Over the past decade, the satellite industry has witnessed the birth and evolution of the CubeSat standard, not only as a technology demonstrator tool but also as a human capacity development platform in universities. The use of commercial off the shelf (COTS) hardware components makes the CubeSat a cost effective and ideal solution to gain access to space in terms of budget and integration time for experimental science payloads. Satellite operations are autonomous and are essentially based on the interaction of interconnected electronic subsystems exchanging data according to the mission requirements and objectives. The onboard computer (OBC) subsystem is developed around a microcontroller and plays an essential role in this exchange process as it performs all the computing tasks and organises the collection of onboard housekeeping and payload data before downlink during an overpass above the ground station. The thesis here presented describes the process involved in the development, design and implementation of a prototype OBC for a CubeSat. An investigation covering previously developed CubeSat OBCs is conducted with emphasis on the characteristics and features of the microcontroller to be used in the design and implementation phases. A set of hardware requirements are defined and according to the current evolution on the microcontroller market, preference is given to the 32-bit core architecture over both its 8-bit and 16-bit counterparts. Following a well defined selection process, Atmel’s AT91SAM3U4E microcontroller which implements a 32-bit Cortex-M3 core is chosen and an OBC architecture is developed around it. Further, the proposed architecture is implemented as a prototype on a printed circuit board (PCB), presenting a set of peripherals necessary for the operation of the OBC. Finally, a series of tests successfully conducted on some of the peripherals are used to evaluate the proposed architecture.

Thesis (M.Com.(quantitative Management)) / Satellite Scheduling Problems (SSP) are NP-hard and constraint programming and metaheuristics solution methods yield mixed results. This study investigates a new version of the SSP, the Satellite Constellation Time-Window Optimization Problem (SCoTWOP), involving commercial satellite constellations that provide frequent earth coverage. The SCoTWOP is related to the dual of the Vehicle Routing Problem with Multiple Timewindows, suggesting binary solution vectors representing an activation of time-windows. This representation fitted well with the MatLab® Genetic Algorithm and Direct Search Toolbox subsequently used to experiment with genetic algorithms, tabu search, and simulated annealing as SCoTWOP solution methods. The genetic algorithm was most successful and in some instances activated all 250 imaging time-windows, a number that is typical for a constellation of six satellites. / Quantitative Management

Thesis (M.Com.(quantitative Management)) / Satellite Scheduling Problems (SSP) are NP-hard and constraint programming and metaheuristics solution methods yield mixed results. This study investigates a new version of the SSP, the Satellite Constellation Time-Window Optimization Problem (SCoTWOP), involving commercial satellite constellations that provide frequent earth coverage. The SCoTWOP is related to the dual of the Vehicle Routing Problem with Multiple Timewindows, suggesting binary solution vectors representing an activation of time-windows. This representation fitted well with the MatLab® Genetic Algorithm and Direct Search Toolbox subsequently used to experiment with genetic algorithms, tabu search, and simulated annealing as SCoTWOP solution methods. The genetic algorithm was most successful and in some instances activated all 250 imaging time-windows, a number that is typical for a constellation of six satellites. / Quantitative Management

This Thesis deals with the national legal aspects of a particular space application: remote sensing by satellites, also referred to as earth observation systems. / Governments have been the leading providers and users of satellite imagery data since the advent of earth observation satellites (i.e. almost 40 years ago). However, this has changed, particularly in the United States, with several private companies having acquired and launched their own imaging satellite systems. This new trend towards commercialization and privatization of the remote sensing industry, which appeared firstly in the United States and which is now being extended to Canada, required a change in policy. The role played by the government policies and regulations in shaping the prospects for the emerging commercial remote sensing satellite firms is of critical importance. In this context, these policies and regulations will determine the conditions that will enable commercial firms to realize their competitive potential in both the domestic and international marketplace. / In this Thesis, a brief overview of the technical and historical legal backgrounds of remote sensing is provided. Then, the international legal framework of remote sensing is briefly analyzed. Finally, a thorough analysis of the policies, laws and regulations applicable within the United States and Canada is presented.

On-orbit servicing (OOS) of space systems provides immense benefits by extending their lifetime, by reducing overall cost of space operations, and by adding flexibility to space missions. Refueling is an important aspect of OOS operations. The problem of determining the optimal strategy of refueling multiple satellites in a constellation, by expending minimum fuel during the orbital transfers, is challenging, and requires the solution of a large-scale optimization problem. The conventional notion about a refueling mission is to have a service vehicle visit all fuel-deficient satellites one by one and deliver fuel to them. A recently emerged concept, known as the peer-to-peer (P2P) strategy, is a distributed method of replenishing satellites with fuel. P2P strategy is an integral part of a mixed refueling strategy, in which a service vehicle delivers fuel to part (perhaps half) of the satellites in the constellation, and these satellites, in turn, engage in P2P maneuvers with the remaining satellites. During a P2P maneuver between a fuel-sufficient and a fuel-deficient satellite, one of them performs an orbital transfer to rendezvous with the other, exchanges fuel, and then returns back to its original orbital position. In terms of fuel expended during the refueling process, the mixed strategy outperforms the single service vehicle strategy, particularly with increasing number of satellites in the constellation. This dissertation looks at the problem of P2P refueling problem and proposes new extensions like the Cooperative P2P and Egalitarian P2P strategies. It presents an overview of the methodologies developed to determine the optimal set of orbital transfers required for cooperative and non-cooperative P2P refueling strategies. Results demonstrate that the proposed strategies help in reducing fuel expenditure during the refueling process.

