1,620 research outputs found
An empirical model of long-term thermospheric density change
No full textPredicting the positions of satellites in Low Earth Orbit (LEO) requires a comprehensive understanding of the dynamic nature of the atmosphere. For objects in LEO the most significant orbit perturbation is atmospheric drag, which is a function of the local atmospheric density from a layer in the atmosphere called the thermosphere. For long-term predictions of satellite orbits and ephemerides, any density trend in the thermosphere is a necessary consideration, not only for satellite operators, but also for studies of the future LEO environment in terms of space debris. Numerous studies of long-term thermospheric density change have been performed.Predictions by Roble & Ramesh (2002), along with evidence by Keating (2000), Emmert et al.(2004), Marcos et al. (2005), Qian et al. (2006) and Emmert et al. (2008), strongly suggest the existence of such a phenomenon. Therefore, the objective of the research presented in this thesis is to provide a novel method to evaluate quantitatively thermospheric density change. Satellite drag data is an effective medium through which one can investigate local thermospheric density and changes thereof. There are many ways of determining atmospheric density, but inferring thermospheric density from satellite drag data is a relatively cost-effective way of gathering in-situ measurements. To do this, knowledge about a satellite’s physical properties that are intrinsic to atmospheric drag is required. A study by Saunders et al. (2009) highlighted problems with estimating a satellite’s physical properties directly from data given explicitly by Two-Line Element (TLE) sets. This prompted an investigation into ways to estimate ballistic coefficients: a required satellite parameter associated with drag coefficient and area-to-mass ratio. A novel way of estimating satellite ballistic coefficients was derived and is presented in this thesis. Additionally, novel consideration of atmospheric chemical composition was applied on long-term drag coefficient variability. Using a quantitative estimate of a ballistic coefficient one can propagate numerically a satellite’s orbit and predict the effects of atmospheric drag. Given an initial satellite orbit from TLE data, one approach is to use an orbital propagator to predict the satellite’s state at some time ahead and then to compare that state with TLE data at the same epoch. The difference between the semi-major axes of the initial orbit and that after the orbit propagation is then integrated and can be used to estimate the global average density. The method employed in this study utilises this process. To achieve this, a specially developed, computer-based, numerical orbital propagator was written in the programming language C/C++. The underlying theories and implementation tests for this propagator are presented in this thesis
A new analysis of debris mitigation and removal using networks
No full textModelling studies have shown that the implementation of mitigation guidelines, which aim to reduce the amount of new debris generated on-orbit, is an important requirement of future space activities but may be insufficient to stabilise the near-Earth debris environment. The role of a variety of mitigation practices in stabilising the environment has been investigated over the last decade, as has the potential of active debris removal (ADR) methods in recent work. We present a theoretical approach to the analysis of the debris environment that is based on the study of networks, composed of vertices and edges, which describe the dynamic relationships between Earth satellites in the debris system. Future projections of the 10 cm and larger satellite population in a non-mitigation scenario, conducted with the DAMAGE model, are used to illustrate key aspects of this approach. Information from the DAMAGE projections are used to reconstruct a network in which vertices represent satellites and edges encapsulate conjunctions between collision pairs. The network structure is then quantified using statistical measures, providing a numerical baseline for this future projection scenario. Finally, the impact of mitigation strategies and active debris removal, which can be mapped onto the network by altering or removing edges and vertices, can be assessed in terms of the changes from this baseline. The paper introduces the network methodology, highlights the ways in which this approach can be used to formalise criteria for debris mitigation and removal. It then summarises changes to the adopted network that correspond to an increasing stability and changes that represent a decreasing stability of the future debris environment
Heartbeat Horizon: Saunders\u27s Presentation to Executive Board of Directors Sept. 2012
No full textSpeech/presentation by Saunders to the Board of Directors. Outlines how Heartbeat changed Saunders\u27s view of God, Jesus, the Bible, and the church; the importance of vision and the compelling drive of Heartbeat\u27s vision; and a proposal for Heartbeat for the next three years of 2012-2015 and the role Saunders feels he should play. Future goals include a book Saunders wants to author, a Heartbeat Institute, and a plan for laying up content and marketing it to a wide audience.
