Dissertations / Theses on the topic 'Very Large Telescope Interferometer'

PRIMA, un futur instrument du VLTI, utilise un système de métrologie laser pour mesurer les variations de chemin optique internes à l’interféromètre. L’étude présentée dans ce mémoire porte sur le développement, l’intégration et le test de sources lasers stabilisées en fréquence pour ce système de métrologie. Dans une première partie, nous présentons le cahier des charges du système dans le contexte de PRIMA et du VLTI. Nous rappelons les bases de l’interférométrie laser et les problèmes qu’impose son application à PRIMA. Nous en déduisons la nécessité de stabiliser la longueur d’onde du laser sur une référence absolue et exposons l’intérêt de transformer ce système en un système de mesure de distances absolues. Dans une seconde partie, nous décrivons notre contribution à la stabilisation en fréquence d’un laser Nd:YAG sur une raie d’absorption de l’iode. Nous mesurons précisément les performances du système avec un peigne de fréquences optiques auto-référencé. Nous améliorons le système pour satisfaire aux exigences du cahier des charges. La troisième partie est consacrée à la transformation du système en un système de mesure de distances absolues par l’utilisation de l’interférométrie à deux longueurs d’onde. Nous proposons un nouveau concept de source laser qui utilise un peigne de fréquences optiques comme référence de fréquence. Cette source permet de générer un choix sans précédent de longueurs d’onde synthétiques avec une précision relative dans le vide meilleure que 10−11. Nous validons le concept sur un prototype et montrons qu’il peut être utilisé en interférométrie à deux longueurs d’onde pour résoudre une longueur d’onde optique
The forthcoming instrument of the Very Large Telescope Interferometer (VLTI), called Phase-Referenced Imaging and Micro-arcsecond Astrometry facility (PRIMA), uses a laser metrology system to monitor the variations of internal path lengths. This dissertation addresses the development, integration and test of frequency stabilized laser sources for the PRIMA Metrology system (PRIMET). In the first part, we present in the context of PRIMA and the VLTI the specifications of PRIMET. We recall the basics of single-wavelength laser interferometry and introduce the problems raised by its application to PRIMET. We present the need for the absolute frequency stabilization of PRIMET laser and the interest for an upgrade of PRIMET towards absolute distance measurements. In the second part, we present our contribution to the absolute frequency stabilization of PRIMET Nd:YAG laser on a transition of iodine. We characterize the system and measure precisely its performance with a self-referenced optical frequency comb. We improve the system to reach the specifications in terms of accuracy and stability of the locking frequency. The third part addresses the upgrade of PRIMET towards absolute distance measurements by the use of two-wavelength interferometry. We propose a new concept of two-wavelength laser source frequency stabilized on an optical frequency comb. This permits the generation of an unprecedented large choice of synthetic wavelength with a relative accuracy better than 10−11 in vacuum. We validate the concept on a prototype and shows that it can be used to resolve an optical wavelength. Finally, we propose to apply this concept to the upgrade of PRIMET

Une etude theorique des grandes deformations elastiques, c'est-a-dire dont l'amplitude est superieure a l'epaisseur de la piece deformee, a ete entreprise dans le cadre de l'optique active afin d'accroitre les possibilites d'utilisation de cette technique. Cette etude prend en compte les deformations de la surface mediane d'un miroir soumis a une charge ou une force centrale, ainsi que les contraintes associees. La resolution numerique des equations d'equilibre d'un tel miroir nous a notamment permis de determiner la limite de validite de la theorie des faibles deformations. Un code de calcul specifique a ete elabore afin de calculer la distribution d'epaisseur d'un miroir permettant d'engendrer une deformation particuliere. Les profils necessaires a l'obtention d'une flexion purement parabolique ont ainsi ete determines dans deux cas de charges exterieures. De tels miroirs a courbure fortement variable, pouvant passer de la forme plane a des rapports d'ouverture de l'ordre de f/2, sont le seul moyen pratique de compenser le champ des futurs interferometres geants tels que le very large telescope interferometer. Ils constituent le cur meme des lignes a retard a il de chat, leur rayon de courbure variant continument pendant le deplacement du systeme. Du fait de la grande flexibilite demandee, les alliages metalliques a la fois tres lineaires et de haute limite elastique sont les seuls materiaux utilisables. La realisation de ces miroirs a courbure variable en acier inoxydable est abordee en detail, ainsi que les resultats des premiers tests de qualification d'un prototype. La comparaison entre la phase experimentale et les predictions theoriques nous permet ainsi de valider le modele numerique utilise

