Dissertation (Ph. D.)--University of Stellenbosch, 1997. / Bibliography. Also available via the Internet

The objective of this project is the development of a mission analysis tool for the nanosatellite company GomSpace Sweden. Although there are many existing software, they can be quite complicated and time consuming to use. The goal of this work is to build a simple app to be used at the earliest stages of space missions in order to obtain key figures of merit quickly and easily. By comparing results, assessing the feasibility of customer needs, analysing how various parameters affect each other, it enables immediate deeper understanding of the implications of the main design decisions that are taken at the very beginning of a mission. The tool shall aid the system engineering process of determining orbit manoeuvre capability specifically for CubeSat electric propulsion systems taking into account the most relevant factors for perturbation in Low Earth Orbit (LEO), i.e. atmospheric drag and Earth’s oblateness effects. The manoeuvres investigated are: orbit raising from an insert orbit to an operating orbit, orbit maintenance, deorbiting within the space debris mitigation guidelines and collision avoidance within the 12 to 24 hours that the system has to react. The manoeuvres cost is assessed in terms of Delta v requirements, propellant mass and transfer times. The tool was developed with MATLAB and packaged as a standalone Linux application. / Målet med detta examensarbete var att utveckla ett verktyg för missionsanalys för nanosatellitföretaget GomSpace Sweden. Det finns många andra mjukvaror för att nå samma mål men de är ofta komplicerade och tidskrävande. Det specifika målet var således att skapa en enkel applikation som kan användas i de tidiga stegen av utformning av rymduppdrag för att snabbt och enkelt få fram viktiga parametrar. Genom att jämföra resultat, uppskatta genomförbarheten av kundbehov och analysera hur olika parametrar påverkar varandra kan omedelbar förståelse erhållas rörande påverkan av designbeslut som tas i början av rymduppdragen. Verktyget ska stödja systemingenjörsprocessen genom att uppskatta banförflyttningskapacitet för elektriska framdrivningssystem för CubeSats och ta i beaktande de mest relevanta faktorerna gällande störningar i låg jordbana (LEO), i.e. atmosfäriskt motstånd och effekterna av Jordens form. De undersökta manövrarna är: banhöjning från injektionsbana till operationell bana, banunderhåll, bansänkning som följer riktlinjerna för rymdskrot och kollisionsundvikande inom de 12 till 24 timmar som systemet har på sig att reagera. Kostnaden för manövrarna är uppskattade genom DeltaV-krav, massan av bränslet och förflyttningstider. Verktyget utvecklades med MATLAB och paketerades som en fristående applikation i Linux.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 1997. / This dissertation considers the feasibility of using atmospheric drag to control constellations of micro-satellites in low Earth orbits. The constellation control requirements include an acquisition phase and a maintenance phase. Optimal strategies are designed to control the relative positions of the satellites during these two phases. It is shown that the feasibility and success of the strategies depend on many factors, including the satellite properties and orbital configuration. A nominal test constellation is presented and used as a generic example for the application of the control strategies. The dissertation also focuses on the accurate modelling and simulation of a typical low Earth orbit satellite, moving under the influence of a variety of significant orbit perturbation forces. The simulations form an integral part of the study and are used to verify the application of all the proposed control strategies.

Submitted by Verena Pereira (verenagoncalves@uefs.br) on 2017-02-17T22:06:12Z No. of bitstreams: 1 Disserta??o Final (Corre??es) - Eduardo Mendes.pdf: 20884254 bytes, checksum: 2f9c97501da8a0259ee7afa7dee7506d (MD5) / Made available in DSpace on 2017-02-17T22:06:12Z (GMT). No. of bitstreams: 1 Disserta??o Final (Corre??es) - Eduardo Mendes.pdf: 20884254 bytes, checksum: 2f9c97501da8a0259ee7afa7dee7506d (MD5) Previous issue date: 2016-08-25 / In this research we studied evasive maneuvers to avoid collisions in an environment with debris, enabling missions to the space. When a collision occurs, usually the space vehicle is completely damaged and destroyed, thus ensuring that the satellite avoids this collision will preserve the objective of the mission. In this study, we will see how a space vehicle can perform an evasive maneuver through thedriveline under the effect of the atmospheric drag force, whose efficiency will be established through the settings of technological parameters, which are the amount of fuel in the space vehicle and the ability to eject the propellant through the propulsion system. The purpose of the evasive maneuver is to avoid the collision but to keep the vehicle in its nominal orbit. At first we found several initial conditions of collision with the space vehicle under the influence of Earth's gravitational force, to ensure that there would be a collision between objects, from that on, the propulsion force was applied, after that, considering only the effect of atmospheric drag on the objects and right after the two collisional objects were brought under the effect of both forces, the force of the atmospheric drag and the propulsion together. In search of the most economical maneuver, from the point of view of fuel consumption, maneuvers were performed with lower propulsion drive time, and at different times of the trajectory of the vehicle and also at random times with the use of the propulsion force . The maneuvers were found through numerical simulations for each mathematical model of disturbances added to the orbital dynamics under the influence of the gravitational force. / Neste trabalho, fizemos o estudo de manobras evasivas para evitar colis?es em ambiente de detritos, viabilizando as miss?es espaciais. Quando ocorre uma colis?o, normalmente o ve?culo espacial fica totalmente danificado e destru?do, portanto, garantir ao sat?lite o desvio da colis?o, preservar? o objetivo da miss?o. Neste estudo, veremos como um ve?culo espacial pode executar uma manobra evasiva, atrav?s do sistema propulsor, sob o efeito da for?a de arrasto atmosf?rico, cuja efici?ncia ser? estabelecida atrav?s das configura??es dos par?metros tecnol?gicos, sendo estes, a quantidade de combust?vel do ve?culo espacial e a capacidade de ejetar propelente pelo sistema propulsor. O objetivo da manobra evasiva ? evitar a colis?o, mas, mantendo o ve?culo em sua ?rbita nominal. A princ?pio foi encontrado um conjunto de condi??es iniciais de colis?o com o ve?culo espacial sob o efeito da for?a gravitacional da Terra, para garantir que haveria a colis?o entre os objetos e, a partir disto, foi aplicada a for?a de propuls?o, depois considerando somente o efeito do arrasto atmosf?rico sobre os objetos e logo ap?s, o ve?culo espacial e o detrito foram postos sob o efeito de ambas da for?a de propuls?o e do arrasto atmosf?rico, juntas. Em busca da manobra mais econ?mica, do ponto de vista do consumo de combust?vel, foram executadas manobras com tempo de acionamento de propuls?o menor, e em diferentes momentos da trajet?ria do ve?culo e tamb?m por tempos aleat?rios de acionamento de for?a de propuls?o. As manobras foram determinadas atrav?s de simula??es num?ricas para cada modelo matem?tico das perturba??es adicionadas ? din?mica orbital sob o efeito da for?a gravitacional.