Typed presentation also contains notes and revisions handwritten by Saunders
Further evidence of long-term thermospheric density change using a new method of satellite ballistic coefficient estimation
No full textBuilding on work from previous studies a strong case is presented for the existence of a long-term density decline in the thermosphere. Using a specially developed orbital propagator to predict satellite orbit evolution, combined with a new and accurate method of determining satellite ballistic coefficients, a long-term thermospheric density change has been detected using a different method compared to previous studies. Over a 40-year period between the years 1970 and 2010, thermospheric density has appeared to reduce by a few percent per decade. However, the results do not show the thermospheric density reduction to vary linearly with time. Therefore, by analyzing the derived density data over varying solar activity levels, as well as performing a Fourier spectral analysis to highlight any periodicities, connections with physical phenomena, where possible, are propose
Photograph of Benk Green and Tom B. Saunders III at Saunders Ranch Museum
No full textPhotograph at the Saunders Ranch Museum of author Benk Green and Tom B. Saunders III
Opt-out organ donation without presumptions
No full textThis paper defends an 'opt-out' scheme for organ procurement, by distinguishing this system from 'presumed consent' (which the author regards as an erroneous justification of it). It, first, stresses the moral importance of increasing the supply of organs and argues that making donation easier need not conflict with altruism. It then goes on to explore one way that donation can be increased, namely by adopting an opt-out system, in which cadaveric organs are used unless the deceased (or their family) registered an objection. Such policies are often labelled 'presumed consent', but it is argued that critics are right to be sceptical of this idea -- consent is shown to be an action, rather than a mental attitude, and thus not something that can be presumed. Either someone has consented or they have not, whatever their attitude to the use of their organs. Thankfully, an opt-out scheme need not rest on the presumption of consent. Actual consent can be given implicitly, by one's actions, so it is argued that the failure to register an objection (given certain background conditions) should itself be taken as sign of consent. Therefore, it is permissible to use the organs of someone who did not opt out, because they have -- by their silence -- actually consented
Prof. Peter Saunders, 1992
No full textProf. Peter Saunders, one of the world's leading urban sociologists and author of six books, including his most recent book, 'A Nation of Home Owners'. Prof. Saunders gave a public seminar on his research into the effects of privatisation of the Water Industry in the United Kingdom. Photograph originally appeared in the 'Staff News', 30th April 1992
J. Saunders Redding, circa 1970
No full textA portrait photo of author Jay Saunders Redding. Written on verso: Saunders Redding (author) - first AA faculty at an Ivy League (Brown).The Atlanta University Center Robert W. Woodruff Library acknowledges the generous support of the Joseph & Evelyn Lowery Institute for Justice and Human Rights, the Joseph Echols Lowery Irrevocable Trust, and other donors in supporting the processing and digitization of Morehouse College's Joseph Echols and Evelyn Gibson Lowery Collection
Still kicking: George Saunders and ‘shadow realism’
No full textInternational audienceEven as George Saunders jettisons the usual trappings of literary realism, he does so not in order to debunk authorship and authority (cf. Barthes) or to reduce a story to the language of its own telling. Rather, he reasserts the writer’s moral role, and thereby defines a space for the figure of the author. With reference to Lionel Trilling’s defence of Nathaniel Hawthorne and ‘shadow realism’ this article situates Saunders in a literary tradition which challenges reductive conceptions of mimesis. It cites examples from Saunders’ short stories and novellas (CivilWarLand in Bad Decline, 1996; Pastoralia, 2000; In Persuasion Nation, 2006), and also addresses an author-sponsored website, with attention to how Internet materials are not only a promotion of Saunders’ work, but also an extension of it. Saunders foregrounds the referential workings of language while remaining attached to a sense that language is a tool for moral questions
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