Análise de viabilidade de implementação de um centro inteligente de motores

Across the industry, regardless of the activity which is intended, the electricity distribution must meet the current and ever growing needs of the market, aiming at reliability and process efficiency. The energy must not only be available to ensure continuity of operation, but also to avoid the costs incurred due to deficiencies and failures. The tendency to migrate to intelligent systems is undeniable and this thesis will be analyzed the advantages that made this kind technology essential, focused on the analysis of the motor control center and as sturdy equipment fit to the concept of intelligent panels. The case study compares in a real scenario the acquisition of a system of low-voltage electrical panels comparing the cost to purchase the same set of panels made with and without the concept of intelligence

Estudo comparativo da proteção da rede secundária de uma distribuidora de energia elétrica utilizando chave fusível e seccionalizador monofásico

The objective of this work is to conduct a comparative study between the fuse key and the single-phase seccionalizador, which are protective equipment used in an electricity distribution networks. This study has also the purpose to reduce the number of electrical power breakdown. Distribution networks are not free from faults, disturbances and failures, then the occurrence of adversities on the network, which may be transient or permanent faults, results in the interruption of electric power. Thus, there are protective systems of distribution networks, which aims to ensure that the electric system continues to function. The incidence of transient faults in the distribution network of this electricity company was used to generate immediate shutdown of customers due to the bad use of fuses as protective equipment by the reclosers. With the use of the fuse switch in the distribution network, there was the immediate shutdown of customers, however, using the single-phase seccionalizador as protective equipment by the reclosers, there are three attempts to restart the electricity power. As the attempts to restart the electricity power are able to eliminate a transient fault, not causing shutdown of any costumer, with the implementation of single-phase sectionalizers to replace the fuses, the number of company shutdowns due to transient faults was reduced by 47.6%

Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Prestazioni energetico-ambientali di sistemi cogenerativi avanzati e analisi di casi applicativi

Lo scopo di questa tesi è quello di analizzare dapprima l’impatto ambientale di tali impianti e poi analizzare il contributo effettivo che oggi la tecnologia innovativa dei cicli Rankine organici può dare nella valorizzazione elettrica del calore di scarto di processi industriali, focalizzando l’obiettivo principalmente sulle turbine a gas ed eseguendo un caso di studio in un settore ancora poco esplorato da questa tecnologia, quello Oil&Gas. Dopo aver effettuato il censimento degli impianti a fonti fossili e rinnovabili, cogenerativi e non, presenti in Emilia-Romagna, è stato sviluppato un software chiamato MiniBref che permette di simulare il funzionamento di una qualsiasi centrale termoelettrica grazie alla possibilità di combinare la tecnologia dell’impianto con il tipo di combustibile consentendo la valutazione delle emissioni inquinanti ed i potenziali di inquinamento. Successivamente verranno illustrati gli ORC, partendo dalle caratteristiche impiantistiche e termodinamiche fino ad arrivare alla scelta del fluido organico, fondamentale per le performance del ciclo. Dopo aver effettuato una ricognizione dello stato dell’arte delle applicazioni industriali degli ORC nel recupero termico, verranno eseguite simulazioni numeriche per ricostruire gli ORC ed avere una panoramica il più completa ed attendibile delle prestazioni effettive di questi sistemi. In ultimo verranno illustrati i risultati di un caso di studio che vede l’adozione di recupero mediante ciclo organico in un’installazione esistente del settore Oil&Gas. Si effettuerà uno studio delle prestazione dell’impianto al variare delle pressioni massime e minime del ciclo ed al variare del fluido impiegato al fine di mostrare come questi parametri influenzino non solo le performance ma anche le caratteristiche impiantistiche da adottare. A conclusione del lavoro si riporteranno i risultati relativi all’analisi condotte considerando l’impianto ai carichi parziali ed in assetto cogenerativo.

