This thesis aims to investigate the potential of a transfer orbit using successive aerocaptures at Saturn and Titan to establish a science orbit around Titan. Titan is an Earth-like moon with a dense atmosphere and organic compounds present. It has many similarities with Earth that are useful to study such as superrotation. Superrotation is when the atmosphere rotates faster than the body it surrounds. In order to study Titan, we need to establish an orbit around it. The Saturn system is distant from Earth, 8.5 Astronomical Units (AU) which makes it difficult to reach from a time and velocity point of view. We propose to use an aerocapture at Saturn to intercept Titan with lower relative velocity in order to perform an aerocapture at Titan. The analysis was performed in primarily MATLAB to simulate the orbits. The results of this showed that we can aerocapture a spacecraft at Saturn and arrive at Titan within roughly 4 to 8 km/s relative velocity regardless of the incoming hyperbolic excess velocity at the Saturn system. This can be improve upon by using intermediate transfer orbits, such as bi-elliptics, to arrive with even lower relative velocities to Titan of as low as 1 km/s. The drag acceleration experienced during the Saturn aerocapture had peak values of between 0.2 and 1.4 g's and acceleration over 50% of the peak is experienced between 6.8 and 8 minutes. This capture method has the potential to make Titan more easily accessible and allow for scientific study of a clear target for improving our understanding of Earth-like processes on other bodies in our solar system. / Master of Science / This thesis aims to investigate the potential of a transfer orbit using successive aerocaptures at Saturn and Titan to establish a science orbit around Titan. Aerocapturing is utilizing the atmosphere of a body to slow down a spacecraft. Titan is an Earth-like moon with a dense atmosphere and organic compounds present. It has many similarities with Earth that are useful to study such as superrotation. Superrotation is when the atmosphere of a body rotates faster than the body it surrounds. In order to study Titan, we need to establish an orbit around it. The Saturn system is distant from Earth, 8.5 Astronomical Units (AU) which makes it difficult to reach from a time and velocity point of view. It takes a large amount of time to get there so we attempt to get there faster by increasing velocity. This means we arrive at the Saturn system with a large amount of velocity that we need to counter-act in order to orbit. We propose to use an aerocapture at Saturn to intercept Titan with lower velocity in order to perform another aerocapture at Titan to slow into an orbit. The analysis was performed in primarily MATLAB to simulate the orbits. The results of this showed that we can aerocapture a spacecraft at Saturn and arrive at Titan within roughly 4 to 8 km/s regardless of the incoming velocity to the Saturn system. This can be improve upon by using intermediate transfer orbits, after capturing at Saturn, to arrive with even lower velocities at Titan of as low as 1 km/s. The drag acceleration experienced during the Saturn aerocapture had peak values of between 0.2 and 1.4 g's and acceleration over 50% of the peak is experienced between 6.8 and 8 minutes. This is relatively gentle for an aerocapture and means the spacecraft likely will not require significant structural support. This capture method has the potential to make Titan more easily accessible and allow for scientific study of a clear target for improving our understanding of Earth-like processes on other bodies in our solar system.

Saturn's ring system is actually comprised of a multitude of separate rings, yet each of these rings has areas with more or less constant structural properties which are hard to uncover by observation alone. By measuring stellar occultations, data is collected in the form of Poisson counts (of over 6 million observations) which need to be denoised in order to find these areas with constant properties. At present, these areas are found by visual inspection or examining moving averages, which is hard to do when the amount of data is huge. It is also impossible to do this using the changepoint analysis-based method by Scargle (1998, 2005). For the purpose of finding areas of constant Poisson intensity, a state-of-the-art Haar-Fisz algorithm for Poisson intensity estimation is employed. This algorithm is based on wavelet-like transformation of the original data and subsequent denoising, a methodology originally developed by Nason and Fryzlewicz (2005). We apply the HaarFisz transform to the original data, which normalizes the noise level, then apply the Haar wavelet transform and threshold wavelet coefficients. Finally, we apply the inverse Haar-Fisz transform to recover the Poisson intensity function. We implement the algorithm using R programming language. The program was first tested using synthetic data and then applied to original Saturn ring observations, resulting in a quick, easy method to resolve data into discrete blocks with equal mean average intensities.

