This thesis takes a closer look at the complex maneuver known as gravity assist, a popular method of interplanetary travel. The maneuver is used to gain or lose momentum by flying by planets, which induces a speed and direction change. A simulation model is created using the General Mission Analysis Tool (GMAT), which is intended to be easily reproduced and altered to match any desired gravity assist maneuver. The validity of its results is analyzed, comparing them to available data from real missions. Some parameters, including speed and trajectory, are found to be extremely reliable. The model is then used as a tool to investigate the way that different parameters impact this complex environment, and the advantages of performing thrusting burns at different points during the maneuver are explored. According to theory, thrusting at the point of closest approach to the planet is thought to be the most efficient method for changing speed and direction of flight. However, the results from this study show that thrusting before this point can have some major advantages, depending on the desired outcome. The reason behind this is concluded to be the high sensitivity of the gravity assist maneuver to the altitude and location of the point of closest approach. / Detta examensarbete tittar närmare på den komplexa manöver inom banmekanik som kallas gravitationsassisterad manöver, vilken är vanligt förekommande vid interplanetära rymduppdrag. Manövern används för att öka eller minska farkostens rörelsemängd genom att flyga förbi nära planeter, vilket ger upphov till en förändring i fart och riktning. En simuleringsmodell är skapad i NASAs mjukvara GMAT med syftena att den ska vara reproducerbar samt möjlig att ändra för olika gravitationsassisterade manövrar. Resultaten från simuleringarna är validerade mot tillgängliga data från riktigt rymduppdrag. Vissa parametrar, som fart och position, har en väldigt bra överenstämmelse. Modellen används sedan för att noggrannare undersöka hur olika parametrar påverkar det komplexa beteendet vid en graviationsassisterad manöver, genom att specifikt titta på effekterna av en pålagd dragkraft från motorn under den gravitationsassisterade manövern. Teoretiskt fås mest effekt på fart och riktning om dragkraften från motorn läggs på vid punkten närmast planeten. Resultaten från denna studie visar att beroende på vilken parameter man vill ändra så kan man erhålla mer effekt genom att lägga på dragkraften innan den närmsta punkten. Förklaringen till detta är att den gravitationsassisterade manövern är väldigt icke-linjär, så en tidigare pålagd dragkraft kan kraftigt förändra farkostens bana nära planeten, så att farkosten t.ex. kommer närmare och då påverkas mer.

As the solar wind reaches Mercury it interacts with the planet’s magnetic field slowing down, forming a bow shock in front of the planet and diverting the flow around it. Along with the solar wind comes the interplanetary magnetic field, an extension of the sun’s magnetic field. The interaction between the bow shock and the interplanetary magnetic field impacts the behaviour of the plasma both up- and downstream of the bow shock. An important factor is the angle between the normal to the bow shock surface and the interplanetary magnetic field, θBN. The angle can be divided into two categories: quasi-parallel for when θBN < 45° and quasi-perpendicular for θBN > 45°. It is expected for a quasi-parallel configuration to have stronger fluctuations in both the solar wind upstream of the bow shock and in the magnetosheath downstream caused by reflected particles backstreaming into the solar wind. Quasi-perpendicular configurations are expected to have less fluctuations in both regions due to fewer solar wind particles being reflected back. In this thesis this connection is investigated at the bow shock at Mercury using magnetic field data from the MESSENGER mission. By looking at the data when the spacecraft travels through the thin bow shock the local θBN angle can be calculated. The fluctuation level is then calculated as the standard deviation of the magnetic field in a 30 second period upstream and downstream of the crossing. The results found are unexpected as the correlation between θBN and the fluctuation levels are weaker and more uniformly distributed than expected compared to similar studies conducted at Earth using the Cluster satellites. This is most likely due to the smaller spatial scale of the Hermean system: the structures perpendicular to the interplanetary magnetic field of upstream activity, such as SLAMS, cover a greater proportion of the bow shock than at Earth allowing them to extend over into neighbouring regions of different θBN values, giving a more uniform distribution of the fluctuation levels. / När solvinden når Merkurius växelverkar den med planetens magnetfält och solvinden saktas ned och avledes till att flöda kring planeten. Då solvinden decelereras formas en chock framför planeten, bogchocken. Tillsammans med solvinden kommer det interplanetära magnetfältet, som är en förlängning av solens magnetfält. Växelverkan mellan bogchocken och det interplanetära magnetfältet påverkar plasmat både upp- och nedströms från bogchocken. En viktigt faktor är vinkeln mellan normalen till bogchocken och det interplanetära magnetfältet, θBN . Bogchocken kan