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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Low earth orbit (LEO) satellite communication presents a unique environment which inherently di ers from most other communication channels. Due to the varying orbital patterns of LEO satellites the link exhibits varying link margins. Limited communication time windows need to be optimised to maximise the volumetric data throughput. Large coding gains can be obtained by the implementation of forward error correction codes. This thesis presents a means for optimising the data throughput of LEO satellite communication through the implementation of a mission speci c error control strategy. Low density parity check (LDPC) codes are versatile and present good error performances at many di erent code rates and block lengths. With power limitations on the space segment and remote ground stations, hardware utilisation e ciency must be optimised to reduce power consumption. In response to this requirement, this thesis evaluates various algorithms for LDPC decoders. An iterative LDPC decoder, implementing an approximation algorithm, is presented as a low complexity solution with good error performance. The proposed solution provides a very good balance between required hardware complexity and coding performance. It was found that many parameters of the decoders and codes can be altered to allow the implementation of these codes in systems with varying memory and processing capabilities. / AFRIKAANSE OPSOMMING: Kommunikasiekanale van satelliete met lae wentelbane, bied 'n unieke omgewing wat inherent verskil van meeste ander kommunikasiekanale. As gevolg van veranderende wentelbaanpatrone, vertoon die kanaal 'n wisselende foutgedrag. Kommunikasievensters is beperk en moet geoptimeer word om die totale deurset van die stelsel te maksimeer. Groot koderingswinste kan verkry word deur die implementering van foutkorreksie kodes. Hierdie tesis voorsien 'n metode om die datadeurset van satelliete met lae wentelbaan te optimeer, deur middel van implementering van 'n missie-spesi eke foutbeheer strategie. Lae digtheid pariteit toetskodes (LDPC) is veelsydige kodes, bied goeie foutbeheer en is doeltre end vir verskillende kodekoerse en bloklengtes. Met drywingsbeperkinge op die ruimtesegment en afgesonderde grondstasies, moet hardeware komponente doeltreffend gebruik word om drywingsverbruik te verminder. Ten einde aan hierdie ontwerpsvereiste te voldoen, evalueer hierdie tesis verskeie LDPC dekodeerderalgoritmes. Deur 'n iteratiewe LDPC dekodeerder met 'n benaderingsalgoritme te implementeer, word 'n oplossing van lae kompleksiteit aangebied, maar wat steeds goeie foutkorreksie eienskappe toon. Die voorgestelde oplossing bied 'n baie goeie balans tussen benodigde hardeware kompleksiteit en koderingsprestasie. Daar is gevind dat heelwat parameters van die dekodeerders en kodes aangepas kan word, ten einde implementering in stelsels met 'n wye verskeidenheid van geheuespasie en verwerkingsvermoëns moontlik te maak.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A joint project between the KU Leuven and Stellenbosch Universities was at the time of this thesis underway to develop a space borne electronically beam steerable antenna and the associated ground-space segments. This thesis covers the development of an aircraft based satellite emulator to facilitate convenient aircraft based testing of an antenna array, intended for low earth orbit satellite deployment and subsystems to control the antenna array. A flight strategy is developed to emulate such a satellite pass as best possible, with the strategy implemented in software on in-flight PC hardware. A full interface between the aircraft avionics and satellite bus system has been developed to enable generation of the required antenna steering commands and to create a satellite bus image to the payload. Successful test results are presented, as obtained from the actual aircraft ight simulator. The thesis describes the successful development and testing of a low altitude flight test strategy for certain satellite borne systems, as a cost-effective and realistic interim step to actual and very expensive space flight testing. / AFRIKAANSE OPSOMMING: 'n Gesamentlike projek deur KU Leuven en Stellenbosch Universiteit was tydens die verloop van hierdie tesis besig met die ontwikkeling om 'n ruimte gebaseerde elektroniese straal beheerde antenna en geassosieerde substelsels daar te stel. Hierdie tesis handel oor die ontwikkeling van 'n vliegtuig gebaseerde satelliet emulator om die toetsing van 'n elektroniese stuurbare antenna, wat bedoel is vir 'n lae aardse wentelbaan, te fasiliteer en die ontwikkeling van substelsels wat die stuurbare antenna beheer. 'n Vlug strategie is ontwikkel om so 'n satelliet wentelbaan so na as moontlik te emuleer. Die strategie word dan geïmplementeer in die sagteware van die aanboord vlug rekenaar. 'n Intervlak tussen die vliegtuig instrumente en satellietbus is ontwikkel om die generering van die nodinge instruksies te fasiliteer en om 'n virtuele satellietbus vir die res van die satelliet stelsel te skep. Suksesvolle toets resultate word getoon wat met behulp van 'n vliegtuig simulator verkry is. Die tesis beskryf die suksesvolle ontwikkeling en toetsing van 'n lae vlugtoets strategie vir satelliet stelsels, as 'n koste effektiewe en realistiese tussenstap, tot baie duur ruimte vlugtoetsing.

