Satellite Formation Flight Results from Phase 1 of the Magnetospheric Multiscale Mission

This paper describes the underlying dynamics of formation flying in a high-eccentricity orbit such as that of the Magnetospheric Multiscale mission. The GPS-based results used for MMS navigation are summarized, as well as the procedures that are used to design the maneuvers used to place the spacecraft into a tetrahedron formation and then maintain it. The details of how to carry out these maneuvers are then discussed. Finally, the numerical results that have been obtained concerning formation flying for the MMS mission to date (e.g. tetrahedron sizes flown, maneuver execution error, fuel usage, etc.) are presented in detail

Effects of droplet size on intrusion of sub-surface oil spills

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2013."February 2013." Cataloged from PDF version of thesis.Includes bibliographical references (p. 86-90).This thesis explores the effects of droplet size on droplet intrusion in sub-surface oil spills. Laboratory experiments were performed where glass beads of various sizes, which serve to simulate oil droplets in deepsea oil spills, were released vertically in a quiescent salinity stratified ambient and descended as multi-phase plumes. The two-tank stratification method was used to create linear density profiles for all experiments. The resulting radial concentration distributions of the dispersed phases were obtained by collecting the settled particles from the bottom of the tank. The radial distributions recorded were found to resemble Gaussian distributions, based on visual observations and analyses of kurtosis, which is consistent with particles being vertically well mixed in the intrusion layer. A new typology was proposed to describe plume structures with UN= us/(BN)¹/⁴ </= 1.4. For UN </=1.4 particle detrain from the plem, but only those with smallest slip velocity (UN </+0.3) intrude. An analytical model assuming well-mixed particle distributions within the intrusion layer was also used to predict the spread of the particle distribution based on initial buoyancy flux B, stratification frequency N, the particle slip velocity us, and the non-dimensional slip velocity UN. Comparison between experimental results and the analytical model suggested that the model accurately predicts the spread of the particles for UN </=1.4. Experiments with beads of difference sizes also suggested that the interaction between two particle groups has minimal effects on their radial particle spread. This indicates that particles of difference sizes can be treated independently when analyzing their radial plume spread. Chemical dispersants produce small oil droplets and the current experiments provide references on the minimum diameter needed for efficient particle spread (Type la* plume). By knowing the following parameters for a scenario - 1) initial buoyancy flux B; 2) the ambient stratification profile N; and 3) the slip velocities of the droplets u, - suitable amounts of dispersant can be determined and applied to reduce the size of the particles exiting the spill, allowing them to intrude and spread for a larger distance in the ocean column. A hypothetical example with conditions taken from the 'Deep Spill' experiment and Deepwater Horizon oil spill was also presented for reference.by Godine Kok Yan Chan.S.M

Operational Techniques for Dealing with Long Eclipses During the MMS Extended Mission

Launch window design for the Magnetospheric Multiscale (MMS) mission ensured that no excessive eclipses would be encountered during the prime mission. However, no orbit solutions exist that satisfy the eclipse constraints indefinitely: most extended mission years contain 1-3 eclipses long enough to potentially damage either the spacecraft or its scientific instruments. Two steps were taken to improve the situation. Firstly, raising apogee radius from 25 to 29.34 Earth radii altered the Sun-Earth-MMS phasing, so efficiently achieving reductions in the long eclipse durations. These maneuvers were performed early this year, in preparation for the first pair of long eclipses in August 2019. Secondly, a set of operational steps were taken around the time of the eclipses to help maintain spacecraft and instrument temperatures while preventing power load shedding. These operational steps included raising key onboard temperatures through adjusting the spacecraft attitude to tilt the instrument deck towards the Sun, and engaging select heaters prior to going into eclipses. In addition, all scientific instruments were turned off, as well as high-power, non-critical spacecraft systems, to conserve energy.These steps each came with trade-offs which will be discussed in the paper. Finally, the results that were obtained when the spacecraft experienced the first extremely long eclipses will be discussed, as will lessons learned for future long eclipses

