1,382,222 research outputs found
Time-optimal trajectories to circumsolar space using solar electric propulsion
No full textThe aim of this paper is to explore the capabilities of a solar electric propelled spacecraft on a mission towards circumsolar space. Using an indirect approach, the paper investigates minimum time of transfer (direct) trajectories from an initial heliocentric parking orbit to a desired final heliocentric target orbit, with a low perihelion radius and a high orbital inclination. The simulation results are then collected into graphs and tables for a trade-off analysis of the main mission parameters. Finally, a comparison of the performance between a solar electric and a (photonic) solar sail based spacecraft is discussed
H2-Reversal Trajectory: a New Mission Application for High-Performance Solar Sails
No full textThe aim of this paper is to quantify the performance of a flat solar sail to perform a double angular momentum
reversal manoeuver and produce a new class of two-dimensional non-Keplerian orbits. The problem is
addressed in an optimal formulation and using a parametric approach. Two main difficulties must be properly
taken into account. On one side the sail must perform a rapid reorientation maneuver when it approaches
the Sun. It is shown by simulation that this assumption is reasonable. In second place the corresponding
trajectories require high performance solar sails, that is, sails with a characteristic acceleration greater than
3mm=s2. Such a value, although well beyond the currently available sail performance, is comparable (or
even lower) to that required by the original H-reversal maneuvers
Three-Dimensional Rapid Orbit Transfer of Diffractive Sail with a Littrow Transmission Grating-Propelled Spacecraft
No full textA diffractive solar sail is an elegant concept for a propellantless spacecraft propulsion system that uses a large, thin, lightweight surface covered with a metamaterial film to convert solar radiation pressure into a net propulsive acceleration. The latter can be used to perform a typical orbit transfer both in a heliocentric and in a planetocentric mission scenario. In this sense, the diffractive sail, proposed by Swartzlander a few years ago, can be considered a sort of evolution of the more conventional reflective solar sail, which generally uses a metallized film to reflect the incident photons, studied in the scientific literature starting from the pioneering works of Tsander and Tsiolkovsky in the first decades of the last century. In the context of a diffractive sail, the use of a metamaterial film with a Littrow transmission grating allows for the propulsive acceleration magnitude to be reduced to zero (and then, the spacecraft to be inserted in a coasting arc during the transfer) without resorting to a sail attitude that is almost edgewise to the Sun, as in the case of a classical reflective solar sail. The aim of this work is to study the optimal (i.e., the rapid) transfer performance of a spacecraft propelled by a diffractive sail with a Littrow transmission grating (DSLT) in a three-dimensional heliocentric mission scenario, in which the space vehicle transfers between two assigned Keplerian orbits. Accordingly, this paper extends and generalizes the results recently obtained by the author in the context of a simplified, two-dimensional, heliocentric mission scenario. In particular, this work illustrates an analytical model of the thrust vector that can be used to study the performance of a DSLT-based spacecraft in a three-dimensional optimization context. The simplified thrust model is employed to simulate the rapid transfer in a set of heliocentric mission scenarios as a typical interplanetary transfer toward a terrestrial planet and a rendezvous with a periodic comet
Filosofi italiani del Novecento e Cultura europea
No full textQuesto volume dal titolo Filosofi italiani del Novecento e Cultura europea raccoglie alcuni dei lavori che Antonio Quarta, Professore Associato di Storia della filosofia contemporanea e di Storia del- la Filosofia Italiana del Corso di Laurea in Filosofia dell’Università del Salento, ha prodotto in un arco di tempo che abbraccia più di quaranta anni di ininterrotta attività intellettuale. I quindici saggi che lo compongono mettono in rilievo la vastità degli interessi del loro autore, che spaziano dallo studio del fenomeno del tarantismo, all’analisi storica del processo di costruzione dell’identità culturale dell’Italia postunitaria. Ma il nucleo centrale di questa raccolta è costituito dagli studi e dalle ricerche che Antonio Quarta ha dedicato alla Storia della filosofia italiana dell’Ot- to e del Novecento, un tema che egli sviluppa puntualmente, con lucidità e rara chiarezza espositiva, in saggi dedicati ad alcune del- le maggiori figure intellettuali della filosofia italiana dei due se- coli appena trascorsi: da Carlo Cattaneo a Salvatore Trinchese, da Giovanni Vailati ad Eugenio Colorni, da Remo Cantoni a Giulio Preti, da Ludovico Geymonat a Ferruccio Rossi-Landi, da Benedetto Croce a Nicola Abbagnano, cui Quarta dedica un particolare interesse.
