Thesis (M. Sc.)--University of Hong Kong, 2004. / Also available in print.

Thesis (M. Sc.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 49-61).

Thesis (M.S.)--Oregon State University, 2001. / Typescript (photocopy). Includes bibliographical references (leaves 45-47). Also available on the World Wide Web.

Planetary systems around other stars have been observed to be far more diverse than what would be expected from the example of the Solar System. Exoplanets have been detected with a wide range of sizes and separations from the host star, with a range of orbital properties including large eccentricities and small inter-planet mutual inclinations. How representative these planetary systems are, however, is unclear due to detection techniques being more sensitive to planets on close orbits around the host star. It is possible therefore that a population of wide-orbit planets could be present in these systems and be evading detection. These planets may play a significant role in forming and shaping planetary systems, resulting in the architecture that is observed today. Currently, one of the major ways of inferring the presence of wide-orbit planets, besides directly detecting them, is to consider the dynamical impact they would have on known planets. In the first part of this thesis I consider how the eccentricities of known planets are affected due to long term dynamical interactions with a wide-orbit planet. I show that the eccentricity of a known planet in a system can periodically be significantly increased due to these interactions, provided that there are a total of two planets in the system. For systems with multiple known planets I show that the inner planets can protect each other against long term eccentricity perturbations from a wide-orbit planet. Following on from this investigation, I show how the inclinations of planets are affected due to long term interactions with a wide-orbit planet. Specifically, I consider how this interaction affects the probability that planetary systems are observed to transit. I find that the presence of wide-orbit planets in transiting planetary systems can help explain the so-called `Kepler-Dichotomy' which describes the apparent excess of observed single transiting systems compared with multi-planet transiting systems. Wide-orbit planets do not just dynamically interact with other planets in a system but also with small debris type bodies, akin to the Asteroid and Kuiper belts in the Solar System. In the second half of this thesis, I consider the planetary system HR8799 which is known to host four planets and two populations of debris which lie both internally and externally to the known planets. I find, through suites of N-body simulations, that a hypothetical planet in HR8799 sculpts an outer debris population that agrees more strongly with observations, compared with what would be expected by considering the known planets in isolation. Finally, for the last part of this thesis, I describe a survey that is looking to observe wide-orbit planets in close-by planetary systems directly. The observations and analysis for this survey is currently on-going, however I show preliminary results including systems with and without potential companion detections.

No description available.

This thesis investigates the orbital debris evolution in the geosynchronous disposal orbit regime and within geosynchronous orbits effected by the geopotential wells. A propagator is developed for the accurate simulation of GEO specific orbits and the required perturbations are determined and described. Collisions are then simulated in the selected regimes using a low velocity breakup model derived from the NASA EVOLVE breakup model. The simulations described in this thesis consider a set of perturbations including the geopotential, solar and lunar gravity, and solar radiation pressure forces. This thesis is based on a prior paper and additionally seeks to address an issue in simulating East-West trapped objects. The results show that this propagator successfully simulates the presence of all wells and the East-West entrapment, and the required perturbations are outlined. Five collision test cases were simulated, one for each type of entrapment and an additional for the disposal orbit.

No description available.

No description available.