Increasing Utilization of US Electric Grids via Smart Technologies: Integration of Load Management, Real Time Pricing, Renewables, EVs and Smart Grid Sensors

Electric power grids throughout the world suffer from serious inefficiencies associated with under-utilization due to demand patterns, engineering design and load following approaches in use today. These grids consume much of the world’s energy and represent a large carbon footprint. From material utilization perspectives significant hardware is manufactured and installed for this infrastructure often to be used at less than 20-40% of its operational capacity for most of its lifetime. These inefficiencies lead engineers to require additional grid support and conventional generation capacity additions when renewable technologies (such as solar and wind) and electric vehicles are to be added to the utility demand/supply mix. Using actual data from the PJM [PJM 2009] the work shows that consumer load management, real time price signals, sensors and intelligent demand/supply control offer a compelling path forward to increase the efficient utilization and carbon footprint reduction of the world’s grids. Underutilization factors from many distribution companies indicate that distribution feeders are often operated at only 70-80% of their peak capacity for a few hours per year, and on average are loaded to less than 30-40% of their capability. By creating strong societal connections between consumers and energy providers technology can radically change this situation. Intelligent deployment of smart sensors, smart electric vehicles, consumer-based load management technology very high saturations of intermittent renewable energy supplies can be effectively controlled and dispatched to increase the levels of utilization of existing utility distribution, substation, transmission, and generation equipment. The strengthening of these technology, society and consumer relationships requires rapid dissemination of knowledge (real time prices, costs & benefit sharing, demand response requirements) in order to incentivize behaviors that can increase the effective use of technological equipment that represents one of the largest capital assets modern society has created.

Time-domain models for power system stability and unbalance

It is an important and difficult challenge to protect modern interconnected power system from blackouts. Applying advanced power system protection techniques and increasing power system stability are ways to improve the reliability and security of power systems. Phasor-domain software packages such as Power System Simulator for Engineers (PSS/E) can be used to study large power systems but cannot be used for transient analysis. In order to observe both power system stability and transient behavior of the system during disturbances, modeling has to be done in the time-domain. This work focuses on modeling of power systems and various control systems in the Alternative Transients Program (ATP). ATP is a time-domain power system modeling software in which all the power system components can be modeled in detail. Models are implemented with attention to component representation and parameters. The synchronous machine model includes the saturation characteristics and control interface. Transient Analysis Control System is used to model the excitation control system, power system stabilizer and the turbine governor system of the synchronous machine. Several base cases of a single machine system are modeled and benchmarked against PSS/E. A two area system is modeled and inter-area and intra-area oscillations are observed. The two area system is reduced to a two machine system using reduced dynamic equivalencing. The original and the reduced systems are benchmarked against PSS/E. This work also includes the simulation of single-pole tripping using one of the base case models. Advantages of single-pole tripping and comparison of system behavior against three-pole tripping are studied. Results indicate that the built-in control system models in PSS/E can be effectively reproduced in ATP. The benchmarked models correctly simulate the power system dynamics. The successful implementation of a dynamically reduced system in ATP shows promise for studying a small sub-system of a large system without losing the dynamic behaviors. Other aspects such as relaying can be investigated using the benchmarked models. It is expected that this work will provide guidance in modeling different control systems for the synchronous machine and in representing dynamic equivalents of large power systems.

Orbits design for Leo space based solar power satellite system

Space Based Solar Power satellites use solar arrays to generate clean, green, and renewable electricity in space and transmit it to earth via microwave, radiowave or laser beams to corresponding receivers (ground stations). These traditionally are large structures orbiting around earth at the geo-synchronous altitude. This thesis introduces a new architecture for a Space Based Solar Power satellite constellation. The proposed concept reduces the high cost involved in the construction of the space satellite and in the multiple launches to the geo-synchronous altitude. The proposed concept is a constellation of Low Earth Orbit satellites that are smaller in size than the conventional system. For this application a Repeated Sun-Synchronous Track Circular Orbit is considered (RSSTO). In these orbits, the spacecraft re-visits the same locations on earth periodically every given desired number of days with the line of nodes of the spacecraft’s orbit fixed relative to the Sun. A wide range of solutions are studied, and, in this thesis, a two-orbit constellation design is chosen and simulated. The number of satellites is chosen based on the electric power demands in a given set of global cities. The orbits of the satellites are designed such that their ground tracks visit a maximum number of ground stations during the revisit period. In the simulation, the locations of the ground stations are chosen close to big cities, in USA and worldwide, so that the space power constellation beams down power directly to locations of high electric power demands. The j2 perturbations are included in the mathematical model used in orbit design. The Coverage time of each spacecraft over a ground site and the gap time between two consecutive spacecrafts visiting a ground site are simulated in order to evaluate the coverage continuity of the proposed solar power constellation. It has been observed from simulations that there always periods in which s spacecraft does not communicate with any ground station. For this reason, it is suggested that each satellite in the constellation be equipped with power storage components so that it can store power for later transmission. This thesis presents a method for designing the solar power constellation orbits such that the number of ground stations visited during the given revisit period is maximized. This leads to maximizing the power transmission to ground stations.