Tropospheric aerosol information from NASA satellites in space has reached the milestone of ten years of continuous measurements. These higher resolution satellite aerosol records allow for a broader regional perspective than can be gained using only sparsely located ground based monitoring sites. Decadal satellite aerosol data have the potential to advance knowledge of the climatic impacts of aerosols through better understanding of solar dimming/brightening and radiative forcings on regional scales, as well as aid in air quality applications. The goal of this thesis is to develop and implement methodologies for using satellite remotely sensed data in conjunction with ground based observations and modeling for characterization of regional aerosol variations with applications to air quality and climate studies in the Southeastern U. S. This region is of special interest because of distinct aerosol types, less warming climate trends compared to the rest of U.S., and growing population. To support this primary goal, a technique is developed that exploits the statistical relationship between PM2.5 (particulate matter that has an aerodynamic radius of 2.5 µm or less) and satellite AOD (Aerosol Optical Depth) from MODIS (Moderate resolution Imaging Spectroradiometer) where a probabilistic approach is used for air quality assessments in the metropolitan Atlanta area. The metropolitan Atlanta area experiences the poorest air quality during the warmer seasons. We found that satellite AODs capture a significant portion of PM2.5 concentration variability during the warmer months of the year with correlation values above 0.5 for a majority of co-located (in time and space) ground based PM2.5 monitors, which is significant at the 95% confidence interval. The developed probabilistic approach uses five years of satellite AOD, PM2.5 and their related AQI (Air Quality Index) to predict future AQI based solely on AOD retrievals through the use of AOD thresholds, e.g., 80% of Code Green AQI days have AOD below 0.3. This approach has broad applicability for concerned stakeholders in that it allows for quick dissemination of pertinent air quality data in near-real time around a satellite overpass. Examination of the use of multiple satellite sensors to aid in investigating the impacts of biomass burning in the region is performed. The utility of data fusion is evaluated in understanding the effects of the large wildfire that burned in May 2007. This wildfire caused PM2.5 in the metropolitan Atlanta area to exceed healthy levels with some measurements surpassing 150 µg/m3 during the month. OMI (Ozone Monitoring Instrument) AI (Aerosol Index), which qualitatively measures absorbing aerosols, have high values of more than 1.5 during May 26 - 31, 2007. CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) a space based lidar was used to determine the vertical structure of the atmosphere across the region during the active fire period. CALIPSO was able to identify wildfire aerosols both within the planetary boundary layer (likely affects local air quality) and aloft where aerosol transport occurs. This has important implications for climatic studies specifically aerosol radiative effects. In-depth analysis of the satellite and ground based aerosol data records over the past decade (2000 - 2009) are performed from a climatic perspective. The long temporal scale allowed for better characterization of seasonality, interannual variability, and trends. Spatial analysis of ten years of AOD from both MODIS and MISR (Multi-angle Imaging Spectroradiometer) showed little variability of AOD during the winter with mean AOD below 0.1 for the entire region, while the summer had decidedly more variability with mean AOD around 0.33 for MODIS and 0.3 for MISR. Seasonal analysis of the PM2.5 revealed that summer means are twice as high as winter means for PM2.5. All of the datasets show interannual variability that suggests with time AOD and PM2.5 are decreasing, but seasonal variability obscured the detection of any appreciable trends in AOD; however, once the seasonal influence was removed through the creation of monthly anomalies there were decreasing trends in AOD, but only MODIS had a trend of -0.00434 (per month) that statistically significant at the 95% confidence level. Satellite and ground-based data are used to assess the radiative impacts of aerosols in the region. The regional TOA (Top Of the Atmosphere) direct radiative forcing is estimated by utilizing satellite AOD from MODIS and MISR both on Terra, along with satellite derived cloud fraction, surface albedo (both from MODIS), and single scattering albedo (SSA) from MISR data from 2000 - 2009. Estimated TOA forcing varied from between -6 to -3 W/m2 during the winter, and during the warmer months there is more variation with ΔF varying between -28 to -12.6 W/m2 for MODIS and -26 to -11 W/m2 for MISR. The results suggest that when AOD, cloud fraction and surface albedo are all consider they add an additional 6 W/m2 of TOA forcing compared to TOA forcing due to aerosol effects only. Varying SSA can create changes in TOA forcing of about 5 W/m2. With removal of the seasonal variability timeseries anomaly trend analysis revealed that estimated TOA forcing is decreasing (becoming less negative) with MODIS based estimates statistically significant at the 95% confidence level. Optical and radiative 1-D radiative transfer modeling is performed to assess the daily mean TOA forcing and forcing at the surface for representative urban and background aerosol mixtures for summer and winter. During the winter, modeled TOA forcing is -2.8 and -5 W/m2 for the WB and WU cases, and the modeled summer TOA forcings (SB = -13.3 W/m2) also generally agree with earlier estimates. While surface forcings varied from -3 to -210 W/m2. The radiative forcing efficiency at the TOA (amount of forcing per unit of AOD at 550 nm) varied from -9 to -72 W/m2 τ-1, and RFE at the surface varied from -50 to -410 W/m2 τ-1. It was found that the forcing efficiency for biomass burning aerosols are similar to the forcing efficiency of background aerosols during the summer that highlights the importance of possible increased biomass burning activity. Ultimately, the methodologies developed in this work can be implemented by the remote sensing community and have direct applicability for society as a whole.