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada
The necessity of supplying precise time information in large telemetry ground stations and astronomical observatories is very similar. Therefore the way of solving this problem as it is done in the Very Large Telescope of the European Southern Observatory can be easily adopted to telemetry stations and ranges, especially when fiber optics are used. The European Southern Observatory (ESO) is building a new observatory in Chile for the Very Large Telescope (VLT). This VLT consists of 4 telescopes, each of them has a primary mirror diameter of 8 meters. the control architecture is based on workstations and VMEbus computers. The VMEbus computers are distributed over the whole building and are using real time operating system. Since the availability of the Global Positioning System (GPS) the generation of highly accurate timing signals on remote locations without the use of expensive Cesium standards does not create problems any more. However, distribution of a timing signal to many computer with high accuracy is an issue. The accuracy of the commonly used IRIG B-code is not adequate if the requirements are in the 10 microseconds range. This paper presents the design of a timing system that is adopted to the VLT. An overview of the requirements of the Time Reference System (TRS) is given. These requirements have been defined on the basis of experiences with the timing system of the ESO NTT telescope. The hardware units are described. These are a Central Time Standard, a Time Distribution System and a VME Time Interface Module. The distribution is based on fiber optic transmission, using a simple digital modulation that outperforms the analog IRIG B modulation. The Time Interface Module in the computer does not only perform the timing signal decoding but contains also user-programmable timers that are synchronously clocked from the time source. Presently all units of the TRS have been tested and the series production of the distribution and the Time Interface Modules are in progress.

Installé au cœur de l'interféromètre du Very Large Telescope (le VLTI, situé au sommet du Mont Paranal, dans le nord du Chili), l'instrument VINCI permet de recombiner la lumière infrarouge de deux télescopes séparés de manière cohérente. Il ouvre ainsi un accès vers la très haute résolution angulaire (quelques millisecondes d'angle), et des programmes de recherche novateurs dans des domaines aussi divers que la physique stellaire, les disques protoplanétaires ou bien encore l'étude des exoplanètes. Mon travail de thèse sur l'instrument VINCI a porté sur sa conception, en particulier la définition fonctionnelle de son logiciel d'exploitation, son installation au sommet du Mont Paranal et ses premières observations scientifiques. Le principe de fonctionnement et les performances de cet instrument sont décrits dans la première partie de ce document.
Dans une seconde partie, j'aborde l'étude des étoiles variables Céphéides par interférométrie. Ces étoiles pulsantes jouent un rôle primordial dans l'estimation des distances astronomiques depuis qu'il a été établi que leur période de variation était liée à leur luminosité intrinsèque par la célèbre relation période-luminosité. Leur observation photométrique permet donc de calculer directement leur distance. Toutefois, notre connaissance du point zéro de cette relation est encore imparfaite, car elle repose sur la mesure des distances aux Céphéides galactiques les plus proches, encore mal connues. La très haute résolution angulaire apportée par l'instrument VINCI et le VLTI permettra bientôt l'étude fine de la pulsation de ces étoiles. Par la mesure simultanée de la vitesse radiale de pulsation et de la variation du diamètre angulaire de l'étoile, il sera possible de calculer directement la distance aux Céphéides les plus proches, et donc d'étalonner la relation période-luminosité. L'enjeu de ce programme : la calibration de cette relation avec une précision de 0,01 magnitude, soit un gain d'un facteur dix par rapport à notre connaissance actuelle.
Au-delà de ce programme fondamental, je décris également les possibilités offertes par VINCI dans le domaine de l'étude des étoiles naines de la séquence principale, notamment de type solaire (avec application au couple d'étoiles Alpha Centauri A et B), et j'aborde brièvement l'étude des exoplanètes.