Computation of Nonlinear Hydrodynamic Loads on Floating Wind Turbines Using Fluid-Impulse Theory

A hydrodynamics computer module was developed to evaluate the linear and nonlinear loads on floating wind turbines using a new fluid-impulse formulation for coupling with the FAST program. The new formulation allows linear and nonlinear loads on floating bodies to be computed in the time domain. It also avoids the computationally intensive evaluation of temporal and spatial gradients of the velocity potential in the Bernoulli equation and the discretization of the nonlinear free surface. The new hydrodynamics module computes linear and nonlinear loads — including hydrostatic, Froude-Krylov, radiation and diffraction, as well as nonlinear effects known to cause ringing, springing, and slow-drift loads — directly in the time domain. The time-domain Green function is used to solve the linear and nonlinear free-surface problems and efficient methods are derived for its computation. The body instantaneous wetted surface is approximated by a panel mesh and the discretization of the free surface is circumvented by using the Green function. The evaluation of the nonlinear loads is based on explicit expressions derived by the fluid-impulse theory, which can be computed efficiently. Computations are presented of the linear and nonlinear loads on the MIT/NREL tension-leg platform. Comparisons were carried out with frequency-domain linear and second-order methods. Emphasis was placed on modeling accuracy of the magnitude of nonlinear low- and high-frequency wave loads in a sea state. Although fluid-impulse theory is applied to floating wind turbines in this paper, the theory is applicable to other offshore platforms as well.United States. Department of Energy (National Renewable Energy Laboratory. Contract DE-AC36-08GO28308)United States. Department of Energy. Office of Energy Efficiency and Renewable Energy. Wind and Water Power Technologies OfficeMassachusetts Clean Energy Cente

Magnetospheric Multiscale Mission Navigation Performance During Apogee-Raising and Beyond

The primary objective of the Magnetospheric Multiscale (MMS) Mission is to study the magnetic reconnection phenomena in the Earths magnetosphere. The MMS mission consists of four identical spinning spacecraft with the science objectives requiring a tetrahedral formation in highly elliptical orbits. The MMS spacecraft are equipped with onboard orbit and time determination software, provided by a weak-signal Global Positioning System (GPS) Navigator receiver hosting the Goddard Enhanced Onboard Navigation System (GEONS). This paper presents the results of MMS navigation performance analysis during the Phase 2a apogee-raising campaign and Phase 2b science segment of the mission

Elementos de hygiene [sic] veterinaria, acompañados de algunas observaciones acerca del muermo, del huérfago, y del asma, y acerca de la cauterización

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Lunisolar Perturbations of High-Eccentricity Orbits Such as the Magnetospheric Multiscale Mission

For highly eccentric orbits such as that of the Magnetospheric Multiscale (MMS)mission, with apogee radius now 29.34 Earth radii, the third-body effects of Sun andMoon are the major perturbations. One key consequence is an oscillation in MMSperigee altitude, on an approximately 6 year cycle. This variation has already requiredperigee-raise maneuvers to avoid an untimely reentry. There is also a long-termevolution in the orientation of the MMS orbit, with period roughly twice as long. Thiseffect may potentially be useful for MMS science studies, as it can bring the spacecraftinto new regions of the magnetosphere

Conjunction Assessment Techniques and Operational Results from the Magnetospheric Multiscale Mission

This paper will describe the results that have been obtained to date during the MMS mission concerning conjunction assessment. MMS navigation makes use of a weak-signal GPS-based system: this allows signals to be received even when MMS is flying above the GPS orbits, producing a highly accurate determination of the four MMS orbits. This data is downlinked to the MMS Mission Operations Center (MOC) and used by the Flight Dynamics Operations Area (FDOA) for both maneuver design and conjunction assessment. The MMS fly in tetrahedron formations around apogee, in order to collect simultaneous particles and fields science data. The original plan was to fly tetrahedra between 10 and 160 km in size; however, after Phase 1a of the mission, the science team requested that smaller sizes be flown if feasible. After analysis (to be detailed in a companion paper), a new minimum size of 7 km was decided upon. Flying at this reduced scale size makes conjunction assessment between the MMS spacecraft even more important: the methods that are used by the MMS FDOA to address this problem will be described in the paper, and a summary given of the previous analyses that went into the development of these techniques. Details will also be given of operational experiences to date. Finally, two CA mitigation maneuver types that have been designed (but never yet required to actually be performed) will also be outlined

