Nanosatelliide kasutamine demonstratsioon- ja teadusmissioonidel

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKosmost on vaadeldud ja uuritud aastatuhandeid, kuid kosmosemissioonid lubasid seda esimest korda kohapeale uurima minna alles 64 aastat tagasi. Satelliidid võimaldavad teha toiminguid, mis maapealsete uuringutega on võimatud, näiteks maanduda teistele taevakehadele, tuua Maale neilt võetud proove vaadelda lähedalt komeete, ja asteroide ning saada paremaid vaatlusandmeid galaktikate, päikesesüsteemide, eksoplaneetide ja muude objektide kohta.. Ajalooliselt korraldasid kosmosemissioone suured riiklikud kosmoseagentuurid, kuid viimase 20 aasta jooksul on valdkond avanenud ka väikeettevõtetele, ülikoolidele ja pea kõigile teistele, kes on satelliidi kosmosesse saatmisest huvitatud. See on saanud võimalikuks tänu kuupsatelliitide standardiseerimisele. Tavaliselt peame kuupsatelliitide all silmas 1–10 kg nanosatelliite. Selle väitekirja autor on aidanud kaasa planeedimissioonide ja -instrumentide miniaturiseerimisele, töötades välja missioone ja missioonikontseptsioone ning arendades selliseid koormused ja simulatsioonivahendeid, mis aitaksid kaasa pikaajalisele eesmärgile uurida kosmost nanosatelliitidega. Lõputöö esimene osa keskendub uuenduslikule kosmosereiside tehnoloogiale: Coulomb Drag Propulsionile. Seda saab kasutada, et madalalt Maa orbiidilt kosmoseprügi eemaldada (plasmapidur) või kosmoses liikuda, kandmata Maalt kaasa võetud raketikütust (elektriline päiksepuri). Kõnealune tõukejõutehnoloogia on paigaldatud satelliitidele ESTCube-2 ja FORESAIL-1, mis peagi kosmosesse lennutatakse. Samuti analüüsib doktoritöö ideed külastada elektrilise päiksepurje juhitava kuupsatelliidilaevastikuga sadu asteroide. Lõputöö teises osas antakse ülevaade jätkuvast protsessist eesmärgiga arendada kaamera Euroopa Kosmoseagentuuri (ESA) ja Jaapani Kosmoseuuringute Agentuuri (JAXA) ellu viidavale Komeedipüüduri (Comet Interceptor) missioonile. Missiooni sondid viib 2029. aastal kosmosesse rakett Ariane 6. Kaamera on varustatud periskoobiga, et kaitsta seda ohtliku keskkonna eest, mistõttu kannab see nime Optical Periscopic Imager for Comets või OPIC. Nimi viitab ühtlasi Eesti astronoomile Ernst Öpikule, kes pakkus esimesena välja, et Päikesesüsteemi ümber asub kauge komeedipilv, mida tänapäeval tuntakse Öpiku–Oorti pilvena. OPIC-u väljatöötamist toetab spetsiaalselt selleks arendatud simulatsioonitööriist SISPO, mida kirjeldatakse doktoritöö viimases osas.Humans have been observing and exploring the cosmos for millennia, yet space missions enabled in-situ examination only during the last 64 years. Artificial satellites enable opportunities unfeasible for ground-based studies, such as landing on other planetary bodies, sample return, close observations of comets and asteroids, and improved observations of galaxies, solar systems, exoplanets, etc. Historically, space missions were operated by large space agencies, but in the last twenty years, the field expanded to small enterprises, universities and practically anyone interested in launching a satellite. This was partially enabled by the standardisation of cubesats, typically 1–10 kg nanosatellites. The author of this dissertation has contributed to the miniaturisation of planetary missions and instruments by developing missions, mission concepts, payloads and simulation tools that commit to the long-term aims of cosmic exploration with nanospacecraft. The first part of the thesis focuses on innovative technology for space travel – Coulomb Drag Propulsion. It can be utilised to remove space debris from Low Earth Orbit (named plasma brake) or travel in space without carrying the propellant from the Earth (named E-sail). This propulsion is accommodated on the ESTCube-2 and FORESAIL-1 satellites, to be launched soon. The dissertation also analyses the concept of visiting hundreds of asteroids with a fleet of cubesats driven by E-sail. The second part of the thesis presents an ongoing camera development for the ESA-JAXA Comet Interceptor mission to be launched in 2029 by the Ariane 6 rocket. The camera is equipped with a periscope to protect it from a hazardous environment. It is therefore named Optical Periscopic Imager for Comets or OPIC shortly, also referring to the Estonian astronomer Ernst Öpik, who was the first to propose the existence of a distant comet cloud around the Solar System, known today as the Öpik–Oort cloud. The development of the OPIC instrument is supported by a custom-made open-source simulation tool called SISPO, described in the last part.  https://www.ester.ee/record=b547253

