1,720,973 research outputs found
Small body gravimetry using SLAM-based autonomous navigation
Full text linkSmall celestial bodies have a complex dynamic environment characterized by irregular gravitational fields from non-uniform mass distributions and other non-gravitational perturbations. To study the orbital dynamics around the body, a good knowledge of the body's gravitational field is essential. This work presents a novel octree-based mascon approach to compute gravitational potential and its derivatives of a small body. The proposed method uses the small body's point cloud data to construct an octree model and the octree nodes represented as mascons. A numerical simulation evaluates the gravitational potential and its derivatives on different asteroid models and compares the results against a well-known polyhedron approach. The octree approaches are computationally efficient, and their performance is comparable to the polyhedron approach.
With an increased focus on missions to small bodies, the need to improve the level of autonomy also increases. To achieve autonomous navigation, a good knowledge of the small body's geometry and the dynamic environment is essential. Navigating and mapping an unknown environment is an interdependent problem and can be solved using a typical Simultaneous Localization and Mapping (SLAM) framework. This work aims to develop a SLAM framework for an orbiting spacecraft near a uniformly rotating asteroid and estimates the spacecraft's state, asteroid's state and reconstructs asteroid's geometry. The framework obtains a maximum-a-posterior estimate of the state variables by combining state space representations into graph nodes and uses sparse matrix factorization and iterative optimization to minimize the error in the estimates.
This work extends the SLAM framework to estimate the mass distribution of an asteroid. It combines the octree mascon model, and the SLAM approach to estimate the density of the octree nodes. The novel density factor presented relates the spacecraft's position, gravitational acceleration and the density of the octree nodes. The proposed approach is validated through numerical simulations. The results show that the framework is robust and achieves a good estimate of the state variables of the spacecraft, reconstructs the asteroid's 3D map and precisely estimates the mass distribution of an asteroid. The reconstructed gravity field improves the computed spacecraft states in orbit around an asteroid over a longer duration
Design and Development of UWE-4 : Integration of Electric Propulsion Units, Structural Analysis and Orbital Heating Analysis
No full textAfter the successful launch and operation of UWE-3 in 2013, UWE-4 is the next picosatellite in the University of Würzburg Experimental satellite program. UWE-4 is first from its series to have integrated propulsion system and with a mission objective to demonstrate attitude and orbit control using the miniature propulsion system. In future, this will pave the way to perform complicated missions such as formation flying using picosatellites. Major challenge in UWE-4 is the integration of the propulsion system (which includes both thrusters and power processing unit) into the 1U CubeSat. Integrating the thruster into the Picosatellite has several constraints, few include accommodation of the system within the structure at minimum mass and volume impact, structural design to withstand the critical launch conditions.In the scope of this master thesis project, the design of UWE-3 system arrangement is studied and the regions of possible integration of thruster units are identified. The two propulsion systems considered for the UWE-4 mission are the Micro Vacuum Arc Thrusters (µVAT) developed at UniBW in Munich, Germany and the NanoFEEP (highly miniaturized Field Emission Electric Propulsion) thrusters developed at TUDresden, Germany. During design phase, different concepts are created for the CubeSat rails to integrate the thrusters and the concepts are validated against the functional requirements as well as the CubeSat design specifications. Detailed CAD designs are completed for UWE-4 satellite using SolidWorks 2014. To validate the structural design, the CAD models are then subjected to Finite Element Modeling and Analysis (structural and thermal) using Siemens NX CAE. During static Structural analysis, various loading conditions and constraints are identified and applied to the system. Later NX NASTRAN solver is used to study and simulate the impact on the UWE-4 model. Also modal analysis was performed to study the natural frequencies of the system. With the motivation to study the thermal behavior of the system in orbit, transient analysis for orbital heating was performed using NX SPACE SYSTEMS THERMAL. The solution results from both structural analysis and thermal analysis are validated for different scenarios. Based on the results the generic design is qualified and expected to serve as a platform for future missions.Validerat; 20150709 (global_studentproject_submitter
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
On-Orbit Relative Navigation Near a Known Target Using Monocular Vision and Convolutional Neural Networks for Pose Estimation
Full text linkIn recent years, there is an increasing demand for orbital robotic missions for various reasons such as life extension of functional satellites, reuse the unique orbital slots and to reduce the risk of orbital collision. In such robotic missions, the satellite’s autonomous navigation capability is a critical component that enables it to perform relative navigation, inspection, and repairwith minimal human-in-loop intervention. Pose estimation is an important task within autonomous GNC for spacecraft in orbit. There have been recent, new development of deep learning based pose estimation algorithms in order to meet growing demands of autonomous orbital applications. This paper presents a new keypoint-based framework using Convolutional Neural Network models for pose estimation of known non-cooperative targets in orbit, which is thoroughly compared to existing state-of-the-art algorithms also based on deep learning. Within the proposed pose estimation pipeline, a ResNet-based architecture used for object detection, a Scale-Aware High-Resolution Network (HigherHRNet) used for keypoint regression and PnP-RANSAC for computing the pose. The framework is benchmarked with the SPEED dataset as well as the Soyuz dataset from STAR LAB Orbital Visual Simulator and the results were presented
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
- …