delas in i två kategorier: kvasi-parallell då θBN < 45° och kvasi-vinkelrät då θBN > 45°. Vid kvasi-parallella förhållanden förväntas starkare fluktuationer i magnetfältet både uppströms i solvinden och nedströms i magnetskiktet, orsakat av reflekterade partiklar som färdas in i den inkommande solvinden. Kvasi-vinkelräta förhållanden förväntas ha mindre fluktuationer då färre partiklar reflekteras. I den här uppsatsen undersöks kopplingen vid Merkurius bogchock med data från rymdsonden MESSENGER. Genom att använda data då rymdsonden färdas igenom den tunna bogchocken kan det lokala värdet på θBN uträknas. Fluktuationsnivåerna räknas ut som standardavvikelsen av magnetfältet under en 30 sekundersperiod uppströms och nedströms från korsningen. Resultaten är ej som förväntade då kopplingen mellan θBN och fluktuationsnivån är mycket svagare och jämnt fördelade än förväntat, baserat på resultat från jorden från Cluster-satelliterna. Den mest troliga förklaringen är att Merkurius och dess bogchock är mindre än jordens: de strukturerna som är vinkelräta till det interplanetära magnetfältet hos uppströmsfenomen, t.ex SLAMS, täcker då en större proportion av bogchocken än vid jorden vilket tillåter dem att sträcka sig in i närliggande regioner med annorlunda θBN värden, vilket ger en mer jämn utbredning av fluktuationsnivåerna.

Thesis (M.S.)--Mississippi State University. Department of Aerospace Engineering. / Title from title screen. Includes bibliographical references.

La spectroscopie de bruit quasi-thermique est une méthode précise de déterminat-ion de la densité et de la température dans les plasmas spatiaux. Lorsqu'une antenne électrique est immergé dans un plasma, elle est capable de mesurer les fluctuations électrostatiques provoquées par le mouvement thermique des particules de plasma. Ces fluctuations sont détectées par la densité de puissance spectrale aux bornes de l'antenne, en observant un spectre à des fréquences comparables à la fréquence plasma électronique aussi bien pour les électrons que pour les protons, car le signal du proton est fortement décalé Doppler vers des fréquences plus élevées en raison de la vitesse de dérive du vent solaire. En plus d'induire le champ électrique fluctuant, une partie des électrons impactent sur la surface de l'antenne, ce qui provoque des perturbations de son potentiel électrique. Le signal provoqué par cette population est directement proportionnelle au flux d'électrons du plasma impactant l'antenne et est dominante si l'antenne a une grande surface. Dans ce travail, nous utilisons la théorie de l'orbite limite pour calculer le flux de particules impactantes pour un plasma non thermique décrit par fonction de distribution de vitesses $kappa$ ou Lorentzienne, communément mesurée dans le vent solaire. L'augmentation de la collecte de particules par des objets cylindriques et sphériques est quantifié et présenté en tant que fonction du potentiel électrostatique de surface et de la fraction des particules supra-thermique. La prise en compte de ces résultats théoriques est absolument nécessaire pour des mesures précises des paramètres du plasma à chaque fois que le bruit d'impact est l'élément dominant dans le spectre de puissance. Ceci est le cas pour STEREO, car les bruit d'impact est dominant pour cette sonde, en raison de la présence d'antennes courtes et épaisses. L'étude approfondie des données sur cette mission est motivée par le fait que ses analyseurs d'électrons sont défectueux depuis le lancement et aucune information sur les électrons thermiques n'est disponible. Les résultats obtenus sont vérifiés en comparant avec les résultats de Wind, montrant une bonne concordance entre les valeurs mesurées par les deux satellites. Les incertitudes des mesures sont déterminées par les incertitudes des instruments utilisés et sont estimés à environ $40%$. Le résultat final de ce travail sera l'établissement d'une base de données des moments d'électrons pour les deux sondes STEREO A et B qui couvriront toute la durée de la mission. Dans une seconde partie de la thèse, nous utilisons l'approche cinétique pour étendre la théorie du bruit quasi-thermique à des plasmas où les collisions des électrons avec les neutres jouent un rôle dominant. Cette technique permet de mesurer la densité et la température des électrons, et aussi la fréquence des collisions en tant que paramètres indépendants. Ceci est obtenu sur une large gamme de fréquences aussi bien en dessous qu'au dessus de la fréquence plasma, pour peu que le rapport entre la fréquence de collision et fréquence de plasma ne soit pas inférieur à 0.1. Les résultats présentés ici peuvent potentiellement être appliqués avec succès dans les plasmas de laboratoire et ionosphères non magnétisés, tandis que pour l'ionosphère de la Terre leur utilisation est limitée aux fréquences basses à cause de la présence d'un champ magnétique fort. / The quasi-thermal noise spectroscopy is an accurate method of determination of density and temperature in space plasmas. When an electric antenna is immersed into a plasma, it is able to measure electrostatic fluctuations caused by the thermal motion of plasma particles. These fluctuations are detected as the power spectral density at the antenna terminals, observing a spectrum at frequencies comparable to the electron plasma frequency