Multiperspective mosaics and layered representation for scene visualization

This thesis documents the efforts made to implement multiperspective mosaicking for the purpose of mosaicking undervehicle and roadside sequences. For the undervehicle sequences, it is desired to create a large, high-resolution mosaic that may used to quickly inspect the entire scene shot by a camera making a single pass underneath the vehicle. Several constraints are placed on the video data, in order to facilitate the assumption that the entire scene in the sequence exists on a single plane. Therefore, a single mosaic is used to represent a single video sequence. Phase correlation is used to perform motion analysis in this case. For roadside video sequences, it is assumed that the scene is composed of several planar layers, as opposed to a single plane. Layer extraction techniques are implemented in order to perform this decomposition. Instead of using phase correlation to perform motion analysis, the Lucas-Kanade motion tracking algorithm is used in order to create dense motion maps. Using these motion maps, spatial support for each layer is determined based on a pre-initialized layer model. By separating the pixels in the scene into motion-specific layers, it is possible to sample each element in the scene correctly while performing multiperspective mosaicking. It is also possible to fill in many gaps in the mosaics caused by occlusions, hence creating more complete representations of the objects of interest. The results are several mosaics with each mosaic representing a single planar layer of the scene

Design of an endoscopic 3-D Particle-Tracking Velocimetry system and its application in flow measurements within a gravel layer

In this thesis a novel method for 3-D flow measurements within a permeable gravel layer is developed. Two fiberoptic endoscopes are used in a stereoscopic arrangement to acquire image sequences of the flow field within a single gravel pore. The images are processed by a 3-D Particle-Tracking Velocimetry (3-D PTV) algorithm, which yields the three-dimensional reconstruction of Lagrangian particle trajectories. The underlying image processing algorithms are significantly enhanced and adapted to the special conditions of endoscopic imagery. This includes methods for image preprocessing, robust camera calibration, image segmentation and particle-tracking. After a performance and accuracy analysis, the measurement technique is applied in extensive systematic investigations of the flow within a gravel layer in an experimental flume at the Federal Waterways Engineering and Research Institute in Karlsruhe. In addition to measurements of the pore flow within three gravel pores, an extended experimental setup enables the simultaneous observation of the near-bed 3-D flow field in the turbulent open-channel flow above the gravel layer and of grain motions in a sand layer beneath the gravel layer. The interaction of the free surface flow and the pore flow can be analyzed for the first time with a high temporal and spatial resolution. The experiments are part of a research project initiated by an international cooperation called Filter and Erosion Research Club (FERC). The longterm goal of this project is to quantify the influence of turbulent velocity and pressure fluctuations on the bed stability of waterways. The obtained experimental data provide new insight into the damping behaviour of a gravel bed and can be used for comparison with numerical, analytical and phenomenological models

Arcades as Intérieur: The Production of Distance in Sophie Calle and Janet Cardiff

The work of French artist Sophie Calle and the Canadian artist partnership Janet Cardiff and George Bures Miller localize this art critical consideration. My lens is Walter Benjamin’s writings on memory, trace, and narrative. Calle parlays her exercises in memorial site-reconstruction, and arbitrary assignments in tracking and detection through the deceptively descriptive media of photography and text. Her dubious construction of narrative, and the demands she makes on trust, result in a practice that requires both our romantic supplication and our skepticism. Cardiff and Miller similarly position their viewer/participants at the interstices of desire and doubt. Their work solicits memorial and sensorial vulnerability, such that we must give ourselves over in order to ‘complete’ the work. In the case of both Calle and Cardiff/Miller, histories are created in the here and now. Linking the distinctions Benjamin made between distance and trace and their intersection’s possibility for aura, I explore the auratic function of artwork that stresses process, produces distance and trace, and brings absence to experience

Meshfree Approximation Methods For Free-form Optical Surfaces With Applications To Head-worn Displays