Since their discovery in 1610 by Galileo Galilei, Saturn's rings continue to fascinate both experts and amateurs. Countless numbers of icy grains in almost Keplerian orbits reveal a wealth of structures such as ringlets, voids and gaps, wakes and waves, and many more. Grains are found to increase in size with increasing radial distance to Saturn. Recently discovered "propeller" structures in the Cassini spacecraft data, provide evidence for the existence of embedded moonlets. In the wake of these findings, the discussion resumes about origin and evolution of planetary rings, and growth processes in tidal environments. In this thesis, a contact model for binary adhesive, viscoelastic collisions is developed that accounts for agglomeration as well as restitution. Collisional outcomes are crucially determined by the impact speed and masses of the collision partners and yield a maximal impact velocity at which agglomeration still occurs. Based on the latter, a self-consistent kinetic concept is proposed. The model considers all possible collisional outcomes as there are coagulation, restitution, and fragmentation. Emphasizing the evolution of the mass spectrum and furthermore concentrating on coagulation alone, a coagulation equation, including a restricted sticking probability is derived. The otherwise phenomenological Smoluchowski equation is reproduced from basic principles and denotes a limit case to the derived coagulation equation. Qualitative and quantitative analysis of the relevance of adhesion to force-free granular gases and to those under the influence of Keplerian shear is investigated. Capture probability, agglomerate stability, and the mass spectrum evolution are investigated in the context of adhesive interactions. A size dependent radial limit distance from the central planet is obtained refining the Roche criterion. Furthermore, capture probability in the presence of adhesion is generally different compared to the case of pure gravitational capture. In contrast to a Smoluchowski-type evolution of the mass spectrum, numerical simulations of the obtained coagulation equation revealed, that a transition from smaller grains to larger bodies cannot occur via a collisional cascade alone. For parameters used in this study, effective growth ceases at an average size of centimeters. / Seit ihrer Entdeckung im Jahre 1610 durch Galileo Galilei faszinieren die Ringe des Saturn sowohl Laien als auch Experten. Planetare Ringe finden sich in der Äquatorialebene aller vier Riesenplaneten unseres Sonnensystems und sind eines der eindruckvollsten Beispiele granularer Gase. Darunter gehören die Saturnringe zu den Bekanntesten. Sie bergen eine Vielzahl von Strukturen und erstrecken sich über mehr als 240 000 Kilometer, wobei sie weit weniger als 100 Meter dick sind. Unzählige kleinerer Körper bewegen sich auf leicht exzentrischen Kepler-ähnlichen Bahnen um den Zentralplaneten und bestehen dabei vorwiegend aus Eis. Die seit Juli 2004 im Orbit um den Saturn befindliche Raumsonde Cassini liefert atemberaubende Bilder und Daten, die nicht nur neue Erkenntnisse liefern, sondern auch alte Fragestellungen neu aufleben lassen. Dazu gehört z.B. die Frage nach dem Ursprung und den Entwicklungsstufen planetarer Ringe. Kürzlich, im äusseren A-Ring entdeckte Kleinmonde, deren Existenz schon viel früher postuliert wurde, weisen auf eventuell stattfindende Wachstumsprozesse hin. Da sich planetare Ringe jedoch hauptsächlich innerhalb der sogenannten Roche-Zone des jeweiligen Planeten befinden, ist ein effektives, allein auf gravitativen Wechselwirkungen beruhendes Größenwachstum nicht zu erwarten. Der Einfluß von Teilchenadhäsion auf diese Prozesse ist bis dato fraglich. Im Rahmen dieser Dissertation ist ein Kontaktmodell für adhäsive, viskoelastische Binärstöße granularer Teilchen entwickelt worden, welches sowohl deren Agglomeration als auch Restitution gestattet. Chakateristisch für granulare Materie ist die dissipative Wechselwirkung der einzelnen Teilchen untereinander. Dieser Energieverlust wird gewöhnlich mittels des Restitutionskoeffizienten erfaßt, der das Verhältnis von Relativgeschwindigkeiten nach zu vor dem Stoß darstellt. Dieser Parameter ermöglicht es, Agglomeration und Restitution nicht nur qualitativ sondern auch quantitativ voneinander zu unterscheiden. Ferner ergibt sich eine maximale Impaktgeschwindigkeit, bei der eine Agglomeration noch immer möglich ist. Basierend auf der Existenz derartiger Grenzgeschwindigkeiten für Agglomeration und Fragmentation, wurde in dieser Dissertation ein selbstkonsistentes, kinetisches