1,721,046 research outputs found
Two and three impulses phasing strategy with a spacecraft orbiting on an Earth–Moon NRHO
No full textThe increasing interests in Moon exploration have led in recent years to international collaborations between space agencies aimed to assemble and operate the Gateway, an orbiting spaceport located on a Near Rectilinear Halo Orbit (NRHO) about the second libration point of the Earth–Moon system (EML-2). In this context, transfer strategies between the Earth and the spaceport cover a key role for both assembly and resupply missions. The presented work is thus focused on one leg of the transfer: the phasing maneuver. This work is conducted under the hypotheses of the Circular Restricted Three-Body problem (CR3BP) in which the Earth and the Moon are the only bodies that influence the spacecraft motion. The primaries are assumed to have a circular motion around their common barycenter. Under these hypotheses, is demonstrated the existence of periodic orbits, such as the Halo orbit family, that are exploited to design a proposed phasing maneuver. Two strategies are investigated: Halo parking orbit to NRHO two-impulses transfer and direct phasing with manifold exploitation. The first strategy is an optimal two-impulses transfer departing an EML-2 southern Halo and targeting the baseline NRHO. The second strategy considers the chaser already injected on the Gateway's NRHO. Poincare maps are employed to identify unstable/stable manifolds intersections in search of low-energy phasing trajectories that leave the reference orbit along the unstable branch before re-entering it via the stable one. Three-impulses transfers with similar costs are found patching together these arcs. The two strategies are thus compared to highlight their advantages and disadvantages with the perspective of a real autonomous cargo mission around the Moon to refurnish the orbiting station
Two and Three Impulses Phasing Strategy with a Spacecraft Orbiting on a Earth-Moon NRHO
No full textThe increasing interests in Moon exploration has led in recent years to international collaborations between space agencies aimed to assemble and operate the Gateway, an orbiting spaceport located on a Near Rectilinear Halo Orbit (NRHO) about the second libration point of the Earth-Moon system (EML2). In this context, transfer strategies between the Earth and the spaceport cover a key role for both assembly and resupply missions. The presented work is thus focused on one leg of the transfer: the phasing manoeuvre. This work is conducted under the hypotheses of the Circular Restricted Three Body problem (CR3BP) in which the Earth and the Moon are the only bodies that influence the spacecraft motion. The primaries are assumed to have a circular motion around their common barycentre. Under these hypotheses, is demonstrated the existence of periodic orbits, such as the Halo orbit family, that are exploited to design a proposed phasing manoeuvre. Two strategies are investigated: Halo parking orbit to NRHO two-impulse transfer and direct phasing with manifold exploitation. The first strategy is an optimal two-impulse transfer departing an EML-2 southern Halo and targeting the baseline NRHO. The second strategy considers the chaser already injected on the Gateway's NRHO. Poincare maps are employed to identify unstable/stable manifolds intersections in search of low-energy phasing trajectories that leave the reference orbit along the unstable branch before re-entering it via the stable one. Three-impulse transfers with similar costs are found patching together these arcs. The two strategies are thus compared to highlight their advantages and disadvantages with the perspective of a real autonomous cargo mission around the Moon to refurnish the orbiting station
Exploiting Coherent Patterns for the Analysis of Qualitative Motion and the Design of Bounded Orbits Around Small Bodies
Get PDFMissions around small bodies present many challenges from their design to the operations, due to the highly non-linear and uncertain dynamics, the limited Δv budget and constraints coming from orbit determination and mission design. Within this context, mathematical tools to enhance the understanding of the dynamics behavior can be proven useful to support the mission design process. Chaos indicators are adopted to reveal patterns of time-dependent dynamical systems and to enable the identification of practical stability regions, which are then exploited to design bounded orbits in the proximity of small bodies. The methodology is applied to study the MMX and Hera missions. In the MMX context, the final goal is to obtain bounded orbits useful for the global surface mapping and gravity potential determination of Phobos. On the other hand, concerning the Hera mission, a qualitative analysis of the natural motion about the Didymos binary asteroid system is carried out to compute bounded orbits convenient for the global characterization of the two asteroids and to investigate potential landing trajectories. Sensitivity analyses via Monte Carlo simulations are performed to prove the robustness of the different bounded orbits
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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