Compact and lightweight optical designs achieving acceptable image quality, field of view, eye clearance, eyebox size, operating across the visible spectrum, are the key to the success of next generation head-worn displays. The first part of this thesis reports on the design, fabrication, and analysis of off-axis magnifier designs. The first design is catadioptric and consists of two elements. The lens utilizes a diffractive optical element and the mirror has a free-form surface described with an x-y polynomial. A comparison of color correction between doublets and single layer diffractive optical elements in an eyepiece as a function of eye clearance is provided to justify the use of a diffractive optical element. The dual-element design has an 8 mm diameter eyebox, 15 mm eye clearance, 20 degree diagonal full field, and is designed to operate across the visible spectrum between 450-650 nm. 20% MTF at the Nyquist frequency with less than 3% distortion has been achieved in the dual-element head-worn display. An ideal solution for a head-worn display would be a single free-form surface mirror design. A single surface mirror does not have dispersion; therefore, color correction is not required. A single surface mirror can be made see-through by machining the appropriate surface shape on the opposite side to form a zero power shell. The second design consists of a single off-axis free-form mirror described with an x-y polynomial, which achieves a 3 mm diameter exit pupil, 15 mm eye relief, and a 24 degree diagonal full field of view. The second design achieves 10% MTF at the Nyquist frequency set by the pixel spacing of the VGA microdisplay with less than 3% distortion. Both designs have been fabricated using diamond turning techniques. Finally, this thesis addresses the question of what is the optimal surface shape for a single mirror constrained in an off-axis magnifier configuration with multiple fields? Typical optical surfaces implemented in raytrace codes today are functions mapping two dimensional vectors to real numbers. The majority of optical designs to-date have relied on conic sections and polynomials as the functions of choice. The choice of conic sections is justified since conic sections are stigmatic surfaces under certain imaging geometries. The choice of polynomials from the point of view of surface description can be challenged. A polynomial surface description may link a designer s understanding of the wavefront aberrations and the surface description. The limitations of using multivariate polynomials are described by a theorem due to Mairhuber and Curtis from approximation theory. This thesis proposes and applies radial basis functions to represent free-form optical surfaces as an alternative to multivariate polynomials. We compare the polynomial descriptions to radial basis functions using the MTF criteria. The benefits of using radial basis functions for surface description are summarized in the context of specific head-worn displays. The benefits include, for example, the performance increase measured by the MTF, or the ability to increase the field of view or pupil size. Even though Zernike polynomials are a complete and orthogonal set of basis over the unit circle and they can be orthogonalized for rectangular or hexagonal pupils using Gram-Schmidt, taking practical considerations into account, such as optimization time and the maximum number of variables available in current raytrace codes, for the specific case of the single off-axis magnifier with a 3 mm pupil, 15 mm eye relief, 24 degree diagonal full field of view, we found the Gaussian radial basis functions to yield a 20% gain in the average MTF at 17 field points compared to a Zernike (using 66 terms) and an x-y polynomial up to and including 10th order. The linear combination of radial basis function representation is not limited to circular apertures. Visualization tools such as field map plots provided by nodal aberration theory have been applied during the analysis of the off-axis systems discussed in this thesis. Full-field displays are used to establish node locations within the field of view for the dual-element head-worn display. The judicious separation of the nodes along the x-direction in the field of view results in well-behaved MTF plots. This is in contrast to an expectation of achieving better performance through restoring symmetry via collapsing the nodes to yield field-quadratic astigmatism

Exploring the Visual Landscape: Advances in Physiognomic Landscape Research in the Netherlands

Exploring the Visual Landscape is about the combination of landscape research and planning, visual perception and Geographic Information Science. It showcases possible ways of getting a grip on themes like: landscape openness, cluttering of the rural landscape, high-rise buildings in relation to cityscape, historic landscapes and motorway panoramas. It offers clues for visual landscape assessment of spaces in cities, parks and rural areas. In that respect, it extends the long tradition in the Netherlands on physiognomic landscape research and shows the state of the art at this moment. Exploring the Visual Landscape offers important clues for theory, methodology and application in research and development of landscapes all over the world, from a specifically Dutch academic context. It provides a wide range of insights into the psychological background of landscape perception, the technical considerations of geomatics and methodology in landscape architecture, urban planning and design. Furthermore, there are some experiences worthwhile considering, which demonstrate how this research can be applied in the practice of landscape policy making

Response surface methods applied to submarine concept exploration

CIVINS (Civilian Institutions) Thesis documentIt is estimated that 70 to 85 percent of a naval ship's life-cycle cost is determined during the concept exploration phase which places an importance in the methodology used by the designer to select the concept design. But trade-off studies are guided primarily by past experience, rules-of-thumb, and designer preference. This approach is ad hoc, not efficient and may not lead to an optimum concept design. Even worse, once the designer has a 'good' concept design, he has no process or methodology to determine whether a better concept design is possible or not. A methodology is required to search the design space for an optimal solution based on the specified preferences from the customer. But the difficulty is the design space, which is non-linear, discontinuous, and bounded by a variety of constraints, goals, and thresholds. Then the design process itself is difficult to optimize because of the coupling among decomposed engineering disciplines and sub-system interactions. These attributes prevent application of mature optimization techniques including Lagrange multipliers, steepest ascent methods, linear programming, non-linear programming, and dynamic programming. To further improve submarine concept exploration, this thesis examines a statistical technique called Response Surface Methods (RSM). The purpose of RSM is to lead to an understanding of the relationship between the input (factors) and Output (response) variables, often to further the optimization of the underlying process. The RSM approach allows the designers to find a local optimal and examine how the design factors affect the response in the region around the generated optimal point.http://archive.org/details/responsesurfacem1094510921CIVIN

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen