1,720,965 research outputs found
Alternative Hybrid Propulsion Transfers for Marco Polo NEOs Sample Return Mission
No full textIn this paper the new concept of hybrid propulsion transfers is applied to the trajectory design for the ESA Marco Polo mission, a NEO sample return mission. The concept of hybrid propulsion transfers combine the features of low-energy transfer, which implies impulsive maneuver accomplished using chemical propulsion, and low-thrust transfer. The optimization is performed with a direct transcription procedure. The problem is formulated as a nonlinear programming problem and solved for a finite set of variables, maximizing the final spacecraft mass. The designed hybrid propulsion transfers have been in-depth compared with the baseline trajectories obtained for Marco Polo mission
Hybrid Propulsion Transfers for Mars Science Missions
No full textSpecial Earth-Mars transfers that exploit both chemical and solar electric propulsion are investigated in this work. A dedicated launch strategy via Soyuz is considered. Firstly, a high-thrust, low-Isp impulse is used to place the spacecraft onto an Earth-escape trajectory, possibly performing a lunar swingby. Then, an heliocentric rendezvous with Mars is achieved via low-thrust, high-Isp propulsion, followed by a ballistic capture leading to a final, low-altitude orbit around Mars. Hybrid propulsion transfers outperform chemical transfers (Hohmann) in terms of propellant consumption. Furthermore, a few considerations at system level are also proposed
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
Attainable sets in space mission design : A method to define low-thrust, invariant manifold trajectories
No full textHybrid propulsion transfers to the Moon
No full textThis work analyzes special Earth–Moon transfers that make use of both chemical and solar electric propulsion. A first high-thrust, low-Isp impulse is used to place the spacecraft into an exterior-like low-energy transfer to the Moon, possibly performing a lunar gravity assist. The subsequent use of low-thrust, high-Isp propulsion makes it possible to perform a lunar ballistic capture leading to a final, low-altitude orbit about the Moon. Hybrid propulsion transfers outperform both the chemical transfers (Hohmann, interior, and exterior) and the fully solar electric propulsion transfers (e.g., SMART-1-like) in terms of propellant consumption, although an assessment of these transfers at system level is still missing
- …