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 mu m). In this paper, we focus on the mid-infrared (8-13 mu m) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star beta Leo. This is equivalent to an exozodiacal disk density of 15-30. zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.

A large multi-aperture telescope has the potential to reach the diffraction limit corresponding to its baseline. To do so, Adaptive Optics (AO) and beam combination are critical to good performance. Operation as an interferometer is a complicated mode for the telescope. The system now has much tighter tolerances and is difficult to align. The alignment process needs to be planned in multiple steps, and tolerance and sensitivity analysis needs to be performed for each step. Alignment tools can be prepared based on the resolution found in the sensitivity analysis in each step.

Random fluctuation is another critical factor that reduces system performance. If noise sources near the telescope are characterized and identified, image quality can be improved by post-image processing.

Measuring the outer scale of atmosphere is also helpful for understanding the system performance. The fringe tracking method in the Large Binocular Telescope Interferometer (LBTI) system provides optical path difference (OPD) variation, and the power spectral density of the OPD variation is used to estimate the size of the outer scale. However, this method is limited by the baseline of the LBTI by 5[special characters omitted] B, where B is the baseline, and by this equation the outer scale size which is able to be estimated should be more than 125 m.

AO simulation can provide an understanding of new AO system concepts and parameter variations before they are applied to the real system. In this dissertation study, we simulated an LBTI system with structural vibration of 10 Hz and 20 Hz and with various amplitudes. From the simulation, we learned that the slower bandwidth of piston-correcting systems allows stars as faint as ~13^the magnitude to be observed. If there is significant vibration on the structure, the increased bandwidth will limit the phasing stars to 10~11^th magnitudes. This demonstrates the limits of the LBTI system regarding structural vibration.

An alternative phasing sensor for the LBTI system, the pseudo phasing sensor, can be used for more than 1000 m of outer scale of atmosphere. If the direct phasing sensor embedded in the LBTI system cannot be used for a very faint star, the pseudo phasing sensor, which approximately estimates the phase difference by AO wavefront sensor, can be useful for atmospheric conditions with estimated outer scale of about 1000 m.

The analyses in this dissertation provide a partial guide for developing large-scale telescopes and astronomical instruments.

Au cours de la dernière décade, la course aux grands et très grands télescopes a été accompagnée d'une augmentation non seulement de la taille et de la complexité des projets instrumentaux en astrophysique, mais aussi des exigences sur les performances des instruments. Cette combinaison de complexité et d'exigences accrues rend de plus en plus nécessaire le développement de modèles sophistiqués pour ces instruments. Ce mémoire de thèse présente le modèle numérique développé au Centre de Recherche Astronomique de Lyon (CRAL) pour simuler l'instrument MUSE. Cet instrument est un spectrographe intégral de champ pour les grands télescopes européens du VLT, en cours de réalisation par le CRAL. Ce modèle intègre l’ensemble de la chaîne d’acquisition, depuis l'atmosphère et le télescope jusqu'aux détecteurs inclus. Il prend en compte les aberrations optiques et les effets de la diffraction, en propageant un front d'onde à travers l'instrument selon le concept de l'optique de Fourier. Cette présentation du logiciel est accompagnée d'une discussion des difficultés rencontrées et des moyens mis en oeuvre pour les résoudre. Elle est suivie par des exemples de simulations et d'utilisations de ce logiciel pour étudier les performances attendues de l'instrument. En parallèle au travail de modélisation décrit ci-dessus, ce travail de thèse a aussi porté sur l'adaptation du logiciel de gestion documentaire du projet MUSE pour permettre son utilisation dans un environnement de travail UNIX. Ce travail est aussi décrit dans ce mémoire
During the last ten years, the race to the large and very large telescopes has been associated with an increase of the size and the complexity of instrumental projects in astrophysics, and of their performance requirements. This combination of complexity and increased requirements encourages the development of sophisticated models for these instruments. This dissertation presents the numerical model developed at the Centre de Recherche Astronomique de Lyon (CRAL) to simulate the MUSE instrument. This instrument, currently being built at CRAL, is an integral field spectrograph which will be installed on one of the large European telescopes of the VLT. This model integrates the whole chain of acquisition from the atmosphere to the telescope and including the detectors. It takes into account both optical aberrations and diffraction effects, by propagating a wavefront through the instrument, according to the Fourier optics concept. The description of the software is associated with a discussion of the problems that have been encountered and the solutions that have been implemented. It is followed by examples of simulations and use cases of the software to study the performances of the instrument. In parallel to the modeling work described above, the product data management software used in the MUSE project has been adapted to the UNIX environment. This work is also described in this dissertation