HOUSEHOLD SOLAR POWER SYSTEM

Photovoltaic power has become one of the most popular research area in new energy field. In this report, the case of household solar power system is presented. Based on the Matlab environment, the simulation is built by using Simulink and SimPowerSystem. There are four parts in a household solar system, solar cell, MPPT system, battery and power consumer. Solar cell and MPPT system are been studied and analyzed individually. The system with MPPT generates 30% more energy than the system without MPPT. After simulating the household system, it is can be seen that the power which generated by the system is 40.392 kWh per sunny day. By combining the power generated by the system and the price of the electric power, 8.42 years are need for the system to achieve a balance of income and expenditure when weather condition is considered.

Pond head level control in a run-of-river hydro power plant using fuzzy controller

The run-of-river hydro power plant usually have low or nil water storage capacity, and therefore an adequate control strategy is required to keep the water level constant in pond. This paper presents a novel technique based on TSK fuzzy controller to maintain the pond head constant. The performance is investigated over a wide range of hill curve of hydro turbine. The results are compared with PI controller as discussed in [1].

Power system stability of a small sized isolated network supplied by a combined wind-pumped storage generation system: a case study in the Canary Islands

Massive integration of renewable energy sources in electrical power systems of remote islands is a subject of current interest. The increasing cost of fossil fuels, transport costs to isolated sites and environmental concerns constitute a serious drawback to the use of conventional fossil fuel plants. In a weak electrical grid, as it is typical on an island, if a large amount of conventional generation is substituted by renewable energy sources, power system safety and stability can be compromised, in the case of large grid disturbances. In this work, a model for transient stability analysis of an isolated electrical grid exclusively fed from a combination of renewable energy sources has been studied. This new generation model will be installed in El Hierro Island, in Spain. Additionally, an operation strategy to coordinate the generation units (wind, hydro) is also established. Attention is given to the assessment of inertial energy and reactive current to guarantee power system stability against large disturbances. The effectiveness of the proposed strategy is shown by means of simulation results.

New selective earth faults only current directional method for isolated neutral systems

In order to achieve total selectivity at electrical distribution networks it is of great importance to analyze the defect currents at ungrounded power systems. This information will help to grant selectivity at electrical distribution networks ensuring that only the defect line or feeder is removed from service. In the present work a new selective and directional protection method for ungrounded power systems is evaluated. The new method measures only defect currents to detect earth faults and works with a directional criterion to determine the line under faulty conditions. The main contribution of this new technique is that it can detect earth faults in outgoing lines at any type of substation avoiding the possible mismatch of traditional directional earth fault relays. This detection technique is based on the comparison of the direction of a reference current to the direction of all earth fault capacitive currents at all the feeders connected to the same bus bars. This new method has been validated through computer simulations. The results for the different cases studied are remarkable, proving total validity and usefulness of the new method.

