Generation of optimal trajectories for Earth hybrid pole sitters

A pole-sitter orbit is a closed path that is constantly above one of the Earth's poles, by means of continuous low thrust. This work proposes to hybridize solar sail propulsion and solar electric propulsion (SEP) on the same spacecraft, to enable such a pole-sitter orbit. Locally-optimal control laws are found with a semi-analytical inverse method, starting from a trajectory that satisfies the pole-sitter condition in the Sun-Earth circular restricted three-body problem. These solutions are subsequently used as first guess to find optimal orbits, using a direct method based on pseudospectral transcription. The orbital dynamics of both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows savings on propellant mass fraction. Finally, it is shown that for sufficiently long missions, a hybrid pole-sitter, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft

An earth pole-sitter using hybrid propulsion

In this paper we investigate optimal pole-sitter orbits using hybrid solar sail and solar electric propulsion (SEP). A pole-sitter is a spacecraft that is constantly above one of the Earth's poles, by means of a continuous thrust. Optimal orbits, that minimize propellant mass consumption, are found both through a shape-based approach, and solving an optimal control problem, using a direct method based on pseudo-spectral techniques. Both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows consistent savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions (more than 8 years), a hybrid spacecraft, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft

Generation of two-photon EPR and Wstates

In this paper we present a scheme for generation of two-photon EPR and W states in the cavity QED context. The scheme requires only one three-level Rydberg atom and two or three cavities. The atom is sent to interact with cavities previously prepared in vacuum states, via two-photon process. An appropriate choice of the interaction times one obtains the mentioned state with maximized fidelities. These specific times and the values of success probability and fidelity are discussed.Comment: 4 pages, 5 figure

La Investigación En La Práctica Pedagógica De Los Docentes De Educación Media

La investigación docente no debe estar limitada a campos específicos de las universidades, por el contrario, es pertinente que los docentes en todos los niveles educativos del sistema escolar, apoyen su práctica pedagógica con la realización de estudios que sistematicen sus experiencias y contribuyan al campo de la educación. El presente artículo exhibe los desarrollos de la tesis doctoral Aproximación Teórica a la Investigación en la Práctica Pedagógica de los Docentes de Educación Media, para el cual se asume una visión epistemológica constructivista, con metodología hermenéutico dialéctica, bajo el paradigma cualitativo y se sigue el método de la teoría fundamentada para el análisis de datos y la generación teórica. El estudio concluye con la presentación de la aproximación teórica según el constructo emergente que se revela en relación a la investigación en la práctica pedagógica de los docentes de educación media

Stability of axially symmetric magnetic fields in stars

The magnetic fields observed in Ap-stars, white dwarfs, and neutron stars are known to be stable for long times. However, the physical conditions inside the stellar interiors that allow these states are still a matter of research. It has been formally demonstrated that both purely toroidal and purely poloidal magnetic fields develop instabilities at some point in the star. On the other hand, numerical simulations have proved the stability of roughly axisymmetric magnetic field configurations inside stably stratified stars. These configurations consist of mutually stabilizing toroidal and poloidal components in a twisted torus shape. Previous studies have proposed rough upper and lower bounds on the ratio of the magnetic energy in the toroidal and poloidal components of the magnetic field. With the purpose of mapping out the parameter space under which such configurations remain stable, we used the Pencil Code to perform 3D magnetohydrodynamic simulations of the evolution of the magnetic field in non-rotating, non-degenerate stars in which viscosity is the only dissipation mechanism, both for stars with a uniform (barotropic) and radially increasing (stably stratified) specific entropy. Furthermore, we considered different conditions regarding the degree of stable stratification and the magnetic energy in each component, roughly confirming the previously suggested stability boundaries for the magnetic field.Comment: 9 pages, 9 figure

Analysis of two heat storage integrations for an Organic Rankine Cycle Parabolic trough solar power plant

Among the concentrated solar power technologies, those based on Organic Rankine Cycles have a very low market presence. However they have favorable characteristics for applications with low temperature and small/medium size (<10 MW), such as off-grid applications or distributed power generation. In this paper is analyzed a 5MW parabolic trough plant integrated with an Organic Rankine cycle power block and thermal storage. On this purpose, two different thermal storage integrations are analyzed. They are based on two different heat storage layouts: direct system using Hitec XL both as Heat Transfer Fluid and as storage medium; indirect system using Therminol VP-1 as Heat Transfer Fluid and Hitec XL as storage medium. Full system performance at rated and off-design conditions is presented operating with different organic working fluids. Its potential application and main challenges for its development are discussed in terms of performance and costs. Among the analyzed working fluids, the best results were obtained for the cycle working with Toluene with an efficiency at the power block of 31.5% and an estimated power block cost of 825 €/kW. The indirect storage layout was the most interesting from the point of view of Levelized Electricity Cost (16.19 c€/kW) and productivity (28.2 GW h/y for a 5 MWel plant) for 10 h of storage However, it results in a storage tanks volume 26% greater than the obtained for the equivalent direct storage layout. The results show the competitiveness and the potential of the proposed integrated small size parabolic trough designs for isolated applications as mines or for some distributed generation uses where grid capacity is limited