Equilibria of Multibody Chain in Orbit Plane

We study equilibria of a multibody system in the orbit plane within the framework of a model of n + 1 material points connected by n light rods into an n-link chain. The junctions are spherical hinges. The center of mass of the system moves along a circular orbit. The equilibrium equations are reduced to a fairly simple form that enables their analysis.We find all the equilibria of an n-link chain in the orbit plane and prove that each rod can occupy one of the following three positions: it can be directed along the tangent to the orbit of the center of mass of the chain; it can be a member of a group of adjacent vertical rods, being the center of mass of this group situated on the tangent to the orbit; and, finally, an oblique orientation is possible if the rod joins either two vertical groups of rods or the end of a vertical group with the tangent to the orbit. It is shown that the number of equilibria does not exceed 2^(2n). We include the analysis of two examples (three- and four-link chains) and represent the schemes of all the realizable equilibria in these cases.info:eu-repo/semantics/publishedVersio

Orbital manoeuvres with single-input control

We study the problem of orbital control under the constraints on the thrust direction for a nonlinear dynamical model. The satellite is equipped with a passive attitude control system providing one-axis stabilization and a propulsion system consisting of one or two thrusters oriented along the stabilized axis. Different applications, such as formation flying and satellite de-orbiting are considered.FC

Linear differential games and high precision attitude stabilization of spacecrafts with large flexible elements

FCT, QREN, FEDER, COMPET

Optimization of parameters of asymptotically stable systems

This work deals with numerical methods of parameter optimization for asymptotically stable systems.We formulate a special mathematical programming problem that allows us to determine optimal parameters of a stabilizer. This problem involves solutions to a differential equation. We show how to chose the mesh in order to obtain discrete problem guaranteeing the necessary accuracy. The developed methodology is illustrated by an example concerning optimization of parameters for a satellite stabilization system.FCT, QREN, FEDER, COMPET

Parameter optimization for stabilizers

The aim of this work is to develop an effective numerical tool oriented to optimization of stabilizer parameters according to different criteria that appear in engineering practice. We formulate a special optimization problem that allows us to determine optimal parameters of a stabilizer. The obtained results are applied to choose parameters of a spacecraft stabilization system. We discuss the choice of optimization criteria comparing the degree of stability objective function, the H _inf norm of the system transfer matrix, and the minimal “peak” criterion.Portuguese National Strategic Reference Framework (QREN)Fundação para a Ciência e a Tecnologia (FCT)European Regional Development Fund (FEDER)Portuguese Operational Programme for Competitiveness Factors (COMPETE

Attitude dynamics and stability of a simple solar photon thruster

This paper is dedicated to the development of a model of the attitude dynamics for a nonideal Simple Solar Photon Thruster (SSPT) and to the analysis of sailcraft motions with respect to their centre of mass. Derivation of the expressions for force and torque due to solar radiation that is valid for the case, when there is a misalignment of the SSPT axis with the sun direction, is followed by study of sailcraft dynamics and stability properties. Analysis of stability shows that an ideally reflecting sail is unstable, while for a sailcraft with nonideal collector, the symmetry axis is stable with respect to the Sun direction for large variety of system parameters. The motion around symmetry axis is always unstable and requires an active stabilizer.FCT, COMPETE, QREN, FEDE

Nanostar, A Collaborative Approach to Nanosatellite Education

The CubeSat standard is today used by many universities and companies as an educational and research tool on space systems. The development of a nanosatellite project requires numerous tools and competences, which makes it an excellent training vector. However, it also requires appropriate experience, facilities and resources, which can be difficult to gather. Hence the need to work in a network. NANOSTAR emerges as a project funded by INTERREG-SUDOE through European Regional Development Fund (ERDF) aiming to develop a network of excellence among universities, the regional industry and the scientific ecosystem in order to create a leading collaborative online platform in Europe for nanosatellites. NANOSTAR aims to provide students with a high level of skills in space engineering and project engineering. In the past year, challenges have been proposed and different education strategies have been adopted. This paper describes the project and gives details about the collaborative online platform and the students challenges. The preliminary mission design challenges are presented, as well as the winner solutions to those challenges. Also, it dis-cusses the methods used to motivate and educate the students. Finally, it draws conclusions based on an analysis of the work development and proposes strategies for the future

Closed relative trajectories for formation flying with single-input control

Em publicação.We study the problem of formation shape control under the constraints on the thrust direction. Formations composed of small satellites are usually subject to serious limitations for power consumption, mass and volume of the Attitude and Orbit Control System (AOCS). If the purpose of the formation flying mission does not require precise tracking of a given relative trajectory, AOCS of satellites may be substantially simplified; however, the capacity of AOCS to ensure a bounded or even periodic relative motion has to be studied first. We consider a formation of two satellites; the deputy one is equipped with a passive attitude control system that provides one-axis stabilization and a propulsion system that consists of one or two thrusters oriented along the stabilized axis. The relative motion of the satellites is modeled by the Schweighart-Sedwick linear equations taking into account the effect of $J_2$ perturbations. We prove that both in the case of passive magnetic attitude stabilization and spin stabilization for all initial relative positions and velocities of satellites there exists a control guaranteeing their periodic relative motion.Quadro de Referência Estratégico Nacional (QREN)Russian Foundation for Basic Research (RFBR), grant 09-01-00431Fundo Europeu de Desenvolvimento Regional (FEDER)Fundação para a Ciência e a Tecnologia (FCT)Programa Operacional Temático Factores de Competitividade (COMPETE

Knowledge and attitudes development through didactic competitions: Spaghetti Bridge Contest at UBI

The main objective of the Spaghetti Bridge Contest promoted by the Department of Electromechanical Engineering of the University of Beira Interior (Portugal) is to encourage the creative capacities of students and improve their attitudes towards learning. The knowledge acquired in the Applied Mechanics course is applied in the project of a bridge built with such a common material as spaghetti. This annual event aims to increase the students' interest in research providing ingenious solutions to problem. Up to date, the contest had twelve editions; it is precursor in Portugal of similar events organized by other institutions of Higher, Secondary and Basic education levels. This paper presents the evolution of the event since its origin, regarding both the solutions found by students to consecutively beat the resistance records, and the motivation in participating in such a didactic contest devoted to engineering educationinfo:eu-repo/semantics/publishedVersio

Averaging methods for design of spacecraft hysteresis damper

This work deals with averaging methods for dynamics of attitude stabilization systems. The operation of passive gravity-gradient attitude stabilization systems involving hysteresis rods is described by discontinuous differential equations. We apply recently developed averaging techniques for discontinuous system in order to simplify its analysis and to perform parameter optimization. The results obtained using this analytic method are compared with those of numerical optimization.This research is supported by the Portuguese Foundation for Science and Technologies (FCT), the Portuguese Operational Programme for Competitiveness Factors (COMPETE), the Portuguese Strategic Reference Framework (QREN),and the European Regional Development Fund (FEDER)