Integración de baterías en sistemas fotovoltaicos conectados a red

La situación actual del mercado energético en España y el imparable aumento de las tasas por parte de las eléctricas, está fomentando la búsqueda de fuentes de energía alternativas que permitan a la población poder abastecerse de electricidad, sin tener que pagar unos costes tan elevados. Para cubrir esta necesidad, la energía fotovoltaica y sobretodo el autoconsumo con inyección a red o balance neto, está adquiriendo cada vez más importancia dentro del mundo energético. Pero la penetración de esta tecnología en la Red Eléctrica Española tiene un freno, la desconfianza por parte del operador de la red, ya que la fotovoltaica es una fuente de energía intermitente, que puede introducir inestabilidades en el sistema en caso de alta penetración. Por ello se necesita ganar la confianza de las eléctricas, haciendo que sea una energía predecible, que aporte potencia a la red eléctrica cuando se le pida y que opere participando en la regulación de la frecuencia del sistema eléctrico. Para tal fin, el grupo de investigación de Sistemas Fotovoltaicos, perteneciente al IES de la UPM, está llevando a cabo un proyecto de investigación denominado PV CROPS, financiado por la Comisión Europea, y que tiene por objetivo desarrollar estas estrategias de gestión. En este contexto, el objetivo de este Proyecto Fin de Carrera consiste en implementar un Banco de Ensayos con Integración de Baterías en Sistemas FV Conectados a Red, que permita desarrollar, ensayar y validar estas estrategias. Aprovechando la disponibilidad para usar el Hogar Digital, instalado en la EUITT de la UPM, hemos montado el banco de ensayos en un laboratorio contiguo, y así, poder utilizar este Hogar como un caso real de consumos energéticos de una vivienda. Este banco de ensayos permitirá obtener información de la energía generada por la instalación fotovoltaica y del consumo real de la "casa" anexa, para desarrollar posteriormente estrategias de gestión de la electricidad. El Banco de Ensayos está compuesto por tres bloques principales, interconectados entre sí:  Subsistema de Captación de Datos y Comunicación. Encargado de monitorizar los elementos energéticos y de enviar la información recopilada al Subsistema de Control. Formado por analizadores de red eléctrica, monofásicos y de continua, y una pasarela orientada a la conversión del medio físico Ethernet a RS485.  Subsistema de Control. Punto de observación y recopilación de toda la información que proviene de los elementos energéticos. Es el subsistema donde se crearán y se implementarán estrategias de control energético. Compuesto por un equipo Pxie, controlador empotrado en un chasis de gama industrial, y un equipo PC Host, compuesto por una workstation y tres monitores.  Subsistema de Energía. Formado por los elementos que generan, controlan o consumen energía eléctrica, en el Banco de Ensayos. Constituido por una pérgola FV, un inversor, un inversor bidireccional y un bloque de baterías. El último paso ha sido llevar a cabo un Ejemplo de Aplicación Práctica, con el que hemos probado que el Banco de Ensayos está listo para usarse, es operativo y completamente funcional en operaciones de monitorización de generación energética fotovoltaica y consumo energético. ABSTRACT. The current situation of the energetic market in Spain and the unstoppable increase of the tax on the part of the electrical companies, is promoting the search of alternative sources of energy that allow to the population being able to be supplied of electricity, without having to pay so high costs. To meet this need, the photovoltaic power and above all the self-consumption with injection to network, it is increasingly important inside the energetic world. It allows to the individual not only to pay less for the electricity, in addition it allows to obtain benefits for the energy generated in his own home. But the penetration of this technology in the Electrical Spanish Network has an obstacle, the distrust on the part of the operator of the electrical network, due to the photovoltaic is an intermittent source of energy, which can introduce instabilities in the system in case of high penetration. Therefore it´s necessary to reach the confidence of the electricity companies, making it a predictable energy, which provides with power to the electrical network whenever necessary and that operates taking part in the regulation of the frequency of the electric system. For such an end, the group of system investigation Photovoltaic, belonging to the IES of the UPM, there is carrying out a project of investigation named PV CROPS, financed by the European Commission, and that has for aim to develop these strategies of management. In this context, the objective of this Senior Thesis consists in implementing a Bank of Tests with Integration of Batteries in Photovoltaic Systems Connected to Network, which allows developing, testing and validating these strategies. Taking advantage of the availability to use the Digital Home installed in the EUITT of the UPM, we have mounted the bank of tests in a contiguous laboratory to use this Home as a real case of energetic consumptions of a house. This bank of tests will allow obtaining information of the energy generated by the photovoltaic installation and information of the royal consumption of the attached "house", to develop later strategies of management of the electricity. The Bank of Tests is composed by three principal blocks, interconnected each other:  Subsystem of Gathering of data and Communication. In charge of monitoring the energetic elements and sending the information compiled to the Subsystem of Control. Formed by power analyzers, AC and DC, and a gateway for the conversion of the Ethernet physical medium to RS485.  Subsystem of Control. Point of observation and compilation of all the information that comes from the energetic elements. It is the subsystem where there will be created and there will be implemented strategies of energetic control. Composed of a Pxie, controller fixed in an industrial range chassis, and a PC Host, formed by a workstation and three monitors.  Subsystem of Energy. Formed by the elements of generating, controlling or consuming electric power, in the Bank of Tests. Made of photovoltaic modules, an inverter, a twoway inverter and a batteries block. The last step has been performing an Example of Practical Application we have proved that the Bank of Tests is ready to be used, it´s operative and fully functional in monitoring operations of energetic photovoltaic generation and energetic consumption.