for both electrons and protons, since the proton signal is strongly Doppler-shifted towards higher frequencies due to the solar wind drift velocity. Beside inducing the fluctuating electric field, some of the electrons are impacting the antenna surface, causing disturbances of the antenna electric potential. The signal caused by this population is directly proportional to the flux of plasma electrons impacting the antenna and is dominant if the antenna has a large surface area. In this work, we use the orbit limited theory to calculate the incoming particle flux for a non-thermal plasma described by $kappa$ velocity distribution function, commonly measured in the solar wind. The increase in the particle collection by cylindrical and spherical objects is quantified and presented as a function of the surface electrostatic potential and the fraction of supra-thermal particles. Including these results into the theory has turned out to be absolutely necessary for accurate measurements of the plasma parameters whenever the shot noise is the dominant component in the power spectrum. This is the case for STEREO because the impact noise is overwhelming on this probe, due to the presence of short and thick antennas. The comprehensive study of data on this mission is motivated by the fact that the electron analyzers are malfunctioning since launch and no information on thermal electrons is available. Results obtained are verified by comparing with the results from Wind, showing a good match between the values measured by the two spacecraft. Uncertainties of the measurements are determined by the uncertainties of the instruments used and are estimated to be around $40%$. The final outcome of this work will be establishing a database of the electron moments in both STEREO A and B that will be covering the entire duration of the mission. In the second part of the thesis, we use the kinetic approach to expand the theory of the quasi-thermal noise to plasmas where electron-neutral collisions play a dominant role. This technique is able to measure the electron density, temperature and the collision frequency as independent parameters using the wide frequency range both below and above the plasma frequency, if the ratio of the collisional to plasma frequency is not smaller than 0.1. The results presented here have can be potentially applied in laboratory plasmas and unmagnetized ionospheres, while at the ionosphere of Earth their use is limited to low frequencies due to the presence of the magnetic field.

Uranus is one of the least explored planets in our solar system. Event though the Uranian Ly-α emission has been a subject of study for decades, there is not a consensus on the sources contribution to the total signal. This thesis aims to analyse the contribution from scattering of the solar flux to the Uranian Ly-α dayglow by solving the radiative transfer equation in a parameter study for the atmosphere. The sources are solar Ly-α resonant scattering and Rayleigh scattering by atomic and molecular hydrogen respectively. The radiative transfer equation is solved using the Feautrier Method Program, a program written by Randall G. Gladstone. The program was adjusted to the Uranian atmosphere and modelled with different variations in parameters, including the atmospheric temperature and particle density of Ly-α scatterers and absorbers. A parameter study is performed to investigate the dependency on the Ly-α signal on these parameters. The results showed a significant Ly-α limb brightening with a maximum intensity located around 400 km outside one planetary radius as seen from the disk center. The contributions to the Ly-α dayglow from Rayleigh scattering by H2 was calculated to be 160 R whereas the contribution from resonant scattering by H was 550 R. One feature that prevents direct comparison to observed data with this thesis is that some sources that contributes to Uranus Ly-α signal are omitted in the simulations. / Uranus är en av solsystemets minst utforskade planeter. Även om dess Ly-α-strålning har undersökt, råder ännu inte konsensus kring de olika källornas bidrag till den totala Ly-α signalen. Genom att lösa ekvationen för strålningstransport i en parameterstudie ämnar examensarbetet att studera bidraget från solens två källor till Uranus Ly-α- signal. De två källorna är resonant- och Rayleigh strålningsspridning från atomärt och molekulärt väte. Ekvationen för strålningstransport beräknas av ett program som heter Feautrier Method Program, skapat av Randall G. Gladstone. Programmet har justeras till Uranus atmosfär för att kunna beräkna strålningstransport för olika atmosfärersmodeller i en parameterstudie. Parameterna som ändras är temperaturen, partikeldensiteten hos spridare och absorberare i atmosfären. Från resultaten kan parameterstudien svara på beroendet av de olika källorna till Ly-α-signalen från Uranus. Resultaten visar en tydlig ökning av ljusintensitet vid Uranus kanter med maximum runt 400 km utanför planetens radie, sett från planetens mitt. Bidraget till Ly-α-signalen från Rayleigh stålningsspridning beräknades till 160 R och från resonant strålningsspridning till 550 R. En egenskap som hindrar direkt jämförelse med resultaten från detta examensarbete och observerad data är att alla bidragande källor till Uranus Ly-α signal inte simulerats.