Ogni contributo restituisce a ciascun pensatore la sua dimensione sovranazionale e mette in evidenza la circolarità della filosofia italiana con quella della storia culturale europea, valorizzando così il ruolo del pensiero italiano nel contesto del dibattito internazionale
Ragionevolezza nella determinazione degli indennizzi. Il danno da ritardata surroga nei finanziamenti bancari
No full textLa novellata disciplina del ritardo nella «portabilità» dei mutui permette di tornare sulla distinzione tra indennizzo e risarcimento. Nel rispetto degli interessi di tutti i partecipanti all’operazione di surroga e delle finalità pro-concorrenziali dell’art. 120 quater, comma 7, t.u.b., l’a. ritiene l’intermediario originario e il subentrante solidalmente responsabili per l’indennizzo del cliente insoddisfatto.
The new remedy envisaged by article 120 quater, paragraph 7, t.u.b. (on loan portability) lies at the uncertain intersection of indemnification and full compensation. Contrary to the majority opinion, and more to the point of the rule’s pro-competitive aims, the author argues that the client may seek the statutory indemnity from the bank responsible for the delay (hence, not only from the original lender)
Thrust Model and Trajectory Design of an Interplanetary CubeSat with a Hybrid Propulsion System
No full textThis paper analyzes the performance of an interplanetary CubeSat equipped with a hybrid propulsion system (HPS), which combines two different types of thrusters in the same deep space vehicle, in a heliocentric transfer between two assigned (Keplerian) orbits. More precisely, the propulsion system of the CubeSat considered in this work consists of a combination of a (low-performance) photonic solar sail and a more conventional solar electric thruster. In particular, the characteristics of the solar electric thruster are modeled using a recent mathematical approach that describes the performance of the miniaturized engine that will be installed on board the proposed ESA’s M-ARGO CubeSat. The latter will hopefully be the first interplanetary CubeSat to complete a heliocentric transfer towards a near-Earth asteroid using its own propulsion system. In order to simplify the design of the CubeSat attitude control subsystem, we assume that the orientation of the photonic solar sail is kept Sun-facing, i.e., the sail reference plane is perpendicular to the Sun-CubeSat line. That specific condition can be obtained, passively, by using an appropriate design of the shape of the sail reflective surface. The performance of an HPS-based CubeSat is analyzed by optimizing the transfer trajectory in a three-dimensional heliocentric transfer between two closed orbits of given characteristics. In particular, the CubeSat transfer towards the near-Earth asteroid 99942 Apophis is studied in detail
Il contributo di Cressey allo sviluppo dei metodi qualitativi in sociologia
No full textIl testo propone la traduzione di un articolo di Paul Goalby Cressey, dal titolo “A Comparison of the Roles of the “Sociological Stranger” and the “Anonymous Stranger” in Field Research” pubblicato postumo nel 1983 da Martin Bulmer. Cressey è noto per aver posto attenzione ad un filone noir della ricerca sociale e per aver analizzato i lati oscuri del tessuto sociale della città, attraverso lo studio delle taxi dance hall. L’autore è meno noto per il suo apporto alla metodologia della ricerca sociale che invece è molto importante perché il suo contributo offre la possibilità, agli studiosi contemporanei, di una rinnovata riflessione su unaquestione molto delicata e dirimente per la ricerca sociale: la centralità della relazione tra il ricercatore e le persone con cui entra in contatto all’interno dei diversi contesti sociali.
