1,720,964 research outputs found
Design and modeling of kinetic impact missions for deflecting near-earth asteroids
No full textThe solar system is full of small bodies such as asteroids and comets that are thought to be remnants of early planetary formation. As of June 2025, there are more than 1.4 million known small bodies in the solar system, more than 4,000 of which are classified as comets. These objects routinely cross the Earth's orbit at close distances. Some have even impacted our home planet in the past, causing significant damage. Therefore, studying them is critical – not just for understanding the history and evolution of the solar system, but for assessing potential existential threats to life on Earth.
The field of planetary defense is dedicated to the study of asteroids and comets that might pose such natural hazards. It also focuses on the development of methods to mitigate these threats. Work done in this field involves discovering and characterizing potentially hazardous objects, predicting their future trajectories, and developing various methods to deflect or disrupt them if they are found to be on a collision course with Earth.
The work presented in this dissertation focuses on the kinetic impact method for deflecting asteroids that could potentially hit the Earth. Kinetic impact deflection entails sending a spacecraft to crash into the threatening object at high speed, thereby altering its trajectory. Over time, this small change in the originally earthbound trajectory can accumulate into a significant change in the object's position, potentially preventing the impact.
Within the time span of the work presented in this dissertation, NASA has launched and successfully completed the Double Asteroid Redirection Test (DART) mission. DART was the world's first demonstration of the kinetic impact deflection method at the (65803) Didymos binary asteroid system. The DART spacecraft collided with the asteroid Dimorphos in September 2022, successfully altering its orbit around its parent body, Didymos.
In the context of the DART mission, I have developed new methodologies for modeling the momentum transfer from the deflection spacecraft to the target, which is crucial for predicting the outcome of kinetic impact. This includes methods for quantifying the measurability of the heliocentric momentum transfer, which characterizes the change in the target's orbit around the Sun. The framework developed here enables planetary defense programs to evaluate the effectiveness of a deflection, as this change is what ultimately determines whether the hazard from an asteroid has been successfully mitigated. Consequently, this dissertation also presents the first-ever measurement of the heliocentric orbit change for a celestial object in the solar system. This measurement for the DART mission is a significant milestone in planetary defense, as it provides concrete evidence of the effectiveness of kinetic impacts for deflecting asteroids.
Additionally, a new method for designing future kinetic impact missions is also presented. This method relies on mapping keyholes onto the surface of a target asteroid. Gravitational keyholes are arbitrary regions in space that, if an asteroid passes through them, will guarantee a future impact with Earth. Keyhole mapping allows mission designers to plan deflection missions that can push asteroids away from the Earth while ensuring that they do not pass through a keyhole after the deflection. This can allow us to permanently push these objects away from Earth. Lastly, this dissertation also presents novel contributions to the broader field of dynamical systems theory by introducing a new method for computing the state transition matrix of a nonlinear dynamical system. Based on the concept of the unscented transform, this method allows for computation of the state transition matrix without the need of tedious analytic partial derivatives or arbitrary finite difference steps.
Therefore, the results presented here provide new insights that extend the state of the art in planetary defense and will aid in the design and successful execution of future deflection missions. The demonstration of the kinetic impact method through the DART mission marked a pivotal moment in our ability to protect Earth from potential impacts. The methodologies developed in this dissertation will help ensure that we are better prepared for any future threats.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2026-02-19 without embargo termsThe student, Rahil Makadia, accepted the attached license on 2025-11-18 at 17:39.The student, Rahil Makadia, submitted this Dissertation for approval on 2025-11-18 at 17:51.This Dissertation was approved for publication on 2025-11-19 at 09:16.DSpace SAF Submission Ingestion Package generated from Vireo submission #22888 on 2026-02-19 at 18:24:5
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
Heliocentric Effects of the DART Mission on the (65803) Didymos Binary Asteroid System
Full text linkThe Double Asteroid Redirect Test (DART) is NASA’s first kinetic impact–based asteroid deflection mission. The DART spacecraft will act as a projectile during a hypervelocity impact on Dimorphos, the secondary asteroid in the (65803) Didymos binary system, and alter its mutual orbital period. The initial momentum transfer between the DART spacecraft and Dimorphos is enhanced by the ejecta flung off the surface of Dimorphos. This exchange is characterized within the system by the momentum enhancement parameter, β, and on a heliocentric level by its counterpart, βe. The relationship between β and the physical characteristics of Dimorphos is discussed here. A nominal set of Dimorphos physical parameters from the design reference asteroid and impact circumstances from the design reference mission are used to initialize the ejecta particles for dynamical propagation. The results of this propagation are translated into a gradual momentum transfer onto the Didymos system barycenter. A high-quality solar system propagator is then used to produce precise estimates of the post-DART encounters between Didymos and Earth by generating updated close approach maps. Results show that even for an unexpectedly high βe, a collision between the Didymos system and Earth is practically excluded in the foreseeable future. A small but significant difference is found in modeling the overall momentum transfer when individual ejecta particles escape the Didymos system, as opposed to imparting the ejecta momentum as a single impulse at impact. This difference has implications for future asteroid deflection campaigns, especially when it is necessary to steer asteroids away from gravitational keyholes
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
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
- …