The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 microns). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the new sensing approach that has been developed at the LBT to measure and monitor the optical path length fluctuations due to dry air and water vapor separately. After reviewing the current performance of the system for dry air seeing compensation, we present simultaneous H-, K-, and N-band observations that illustrate the feasibility of our feedforward approach to stabilize the path length fluctuations seen by the LBTI nuller.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada
The Hubble Space Telescope (HST) Observatory Management System (HSTOMS), located at the Goddard Space Flight Center (GSFC), provides telemetry, command, analysis and mission planning functions in support of the HST spacecraft. The Telemetry and Command System (TAC) is an aging system that performs National Aeronautics and Space Administration (NASA) Communications (Nascom) block and telemetry processing functions. Future maintainability is of concern because of the criticality of this system element. HSTOMS has embarked on replacing the TAC by using functional elements developed by the Microelectronics Systems Branch of the GSFC. This project, known as the Transportable TAC (TTAC) because of its inherent flexibility, is addressing challenges that have resulted from applying recent technological advances into an existing operational environment. Besides presenting a brief overview of the original TAC and the new TTAC, this paper also describes the challenges faced and the approach to overcoming them.

Aujourd’hui, plus de 1800 planètes qui orbitent autour d’étoiles en dehors du système solaire ont été découvertes. La plupart des planètes découvertes actuellement a été révélée grâce aux méthodes indirectes. Par contre, avec ce type de techniques, la caractérisation des planètes ne peut pas être complète si on n’utilise pas plusieurs techniques simultanément. Aussi, pour obtenir le spectre de la planète, il doit y avoir un transit et même dans ce cas là,le signal est très faible par rapport au signal de l’étoile. L’observation directe de ces objets, appellée imagerie directe, est maintenant possible grâce à des systèmes très avancés d’optique adaptative installés sur des télescopes de classe 8m. L’imagerie directe permet l’observation des planètes sufisamment lumineuses et éloignées de l’étoile principale en utilisant un masque qui cache la lumière de la dernière. Cette technique est donc efficace en particulier pour des systèmes jeunes et voisins car la luminosité intrinsèque de la planète diminue avec l’âge et la séparation réelle de la planète dépend de la distance du système. Dans le VLT au Paranal (Chili), deux instruments sont dédiés à ce type de recherche : NACO et SPHERE. SPHERE a vu sa première lumière en Mai 2014, et est maintenant prêt à commencer une enquête consacrée à la découverte de planètes autour de systèmes jeunes et voisins, NIRSUR. Cet instrument se compose de trois sous-systèmes : IRDIS, IFS et ZIMPOL
In the year of the 20th anniversary of the discovery of the first extrasolar planet we can count more than 1800 companions found with different techniques. The majority of them are indirect methods that infer the presence of an orbiting body by observing the parent star (radial velocity, transits, astrometry). In this work we explore the technique that permits to directly observe planets and retrieve their spectra, under the conditions that they are bright and far enough from their host star. Direct imaging is a new technique became possible thanks to a new generation of extreme adaptive optics instruments mounted on 8m class telescopes. On the Very Large Telescope two instruments dedicated to the research for exoplanets with direct imaging are now operative: NACO and SPHERE. This thesis will describe the development and results of SPHERE from its predecessor NACO to its integration in laboratory and the final on sky results