Strukturbildungsmodell vorgestellt und im Hinblick auf die Koagulation von Teilchen weitergehend untersucht. Eine Koagulationsgleichung, die einer eingeschränkten Haftwahrscheinlichkeit Rechnung trägt, ist analytisch hergeleitet worden. Aus ihr läßt sich die allgemein bekannte, aber ansonsten phenomenologische Smoluchowski Gleichung als ein Grenzfall ableiten, bei dem jeder mögliche Kontakt zur Koagulation führt. Qualitative und quantitative Untersuchungen der Relevanz von Adhäsion in kräftefreien und Kepler-gescherten Systemen beziehen sich auf die Stabilität von Zwei-Teilchen-Agglomeraten, die Wahrscheinlichkeit eines gegenseitigen "Einfangens" beider Teilchen, und die zeitliche Entwicklung der Größenverteilung unter Berücksichtigung der im ersten Teil dieser Arbeit eingeführten Kollisionsdynamik. Dabei ergab sich ein kritischer Abstand zum Zentralkörper, der das ansonsten in diesem Rahmen benutzte Roche Kriterium erweitert. Numerische Simulationen der vorgestellten Koagulationsgleichung zeigen deutlich, daß im Vergleich zu Smoluchowski-ähnlichem Verhalten, ein kollisionsbasiertes Wachstum von kleineren zu größeren Körpern nicht notwendigerweise auftritt. Lediglich Größen von Zentimetern konnten an dieser Stelle erreicht werden. Die Relevanz von adhäsiven Teilchenwechselwirkungen konnte damit nachgewiesen werden. Vermögen diese auch nicht für ein effektives Wachstum aufzukommen, so sind sie dennoch von Bedeutung für die kollektive Dynamik planetarer Ringe.

The cloud and haze properties in the troposphere and stratosphere of Saturn are investigated in this thesis by analysing Cassini/VIMS spectra at 0.8-3.5 μm and 4.5-5.1 μm. The aerosol properties are derived from VIMS data by using the retrieval tool NEMESIS developed at the University of Oxford. Near-infared VIMS data between 4.5 and 5.1 μm are mainly sensitive to deeper tropospheric levels down to approximately 5 bar. At such pressure levels, thermochemical models predict the formation of condensed clouds made of ammonia and ammonium hydrosulphide ices, although none of these species has been spectrally detected so far. In addition, phosphine and ammonia are responsible for most of the gaseous absorption at these wavelengths. Therefore, the cloud properties and gas distributions can be retrieved from VIMS near-infared spectra. In this thesis, the analysis of limb-darkening data at 4.5-5.1 μm is performed in order to constrain the aerosol properties in Saturn’s atmosphere. The best-fitting model consists of a scattering cloud between 2 and 3 bar, and a scattering haze layer which can be placed anywhere between 10 and 500 mbar. The composition is still poorly constrained for both the deep cloud and haze layer. The haze physical and optical properties can however be independently retrieved from VIMS near-infrared spectra at shorter wavelengths in the 0.8-3.5 μm spectral range. Saturn’s hazes in the troposphere and stratosphere reflect the sunlight at 0.8-3.5 μm. The properties and vertical structure of tropospheric and stratospheric hazes are then investigated from VIMS reflection spectra in the near-infared. The latitudinal variation of haze properties is compared to a thermal feature known as "the temperature knee", corresponding to a local increase of temperature right below the tropopause. The north-south temperature variations in the troposphere are obtained from the analysis of thermal infrared data measured with the Composite InfraRed Spectromete (CIRS) instrument on board Cassini. Finally, VIMS near-infrared data at 0.8-3.5 and 4.5-5.1 μm are combined in order to obtain a cloud and haze model coherent with both wavelength ranges.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / Exploration of Titan is one of the primary objectives of the Cassini/Huygens mission Saturn due to launch in 1997. Limited data will be provided by Huygens as it descends to the surface via parachute and by Cassini as it orbits Saturn and occasionally passes near Titan. Interest in Titan is high because of its planet-class size, dense atmosphere, and the possibility of continents and seas. Already, there are discussions for a follow-on mission to Titan. There are several proposed designs such as balloons and boats to explore Titan's ethane seas. In all cases, reliable data links back to Earth are absolutely essential. However, simply increasing the power has its limits due to constraints on launch weights. There are a number of possible options for getting data back from Titan. These alternatives, and their effect on the mission profile are discussed.

