamente plasmato la superficie marziana generando vasti altipiani desertici, promontori frastagliati e panorami ostili. Inoltre, le fini polveri iniettate in atmosfera dai fenomeni ventosi hanno proprietà radiative tali da influire sulla meteorologia di Marte, causando eventi globali con rilevanti effetti sul clima. Nonostante la comprensione del dust cycle (iniezione, trasporto e deposizione di polveri) sia essenziale ai fini di migliorare i modelli esistenti riguardanti climatologia, litologia e geologia del Pianeta Rosso, gran parte dei dati a disposizione sono stati acquisiti via telerilevamento. MicroMED è stato selezionato per la missione ESA ExoMars 2020, a completamento della gamma di strumenti assegnati alla Dust Suite (a bordo del lander Kazachok, nel gruppo Humboldt Payload) e impiegherà tecniche di diffusione laser in loco volte a caratterizzare per la prima volta la dimensione e la distribuzione di polveri dell'aerosol marziano nella bassa troposfera. A tale scopo, MicroMED prevede una selezione di componenti progettati e qualificati per applicazioni spaziali, incluso un banco ottico il cui progetto e performances sono state argomento di molteplici precedenti studi. Nella tesi in oggetto sono state indagate diverse proposte alternative di banco ottico, volte a far fronte ad una modifica preliminare effettuata sul gruppo ottico, apparato dedicato alla generazione del fascio laser e collimazione nella fibra ottica. In particolare, il nuovo gruppo ottico garantisce leggerezza e minor ingombro, offrendo la possibilità di migliorare le performances di MicroMED in termini di massa e rigidezza meccanica. La progettazione delle alternative è stata portata avanti secondo un approccio FEM, sviluppando diversi modelli atti a soddisfare i vincoli di resistenza meccanica (sottoponendo il banco a sollecitazioni meccaniche e termiche) e di comportamento modale. Inizialmente sono stati valutati gli effetti previa implementazione del nuovo gruppo ottico nel banco, soggetto ad analisi FEM. Successivamente è stato condotto lo studio su due soluzioni ottimali volte rispettivamente a massimizzare le performances dinamiche del banco e minimizzare la massa dedicata allo stesso. Le soluzioni sono entrambe accompagnate da proposte equivalenti ottenute mediante ottimizzazione topologica. Per concludere, ai fini di verificare la fattibilità del nuovo gruppo ottico, un'attività di test in condizioni di termo - vuoto è stata avviata, gettandone le basi attestando le performances del gruppo ottico originale. Un setup sperimentale, predisposto per misurare il disallineamento ottico e la potenza del fascio nel range operativo di temperature, è stato progettato e implementato in maniera efficace per la verifica della potenza su un mock - up del gruppo ottico di MicroMED.
Optimal structural design of the MicroMED dust analyzer
CORTI, MARCO GIOVANNI
2019/2020
Abstract
Mars is universally acknowledged as an exceptionally dusty planet. Its harsh landmass is continuously swept by the action of colossal dust storms that progressively carved Martian surface, producing vast desert plateaus, jagged ridges and hostile landscapes. Furthermore, strongly radiatively active fines injected in atmosphere by aeolian processes interfere with the planetary meteorology, shielding Mars in planet - encircling phenomena influencing globally the climate. Despite understanding dust cycle mechanisms is essential for refining existing models concerning climatology, lithology and geological chronicle of the Red Planet, most of the knowledge has been acquired through remote sensing via orbiters. MicroMED, selected for the ESA’s ExoMars 2020 mission to complete the Dust Suite (Humboldt Payload on board the Kazachok lander), will exert in situ laser scattering technique aimed to characterize size and distribution of aerosol dust at Martian lowest troposphere, target never addressed yet. MicroMED instrument encompasses a selection of space - qualified and designed components and subsystems to perform dust analysis on Mars. The main part of the instrument is the optical bench, whose design and performances have been investigated in previous studies. In this thesis, different design alternatives have been probed in order to cope with modification of the optical group devoted to the generation of the laser beam and its collimation into the optical fibre. The latter group is an off - the - shelf component and is a modified version of the original one, with less mass and size, therefore providing the possibility to improve MicroMED performances, both in terms of mass budget and mechanical stiffness. The design has been performed by means of FE approach, developing different models to fulfil the design requirements in terms of mechanical resistance within expected mechanical and thermal environments and modal behaviour. Firstly, the accommodation of the new optical group has been evaluated on the current optical bench through thermal, modal and quasi - static FE analyses. Then, main activity has been the study of two optimized solutions aiming to improve the dynamic performances and to minimize the mass of the optical bench. Moreover, a comparison between the obtained solutions and outcome from topology optimization has been presented. Finally, in order to verify the feasibility of the new optical group, a testing activity in thermal vacuum environment has been initiated, laying the bases proving the performances of the original optical group. An experimental setup arranged to measure the optical misalignment and the beam power within the operative temperature range has been designed and implemented effectively for measuring the power of a MicroMED optical group mock - up.| File | Dimensione | Formato | |
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Optimal structural design of the MicroMED dust analyzer.pdf
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https://hdl.handle.net/10589/152757