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.

This thesis examines the current technological and legal issues concerning orbital debris (space debris). The unique physical characteristics of the space environment are identified and explained. The thesis then explores the causes of orbital debris and examines the risk posed by debris to the most frequently used orbital areas. Significant environmental, legal, political, and economic consequences of orbital debris are described. The current technical and legal controls on the creation of debris are discussed and evaluated. Finally, proposed solutions are considered and critiqued. The thesis concludes with a non-binding treaty-based proposal for a new legal debris control regime that can encourage compliance and enhance accountability.

No description available.

A systematic examination of 1836 images of the sky constructed from scans made by the Infrared Astronomical Satellite has resulted in the detection of 466 objects which are shown to be in Earth orbit. Analysis of the spatial and size distribution and thermal properties of these objects, which may include payloads, rocket bodies and debris particles, is being conducted as one step in a feasibility study for space -based debris detection technologies.

Techn. Univ., Diss.--Braunschweig, 2003.

Since the launch of the first rocket by the scientists during the World War II , mankind continues their exploration of space. Those space explorations bring the benefits to human, such as high technology products like GPS, cell phone, etc. and in-depth insight of outside of the earth. However, they produce millions of debris with a total estimated mass of more than 3,000,000 kg in the space around the earth, which has and will continue to threat the safety of manned or unmanned space exploration. According to the research, at least tens of spacecraft were considered been damaged or destroyed by the debris left in the space. Thus, the increasingly cluttered environment in space is placing a premium on techniques capable of tracking and estimating the trajectory of space debris. Among debris, the pieces smaller than 1cm are unable to damage spacecraft because of the crafts’ shields, while the pieces larger than 10cm can be tracked by ground-based radars or a radar network. However, unlike the debris within these size ranges, the debris larger than 1 cm and smaller than 10 cm are able to hurt the shield of space craft and are hard to be detected by the exiting technical equipments because of their small size and cross-section area. Accordingly it is always a challenge for spacecraft or satellite mission designers to consider explicitly the ones ranged from 1 cm to 10 cm a priori. To tackle this challenge, a vision based debris’ trajectory tracking method is presented in the thesis. Unlike radar tracking, vision based tracking doesn’t require knowledge of a debris’ cross-section, regardless of its size. In this work, two cameras onboard of satellites in a formation are used to track the debris in iv close proximity. Also to differentiate the target debris from other clutters (i.e. the debris that are not tracked intentionally), a data association technique is investigated. A two-stage nonlinear robust controller is developed to adjust the attitude of the satellites such that the target debris is always inside of the field of view of the cameras. Capabilities of the proposed integrated estimation and control methods are validated in the simulations.

No description available.

Tidal debris structures are striking evidence of hierarchical assembly -- the premise that the Milky Way and galaxies like it have been built over cosmic time through the coalescence of many smaller objects. In the prevailing Lambda -- Cold Dark Matter cosmology, the vast majority of mergers by number are minor; one dark matter halo, hosting a larger galaxy, dominates the interaction and a smaller object, the satellite, is stripped of mass by tidal forces. When the luminous component of the satellite is disrupted the debris may form structures such as stellar tidal streams or shells, depending on the parameters of the interaction. In this Thesis we examine the properties of this debris left behind by minor mergers theoretically, computationally, and observationally, making strides towards a more complete understanding of what tidal debris can tell us about the history of galaxy formation in the Universe. Around the Milky Way itself we have examined the properties of the Orphan Stream, a stellar tidal stream so named due to uncertainty about the position and current state of its progenitor. Using 3.6 um observations taken as part of the Spitzer Merger History and Shape of the Galactic Halo program, the latest period--luminosity--metallicity relations, and archival data, we compute precise distances to RR Lyrae stream members with state--of--the--art 2.5% relative uncertainties. Fitting an orbit to the data, we measure an enclosed mass for the Milky Way that is in good agreement with other recent results, once the biases in orbit fitting are taken into account. By applying the same technique to N--body simulations we determined that the Orphan progenitor is most likely similar to the classical dwarf spheroidal satellites. We also examined tidal debris more generally, in particular by investigating the source of the morphological dichotomy between shells and streams. We find that the transition from a stream--like to a shell--like morphology occurs when the differential azimuthal precession between the orbits of stars exceeds the position angle subtended by individual petals of the progenitor orbit's rosette. This statement is cast more precisely in terms of scaling relations that control the dispersion of energy and angular momentum in the debris, and we find that the observed morphology can be predicted for a given host, orbit, and mass ratio. This leads us to the idea that the observed occurrence rates of different morphologies can be used to recover, at the population statistics level, the progenitor satellites' orbital infall distribution. This a part of the cosmological accretion history that is otherwise inaccessible. To achieve this in practice requires an unbiased and automated method to detect and classify substructure; we have developed just such a tool and demonstrate its effectiveness. In the upcoming era of LSST and WFIRST the methods and insights developed in this Thesis will be useful in decoding the information about the current state and assembly of galaxies encoded in tidal debris.

No description available.

Thesis (M.S. in Space Systems Operations)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Eric Christiansen, Rudy Panholzer, Dan Bursch. Includes bibliographical references (p. 75-76). Also available online.