1,720,969 research outputs found
Rendezvous approach guidance for uncooperative tumbling satellites
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 125-136).The development of a Rendezvous and Proximity Operations (RPO) guidance algorithm for approaching uncooperative tumbling satellites has multiple purposes including on-orbit satellite servicing, space debris removal, asteroid mining, and on-orbit assembly. This thesis develops a guidance algorithm within the framework of on-orbit satellite servicing, but is extendable to other mission scenarios. The author tests the algorithm in an RPO simulation with an uncooperative tumbling satellite near Geo-stationary Orbit (GEO) starting at a relative distance of 50 m and ending at a relative distance of 5 m. Examples of potential uncooperative tumbling clients include decommissioned satellites or satellites with malfunctioning thrusters. Due to the low Technology Readiness Level (TRL) of autonomous (RPO) missions, first missions prefer to use flight proven technologies. This thesis implements a guidance algorithm based on the flight proven Clohessy-Wiltshire (CW) and space shuttle glideslope equations which command a sequence of burns to close the distance between the servicer and client while matching the client satellite's rotation rate. The author validates the guidance algorithm through Monte Carlo (MC) analysis in a Three Degrees of Freedom (3DOF) simulation. Fuel use metrics characterize the sensitivity of the algorithm. Fuel consumption is measured by the total velocity changes, or [delta]V, needed to complete the maneuvers. Cumulative [delta]V sensitivity is measured against navigational uncertainty in the rotational axis to summarize the key requirements and trade-offs associated with implementing this algorithm."Draper provided the financial support and expertise that helped me write my thesis"--Page 5by Manwei Chan.S.M.S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautic
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
Toward Real-time Earth Observation with Satellite Constellation Crosslinks and Propulsion
No full textThe development of remote sensing small satellite constellations has created the potential for high-resolution Earth-observation data to reach end users faster. This work investigates how propulsion and intersatellite links enable constellations to continuously collect and deliver data faster than constellations without these capabilities.
This work has four contributions. The first contribution is a constellation simulation framework that is based on open-source libraries. This simulation framework can propagate satellites and execute propulsive maneuvers. The second contribution is a planning and scheduling algorithm for propulsive maneuvers, target observation times, and optimal data routing paths. The third contribution is the development of high performance constellation designs with respect to constellation cost and the following metrics: age of information, system response time, and total pass time. The cost model is developed from two separate models: the Small Satellite Cost Model (SSCM) and a launch cost model developed in this work. The fourth contribution is a set of cost-estimating relationships (CERs) that models the trade-off between cost and system performance in terms of the aforementioned metrics.
The new simulation framework of contribution 1 is verified against the industry-standard software Systems Tool Kit (STK). The simulation framework is used to run 21 different constellation designs, 3 different satellite models, and 432 distinct ground targets. These scenarios are run during each of the four seasons to eliminate geometric biases for a total of 108,864 individual scenario simulations. A single satellite executing the reconfiguration algorithm produces up to a 125% increase in pass time over seven days when compared to an identical satellite without propulsive capabilities. For an access cone with a nadir half-angle of 20 ,thereconfigurationalgorithm produces a 67% increase in pass time. Comparing the cost of inter-satellite link (ISL) and reconfiguration-capable satellites versus (i) only ISL-capable satellites and (ii) a baseline satellite without ISL or reconfigurable capabilities, a Pareto optimal analysis revealed 29% of designs had both propulsion and intersatellite link capabilities when optimizing for age of information, 7% of designs had both propulsion and intersatellite link capabilities when optimizing for system response time, and 33% of designs had both propulsion and intersatellite link capabilities when optimizing for total pass time. The CERs show that for constellations costing between 1B (FY24), age of information can be reduced by 32 seconds for every million dollars spent, system response time can be reduced by 35 seconds for every million dollars spent, and total pass time over 3 days can be increased by 2 seconds for every million dollars spent.Ph.D
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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