Made available in DSpace on 2016-04-28T14:16:25Z (GMT). No. of bitstreams: 1 CARLOS A LOIOLA DE SOUZA.pdf: 415449 bytes, checksum: d861caf6da8174df5e70f24cd0bc6748 (MD5) Previous issue date: 2006-05-29 / Sci - fi books depending on how they are structured by their authors, might be in our case, the astronomer Carl Sagan, be used as reference texts in Science History by his indisciplinity. The specific case of interplanetary trips, theorized and thought scientificaly and advertised under a sci - fi language in books of Carl Sagan, is what this dissertation talks about.The authors of fiction texts, such as Sagan Arthur Charles Clarke and Issac Asimov, try to found their extrpolate in careful notes of trends that happen in society and science, and develop the ( narration, in Asmov and Clarke´s case ) implication or advertising with rigidity and consistency.On the other hand, part of the futuristic literature would be an important History of Science analysis instrument, for it to be possible of thinking in alternative proposals for a scientific policy and taught which may have a social reach. A kind of experiment or imaginary exercise. In other words, what is studied here, is the relation between sci - fi and science, which talks about interplanetary trips, and how they are explained in Sagan´s books. However, the dissertation, delimitates, in the first instance, must be considered about interplanetary trips, its dissimilation from the 30´s to the 60´s and the adverstising through two of the best sci - fi writers of the twentieth century, whose work was to advertise scientific ideas or Astronautic for a better understanding of the science, its role and the impact of science and technology, in a society which moves really fast, but without many details. After all, as it was a relevant realization of some of these realized fantasies by Carl Sagan´s commitment, initially, with the American industial military complexduring the Cold War against USSR, and after that by NASA.And what we have learned scientifically from the exploration of the Solar Sistem and the nearest planets, in a way that the results of this spacial exploration could be advertised with the help from literature and fiction, in a type of alert about the problems that we will have to face in a near future. At last, the mankind destiny, imagined by Sagan in a kind of manifest advertised by himself in his main books and analysed here for it to be possible to keep its parallelism of contents and trends between sci - fi books and the academic literatureabout the development of science and technology and the destiny of mankind and the individuals that make itself. This is a conclusion that History students having a beginning or complementary graduation in humanities, will be able to find on the shelves of science history, a worthy manifest for an unexpective reflection or for a militancy / Obras de ficção científica podem, dependendo de como estiverem estruturadas por seus autores, em nosso caso, o astrônomo Carl Sagan, ser usadas como textos de referência em História da Ciência por sua interdisciplinaridade. O caso específico das viagens interplanetárias, pensadas e teorizadas cientificamente e divulgadas sob a linguagem da ficção científica nos livros de Carl Sagan, é o de que se ocupa esta dissertação. Os autores de textos de ficção, como os colegas de Sagan Arthur Charles Clarke e Isaac Asimov, procuram, como acontece com textos teóricos acadêmicos, assim como também eram alguns dos textos de Sagan, fundamentar suas extrapolações em observações cuidadosas de tendências em ação na sociedade e na ciência e desenvolver sua (narração, no caso de Asimov e Clarke) implementação ou divulgação com rigor e consistência. Ou seja, parte da literatura futurística seria um instrumento importante de análise de História da Ciência para que esta possa pensar em propostas alternativas para uma política científica e de ensino científico que tenha um alcance social. Uma espécie de experimento ou exercício imaginário. Em outras palavras, o que aqui se estuda é a relação entre ficção científica e ciência que fale das viagens interplanetárias e como elas estão expressas nas obras de Sagan. Portanto, a dissertação delimita o que, em primeiro lugar, deve-se considerar sobre as viagens interplanetárias, sua disseminação nos anos de 1930 a 1960 e sua divulgação através de dois dos melhores escritores de ficção científica do século XX, que se empenharam em divulgar idéias científicas ou de Astronáutica para uma melhor compreensão da ciência, do papel da ciência e do impacto da ciência e tecnologia numa sociedade com uma velocidade em movimento rápido, mas sem muitos detalhes. Depois, como foi a realização primordial de algumas dessas fantasias realizadas pelo envolvimento de Carl Sagan, inicialmente, com