1,721,023 research outputs found
Satellite on-board solutions for precise orbit determination on Earth and Moon orbit
Full text linkPrecise Orbit Determination, which is the problem of finding the satellite ephemeris by estimating the satellite position and velocity based on Earth observations data, has always been one of the most important aspects of satellite navigation. Satellite positioning is used daily by smartphones to provide several features and also by military personnel. Both of these users require different levels of accuracy. In the last decades the increasing interest in space exploration has brought forward the necessity to provide the satellites with on-board estimation algorithms. The ability to self-estimate their position and velocity is of utmost importance in scenarios in which data from Earth are not available, like in Moon or Mars orbiting. Artificial Intelligence has proven to be one of the best solutions, able to provide the satellite with non-standard measurements. The abstraction and generalization capability of neural networks allow to perform complex tasks while satisfying real-time constraints. In this context Crater Matching is one of the most promising solutions for orbit determination.
In this thesis two different approaches for on-board Precise Orbit Determination will be proposed: one making use of standard GNSS measurements coming from Earth and the other one making use of non-standard ones provided by neural networks. In the former case an end-to-end analysis, going from satellite propagation to satellite visibility has been performed. In the latter case a first step toward the development of a full Terrain Relative Navigation system has been carried out: a benchmarking of different neural networks architectures has been performed, by using a space-qualified processor, in order to identify the best on-board solution to deal with the crater detection problem.
Two additional research projects tackling important aspects of the space domain, satellite communication and Earth observation respectively, will also be detailed. A mixed Artificial Intelligence and Reinforcement Learning solution has been proposed for the first topic with extensive simulations and comparisons to validate the approach. A full Artificial Intelligence approach has instead been taken to tackle the second project, in which a Convolutional Neural Network has been trained to detect wildfires in real-time and has been tested over a space-qualified processor to verify its feasibility to be deployed on-board
A security event detection approach based on neural network for the ESW broadband satellite system
No full textNetwork management and in particular security management of a world-wide satellite system are
challenging tasks. EuroSkyWay (ESW) as a broadband satellite system will be provided with a
hierarchical management architecture distributed up to the ESW terminals population by means of
agents whose Fault, Configuration, Accounting, Performance and Security (FCAPS) capabilities are
used both by private's network management systems and by a centralised network management centre
(ESW-NMC). Different management domains partially overlapped have to be interfaced and
management information have to be exchanged between the different involved domains. Security is a
competitive driver for services supplied by ESW to service providers and telecom operator in a datacommunication
networks market scenario.
Many design factors contribute to determine the overall security; they can be neatly related to the
suitability of the adopted system security services and mechanisms and to the effectiveness of the
security management. A timely and accurate security event detection capability is a criticaI feature for
a data-communication security management. Security event detection is concerned with any activity
that may be tracked as a security violation. A violation is considered to be any event explicitly or
implicitly in contrast with ESW security policy.
A valid detection of specific security events triggers a suitable action chain according with network
management containment and recovery functionality. This firstly requires the choice of conditions
whose occurrence triggers security alarm and then requires the specification of the correlation logic
that detects security events on alarms basis. This approach is strictly dependent on system threat
analysis comprehensiveness and consistency. Threat analysis, even if correctly conducted is not able
to reveal every possible threat. Ongoing ESW threat analysis, outlines the difficulty to perform an
exhaustive threats identification and the amount of patterns needed for a comprehensive knowledge
base. On the other hand the constantly changing nature of network attacks the set-up of a stati c rules as
input for expert systems like approaches.
The above mentioned considerations have addressed a neural network based solution to ESW
security event detection. The neural networks are in fact able to correctly analyse patterns, even if they
are incomplete or distorted. Thus, a neural network has the ability to learn the characteristics of
security attacks and identifY them on the basis of input pattems that are unlike from the ones observed
in previous leaming cycles.
A neural network that implements the ESW security event detection is presented in this paper. This
neural network provides the capability to classifY security alarm pattems as signatures of attacks with
a certain confidence value. Such a signature, is finally detected as security event if its likelihood
exceeds a given threshold. The neural network training phase, with learning samples based on both possible ESW normal and abnormal operation system states, will be also described. The model of the
proposed classification system for security violation events based on neural network is further on
evaluated with respect to the ESW security objectives
A wireless Broadband Communication System based on SkyplexNet / Wi - Fi Networks Interoperability for Multimedia Applications
No full textFlexible Resource Allocation Scheme Performance Evaluation in EuroSkyWay Multimedia Satellite System
No full textNeural Network Application to Traffic Shaping Architecture for the EuroSkyWay Broadband Satellite System
No full text
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
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