La nouvelle generation de telescopes de huit metres de diametre et plus (keck telescope, gemini, subaru, very large telescope) ne vient pas sans de nouveaux instruments acceptant la grande etendue geometrique des plans focaux et adaptes a l'utilisation des detecteurs ccd grand format actuels. Parmi ces instruments, les spectrographes multiobjets capables d'enregistrer simultanement les spectres de plusieurs dizaines d'objets sont des instruments de choix pour rentabiliser le temps d'observation. Fuegos est un spectrographe astronomique, alimente par fibres optiques, multiobjets et haute resolution pour un des telescopes de huit metres de l'eso. Cet instrument doit permettre l'observation spectroscopique simultanee de 80 a 100 objets distincts avec une resolution spectrale de 30 000 environ. Pour combiner le multiplexage d'un grand nombre d'objets avec la haute resolution spectrale, deux concepts instrumentaux bases sur des architectures et des strategies differentes, ont ete etudies. L'un optimise la collection d'information au detriment de l'efficacite lumineuse et l'autre reciproquement privilegiera la transmission vis a vis du nombre d'objets. Une comparaison detaillee des performances de chaque solution est faite. En plus de la possibilite de collecter le flux en differents points du champ du telescope, les fibres optiques permettent de lisser les fluctuations photometriques du barycentre des raies spectrales rendant possible la mesure de decalages doppler-fizeau de tres faible amplitude. Pour ameliorer encore cette stabilite spectrale, il a ete suggere que l'emploi de microlentilles en entree et sortie de fibre permette de gagner en precision sur la mesure de la position du barycentre des raies spectrales. Un banc de test a donc ete mis en uvre pour evaluer la stabilite photometrique de differents systemes de liaisons par fibres optiques

In this thesis, I present the properties of IRAS 19306+1407 central source and its sur- rounding circumstellar envelope (CSE), from the analysis of near-infrared (near-IR) polarimetry and integral field spectroscopy (IFS), with supporting archived HST im- ages and sub-millimetre (sub-mm) photometry. This is supported by axi-symmetric light scattering (ALS), axi-symmetric radiative transfer (DART) and molecular hy-drogen (H2) shock models. The polarimetric images show that IRAS 19306+1407 has a dusty torus, which deviates from axisymmetry and exhibits a ‘twist’ feature. The DART and ALS modelling shows that the CSE consists of Oxygen-rich sub-micrometre dust grains, with a range in temperature from 130±30 to 40±20 K at the inner and outer radius, respectively, with inner and outer radii of 1.9±0.1×1014 and 2.7±0.1×1015 m. The CSE detached 400±10 years ago and the mass loss lasted 5700±160 years, assuming a constant asymptotic giant branch (AGB) outflow speed of 15 km s−1. The dust mass and total mass of the CSE is 8.9±5×10−4 and 1.8±1.0×10 −1 M⊙, assuming a gas-to-dust ratio of 200. The mass loss rate was 3.4±2.1×10−5 M⊙ year−1. The central source is consistent with a B1I-type star with a radius of 3.8 ± 0.6 R⊙, luminosity of 4500 ± 340 L⊙ at a distance of 2.7 ± 0.1 kpc. A purpose built idl package (fus) was developed and used in the SINFONI IFS data critical final reduction steps. It also produced emission line, kinematic and line ratio images. The IFS observations show that H2 is detected throughout the CSE, located in bright arcs and in the bipolar lobes. The velocity of the H2 is greatest at the end of the lobes. Brγ emission originates from, or close, to the central source – produced by a fast jump (J) shock or photo-ionised atomic gas. The 1-0 S(1)/2- 1 S(1) and 1-0 S(1)/3-2 S(3) ratios were used as a diagnostic and determined that H2 was excited by bow shaped shocks; however, these shock models could not wholly explain the observed rotational and vibrational temperatures. The CDR values were fitted by combining continuous (C) or J-bow shock and fluorescence models, with a contribution from the latter, observed throughout the CSE (5–77 per cent). The majority of shock can be described by a C-bow shock model with B = 0.02 to 1.28 mG. Shocks are predominately seen in the equatorial regions. Polarimetry and IFS highlight a ‘twist’ feature, which could be due to an episodic jet undergoing a recent change in the outflow direction. The sub-arcsecond IFS observations reveal a flocculent structure in the south- east bright arc, consisting of several clumps interpreted as a fast-wind eroding an equatorial torus, possibly forming H2 knots seen in (some) evolved planetary nebulae (PNe). My analysis has effectively constrained the following: spectral type, stellar radius, luminosity and distance, chemistry, dust grain properties, geometry, age, mass loss, excitation mechanism and evolutionary state of the post-AGB star and its surrounding CSE. I conclude that IRAS 19306+1407 is a post-AGB object on the verge becoming a PN.