Wind intermittency and CO2 reductions: the case of the spanish power system

Renewable energy sources are believed to reduce drastically greenhouse gas emissions that would otherwise be generated from fossil fuels used to generate electricity. This implies that a unit of renewable energy will replace a unit of fossil-fuel, with its CO2 emissions, on an equivalent basis (with no other effects on the grid). But, the fuel economy and emissions in the existing power systems are not proportional with the electricity production of intermittent sources due to cycling of the fossil fuel plants that make up the balance of the grid (i.e. changing the power output makes thermal units to operate less efficiently). This study focuses in the interactions between wind generation and thermal plants cycling, by establishing the levels of extra fuel use caused by decreased efficiencies of fossil back-up for wind electricity in Spain. We analyze the production of all thermal plants in 2011, studying different scenarios where wind penetration causes major deviations in programming, while we define a procedure for quantifying the carbon reductions by using emission factors and efficiency curves from the existing installations. The objectives are to discuss the real contributions of renewable energies to the environmental targets as well as suggest alternatives that would improve the reliability of future power systems.

Electrodynamic Tethers For Planetary And De-orbiting Missions

Nuevas aplicaciones tecnológicas y científicas mediante amarras electrodinámicas son analizadas para misiones planetarias. i) Primero, se considera un conjunto de amarras cilíndricas en paralelo (veleros electrosolares) para una misión interplanetaria. Los iones provenientes del viento solar son repelidos por el alto potencial de dichas amarras generando empuje sobre el velero. Para conocer el intercambio de momento que provocan los iones sobre las amarras se ha considerado un modelo de potencial estacionario. Se ha analizado la transferencia orbital de la Tierra a Júpiter siguiendo un método de optimización de trayectoria indirecto. ii) Una vez que el velero se encuentra cerca de Júpiter, se ha considerado el despliegue de una amarra para diferentes objetivos científicos. iia) Una amarra podría ser utilizada para diagnóstico de plasmas, al ser una fuente efectiva de ondas, y también como un generador de auroras artificiales. Una amarra conductora que orbite en la magnetosfera jovial es capaz de producir ondas. Se han analizado las diferentes ondas radiadas por un conductor por el que circula una corriente constante que sigue una órbita polar de alta excentricidad y bajo apoápside, como ocurre en la misión Juno de la NASA. iib) Además, se ha estudiado una misión tentativa que sigue una órbita ecuatorial (LJO) por debajo de los intensos cinturones de radiación. Ambas misiones requiren potencia eléctrica para los sistemas de comunicación e instrumentos científicos. Las amarras pueden generar potencia de manera más eficiente que otros sistemas que utlizan paneles solares o sistemas de potencia de radioisótopos (RPS). La impedancia de radiación es necesaria para determinar la corriente que circula por todo el circuito de la amarra. En un modelo de plasma frío, la radiación ocurre principalmente en los modos de Alfven y magnetosónica rápida, mostrando un elevado índice de refracción. Se ha estudiado la impedancia de radiación en amarras con recubrimiento aislante para los dos modos de radiación y cada una de las misiones. A diferencia del caso ionosférico terrestre, la baja densidad y el intenso campo magnético que aparecen en el entorno de Júpiter consiguen que la girofrecuencia de los electrones sea mucho mayor que la frecuencia del plasma; esto hace que el espectro de potencia para cada modo se modifique substancialmente, aumentando la velocidad de Alfven. Se ha estimado también la impedancia de radiación para amarras sin aislante conductor. En la misión LJO, un vehículo espacial bajando lentamente la altitud de su órbita permitiría estudiar la estructura del campo magnético y composición atmosférica para entender la formación, evolución, y estructura de Júpiter. Adicionalmente, si el contactor (cátodo) se apaga, se dice que la amarra flota eléctricamente, permitiendo emisión de haz de electrones que generan auroras. El continuo apagado y encendido produce pulsos de corriente dando lugar a emisiones de señales, que pueden ser utilizadas para diagnóstico del plasma jovial. En Órbita Baja Jovial, los iones que impactan contra una amarra polarizada negativamente producen electrones secundarios, que, viajando helicoidalmente sobre las líneas de campo magnético de Júpiter, son capaces de alcanzar su atmósfera más alta, y, de esta manera, generar auroras. Se han identificado cuáles son las regiones donde la amarra sería más eficiente para producir auroras. iic) Otra aplicación científica sugerida para la misión LJO es la detección de granos cargados que orbitan cerca de Júpiter. Los electrones de alta energía en este ambiente pueden ser modelados por una distribucción no Maxwelliana conocida como distribución kappa. En escenarios con plasmas complejos, donde los campos eléctricos en Júpiter pueden