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"Swinerd, Graham"
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Further evidence of long-term thermospheric density change using a new method of satellite ballistic coefficient estimation
Building 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 proposed. Key Points Long‐term thermospheric density decline Ballistic coefficient determination using TLE data Validation of existing theories
Journal Article
How spacecraft fly : spaceflight without formulae
Sputnik was launched almost fifty years ago, and most people still don't understand how. Written for the layman, this text explains aerodynamic and astrodynamic spaceflight using informal language free of mathematics and technical jargon.
eBook
Effect of thermospheric contraction on remediation of the near-Earth space debris environment
Historically, computer simulations of the near‐Earth space debris environment have provided a basis for international debris mitigation guidelines and, today, continue to influence international debate on debris environment remediation and active debris removal. Approximately 22,500 objects larger than 10 cm are known to exist in Earth orbit, and less than 5% of these are operational payloads, with the remaining population classed as space debris. These objects represent a significant risk to satellite operations because of the possibility of damaging or catastrophic collisions, as demonstrated by the collision between Iridium 33 and Cosmos 2251 in February 2009. Indeed, recent computer simulations have suggested that the current population in low Earth orbit (LEO) has reached a sufficient density at some altitudes for collision activity there to continue even in the absence of new launches. Even with the widespread adoption of debris mitigation guidelines, the growth of the LEO population, in particular, is expected to result in eight or nine collisions among cataloged objects in the next 40 years. With a new study using the University of Southampton's space debris model, entitled DAMAGE, we show that the effectiveness of debris mitigation and removal strategies to constrain the growth of the LEO debris population could be more than halved because of a long‐term future decline in global thermospheric density. However, increasing debris remediation efforts can reverse the impact of this negative density trend. Key Points Thermospheric decline reduces debris mitigation efficacy Thermospheric decline reduces efficacy of debris removal Increasing removal rate restores benefit of debris removal
Journal Article
Global Vulnerability to Near-Earth Object Impact
A clear appreciation of the consequences resulting from an asteroid impact is required in order to understand the near-Earth object (NEO) hazard. Three main processes require modelling to analyse the entire impact event. These are the atmospheric entry phase, land impact events and ocean impact events. A range of impact generated effects (IGEs) are produced by different impact scenarios. It is these IGEs that present the threat to human populations worldwide, and the infrastructure they utilise. A software system for analysing the NEO threat has been developed, entitled NEOimpactor, to examine the social and economic consequences from land and ocean impacts. Existing mathematical models for the three principal impact processes have been integrated into one complete system, which has the capability to model the various effects of a terrestrial asteroid impact and, critically, predict the consequences for the global population and infrastructure. Analysis of multiple impact simulations provides a robust method for the provision of an integrated, global vulnerability assessment of the NEO hazard. The primary graphical outputs from NEOimpactor are in the form of 'relative consequence' maps, and these have been designed to be comprehensible to a non-specialist audience. By the use of a series of multiple-impact simulations, the system has identified the five countries most at risk from the impact hazard, as well as indicating the various factors influencing vulnerability.
Journal Article
Near Earth Object impact simulation tool for supporting the NEO mitigation decision making process
This paper describes the development of a computer simulation tool, NEOSim, capable of modelling small NEO impacts and their effect on the global population. The development of the tool draws upon existing models for the atmospheric passage and impact processes. Simulation of the land and ocean impact effects, combined with a population density model, leads to casualty estimation at both a regional and global level. Casualty predictions are based upon the intensity of each impact effect on the local population density, with consideration given to the population inside or outside local infrastructure. Two case studies are presented. The first evaluates the potential threat to the UK, and highlights coastal locations as being at greatest risk. Locations around Cornwall demonstrate an increase in casualties above the local average. The second case study concerns the potential impact of asteroid (99942) Apophis in 2036. Propagation of the possible orbits along the line of variance leads to an extensive path of risk on the Earth. Deflection of the asteroid, by a variety of means, will move the projected impact site along this path. Results generated by NEOSim for the path indicate that South American countries such as Colombia and Venezuela are at a greatest risk with estimated casualty figures in excess of 10 million. Applications of this software to the NEO threat are discussed, along with the next stage of NEO impact simulation development.
Journal Article