Thesis (PhD)--Stellenbosch University, 2015.
AFRIKAANSE OPSOMMING : Die vierkantkilometer-radioteleskoop SKA (―Square Kilometre Array‖) sal na verwagting die grootste teleskoop op aarde en die grootste wetenskapprojek in Afrika wees. Hierdie verhandeling konsentreer op hoe die SKA vanaf September 2011 tot Augustus 2012 in die Suid-Afrikaanse media uitgebeeld is. Dit handel oor die leemtes in die literatuur oor wetenskapkommunikasie, veral wat betref wetenskapkommunikasie in Afrikaverband. Deur uit massa- en wetenskapkommunikasieteorie te put, modelleer die studie kommunikasieprosesse en -uitsette met behulp van ‘n konseptuele raamwerk wat op die gedagte van die openbare sfeer berus. Die navorsing word in die besonder onderstut deur onderhoude met sleutelinformante en die ontleding van nuus- en sosiale media. Die wetenskapkommunikasie oor die SKA gedurende hierdie tydperk was stelselmatig gekenmerk deur ‘n hoë vlak van koördinasie tussen die aansporings, strategieë en strukture van alle hoofrolspelers oor die kommunikasiestelsel heen. Al die hoofrolspelers buite die media het die SKA op so ‘n manier in die openbare sfeer probeer uitbeeld dat dit openbare steun sou werf. Primêre hekwagterfunksies is aan die voorste SKA-organisasie- en openbaresektor-rolspelers toegewys, maar was verder afgewentel binne universiteite. Hekwagterfunksies in die media is hoofsaaklik deur nuuswaarde sowel as institusionele kultuur en organisatoriese kenmerke bepaal. Verhoudings tussen wetenskaplikes en joernaliste was oënskynlik oor die algemeen positief en gegrond op vertroue. Die beduidendste bron van inligting vir joernaliste was die SKA self, gevolg deur rolspelers in die openbare sektor. Tog is ander rolspelers, bepaald plaaslike belanghebbendes, gemarginaliseer. Die Afrikaanstalige media het veral onder plaaslike gemeenskappe ‘n belangrike rol gespeel en het meer dikwels as ander oor die SKA berig. Die sosiale media het die SKA merendeels op ‘n soortgelyke wyse as die nuusmedia hanteer, maar die struktuur van kommunikasie-uitsette is beïnvloed deur die kenmerkende eienskappe van sosiale media self, waaronder die virale verspreiding van boodskappe en hoër vlakke van vryewilsoptrede (―agency‖) deur individuele rolspelers. Tog was daar aanduidings van beduidende media-integrasie, in die sin dat groot Suid-Afrikaanse mediahuise die bron was van die meeste boodskappe in sowel die nuus- as sosiale media.
ENGLISH ABSTRACT : The Square Kilometre Array (SKA) radio telescope is set to become the largest telescope on Earth, and also the largest science project in Africa. This dissertation focuses on the manner in which the SKA was represented in the South African media from September 2011 to August 2012. This addresses gaps in the literature on science communication, particularly with respect to science communication in an African context. By drawing on mass communication theory and science communication theory, it models communication processes and outputs using a conceptual framework based on the notion of the public sphere. Empirically, the study is underpinned by key informant interviews and the analysis of news media and social media content. Systemically, the science communication of the SKA during this period was characterized by a high level of alignment of incentives, strategies, and structures across the main actors in the communication system. Main actors outside the media all aimed to position the SKA in the public sphere in a manner that would grow public support. Primary gatekeeping functions were positioned at the apex of the SKA organisation and public sector actors, but were more devolved within universities. Gatekeeping in the media was primarily driven by news value, as well as institutional culture and organisational attributes. Relationships between scientists and journalists were found to be generally positive and trust-based. The most significant source of information for journalists was the SKA itself, followed by public sector actors. However, other actors were marginalized, particularly local stakeholders. The Afrikaans language media played an important role, particularly among local communities, and published about the SKA relatively more often. The social media represented the SKA in a broadly similar manner to the news media, but the structure of communication outputs was influenced by the distinct attributes of the social media, including the viral propagation of messages and higher levels of agency by individual actors. However, there were indications of substantial media integration, in that major South African media corporations were the source of the majority of messages in both the news and social media. The tone of media outputs was largely neutral or positive, framing the SKA as a 'good news story‘. The overarching dominant frame for representing the SKA was the site allocation process, in which South Africa and Australia competed in a bid to host the telescope for the international SKA consortium. Science and technology aspects of the project constituted the second most common framing, within which the search for extra-terrestrial intelligence was the most commonly represented research question. Representations of technological aspects of the SKA were generally shallow, with most articles mentioning only one aspect of the project‘s technology. The SKA was also constructed as a symbol, representing an instance of African scientific and technological achievement, African participation in globalized science, and a refutation of Afro-pessimism. The impact of the SKA on the public imagination, and the public sphere, was thus clearly far wider and deeper than only its science and technology accomplishments and contributions.