acelerar las cargas hasta velocidades que superen la velocidad térmica, este tipo de distribuciones son muy útiles. En este caso las colas de las distribuciones de electrones siguen una ley de potencias. Se han estudiado las fluctuaciones de granos cargados para funciones de distribución kappa. iii) La tesis concluye con el análisis para deorbitar satélites con amarras electrodinámicas que siguen una Órbita Baja Terrestre (LEO). Una amarra debe presentar una baja probabilidad de corte por pequeño debris y además debe ser suficientemente ligero para que el cociente entre la masa de la amarra y el satélite sea muy pequeño. En este trabajo se estiman las medidas de la longitud, anchura y espesor que debe tener una amarra para minimizar el producto de la probabilidad de corte por el cociente entre las masas de la amarra y el satélite. Se presentan resultados preliminares del diseño de una amarra con forma de cinta para deorbitar satélites relativamente ligeros como Cryosat y pesados como Envisat. Las misiones espaciales a planetas exteriores y en el ámbito terrestre plantean importantes retos científico-tecnológicos que deben ser abordados y solucionados. Por ello, desde el inicio de la era espacial se han diseñando novedosos métodos propulsivos, sistemas de guiado, navegación y control más robustos, y nuevos materiales para mejorar el rendimiento de los vehículos espaciales (SC). En un gran número de misiones interplanetarias y en todas las misiones a planetas exteriores se han empleado sistemas de radioisótopos (RPS) para generar potencia eléctrica en los vehículos espaciales y en los rovers de exploración. Estos sistemas emplean como fuente de energía el escaso y costoso plutonio-238. La NASA, por medio de un informe de la National Academy of Science (5 de Mayo del 2009), expresó una profunda preocupación por la baja cantidad de plutonio almacenado, insuficiente para desarrollar todas las misiones de exploración planetaria planeadas en el futuro [81, 91]. Esta circustancia ha llevado a dicha Agencia tomar la decisión de limitar el uso de estos sistemas RPS en algunas misiones de especial interés científico y una recomendación de alta prioridad para que el Congreso de los EEUU apruebe el reestablecimiento de la producción de plutonio-238, -son necesarios cerca de 5 kg de este material radiactivo al año-, para salvaguardar las misiones que requieran dichos sistemas de potencia a partir del año 2018. Por otro lado, la Agencia estadounidense ha estado considerando el uso de fuentes de energía alternativa; como la fisión nuclear a través del ambicioso proyecto Prometheus, para llevar a cabo una misión de exploración en el sistema jovial (JIMO). Finalmente, dicha misión fue desestimada por su elevado coste. Recientemente se han estado desarrollando sistemas que consigan energía a través de los recursos naturales que nos aporta el Sol, mediante paneles solares -poco eficientes para misiones a planetas alejados de la luz solar-. En este contexto, la misión JUNO del programa Nuevas Fronteras de la NASA, cuyo lanzamiento fue realizado con éxito en Agosto de 2011, va a ser la primera misión equipada con paneles solares que sobrevolará Júpiter en el 2015 siguiendo una órbita polar. Anteriormente se habían empleado los antes mencionados RPS para las misiones Pioneer 10,11, Voyager 1,2, Ulysses, Cassini-Huygens y Galileo (todas sobrevuelos excepto Galileo). Dicha misión seguirá una órbita elíptica de alta excentricidad con un periápside muy cercano a Júpiter, y apoápside lejano, evitando que los intensos cinturones de radiación puedan dañar los instrumentos de navegación y científicos. Un tether o amarra electrodinámica es capaz de operar como sistema propulsivo o generador de potencia, pero también puede ser considerado como solución científicotecnológica en misiones espaciales tanto en LEO (Órbita Baja Terrestre) como en planetas exteriores. Siguiendo una perspectiva histórica, durante las misiones terrestres TSS-1 (1992) y TSS-1R (1996) se emplearon amarras estandard con recubrimiento aislante en toda su longitud, aplicando como terminal anódico pasivo un colector esférico para captar electrones. En una geometría alternativa, propuesta por J. R. Sanmartín et al. (1993) [93], se consideró dejar la amarra sin recubrimiento aislante (“bare tether”), y sin colector anódico esférico, de forma que recogiera electrones a lo largo del segmento que resulta polarizado positivo, como si se tratara de una sonda de Langmuir de gran longitud. A diferencia de la amarra estandard, el “bare tether” es capaz de recoger electrones a lo largo de una superficie grande ya que este segmento es de varios kilómetros de longitud. Como el radio de la amarra es del orden de la longitud de Debye y pequeño comparado con el radio de Larmor de los electrones, permite una recolección eficiente de electrones en el régimen OML (Orbital Motion Limited) de sondas de Langmuir. La corriente dada por la teoría OML varía en función del perímetro y la longitud. En el caso de una cinta delgada, el perímetro depende de la anchura, que debe ser suficientemente grande para evitar cortes producidos por debris y micrometeoritos, y suficientemente pequeño para que la amarra funcione en dicho régimen [95]. En el