1,721,149 research outputs found
Mixed-integer GA optimization for the tracking control of a formation of small satellites equipped with multi-constrained electric thrusters
No full textA formation mission scenario is considered, consisting of small satellites (Chasers) that must keep a reference trajectory with respect to a larger and non-cooperating Target satellite. The Chaser must perform its formation guidance and control tasks within the framework of its thruster constraints: the case of a low thrust electrical engine is here considered. The constraints of such a thruster are relevant to number and orientation of thrusters, the admissible thrust levels and minimum and maximum ON time. The control algorithm developed to satisfy all these constraints is a model predictive control based on a mixed-integer genetic algorithm optimization, which provides a fast estimate of the necessary scheduled actions. The algorithm takes J2 and drag perturbations into account; at the scope a differential orbital parameters linear relative dynamics model has been used, while the real-world dynamics is represented by a high precision orbital propagator. The developed orbital controller is particularly effective when trajectory keeping is required; different relative configurations, like Helix or Train formations, are taken as benchmark trajectories. The results show promising and robust performance in counteracting
differential perturbations, even in the case in which the Target satellite performs scheduled orbital maneuvers which are not timely communicated to the Chaser satellite
Mixed-Integer GA optimization for the control of a formation of small satellites equipped with multi-constrained electric thrusters
No full textA formation mission scenario is considered, consisting of small satellites (Chasers) that must acquire and maintain a reference trajectory with respect to a larger and non-cooperating Target satellite. The Chaser must perform its formation guidance and control tasks within the framework of its thruster constraints: the case of a low thrust electrical engine is here considered. The constraints of such a thruster are relevant to: (a) single-axis orientation of the thrust (since only one engine is present); (b) the thrust level (only two levels are possible: maximum and zero); (c) maximum ON time (due to power consumption and temperature issues); (d) minimum ON time (because of the time required to prepare the motor ignition, it is preferrable not to have very short ignitions); (e) maximum number of ignitions; (f) minimum time between two subsequent ignitions. The control algorithm developed to satisfy all these constraints is a model predictive control based on a mixed-Integer genetic algorithm optimization, which provides a fast estimate of the necessary scheduled actions. The algorithm takes J2 and drag perturbations into account; at the scope a differential orbital parameters linear relative dynamics model has been used, while the real-world dynamics is represented by a high precision orbital propagator. The developed orbital controller is particularly effective when trajectory keeping is required, while a different (not optimal) controller is used when large reconfigurations are needed. Developing a guidance logic that opportunely switches between the two controllers, the results show that even such a multi-constrained control system can perform a wide range of typical formation operations, such as station keeping in normal mode and during Target's scheduled operations, and acquisition of different relative configurations, like Helix or Train formations
Conjectures and problems surrounding the Jacobian Conjecture
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L’Università per l’educazione al patrimonio culturale: tra storia, possibilità e prospettive/ The University for heritage education: between history, possibilities and perspectives
No full textSe già dagli inizi del secolo scorso la funzione sociale ed educativa del museo era al centro di dibattiti e pioneristiche iniziative a livello internazionale, ripercorrendo gli snodi significativi in Italia per l’instaurarsi di un ruolo attivo delle università in questo settore si vedrà come esso avvenga in maniera tardiva e, ancora oggi, non pienamente risolta sul piano normativo.A fronte del delinearsi delle tre missioni universitarie di didattica, ricerca e terza missione, se ne metteranno qui in evidenza peculiarità e prospettive nell’ambito dell’educazione al patrimonio culturale: se da un lato è necessario un cambio di paradigma nell’analisi della formazione universitaria per i professionisti dell’educazione, intendendo qui dimostrare come le attuali possibilità siano indissolubilmente legate al riconoscimento della figura professionale, dall’altro ricerca e terza missione non solo smentiscono lo scollamento precedentemente evidenziato tra accademia e società, ma evidenziano il reciproco arricchimento derivante dai rapporti intessuti e un potenziale ancora da sviluppare. Since the beginning of the last century the social and educational function of the museum was at the center of debates and pioneering initiatives at an international level. Retracing the significant junctions in Italy for the establishment of an active role of universities in this sector, it will be seen how it happens belatedly and, still today, not fully resolved on the regulatory level.Given the emergence of the three university missions of teaching, research and third mission, their peculiarities and perspectives in the field of heritage education will be highlighted here. If on the one hand a paradigm shift is necessary in the analysis of training university for education professionals, intending here to demonstrate how the current possibilities are inextricably linked to the recognition of the professional figure, on the other research and third mission not only deny the previously highlighted disconnect between academia and society, but highlight the mutual enrichment deriving from interwoven relationships and potential yet to be developed
Aerodynamic coordinated control of attitude and relative position of a formation of microsatellites
No full textSatellites in very low Earth orbits can leverage the aerodynamics forces for control purposes. Three-axis attitude control can be achieved by adjusting the orientation of aerodynamic surfaces, benefiting from both drag and lift forces. However, complete control over the orbital motion of a satellite is unattainable using aerodynamic forces alone, as positive thrust cannot be generated. Nonetheless, this limitation does not apply when focusing on the control of a satellite formation. By properly modulating the orientation of panels, positive and negative relative forces can be generated. This paper shows that even in a formation of simple microsatellites, it is possible to achieve formation and attitude simultaneous control by using no other actuators than the aerodynamics surfaces. Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved
Periodic solutions of perturbed Hamiltonian systems in the plane by the use of the Poincaré-Birkhoff theorem
No full textWe prove the existence of periodic solutions for a planar non-autonomous Hamiltonian system which is a small perturbation of an autonomous system, in the presence of a non-isochronous period annulus. To this aim we use the Poincar\'e-Birkhoff fixed point theorem, even if the boundaries of the annulus are neither assumed to be invariant for the Poincar\'e map, nor to be star-shaped. As a consequence, we show how to deal with the problem of bifurcation of subharmonic solutions near a given nondegenerate periodic solution. In this framework, we only need little regularity assumptions, and we do not need to introduce any Melnikov type functions
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