The goal of the very large optical telescope (VLOT) project is to design and construct a 20 m segmented mirror telescope, which will surpass the limits of the current generation of telescopes. This significant expansion of the telescope's geometry will present many design and fabrication challenges simply through its sheer size of the structure and demand for fine accuracy. The telescope enclosure is a crucial component of the VLOT project; its feasibility will have a great effect in whether or not a project of this magnitude will ever see the light of day. The aim of this thesis is to determine an optimal enclosure design for the VLOT by comparing previous designs along with newer, innovative designs. A thorough investigation will be performed by an in-depth examination of available research material, conceptual designs, structural analysis and decision analysis. A review of telescopes as they have developed through out history will be conducted to illustrate the significance of VLOT's influence on the future of astronomy. Moreover, by collecting information on current design cases and ideas regarding telescope enclosures, an information database of enclosure designs will be prepared, providing valuable references for the VLOT enclosure development. Conceptual deigns of various types of potential VLOT enclosures are examined in this thesis. The telescope enclosure designs will be primarily based on structural safety and serviceability performance criteria. Furthermore, a finite element analysis will provide valuable insight into each enclosure design explored. Characteristics of enclosure designs are compared from various perspectives. With respect to the comparative analysis results, a comprehensive decision analysis will be used to determine the final optimal solution. The work within this thesis will provide academic and engineering references for the further development of the VLOT project.