The aim of this study is to outline circumstances and reasons which caused a birth of an ambitious plan which enabled the USA to land a man on the Moon and return him safely to the Earth. The impact of this thesis is to chart individual pilot expeditions also from the eyes of real participants. One part of this study is a chapter dealing with astronauts' preparation and training. The thesis also reminds the fact that among people who landed on the Moon was also the astronaut of the Czech origin, Eugene A. Cernan. In the end the study deal with technology that helped to include program Apollo among the greatest events of the 20th century.

Trataremos de dois livros de epigramas do poeta latino Marcial: Xênia e Apoforeta, dados a lume, respectivamente, nas Saturnais de 83 (ou 84) e 85 d.C. sob o principado de Domiciano. Nosso objetivo, em primeiro lugar, será discutir as características intensamente apotropaicas e propiciatórias tanto das Saturnais, como do próprio deus Saturno a despeito dos elementos lúgubres comumente a ele associados , para, em seguida, tentar demonstrar de que maneira a festividade romana interfere na fruição dos epigramas que compõem as referidas recolhas e exige que o poeta abandone, temporariamente, a comum acerbidade de seus versos. Tanto pelas Saturnais constituírem o princípio de unidade desses livros, como por Marcial buscar emular um conjunto de tratados antigos de natureza jocosa, populares durante os festejos consagrados a Saturno, acreditamos que o poeta legitima a existência de novo subgênero epigramático que é corolário das próprias Saturnais romanas. No final, apresentamos, como resultado de nossa investigação, tradução poética de Xênia e Apoforeta, inédita em língua portuguesa. / We will discuss two books of epigrams by the Latin poet Martial: Xenia and Apophoreta, published, respectively, in the Saturnalia of 83 (or 84) and 85 A.D. under the reign of Domitian. Our goal, in the first place, is to discuss the highly apotropaic and propitiatory features of both the Saturnalia, as the god Saturn itself despite the gloomy elements commonly associated with him. Then well try to demonstrate how the Roman festival interferes with the fruition of the epigrams in these collections, and demands that the poet abandons temporarily the common poignancy of his verses. Not only because Saturnalia constitute the principle of unity of these books, but because Martial seek to emulate a set of ancient treatises of facetious nature, popular during the festival dedicated to Saturn, we believe that the poet legitimate the existence of new epigrammatic subgenre which is corollary of the very Roman Saturnalia. Finally, we will present as a result of our investigation an original translation into Portuguese verse of Xenia and Apophoreta.

