1,720,962 research outputs found
Floquet modes and stability analysis of periodic orbit-attitude solutions along Earth–Moon halo orbits
Full text linkFuture space programmes pose some interesting research problems in the field of non-Keplerian dynamics, being the Moon and the cislunar space central in the proposed roadmap for the future space exploration. In these regards, the deployment of a cislunar space station on a non-Keplerian orbit in the lunar vicinity is a fundamental milestone to be achieved. The paper investigates the natural orbit-attitude dynamics and the attitude stabilisation of coupled motions for extended bodies in the Earth-Moon system. The discussion is carried out analysing the phase space of natural dynamics, constituted by both the orbital and the rotational periodic motions of a spacecraft in cislunar orbits. Floquet theory is applied to periodic orbit-attitude solutions in lunar proximity, to characterise their attitude stability properties and their attitude manifolds, which are discussed and analysed focusing on their dynamical features applicable to cislunar environment. Attitude stabilisation methods are proposed and developed, with particular attention to spin-stabilised solutions. Periodic orbit-attitude dynamics are studied to highlight possible favourable conditions that may be exploited to host a cislunar space station with a simplified control action. The focus of the analysis is dedicated to halo orbits and near-rectilinear halo orbit in the circular restricted three-body problem Earth-Moon system
Characterisation of 6DOF natural and controlled relative dynamics in cislunar space
Full text linkAt the 50th anniversary of Apollo 11, the Moon is back to the scene of scientific and commercial space exploration interests. During the next decade, the establishment of a Gateway in cislunar non-Keplerian orbits will open the space frontiers to sustainable manned and robotic missions on and around the Moon. Such infrastructure will require several logistic operations for its assembly and maintenance, which lean on rendezvous and docking capabilities. Even if few missions have flown on non-Keplerian orbits, Rendezvous and Docking (RV&D) operations have not been performed but in Low Earth Orbit (LEO). Investigations about 6 Degrees Of Freedom (DOF) relative dynamics in non-Keplerian environment are now mandatory to highlight criticalities in the design of the cislunar gateway and to translate RV&D protocols, consolidated in LEO for the International Space Station (ISS), to the new non-Keplerian environment. In this direction, the paper analyses the 6DOF natural orbit-attitude dynamics within the Circular Restricted Three-Body Problem (CR3BP) framework. A novel perspective of the dynamical structures, constituting 6DOF manifolds, allows to better characterise the natural relative dynamics in proximity of non-Keplerian orbits. The importance of orbit-attitude manifolds exploitation is underlined for designing reliable and efficient rendezvous trajectories, enhanced by natural cislunar dynamics. Then, an ephemeris cislunar dynamical model is exploited to address guidance laws for proximity operations. The control capability is included in the dynamics of a chaser vehicle, which is employed to solve the 6DOF guidance problem in proximity of a target spacecraft. The results obtained with the controlled dynamics are compared to those available thanks to natural motion, discussing the energetic and time costs to complete the manoeuvres. A control parametrisation to solve the optimal energy rendezvous problem is proposed. Finally, a feasible operational rendezvous scenario is discussed about the identified favourable locations along the non-Keplerian orbit to perform complex proximity operations. Significant relations between RV&D time and non-Keplerian orbit’s period are discussed as well
The role of secondary prospectivity of mine waste for enhancing critical metals recovery in South Australia
Full text linkGuidance, navigation and control for 6DOF rendezvous in Cislunar multi-body environment
Full text linkRecent studies highlighted the benefits of a support infrastructure located in Cislunar environment, which would ease the design of forthcoming space missions with a favorable access from and to the lunar surface, the Earth and many interplanetary destinations. Multi-body orbits rose a peculiar interest and were selected to stage a human-robotic exploration outpost; the family of Near Rectilinear Halo Orbits (NRHO), in particular, appears specifically suitable in these regards. Among the different capabilities that such outpost will tend to, the docking with other crewed or autonomous vehicles is a key feature that shall be present. Although low Earth orbit (LEO) rendezvous and docking is well assessed, no mission has performed such task in a multi-body gravitational environment. The paper presents a guidance, navigation and control (GNC) framework for 6 degrees of freedom (6DOF) coupled Cislunar rendezvous and docking. A feasible operational rendezvous scenario is detailed and exploited to define open-loop and closed-loop GNC functions for far-range and close-range. Then, the final approach is analyzed, proposing a closed-loop GNC that encompasses coupled translational-rotational dynamics. Vision-based only relative navigation techniques are applied to Cislunar multi-body dynamics to guarantee a coupled state estimation with a simple suite of sensors and a broad applicability range, ranging from passively cooperative to non-cooperative or unknown target spacecraft
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Full text linkWe 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
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