Robustness Analysis of Eigenstructure Assignment Controllers on Rigid-Flexible Satellites

Flexible spacecraft with attached solar panels may exhibit undesired vibrations and structural deformations. These types of vehicles show an intrinsic coupling of the elements of the structure. The attitude maneuvers performed by flexible spacecraft may cause non-desired deflections of attached flexible elements. Any attitude and orbit control system generally solves these problems using filters that are designed to attenuate the relative deflections of flexible appendages. In this paper, we propose a method for designing attitude static controllers using an eigenstructure assignment (EA) method. A set of requirements were specified from our understanding of the system modes in an open loop. Exhaustive theoretical and numerical simulations were performed on special cases to verify the controller design procedure. In the design of the controller, we considered all of the aspects that relate to the eigenstructure assignment. The primary objective of this paper is to demonstrate the feasibility of obtaining a high degree of decoupling for some selected modes via the application of an EA method. Finally a robustness analysis is perform to the system together with the designed controller by means of a mu-analysi

Criteria for Positioning Active Multilateration Stations Located Close to Distance Measuring Equipment

The need for the use of another surveillance system when radar cannot be used is the reason for the development of the Multilateration (MLT) Systems. However, there are many systems that operate in the L-Band (960-1215MHz) that could produce interference between systems. At airports, some interference has been detected between transmissions of MLT systems (1030MHz and 1090MHz) and Distance Measuring Equipment (DME) (960-1215MHz)

Software tool for simulation of aircraft trajectories

New concepts in air navigation have been introduced recently. Among others, are the concepts of trajectory optimization, 4D trajectories, RBT (Reference Business Trajectory), TBO (trajectory based operations), CDA (Continuous Descent Approach) and ACDA (Advanced CDA), conflict resolution, arrival time (AMAN), introduction of new aircraft (UAVs, UASs) in air space, etc. Although some of these concepts are new, the future Air Traffic Management will maintain the four ATM key performance areas such as Safety, Capacity, Efficiency, and Environmental impact. So much, the performance of the ATM system is directly related to the accuracy with which the future evolution of the traffic can be predicted. In this sense, future air traffic management will require a variety of support tools to provide suitable help to users and engineers involved in the air space management. Most of these tools are based on an appropriate trajectory prediction module as main component. Therefore, the purposes of these tools are related with testing and evaluation of any air navigation concept before they become fully operative. The aim of this paper is to provide an overview to the design of a software tool useful to estimate aircraft trajectories adapted to air navigation concepts. Other usage of the tool, like controller design, vertical navigation assessment, procedures validation and hardware and software in the loop are available in the software tool. The paper will show the process followed to design the tool, the software modules needed to perform accurately and the process followed to validate the output data

Análisis de algoritmos para posicionamiento de aeronaves mediante respuestas SSR utilizando recepción omnidireccional