The safety of future spaceflight depends on space surveillance and space traffic management, as the density of objects in Earth orbit has reached a level that requires collision avoidance maneuvers to be performed on a regular basis to avoid a mission or, in the context of human space flight, life-endangering threat. Driven by enhanced sensor systems capable of detecting centimeter-sized debris, megaconstellations and satellite miniaturization, the space debris problem has revealed many parallels to the plastic waste in our oceans, however with much less visibility to the eye. Future catalog sizes are expected to increase drastically, making it even more important to detect potentially dangerous encounters as early as possible. Due to the limited number of monitoring sensors, continuous observation of all objects is impossible, resulting in the need to predict the orbital paths and their uncertainty via models to perform collision risk assessment and space object catalog maintenance. For many years the uncertainty models used for orbit determination neglected any uncertainty in the astrodynamic force models, thereby implicitly assuming them to be flawless descriptions of the true space environment. This assumption is known to result in overly optimistic uncertainty estimates, which in turn complicate collision risk analysis. The keynote of this doctoral thesis is to establish uncertainty realism for low Earth orbiting satellites via a physically connected quantification of the dominant force model uncertainties, particularly multiple sources of atmospheric density uncertainty and orbital gravity uncertainty. The resulting process noise models are subsequently integrated into classical and state of the art orbit determination algorithms. Their positive impact is demonstrated via numerical orbit determination simulations and a collision risk assessment study using all non-restricted objects in the official United States space catalogs. It is shown that the consideration of atmospheric density uncertainty and gravity uncertainty significantly improves the quality of the orbit determination and thus makes a contribution to future spaceflight safety by increasing the reliability of the uncertainty estimates used for collision risk assessment. / Die Sicherheit der künftigen Raumfahrt hängt von der Weltraumüberwachung und dem Weltraumobjektmanagement ab, da inzwischen die Dichte an Objekten im Erdorbit ein Niveau erreicht hat, welches regelmäßige Kollisionsvermeidungsmanöver erfordert um eine missions- oder, im Kontext der bemannten Raumfahrt, lebensgefährdende Situation zu vermeiden. Durch verbesserte Sensorsysteme, die in der Lage sind, zentimetergroße Objekte zu erkennen, Megakonstellationen und die Satellitenminiaturisierung hat das Weltraummüllproblem viele Parallelen zu den Plastikabfällen in unseren Weltmeeren offenbart, jedoch mit deutlich geringerer Sichtbarkeit für das Auge. Es ist zu erwarten, dass die Größe der Weltraumobjektkataloge in Zukunft drastisch ansteigen wird, was es umso wichtiger macht, potenziell gefährliche Begegnungen so früh wie möglich zu erkennen. Durch die begrenzte Anzahl an Überwachungssensoren ist eine kontinuierliche Beobachtung aller Objekte unmöglich, sodass die Umlaufbahnen und deren Unsicherheiten über Modelle vorausberechnet werden müssen, um die Bewertung von Kollisionsrisiken vorzunehmen und die Wartung der Objektkataloge sicherzustellen. Viele Jahre haben die zur Bahnbestimmung verwendeten Unsicherheitsmodelle jegliche Unsicherheit in den astrodynamischen Kräftemodellen vernachlässigt und somit implizit angenommen, dass diese fehlerfreie Beschreibungen der wahren Weltraumumgebung darstellen. Diese Annahme ist jedoch dafür bekannt, zu übermäßig optimistischen Unsicherheitsabschätzungen zu führen, was die Kollisionsrisikobewertung erschwert. Das Leitthema dieser Doktorarbeit ist die Berechnung realistischer Unsicherheiten von Objekten in einer niedrigen Erdumlaufbahn anhand einer Unsicherheitsquantifizierung mit physikalischem Bezug zu den Kräftemodellen, welche die größten Anteile an der Propagationsunsicherheit aufweisen. Dies sind insbesondere mehrere Quellen von atmosphärischer Dichteunsicherheit, sowie Gravitationsunsicherheit. Die resultierenden Prozessrauschmodelle werden anschließend in klassische und moderne Algorithmen zur Umlaufbahnbestimmung integriert. Die positiven Auswirkungen dieser Technik werden durch numerische Simulationen zur Orbitbestimmung, sowie durch eine Risikobewertungsstudie anhand aller nicht-sensitiven Objekte in den amerikanischen Weltraumkatalogen belegt. Es wird gezeigt, dass die Berücksichtigung von Unsicherheiten in der atmosphärischen Dichte und dem Gravitationsmodell die Qualität der Umlaufbahnbestimmung signifikant verbessert und somit durch zuverlässigere Unsicherheitsschätzungen bei der Kollisionsrisikobewertung einen Beitrag zur künftigen Sicherheit im Weltraum leistet.

No description available.