1,720,967 research outputs found
Mass breakdown model of solar-photon sail shuttle: The case for Mars
No full textThe main aim of this paper is to set up a many-parameter model of mass breakdown to be applied to a reusable Earth–Mars–Earth solar-photon sail shuttle, and analyze the system behavior in two sub-problems: (1) the zero-payload shuttle, and (2) given the sailcraft sail loading and the gross payload mass, find the sail area of the shuttle. The solution to the subproblem-1 is of technological and programmatic importance. The general analysis of subproblem-2 is presented as a function of the sail side length, system mass, sail loading and thickness. In addition to the behaviors of the main system masses, useful information for future work on the sailcraft trajectory optimization is obtained via (a) a detailed mass model for the descent/ascent Martian Excursion Module, and (b) the fifty–fifty solution to the sailcraft sail loading breakdown equation. Of considerable importance is the evaluation of the minimum altitude for the rendezvous between the ascent rocket vehicle and the solar-photon sail propulsion module, a task performed via the Mars Climate Database 2014–2015. The analysis shows that such altitude is 300 km; below it, the atmospheric drag prevails over the solar-radiation thrust. By this value, an example of excursion module of 1500 kg in total mass is built, and the sailcraft sail loading and the return payload are calculated. Finally, the concept of launch opportunity-wide for a shuttle driven by solar-photon sail is introduced. The previous fifty–fifty solution may be a good initial guess for the trajectory optimization of this type of shuttle
Wrinkling analysis for small solar-photon sails: an experimental and analytic approach for trajectory design
No full textA good model of solar-radiation pressure induced thrust is one of the key points in sailcraft trajectory design. The sail membrane’s local topographic deformations, i.e. wrinkles and creases, are among the main aspects that such a model should include. We have analyzed the influence of wrinkles/creases, as a whole, by measuring the related deformations on small samples of sail membrane, 2.5 lm thick, consisting of CP1 and physical-vapor-deposition Aluminum. Experimental outcomes from our laboratory facility have been processed, statistically investigated, and inserted into the lightness vector formalism. We have used such formalism for accurate sailcraft trajectory computation via a non-ideal reflection sail thrust model. Finally, we computed the deviations of wrinkled-sail sailcraft final orbital states with respect to the no-wrinkle sail final orbital ones for a circular to circular 2D inward transfer. The radii of the orbits are 1 AU and the semi-major axis of Mercury, respectively. It appears that sail wrinkles and creases are no longer negligible in the sailcraft trajectory design
Coronal Mass Ejection early-warning mission by solar-photon sailcraft
No full textA preliminary investigation of the early warning of solar storms caused by Coronal Mass Ejection has been carried out. A long warning time could be obtained with a sailcraft synchronous with the Earth-Moon barycenter, and stationed well below the L1 point. In this paper, the theory of heliocentric synchronous sailcraft is set up, its perturbed orbit is analyzed, and a potential solution capable of providing an annual synchrony is carried out. A simple analysis of the response from a low-mass electrochromic actuator for the realization of station-keeping attitude maneuvers is put forwards, and an example of propellantless re-orientation maneuver is studied
Solar sail H-reversal trajectory: a review of its advances and applications
No full textThe set of the orbital angular-momentum reversal, or H-reversal, sailcraft trajectory was born as a type of unconventional precursor interstellar mission trajectory by using highperformance solar sails. Starting from an outline of the H-reversal sail trajectory, this paper mainly focuses on the 2D reversal-mode solution to the general solar-photon sail motion equations. The feasible region for H-reversal trajectories in fixed sail attitude angles is illustrated. Some interesting applications of the H-reversal trajectory are presented in detail to show its advantages. As a special case, a precursor interstellar probe can be delivered with a constant sail orientation in the H-reversal trajectory to be compared with the direct-motion sail flyby of the Sun. Of importance are the heliocentric periodic orbits in double H-reversal modes, obtained via both fixed and time-varying sail attitude angles. Two more applications involving H-reversal trajectories are discussed in terms of asteroid deflection and transfer trajectory to rectilinear orbits. Finally, some items of the mathematics behind the 3D motion-reversal trajectories are summarized
Analysis of the solar sail deformation based on the point cloud method
No full textThe deformation of the solar-sail membrane is an important factor for causing inaccuracies in the solar-sail missions. This paper
describes the solar sail under deformation by using a new modelling technique based on point cloud and triangular mesh generation.
Two types of deformation, stemming from wrinkling and billowing, are modelled. The changes in the solar radiation pressure force
and the moment caused by deformation are calculated and compared to the ideal non-deformed case. The heliocentric spiral trajectory
and the orbital angular momentum reversal trajectory are taken as examples to quantify the influence of the deformation from an orbit
point of view. Additionally, point cloud simplification, based on the normal vector and bounding box, is utilized to simplify the original
deformed-sail model. It involves a reasonable reduction and renewal of the points in the model considering the variation of surface curvature.
The simplification and its modelling accuracy are numerically investigated as well as computational efficiency
Wrinkling analysis of solar-photon sails
No full textThis paper regards small/midsize square sails on which a field of wrinkles appears owing to the necessary sail-membrane operations
before and during the deployment. We collected a large amount of data in our laboratory. Many ten thousands of measurements had
been statistically processed for characterizing some sail’s sampled membranes consisting of aluminized-polyimide layers ð2:5 þ 0:1Þlm
thin, and loaded at vertices. Such samples have exhibited area and orientation alterations, as a whole, which can affect the propulsive
acceleration of a sailcraft. Wrinkled-sail orientation has been given a thrust-specialized meaning for trajectory computation. Threedimensional
heliocentric minimum-time orbit transfer between Earth and Mercury orbits had been investigated. This had resulted in
wrinkled-sail sailcraft moving on trajectories remarkably different from those ones of the corresponding ideal unwrinkled-sail sailcraft.
Nevertheless, at least in the current framework, the most important result is that sail-wrinkled sailcraft’s interplanetary trajectories could
be optimized without resorting to stochastic differential equations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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