El transporte aéreo constituye un sector estratégico para el crecimiento económico de cualquier país. El sistema de gestión de tráfico aéreo ATM tiene como objetivo el movimiento seguro y eficiente de las aeronaves dentro del espacio aéreo y de los aeropuertos, siendo la seguridad, en la fase táctica, gestionada por el servicio de control de la circulación aérea. Mediante los procesos de control el tráfico aéreo es vigilado a través de sensores, regulado y guiado de forma organizada y segura. Es precisamente sobre la vigilancia donde se enfoca el contenido de la tesis, en el desarrollo de nuevos conceptos que proporcionen información de vigilancia de ‘bajo coste’ basados en las señales existentes proporcionadas por la infraestructura actual de radar secundario y por los sistemas de posicionamiento basados en satélite que utiliza la ADS-B. El conocimiento y acceso en tiempo real a las trayectorias de las aeronaves es un elemento de valor añadido no sólo para la provisión de los servicios de control de tránsito aéreo, sino para todos los actores del transporte aéreo o de la investigación, siendo uno de los elementos clave en el concepto operacional de los dos grandes proyectos tecnológicos, SESAR en Europa y NextGen en EE.UU.. En las últimas décadas el control de la circulación aérea en espacios aéreos de media y alta densidad de tráfico se ha basado en tecnologías complejas que requieren importantes infraestructuras como son el radar primario de vigilancia (PSR) y el radar secundario de vigilancia (SSR). La filosofía de los programas SESAR y NextGen siguiendo las directrices de la OACI es la de alejarse de las tecnologías basadas en tierra para evolucionar hacia nuevas tecnologías más dinámicas basadas en satélite como la ADS-B. Pero hasta que la implementación y operación de la ADS-B sea completa, existirá un período de transición que implica la coexistencia de aeronaves equipadas o no con ADS-B. El objetivo de la presente Tesis es determinar las metodologías y algoritmos más adecuados para poder hibridar las dos tecnologías descritas anteriormente, utilizando para ello un receptor de bajo coste con antena estática omnidireccional, que analice todas las señales presentes en el canal que comparten el SSR y ADS-B. Mediante esta hibridación se podrá obtener la posición de cualquier aeronave que transmita respuestas a interrogaciones SSR, en cualquiera de sus modos de trabajo, o directamente mensajes de posición ADS-B. Para desarrollar los algoritmos propuestos, además del hardware correspondiente, se han utilizado las aplicaciones LabVIEW para funciones de adquisición de datos reales, y el software MATLAB® para el desarrollo de algoritmos y análisis de datos. La validación de resultados se ha realizado mediante los propios mensajes de posición ADS-B y a través de las trazas radar proporcionadas por la entidad pública empresarial ENAIRE. La técnica desarrollada es autónoma, y no ha requerido de ninguna otra entrada que no sea la recepción omnidireccional de las señales. Sin embargo para la validación de resultados se ha utilizado información pública de las ubicaciones de la red de estaciones SSR desplegadas sobre territorio español y portugués y trazas radar. Los resultados obtenidos demuestran, que con técnicas basadas en superficies de situación definidas por los tiempos de llegada de las respuestas, es posible determinar con una precisión aceptable la posición de las estaciones SSR y la posición de cualquier aeronave que responda mediante el Modo A a éstas. ABSTRACT Air transport is a strategic sector for the economic growth of any country. The air traffic management system (ATM) aims at the safe and efficient movement of aircraft while operating within the airspace and airports, where safety, in the tactical phase, is managed by the air traffic control services. Through the air traffic control processes, aircraft are monitored by sensors, regulated and guided in an organized and safe manner. It is precisely on surveillance where this thesis is focused, developing new concepts that provide a 'low cost' surveillance information based on existing signals provided by currently secondary radar infrastructure and satellite-based positioning systems used by ADS-B. Having a deeper knowledge and a real-time access to the trajectories of the aircraft, is an element of added value not only for the provision of air traffic control services, but also for all air transport or research actors. This is one of the key elements in the operational concept proposed by the two large scale existing technological projects, SESAR in Europe and NextGen in the US. In recent decades, air traffic control in medium and high traffic density areas has been based on complex technologies requiring major infrastructures, such as the primary surveillance radar (PSR) and secondary surveillance radar (SSR). The philosophy of SESAR and NextGen programs, both following the guidelines of ICAO, is to move away from land-based technologies and evolving into some new and more dynamic satellite-based technologies such as ADS-B. Nevertheless, until the ADS-B implementation and operation is fully achieved, there will be a transitional period where aircraft with and without ADS-B equipment will have to coexist. The main objective of this thesis is to determine those methodologies and algorithms which are considered more appropriate to hybridize those two technologies, by using a low cost omnidirectional receiver, which analyzes all signals on the SSR and ADS-B shared channel. Through this hybridization, it is possible to obtain the position of any aircraft answering the SSR interrogations, in any of its modes of operation, or through the emission of ADS-B messages. To develop the proposed algorithms, LabVIEW application has been used for real-time data acquisition, as well as MATLAB software for algorithm development and data analysis, together with the corresponding hardware. The validation of results was performed using the ADS-B position messages and radar tracks provided by the Public Corporate Entity ENAIRE The developed technique is autonomous, and it does not require any other input other than the omnidirectional signal reception. However, for the validation of results, not only radar records have been used, but also public information regarding the position of SSR stations spread throughout the Spanish and Portuguese territory. The results show that using techniques based in the definition of positioning surfaces defined by the responses’ times of arrival, it is possible to determine with an acceptable level of accuracy both the position of the SSR stations as well as the position of any aircraft which transmits Mode A responses

Vorapaxar in the secondary prevention of atherothrombotic events

Item does not contain fulltextBACKGROUND: Thrombin potently activates platelets through the protease-activated receptor PAR-1. Vorapaxar is a novel antiplatelet agent that selectively inhibits the cellular actions of thrombin through antagonism of PAR-1. METHODS: We randomly assigned 26,449 patients who had a history of myocardial infarction, ischemic stroke, or peripheral arterial disease to receive vorapaxar (2.5 mg daily) or matching placebo and followed them for a median of 30 months. The primary efficacy end point was the composite of death from cardiovascular causes, myocardial infarction, or stroke. After 2 years, the data and safety monitoring board recommended discontinuation of the study treatment in patients with a history of stroke owing to the risk of intracranial hemorrhage. RESULTS: At 3 years, the primary end point had occurred in 1028 patients (9.3%) in the vorapaxar group and in 1176 patients (10.5%) in the placebo group (hazard ratio for the vorapaxar group, 0.87; 95% confidence interval [CI], 0.80 to 0.94; P<0.001). Cardiovascular death, myocardial infarction, stroke, or recurrent ischemia leading to revascularization occurred in 1259 patients (11.2%) in the vorapaxar group and 1417 patients (12.4%) in the placebo group (hazard ratio, 0.88; 95% CI, 0.82 to 0.95; P=0.001). Moderate or severe bleeding occurred in 4.2% of patients who received vorapaxar and 2.5% of those who received placebo (hazard ratio, 1.66; 95% CI, 1.43 to 1.93; P<0.001). There was an increase in the rate of intracranial hemorrhage in the vorapaxar group (1.0%, vs. 0.5% in the placebo group; P<0.001). CONCLUSIONS: Inhibition of PAR-1 with vorapaxar reduced the risk of cardiovascular death or ischemic events in patients with stable atherosclerosis who were receiving standard therapy. However, it increased the risk of moderate or severe bleeding, including intracranial hemorrhage. (Funded by Merck; TRA 2P-TIMI 50 ClinicalTrials.gov number, NCT00526474.)