MMS Extended Mission Design: Evaluation of a Lunar Gravity Assist Option

This paper will describe a study that was carried out on the design of a set of maneuvers that were considered for the later stages of an extended mission of the Magnetospheric Multiscale (MMS) mission. The goal of these maneuvers was to put MMS into a significantly different orbit from those flown heretofore, so allowing science collection in a different region of the magnetosphere. This study was made feasible by the fact that the rate at which fuel is being consumed to maintain small formations on the MMS high-apogee orbit is less than expected pre-flight: the current consumption rate is only about 2 kg/yr/spacecraft. In addition, the spacecraft finished the prime mission with a significant amount of fuel remaining: this was about 1-sigma above the mean when compared with pre-launch Monte Carlo simulations. The resulting situation is similar to that of a libration orbit mission, where station-keeping requires so little fuel that any margin at all will lead to an extensive mission lifetime. In the case of MMS, the spacecraft could, if desired, perform formation flying in the current orbit for several decades. Alternatively, the spacecraft could use a significant fraction of the remaining fuel to perform major orbit modifications, while still leaving enough to conduct formation flying for on the order of a decade. The extended mission maneuvers studied here are further apogee-raises, with the goal of setting up one or more lunar gravity assists. Geometry dictates that a lunar encounter is only achievable when the MMS apogee vector lies approximately in the lunar orbit plane: this limits the possible dates to mid-2021 or early 2027

Acompañamiento Pedagógico que recibe la docente de III Nivel “A”, del II Ciclo de Educación Inicial para el desarrollo de las actividades lúdicas en el proceso enseñanza aprendizaje del Centro Escolar Alfonso Cortés, ubicado en el Barrio La Primavera del Distrito IV del Municipio de Managua, Departamento de Managua en el I Semestre 2015

En la educación de la primera infancia, las actividades lúdicas tienen gran importancia para un adecuado desarrollo del proceso de enseñanza-aprendizaje, y por consiguiente de la obtención de aprendizajes desarrolladores en los niños y niñas; en esta investigación, se explicitan los diferentes conceptos y actividades lúdicas, su importancia, los tipos, características, beneficios, el rol del docente ante estas actividades, como el fundamento teórico practico que sustenta nuestro trabajo de investigación. La palabra lúdico es un adjetivo que califica todo lo relacionado al juego cuyo significado es precisamente Juego, como actividad placentera donde el ser se libera de tensiones y de las reglas impuestas por la cultura, es un ejercicio que proporciona alegría, placer, gozo, satisfacción. La presente investigación se llevó a cabo bajo un enfoque de investigación - acción, cuyas características permitieron acercarnos al campo de estudio, aplicar métodos, estrategias y técnicas para la recolección y análisis de datos; incorporarnos en el aula de clases y conocer lo más cercana posible los que acontece para poder tener una comprensión de los hechos y sucesos que nos motivaron a investigar el caso encontrado. La investigación fue realizada en el centro Escolar Alfonso Cortes, ubicado en el Barrio La Primavera, En el distrito VI del Municipio de Managua, en el Primer semestre del año dos mil quince. En una primera fase realizamos un diagnóstico que nos permitiera identificar el caso de investigación, para lo cual se diseñaron instrumentos a fin de recolectar la información necesaria, seguidamente se analizó esta información y en función de los resultados se pasó a la siguiente etapa que consistió en el diseño y aplicación de planes de acción que permitieran solventar la situación encontrada. En una tercera fase se llegó a la reflexión con las educadoras a fin de que ellas incorporaran la experiencia vivida como un aprendizaje practico para dar seguimiento y respuesta a situaciones similares