Made available in DSpace on 2014-06-11T19:25:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-13Bitstream added on 2014-06-13T19:32:38Z : No. of bitstreams: 1 pereira_aj_me_guara.pdf: 1147049 bytes, checksum: 5c149bbd658e37d0e33085f764c18b50 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Uma abordagem analítica para o movimento rotacional de satélites artificiais estabilizados por rotação é apresentada, considerando os satélites em órbita elíptica e a influência conjunta do torque aerodinâmico, o torque de gradiente de gravidade, o torque magnético residual e o torque magnético devido às correntes de Foucault. Modelos matemáticos são apresentados para todos os torques e os componentes médios de cada torque são determinados para um período orbital. O torque médio já inclui os principais efeitos de cada torque sobre o movimento rotacional e são necessários nas equações do movimento. As equações do movimento são descritas em termos do módulo da velocidade angular de rotação do satélite, da declinação e da ascensão reta do eixo de rotação do satélite. Uma solução analítica para as equações do movimento rotacional é determinada, considerando os valores do torques externos médios em um período orbital, sendo válida para um período orbital. Por esta solução observa-se que o torque gradiente de gravidade e torque magnético devido às correntes de Foucault afetam o módulo da velocidade angular de rotação, contribuindo também para as variações temporais da ascensão reta e declinação do eixo de rotação, associadas com a precessão e deriva do eixo de rotação do satélite. O torque magnético residual e o torque aerodinâmico afetam apenas a ascensão reta e declinação do eixo de rotação, pois seu componente no eixo z são nulo. Aplicações são realizadas para os Satélites de Coleta de Dados Brasileiros SCD1 e SCD2, através de uma primeira abordagem com atualização diária dos dados de atitude e órbita e uma segunda abordagem sem a atualização diária destes dados. Os resultados mostram uma boa concordância entre os resultados obtidos pela teoria e os dados fornecidos pelo Centro de Controle de... / An analytical approach for the rotational motion of artificial satellites stabilized by rotation is presented, considering the satellites in elliptical orbit and the influence of the aerodynamic torque, gravity gradient torque, residual magnetic torque and magnetic torque due to the Foucault currents. Mathematical models for all the torques are shown and average components of each torque are determined for an orbital period. These components are needed in the equations of rotational motion. The average torque already included the main effects of each torque upon the rotational motion. The equations of rotational motion are described in terms of the satellite’s spin velocity, the declination and right ascension of the spin axis of the satellite. An analytical solution for the equations of the rotational motion is determined, considering mean values in an orbital period for the external torques. This solution is valid for an orbital period. Through this solution, it is noticed that the gravity gradient torque and the magnetic torques affects the spin velocity and the spin axis. The temporal variations of right ascension and declination of the spin axis causes the precession and drift of the spin. The residual magnetic torque and the aerodynamic torque, doesn´t affect the spin velocity because its component at z-axis is null. Applications are made for the Brazilian Data Collection Satellites SCD1 and SCD2, through a first approach with daily updates of the attitude and orbit data, and a second approach without the daily update of these data. The results show a good agreement between the results obtained by theory and data supplied by the Satellite Control Center of INPE in the first approach during 10 days. For the approach without updates, the results prove to be suitable only for 3 days of simulation. To validate the analytical solution, the pointing error (deviation from the rotational... (Complete abstract click electronic access below)