experimento espacial TSS-1R mencionado anteriormente, se identificó una recolección de corriente más elevada que la que predecía el modelo teórico de Parker- Murphy, debido posiblemente a que se utilizaba un colector esférico de radio bastante mayor que la longitud de Debye [79]. En el caso de una amarra “bare”, que recoge electrones a lo largo de gran parte de su longitud, se puede producir un fenómeno conocido como atrapamiento adiabático de electrones (adiabatic electron trapping) [25, 40, 60, 73, 74, 97]. En el caso terrestre (LEO) se da la condición mesotérmica en la que la amarra se mueve con una velocidad muy superior a la velocidad térmica de los iones del ambiente y muy inferior a la velocidad térmica de los electrones. J. Laframboise y L. Parker [57] mostraron que, para una función de distribución quasi-isotrópica, la densidad de electrones debe entonces ser necesariamente inferior a la densidad ambiente. Por otra parte, debido a su flujo hipersónico y a la alta polarización positiva de la amarra, la densidad de los iones es mayor que la densidad ambiente en una vasta región de la parte “ram” del flujo, violando la condición de cuasi-neutralidad,-en una región de dimensión mayor que la longitud de Debye-. La solución a esta paradoja podría basarse en el atrapamiento adiabático de electrones ambiente en órbitas acotadas entorno al tether. ABSTRACT New technological and scientific applications by electrodynamic tethers for planetary missions are analyzed: i) A set of cylindrical, parallel tethers (electric solar sail or e-sail) is considered for an interplanetary mission; ions from the solar wind are repelled by the high potential of the tether, providing momentum to the e-sail. An approximated model of a stationary potential for a high solar wind flow is considered. With the force provided by a negative biased tether, an indirect method for the optimization trajectory of an Earth-to-Jupiter orbit transfer is analyzed. ii) The deployment of a tether from the e-sail allows several scientific applications in Jupiter. iia) It might be used as a source of radiative waves for plasma diagnostics and artificial aurora generator. A conductive tether orbiting in the Jovian magnetosphere produces waves. Wave radiation by a conductor carrying a steady current in both a polar, highly eccentric, low perijove orbit, as in NASA’s Juno mission, and an equatorial low Jovian orbit (LJO) mission below the intense radiation belts, is considered. Both missions will need electric power generation for scientific instruments and communication systems. Tethers generate power more efficiently than solar panels or radioisotope power systems (RPS). The radiation impedance is required to determine the current in the overall tether circuit. In a cold plasma model, radiation occurs mainly in the Alfven and fast magnetosonic modes, exhibiting a large refraction index. The radiation impedance of insulated tethers is determined for both modes and either mission. Unlike the Earth ionospheric case, the low-density, highly magnetized Jovian plasma makes the electron gyrofrequency much larger than the plasma frequency; this substantially modifies the power spectrum for either mode by increasing the Alfven velocity. An estimation of the radiation impedance of bare tethers is also considered. iib) In LJO, a spacecraft orbiting in a slow downward spiral under the radiation belts would allow determining magnetic field structure and atmospheric composition for understanding the formation, evolution, and structure of Jupiter. Additionally, if the cathodic contactor is switched off, a tether floats electrically, allowing e-beam emission that generate auroras. On/off switching produces bias/current pulses and signal emission, which might be used for Jovian plasma diagnostics. In LJO, the ions impacting against the negative-biased tether do produce secondary electrons, which racing down Jupiter’s magnetic field lines, reach the upper atmosphere. The energetic electrons there generate auroral effects. Regions where the tether efficiently should produce secondary electrons are analyzed. iic) Other scientific application suggested in LJO is the in-situ detection of charged grains. Charged grains naturally orbit near Jupiter. High-energy electrons in the Jovian ambient may be modeled by the kappa distribution function. In complex plasma scenarios, where the Jovian high electric field may accelerate charges up superthermal velocities, the use of non-Maxwellian distributions should be considered. In these cases, the distribution tails fit well to a power-law dependence for electrons. Fluctuations of the charged grains for non-Mawellian distribution function are here studied. iii) The present thesis is concluded with the analysis for de-orbiting satellites at end of mission by electrodynamic tethers. A de-orbit tether system must present very small tether-to-satellite mass ratio and small probability of a tether cut by small debris too. The present work shows how to select tape dimensions so as to minimize the product of those two magnitudes. Preliminary results of tape-tether design are here discussed to minimize that function. Results for de-orbiting Cryosat and Envisat are also presented.