o complexo militar industrial dos Estados Unidos da América durante a Guerra Fria com a URSS e depois pela NASA. E o que se aprendeu, cientificamente, com a exploração de nosso sistema solar e de nossos planetas mais próximos, de maneira que esses resultados da exploração espacial pudessem ser divulgados com a ajuda da literatura de ficção em forma de alerta sobre os problemas que teremos de enfrentar num futuro bem próximo. E, por último, o destino da humanidade imaginado por Sagan numa espécie de manifesto divulgado por ele mesmo em seus principais livros e aqui analisado para que se pudesse manter o paralelismo de conteúdo e tendências entre as obras de ficção e a literatura acadêmica sobre o desenvolvimento da ciência e da tecnologia e o destino da humanidade e dos indivíduos que a compõem. Isto nos leva a concluir que o estudante de História da Ciência, tendo uma formação inicial ou complementar em humanidades, poderá encontrar na estante de História da Ciência um valioso manifesto para uma reflexão despretensiosa ou para a militância

Preliminary interplanetary trajectory designs frequently use simplified two-body orbital mechanics and linked conics methodology to model the complex trajectories in multi-body systems. Incorporating gravity assists provides highly efficient interplanetary trajectories, enabling otherwise infeasible spacecraft missions. Future missions may employ powered gravity assists, using a propulsive maneuver during the flyby, improving the overall trajectory performance. This dissertation provides a complete description and analysis of a new interplanetary trajectory design tool known as TRACT (TRAjectory Configuration Tool). TRACT is capable of modeling complex interplanetary trajectories, including multiple ballistic and/or powered gravity assists, deep space maneuvers, parking orbits, and other common maneuvers. TRACT utilizes an adaptable architecture of modular boundary value problem (BVP) algorithms for all trajectory segments. A bi-level optimization scheme is employed to reduce the number of optimization variables, simplifying the user provided trajectory information. The standardized optimization parameter set allows for easy use of TRACT with a variety of optimization algorithms and mission constraints. The dissertation also details new research in powered gravity assists. A review of literature on optimal powered gravity assists is presented, where many optimal solutions found are infeasible for realistic spacecraft missions. The need was identified for a mission feasible optimal powered gravity assist algorithm using only a single impulsive maneuver. The solution space was analyzed and a complete characterization was developed for solution types of the optimal single-impulse powered gravity assist. Using newfound solution space characteristics, an efficient and reliable optimal single-impulse powered gravity assist BVP algorithm was formulated. The mission constraints were strictly enforced, such as maintaining the closest approach above a minimum radius and below a maximum radius. An extension of the optimal powered gravity assist research is the development of a gravity assist BVP algorithm that utilizes an asymptote ΔV correction maneuver to produce ballistic gravity assist trajectory solutions. The efficient algorithm is tested with real interplanetary mission trajectory parameters and successfully converges upon ballistic gravity assists with improved performance compared to traditional methods. A hybrid approach is also presented, using the asymptote maneuver algorithm together with traditional gravity assist constraints to reach ballistic trajectory solutions more reliably, while improving computational performance.

The International Space Station utilizes many different forms of written and verbal communication between the flight crews and ground control personnel. This study analyzes the historical use of three regular communication methods, Daily Planning Conferences, Weekly Planning Conferences and written Daily Summaries, as well as specific, science and internal maintenance events for characteristics and perceived effectiveness across eight expeditions (4 ? 11). The results are recommendations for the continued use of, or substitution for, these methods for future long-duration human space missions, specifically to the Moon and to Mars. General conclusions are that most of the conference content could have been relayed through written/electronic methods, and that the Daily Summaries are considered succinct and effective as a communication cornerstone. Conclusions formed from the study of individual events involved the importance of well-written crew procedures, the effective stowage and retrieval of necessary materials and the selection of well-defined science experiments.