Submitted by Verena Pereira (verenagoncalves@uefs.br) on 2018-11-14T22:49:02Z No. of bitstreams: 1 Disserta??o de Jadiane(C).pdf: 1600835 bytes, checksum: 6b3162236247731029b8ced5d94cc873 (MD5) / Made available in DSpace on 2018-11-14T22:49:02Z (GMT). No. of bitstreams: 1 Disserta??o de Jadiane(C).pdf: 1600835 bytes, checksum: 6b3162236247731029b8ced5d94cc873 (MD5) Previous issue date: 2018-07-07 / Earth's operational orbiting satellites are very useful for space science because it has great features as these services enable research and space explorations for scientific, commercial, and military interests as well. However, the increasing flow of space activities has increased the amount of debris orbiting in the operating regions, thereby increasing the chances of collisions in those areas, and allowing immeasurable damages if the satellite remains in this collision orbit. In view of the large number of operational objects, the study of evasive maneuvers for space vehicles has been growing, and this one is important in face of the possibility of collisions, not only with a single debris but with clouds of space debris. The objective of the evasive maneuver is to avoid collision, but by keeping the vehicle in its orbit nominally. The history of the phenomenon, that is, how it evolves over time, is found when the differential equation that represents the phenomenon is solved. From the point of view of Physics and Mathematics, the more realistic the model, the more difficult is the solution of the differential equations representing the phenomenon. Thus, this work seeks to present the analytical and semi-analytical solutions for the equations describing the relative dynamics between two bodies subjected to gravitational force, Chohessy-Wiltshire equations, under the influence of forces: gravitational, atmospheric drag, chemical propulsion ( exponential model and linear model), atmospheric drag plus chemical propulsion and plasma propulsion, and finally present their respective computational simulations. These simulations made it possible to show what happens to the operational satellites against a collision, for each specified model. With the contribution of the development of the atmospheric drag equation, with the drag coefficient varying / Os sat?lites operacionais em ?rbita da Terra s?o muito ?teis para a Ci?ncia Espacial, pois possuem grandes aplica??es e fun??es. Seus servi?os possibilitam pesquisas e explora??es espaciais para interesses cient?ficos, comerciais e tamb?m militares. Por?m, o crescente fluxo das atividades espaciais tem elevado a quantidade de detritos orbitando nas regi?es operacionais e, desse modo, aumentando as chances de colis?es nessas ?reas, e possibilitando imensur?veis preju?zos, caso o sat?lite permane?a nessa ?rbita de colis?o. Diante da grande quantidade de objetos operacionais e n?o operacionais, o estudo de manobras evasivas para os ve?culos espaciais torna-se urgente e necess?rio, visto a possibilidade de colis?es, n?o s? com um ?nico detrito, mas com nuvens de detritos espaciais. O objetivo da manobra evasiva ? evitar a colis?o, mas, mantendo o ve?culo em sua ?rbita nominal. A hist?ria do fen?meno, ou seja, como ele evolui no tempo, ? encontrada quando a equa??o diferencial que o representa ? resolvida. Assim obtemos a posi??o relativa entre os objetos colisionais no tempo. Do ponto de vista da F?sica e da Matem?tica, quanto mais realista for o modelo, mais dif?cil ser? a solu??o das equa??es diferenciais representantes do fen?meno. Assim, este trabalho busca apresentar as solu??es anal?ticas e semi-anal?tica para as equa??es que descrevem a din?mica relativa entre dois corpos sob a atua??o das for?as: gravitacional, de arrasto atmosf?rico, propuls?o qu?mica (modelo exponencial e modelo linear) e propuls?o plasma. Por fim, busca apresentar suas respectivas simula??es computacionais. Estas simula??es possibilitaram mostrar o que acontece com os sat?lites operacionais frente ? uma colis?o, para cada um modelo especificado. Outra contribui??o deste trabalho ? solu??o semi-anal?tica da din?mica relativa com arrasto atmosf?rico para densidade atmosf?rica n?o constante