Tether radiation in Juno-type and circular-equatorial Jovian orbits

Wave radiation by a conductor carrying a steady current in both a polar, highly eccentric, low perijove orbit, as in NASA's planned Juno mission, and an equatorial low Jovian orbit (LJO) mission below the intense radiation belts, is considered. Both missions will need electric power generation for scientific instruments and communication systems. Tethers generate power more efficiently than solar panels or radioisotope power systems (RPS). The radiation impedance is required to determine the current in the overall tether circuit. In a cold plasma model, radiation occurs mainly in the Alfven and fast magnetosonic modes, exhibiting a large refraction index. The radiation impedance of insulated tethers is determined for both modes and either mission. Unlike the Earth ionospheric case, the low-density, highly magnetized Jovian plasma makes the electron gyrofrequency much larger than the plasma frequency; this substantially modifies the power spectrum for either mode by increasing the Alfven velocity. Finally, an estimation of the radiation impedance of bare tethers is considered. In LJO, a spacecraft orbiting in a slow downward spiral under the radiation belts would allow determining magnetic field structure and atmospheric composition for understanding the formation, evolution, and structure of Jupiter. Additionally, if the cathodic contactor is switched off, a tether floats electrically, allowing e-beam emission that generate auroras. On/off switching produces bias/current pulses and signal emission, which might be used for Jovian plasma diagnostics.