1,721,185 research outputs found
A CubeSat-sized servicer for Space Debris removal
No full textThe escalating population of space debris poses a significant threat to operational satellites. Among others, the removal of large non-operative satellites from their orbits emerges as a solution to mitigate the problem. For this purpose, a servicing spacecraft is required for the removal of these resident objects, necessitating an In-Orbit Servicing (IOS) mission. These missions typically involve large, complex spacecraft equipped with robotic arms, contributing to high economic costs that may outweigh the benefits for operators dealing with failed spacecraft. This study introduces an innovative approach to satellite removal. This work proposes leveraging on affordable and standardized CubeSat technology to perform simple servicing task. A 12U CubeSat equipped with a robotic arm is used to attach a deorbiting kit to a target satellite. It contains a drag augmentation device designed for de-orbiting Low Earth Orbit (LEO) satellites. A mock-up of the proposed system has been developed to validate the proposed solution during a servicing manoeuvre performed on a low-friction table. A Guidance, Navigation and Control (GNC) algorithm has been developed to control the system during the autonomous servicing manoeuvre. Alongside presenting the system architecture, this work shows the preliminary results obtained from the test campaign
Development of On Orbit Assembly technologies to enable spacecraft servicing
No full textThe growing population of space debris represents a significant threat to operational satellites, increasing the need for effective mitigation strategies. Over the past decade, In-Orbit Servicing (IOS) and Active Debris Removal (ADR) missions have emerged as promising solutions to mitigate their growth. IOS missions aim to extend satellite lifespan by enabling refuelling, repairs, or upgrades, while ADR missions focus on capturing and safely deorbiting debris, ensuring long-term stability of the Earth orbits.
This work investigates innovative technologies and methodologies aimed at supporting IOS and ADR missions, with a specific focus on enhancing key building blocks to improve the safety, reliability, and robustness of these missions. Typically, proposed or flown IOS and ADR missions involve the use of a large servicer satellite equipped with a robotic arm for performing the required tasks.
To enhance the reliability and robustness of robotic arm operations in space, two control strategies are examined: the minimum base reaction control, investigating the kinetic energy minimization method, and the combined control approach. Particular focus is posed on the latter, presenting the validation, verification and testing of a novel Guidance, Navigation, and Control (GNC) system designed for close proximity operations between a servicer and a target satellite and developed under an ESA's project. The guidance and control functionalities were developed by Politecnico di Milano and the navigation algorithms by Università di Napoli. A realistic simulator was developed in the MATLAB/Simulink environment to test the GNC system in three different scenarios spanning from servicing to debris removal missions.
However, large, complex, and expensive spacecrafts equipped with robotic arms used in IOS/ADR missions lead to high economic costs that can outweigh the benefits for operators. To address these challenges, the Thesis proposes to employ a 12U CubeSat equipped with a robotic arm for performing servicing or removal tasks. This approach addresses the limitations of traditional large servicer satellites, offering a low-cost, flexible alternative that reduces mission risks and debris generation. After the presentation of the mission concept that consists of a CubeSat that autonomously creates an assembly with the target satellite, the preliminary design of the CubeSat is presented. In addition, laboratory tests were performed for an initial validation of the proposed manoeuvre.
The development of this concept builds upon the knowledge gained from the Alba CubeSat UniPD project that I founded and have managed since 2019. The project is developing a 2U CubeSat with four independent objectives. The team participated to the ESA's Fly Your Satellite! -- Design Booster programme and consolidated the system and payloads design.
This thesis contributes to advancing the field of IOS and ADR by introducing and validating several innovative technologies. The study of free-flying space robots control strategies addresses critical challenges in IOS and ADR operations. The successful development and testing of a new GNC system represent a significant step forward in ensuring the robustness and safety of close proximity manoeuvres between satellites. Additionally, the proposal of a 12U CubeSat servicer offers a low-cost, flexible alternative to traditional servicer satellites
A Simulation Tool for Robotic Active Debris Removal with minimum reaction space manipulator
No full textSimulation of robotic space operations with minimum base reaction manipulator
No full textAutonomous robotic capture has been identified as a key technology for On-Orbit Servicing (OOS) and Active Debris Removal (ADR) missions. However, manoeuvring spacecraft-mounted manipulators is a challenging task since it generates disturbance torques on the satellite. To mitigate this problem several minimum reaction control strategies have been developed to reach the desired End-Effector (EE) pose while minimizing the dynamic disturbances transferred to the spacecraft by the robotic arm.
This paper presents the development of a Simulation Tool in the MATLAB/Simulink environment capable of simulating the dynamics of a satellite equipped with a 7-DoF robotic arm during the target capture phase. The manipulator, as well as the spacecraft, is implemented by using Simscape Multibody and joint actuators are modelled as Brushless DC motors controlled by PID controllers. The spacecraft attitude is Nadir-Pointing, it is controlled by means of quaternion feedback and Linear-Quadratic-Regulator (LQR) and it is actuated by three Reaction Wheels (RW). Orbital perturbations such as non-spherical gravity potential (EGM2008 model) and atmospheric drag are considered. In addition, the minimum reaction control strategy called Kinetic Energy Minimization (MKE) is employed during the robotic arm manoeuvres.
The goal of this study is to compare the performances obtained with the MKE method with those achieved by using the classic Inverse Kinematics (IK) in the free-flying case. The numerical results confirmed that MKE method is to be preferred since it minimizes the control torque that the Attitude Control Subsystem (ACS) must provide and reduces the EE orientation and position errors
GNSS spoofing detection techniques by cellular network cross-check in smartphones
No full textThe spoofing attack is a well known threat for global navigation satellite systems (GNSSs), where a malicious entity forges fake GNSS signals in order to trick a victim receiver into computing the desired false position and time. Only in recent years the interest in anti-spoofing techniques has been extended to mobile-device applications. As location-based services (LBS) are now deeply integrated in billions of people's everyday life, the security of positioning in mobile phones has become a concern. Indeed, it has been proven that even modern smartphones are vulnerable to position and time spoofing attacks. Previous studies have shown that current smartphones perform little or no cross-check on GNSS positioning, about the navigation message correctness, or the consistency of the obtained position estimate with data from other sensors that may be available on the same device. In this paper, as a response to the spoofing threat, we develop a novel technique that checks the consistency between the position estimates obtained by GNSS and data relative to the neighbouring cell. For the latter estimate we propose two solutions: one is based on the position of the base stations and the other directly on the smartphone position estimated from the cellular network. We also implement the proposed techniques in an Android application and test its effectiveness in detecting spoofing attacks and giving a warning to the user
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
Overview of Spacecraft-Fragmentation Testing
Get PDFSpacecraft fragmentation due to collisions with space debris is a major concern for space agencies and commercial entities, since in the next years the production of collisional fragments is expected to become the major source of space debris. Experimental studies have shown that the fragmentation process is highly complex and influenced by various factors, such as the satellite design, the material properties, the velocity and angle of the debris impact, and the point of collision (e.g., central, glancing, on spacecraft appendages). This paper summarizes the current state of research in spacecraft fragmentation, including the methods and techniques used to simulate debris impacts, the characterization of fragment properties and the analysis of the resulting debris cloud. It provides an overview of the main experiments performed, underlining the most critical issues observed. Moreover, it presents a set of experiments performed at the University of Padova and proposes some future directions for this research
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