Orientador: Oton Cabo Winter / Banca: Ernesto Vieira Neto / Banca: Nelson Callegari Júnior / Resumo: Neste trabalho propõe-se analisar a dinâmica do sistema Prometeu - Pandora - Anel F de Saturno, buscando soluções para alguns comportamentos anômalos observados em seus componentes. É realizada uma descrição geral, contextualizando este sistema dentro da estrutura de satélites e anéis de Saturno. A seguir, apresenta-se dados de interesse obtidos até o presente, a partir de observações realizadas pelas sondas espaciais Pioneer 11 e Voyager 1 e 2 e pelo Hubble Space Telescope, citando os pontos problemáticos deste sistema. A teoria necessária para a compreensão de alguns aspectos é colocada e discutida através de breves explanações. As principais publicações relacionadas ao tema são analisadas e comentadas, em ordem cronológica, demonstrando os avanços realizados no conhecimento deste sistema. Elabora-se uma proposta de investigação na tentativa de reproduzir os resultados mais importantes e através deles evoluir para a busca de novas informações que venham auxiliar no entendimento da dinâmica deste sistema, utilizando-se de ferramentas de simulação numérica, nas quais são acrescentados parâmetros e influências muitas vezes não-consideradas. Em trabalhos futuros, pretende-se realizar uma análise acurada dos resultados deste trabalho, introduzindo novas variáveis e elementos que possam enriquecer a teoria que vem sendo construída e que explique de maneira cada vez mais satisfatória os enigmas existentes no sistema Prometeu - Pandora - Anel F de Saturno. / Abstract: In this work, we propose to analyze the dynamic of the Prometheus - Pandor - Saturn F ring system, searching for answers to the anomalous behavior of these bodies. We've made a general description, talking about this system and also about the ring and satellites structures of Saturn. Next, we show interesting data obtained until the moment from observations realized by the spacecrafts Pioneer 11 and 12 and Hubble Space Telescope, enumerating problematic points. We present the necessary theory to understand some aspects in evidence, discussing it through soon explanations. The main publications related to the topic are commented, in chronological order, showing advances in the understanding of this system. We've made an investigative offer to reproduce the most important results and through them develop new information to help the understanding of this dynamic system, using numerical simulations tools, in which we add new parameters and influences that wasn't consider. In future works, we'll try realize an accurate analyze of this work results, introducing new variables and elements to enrich the theory that has been built and to explain in a more clear manner the puzzle that exists in the Prometheus - Pandora - F ring system of Saturn. / Mestre

Dissertação apresentada para obtenção do grau de Doutor em Engenharia Civil, na Faculdade de Engenharia da Universidade do Porto, sob a orientação dos Professores Álvaro Jorge da Maia Seco e Américo Henrique Pires da Costa

Les ceintures de radiation provoquent des dégâts irréversibles sur les satellites les traversant, détériorant ainsi les instruments de mesure embarqués. Les étudier est utile au développement de matériaux adaptés et résistants. Depuis les années 90, l'ONERA-DESP étudie les ceintures de radiations des planètes magnétisées, telle que la Terre ou Jupiter, grâce au modèle Salammbô. Salammbô prend en compte les processus physiques de l'environnement radiatif pour recréer les populations d'électrons peuplant les ceintures. Dans cette étude, il s'agit de développer un modèle des ceintures de radiations internes de Saturne, basé sur les travaux précédents. Avant les années 2000, Pioneer 11 et Voyager 2 ne permettaient pas un développement suffisamment avancé d'un modèle de ceintures de radiations de Saturne. La mission Cassini apporte ensuite quantités d'observations et de données pour mener une étude plus approfondie de ces ceintures. Cette thèse débute par l'analyse de la magnétosphère interne de Saturne : anneaux, satellites, nuages de neutres...L'interaction des particules des ceintures de radiations avec ces différents paramètres se traduit par le calcul de coefficients de diffusion. Ces coefficients sont intégrés à l'équation de transport et permettent de comprendre les mécanismes perturbant la distribution des électrons au sein des ceintures de radiations. Les résultats obtenus sont comparés aux mesures faites par les sondes Pioneer 11, Voyager 2 et Cassini. / Radiation belts cause irreversible damages to on-board instrument materials. Studies about radiation belts can be useful for development of materials that will stand such environment. Since the 1990's, ONERA develops models of radiation belts of magnetized planets, such as the Earth or Jupiter. These previous work lead to a physical model, named Salammbô. Salammbô is based on physical processes that dominate the planetary magnetosphere in order to recreate electron populations of radiation belts. ONERA is now able to develop an electron radiation belt model for Saturn's environment, i.e., a new version of Salammbô. Before the 2000's, Pioneer 11 and Voyager 2 did not allow a good development of a Salammbô model in the case of Saturn. Nowadays, the Cassini mission gives a lot of information about Saturn, its magnetosphere and its environment to start a study about radiation belts of Saturn. This thesis begins with the analyse of the kronian magnetosphere : rings, satellites, neutral clouds, etc. Interaction between radiation belt particle and these different parameters lead to diffusion coefficients. Diffusion coefficients are integrated into the Salammbô code and imply a better comprehension of mechanisms that can interfere with the electron distribution of radiation belts. Results have been compared with observations of Pioneer 11, Voyager 2 and Cassini spacecrafts.