In-flight scale/distortion calibration of the Hubble Space Telescope fixed-head star trackers

This paper describes an in-flight scale and distortion calibration procedure that has been developed for the Ball Aerospace Systems Division Fixed-Head Star Trackers (FHST's) used on the Hubble Space Telescope (HST). The FHST is a magnetically focused and deflected imaging sensor that is designed to track stars as faint as m(sub v) = 5.7 over an 8 degree by 8 degree field of view. Raw FHST position measurements are accurate to approximately 200 arcseconds, but this can be improved to 10-15 arcseconds by processing the raw measurements through calibration polynomials that correct for flat field, temperature intensity, and magnetic field effects. The coefficients for these polynomials were initially determined using ground test data. On HST the use of three FHST's is an integral part of the preliminary attitude update procedures required before the acquisition of guide stars for science observations. To this end, FHST-based attitude determination having single-axis errors no worse than 22 arcseconds (1 sigma) is required. In early 1991 it became evident that one of the HST FHST's was experiencing a significant change in its optical scale. By mid-1993 the size of this error had grown to a point that, if not corrected, it would correspond to a maximum position error on the order of 100 arcseconds. Subsequent investigations demonstrated that substantial, uncompensated cubic distortion effects had also developed, the maximum contribution to position errors from the cubic terms being on the order of 30 arcseconds. To ensure accurate FHST-based attitude updates, procedures have been developed to redetermine the FHST scale and distortion calibration coefficients based on in-flight data gathered during normal HST operations. These scale and distortion calibrations have proven very effective operationally, and procedures are in place to monitor FHST calibration changes on a continuing basis

A note on dynamic surface displacements in an elastic half-space

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41710/1/707_2005_Article_BF01260886.pd

Movilidad urbana y pobreza: Aprendizajes de Medellín y Soacha, Colombia

Este libro es un análisis de la experiencia de Medellín, la segunda ciudad de Colombia, en intentar reducir la pobreza e integrar en el tejido urbano barrios marginalizados y estigmatizados durante muchos años por la pobreza y la violencia. En particular, examina el impacto de dos cables aéreos que conectan densos barrios en colinas empinadas con el resto de la ciudad, y un programa de mejoramiento urbano asociado a estos. También contrasta la experiencia exitosa de Medellín con la de Soacha, un municipio adyacente a Bogotá, la capital colombiana, donde se ha propuesto un cable aéreo como medio de conexión de dos barrios en colina con una vía arteria. El contraste entre un municipio bien gestionado y abundante en recursos como Medellín con un municipio denso, homogéneamente pobre e institucionalmente débil como Soacha ofrece aprendizajes muy valiosos para otras ciudades en América Latina y otras regiones del mundo. La mayor parte de los capítulos se apoyan en un proyecto de investigación de dos años coordinado por la Development Planning Unit, University College London (UCL), en asocio con la Universidad Nacional de Colombia (sede Medellín) y la Universidad de los Andes de Bogotá. Además de estudios de caso detallados de Medellín y Soacha, el libro agrupa también casos en América Latina en donde se han construido o se han propuesto cables aéreos en barrios de bajos ingresos, como Caracas y Rio de Janeiro

Urban Mobility and Poverty: Lessons from Medellin and Soacha, Colombia

This book examines the experience of Medellín, Colombia's second largest city, in seeking to reduce poverty and integrate large marginalised areas, marked by years of severe poverty and violence, into the urban fabric. It pays particular attention to the impact of two aerial cable-cars connecting high density hilly neighbourhoods with the rest of the city, and an associated urban upgrading programme. It also contrasts Medellín’s successful experience with that of Soacha, a municipality adjacent to Bogotá, Colombia’s capital city, where an aerial cable-car has been proposed as a means of linking two low-income hilly neighbourhoods with a main arterial road. The contrast between a well-resourced, well-managed municipality like Medellín with a dense and homogenously poor and institutionally weak municipality like Soacha offers valuable lessons to other cities in Latin America and elsewhere. Contributions draw from a two-year research project coordinated by the Development Planning Unit, University College London (UCL), in conjunction with Universidad Nacional de Colombia (Medellín campus) and Universidad de los Andes in Bogotá. In addition to the detailed case studies of Medellín and Soacha, the book also brings together cases in Latin America where aerial cable-cars have either been built or proposed in low-income neighbourhoods, including Caracas and Rio de Janeiro

Rationaliser la planification des projets de transport urbain pour le Caire, Egypte

The preparation and execution of transportation projects in Cairo involves the participa¬tion of several local and national agencies, each with its own perspectives on the problems and preferences among projects. Together this participation creates a "slate" of projects, a set of projects which by mutual agreement will be executed in the near future. This form of agreeing on project selection has significant strengths in that, for example, it produces a program which has the active support of all the agencies in the transportation sector. One the other hand, it means the detailed programming must be handled in a special way. In the absence of a central rationale for project selection, comparative evaluation between projects has a limited role, and implementation must always include several projects simultaneously to keep the interests of concerned agencies in balance. But one must remember: the slate is a plan, and for all its lack of scientific refinement, a robust, realistic plan.La préparation et l'exécution des projets de transport au Caire réunissent la participation de plusieurs services à l'échelon local et national, chacun avec ses propres perspectives sur les problèmes, et ses préférences parmi les projets. De cette participation collective résulte une liste d'accords mutuels, un ensemble de projets qui doivent être exécutés. Cette forme d'accord sur le choix des projets a une portée significative en ce que, par exemple, elle établit un programme qui joint le support actif des services principaux de secteur des transports. D'autre part, elle signifie que la programmation détaillée doit être effectuée de manière spécifique. En l'absence d'une rationalité centrale pour le choix des projets, l'évaluation comparative de ceux-ci a seulement un rôle limité et la mise en œuvre proprement dite doit toujours inclure plusieurs projets simultanément afin de conserver l'équilibre entre les intérêts des services concernés. Mais il faut rappeler que la liste d'accords mutuels constitue un plan qui, malgré son manque de raffinement scientifique, n'en est pas moins solide et réaliste