On the use of controlled radiation pressure to send a satellite to a graveyard orbit

A very important topic in modern astrodynamics is the removal of satellites from their orbits, after the end of their missions. In this work, we propose the use of the solar radiation pressure to change the orbital energy of a satellite, to remove it from the operational region to a graveyard orbit. A mechanism for changing the area-to-mass ratio of the satellite and/or its reflectivity coefficient is used to accomplish this task. We derive an analytical model to find the maximum eccen- tricity achieved during the removal trajectory, for different initial conditions for the argument of perigee and the longitude of the ascending node. After that, the best trajectories, i.e., trajectories with low eccentricity, are integrated using a numerical model. These low eccentricity trajectories are important because satellites with disposal orbits with low eccentricity pose a lower risk of crossing the operational region during the de-orbiting.Un tema importante en la astrodinámica moderna es la remoción de satélites de sus órbitas al finalizar sus misiones. En este trabajo proponemos utilizar la presión de la radiación solar para modificar la energía orbital del satélite, y así alejarlo de la región operacional y enviarlo a una órbita “en el cementerio”. Para este propósito, se propone un mecanismo para cambiar la razón área-masa y/o la reflectividad del satélite. Obtenemos un modelo analítico para encontrar la máxima excentricidad alcanzada durante la trayectoria de remoción, para diferentes valores iniciales del argumento del perigeo y de la longitud del nodo ascendente. A continuación, las mejores trayectorias, esto es, las de menor excenticidad, se integran numéricamente. Estas trayectorias de baja excentricidad son importantes pues los satélites con ´orbitas de desecho de baja excentricidad tienen un menor riesgo de cruzar las regiones operacionales durante su eliminación.The author is thankful for the grants # 406841/2016-0 and 301338/2016-7 from the National Council for Scientific and Technological Development (CNPq); and grants # 2014/22295-5, 2011/08171-3, 2016/14665-2 and 2016/07248-6 from São Paulo Research Foundation (FAPESP).info:eu-repo/semantics/publishedVersio

Processing and characterization of glass-ceramic foams belonging to the Li2O-ZrO2-Al2O3-SiO2 (LZSA) system produced by gelcasting

In this work the viscosimetry technique was used to evaluate the rheological characteristics of ceramic suspensions prepared with a LZSA (Li2O-ZrO2-SiO2-Al2O3) glass. From the rheological characterization it was possible to establish optimized conditions of solid fraction, dispersant, organic monomers and foaming agent for the production of glass-ceramic foams by gelcasting. The resulting foams were subjected to heattreatments at 200-500ºC/60 min, for degradation of organics and at 950ºC/60 min for sintering and crystallization. With the obtained porous ceramic bodies linear thermal shrinkage, apparent density and mechanical strength measurements as well as microstructural analysis were performed. The adaptation of the rheological characteristics of the LZSA parent glass powder with the gelcasting processing technique allowed the production of ceramic foams with high open and interconnected porosity (>90%) with good thermal stability and with mechanical strength suitable for the production of porous ceramics.Neste trabalho, a técnica de viscosimetria foi utilizada para avaliar as características reológicas de suspensões preparadas com precursor vitrocerâmico do sistema LZSA (Li2O-ZrO2-SiO2-Al2O3). A partir da caracterização reológica, foi possível estabelecer condições composicionais adequadas de fração de sólidos, dispersante e monômeros orgânicos. A quantidade de agente espumante para produção de espumas vitrocerâmicas por gelcasting foi determinada pela variação volumétrica após agitação. As espumas resultantes foram submetidas a tratamentos térmicos no intervalo de temperatura compreendido entre 200 e 500ºC/60 min, para degradação da matéria orgânica e a 950ºC/60 min para sinterização e cristalização. Com os corpos cerâmicos porosos foram realizadas medidas de retração térmica, densidade aparente, análise microestrutural e resistência mecânica. A adequação das características reológicas do precursor LZSA por gelcasting permitiu a produção de espumas com elevada porosidade (> 90%) aberta e interconectada com boa estabilidade térmica e com resistência mecânica compatível com cerâmicas [email protected]@[email protected]@emc.ufsc.brUniversidade Federal de Santa Catarina Departamento de Engenharia Mecânica Programa de Pós-Graduação em Ciência e Engenharia de MateriaisCentro Universitário Barriga Verde - UNIBAVEUniversidade Federal de São Paulo (UNIFESP) Departamento de Ciência e TecnologiaUNIFESP, Depto. de Ciência e TecnologiaSciEL

Finite temperature mobility of a particle coupled to a fermion environment

We study numerically the finite temperature and frequency mobility of a particle coupled by a local interaction to a system of spinless fermions in one dimension. We find that when the model is integrable (particle mass equal to the mass of fermions) the static mobility diverges. Further, an enhanced mobility is observed over a finite parameter range away from the integrable point. We present a novel analysis of the finite temperature static mobility based on a random matrix theory description of the many-body Hamiltonian.Comment: 11 pages (RevTeX), 5 Postscript files, compressed using uufile

Motion-Induced Radiation from a Dynamically Deforming Mirror

A path integral formulation is developed to study the spectrum of radiation from a perfectly reflecting (conducting) surface. It allows us to study arbitrary deformations in space and time. The spectrum is calculated to second order in the height function. For a harmonic traveling wave on the surface, we find many different regimes in which the radiation is restricted to certain directions. It is shown that high frequency photons are emitted in a beam with relatively low angular dispersion whose direction can be controlled by the mechanical deformations of the plate.Comment: 4 pages, 2 eps figues included, final version as appeared in PR

Fluctuations, dissipation and the dynamical Casimir effect

Vacuum fluctuations provide a fundamental source of dissipation for systems coupled to quantum fields by radiation pressure. In the dynamical Casimir effect, accelerating neutral bodies in free space give rise to the emission of real photons while experiencing a damping force which plays the role of a radiation reaction force. Analog models where non-stationary conditions for the electromagnetic field simulate the presence of moving plates are currently under experimental investigation. A dissipative force might also appear in the case of uniform relative motion between two bodies, thus leading to a new kind of friction mechanism without mechanical contact. In this paper, we review recent advances on the dynamical Casimir and non-contact friction effects, highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni, David Roberts, and Felipe da Rosa. Minor changes, a reference adde

Minimizing inter-genotypic competition effects to predict genetic values and selection in forestry genetic tests

The effect of competition is an important source of variation in breeding experiments. This study aimed to compare the selection of plants of open-pollinated families of Eucalyptus with and without the use of competition covariables. Genetic values were determined for each family and tree and for the traits height, diameter at breast height and timber volume in a randomized block design, resulting in the variance components, genetic parameters, selection gains, effective size and selection coincidence, with and without the use of covariables. Intergenotypic competition is an important factor of environmental variation. The use of competition covariables generally reduces the estimates of variance components and influences genetic gains in the studied traits. Intergenotypic competition biases the selection of open-pollinated eucalypt progenies, and can result in an erroneous choice of superior genotypes; the inclusion of covariables in the model reduces this influence