Utilizzando il paradigma dello straniero, ispirato da Simmel e Sombart, lo studioso sviscera una questione epistemologica e metodologica che ha caratterizzato un passaggio d’epoca e che possiamo rinvenire nell’attenzione alla relazione tra ricercatore e (s)oggetto studiato, nelle caratteristiche di questa relazione sulla base delle quali possono cambiare le modalità di accesso e di permanenza nel contesto studiato, nella natura delle informazioni prodotte che può inevitabilmente cambiare in base ai termini della relazione posta in essere nel campo d’indagine
Heliocentric Orbital Repositioning of a Sun-Facing Diffractive Sail with Controlled Binary Metamaterial Arrayed Grating
No full textThis paper investigates the performance of a spacecraft equipped with a diffractive sail in a heliocentric mission scenario that requires phasing along a prescribed elliptical orbit. The diffractive sail represents an evolution of the more traditional reflective solar sail, which converts solar radiation pressure into thrust using a large reflective surface typically coated with a thin metallic film. In contrast, the diffractive sail proposed by Swartzlander leverages the properties of an advanced metamaterial-based film to generate a net transverse thrust even when the sail is Sun-facing, i.e., in a configuration that can be passively maintained by a suitably designed spacecraft. Specifically, this study considers a sail membrane covered with a set of electro-optically controlled diffractive panels. These panels employ a (controlled) binary metamaterial arrayed grating to steer the direction of photons exiting the diffractive film. This control technique has recently been applied to achieve a circle-to-circle interplanetary transfer using a Sun-facing diffractive sail. In this work, an optimal control law is employed to execute a rapid phasing maneuver along an elliptical heliocentric orbit with specified characteristics, such as those of Earth and Mercury. The analysis also includes a limiting case involving a circular heliocentric orbit. For this latter scenario, a simplified and elegant control law is proposed based on a linearized form of the equations of motion to describe the heliocentric dynamics of the diffractive sail-based spacecraft during the phasing maneuver
Optimal Guidance for Heliocentric Orbit Cranking with E-Sail-Propelled Spacecraft
No full textIn astrodynamics, orbit cranking is usually referred to as an interplanetary transfer strategy that exploits multiple gravity-assist maneuvers to change both the inclination and eccentricity of the spacecraft osculating orbit without changing the specific mechanical energy, that is, the semimajor axis. In the context of a solar sail-based mission, however, the concept of orbit cranking is typically referred to as a suitable guidance law that is able to (optimally) change the orbital inclination of a circular orbit of an assigned radius in a general heliocentric three-dimensional scenario. In fact, varying the orbital inclination is a challenging maneuver from the point of view of the velocity change, so orbit cranking is an interesting mission application for a propellantless propulsion system. The aim of this paper is to analyze the performance of a spacecraft equipped with an Electric Solar Wind Sail in a cranking maneuver of a heliocentric circular orbit. The maneuver performance is calculated in an optimal framework considering spacecraft dynamics described by modified equinoctial orbital elements. In this context, the paper presents an analytical version of the three-dimensional optimal guidance laws obtained by using the classical Pontryagin’s maximum principle. The set of (analytical) optimal control laws is a new contribution to the Electric Solar Wind Sail-related literature
Low-Thrust Earth-Venus Trajectories
No full textChapter 6, by Alessandro A. Quarta, Giovanni Mengali and Generoso Aliasi, discusses the simulation results involving the minimum-time trajectories for an Earth-Venus mission transfer using a spacecraft with an electric propulsion system, with both a nuclear and a solar electric power source. The analysis has been performed in a parametric way as a function of some design parameters, such as the available thruster electric power and the initial in-flight mass. Various models have been considered to describe the propulsion system behavior with different levels of
approximations and obtain increasingly refined information about the mission performance. Some simplifying assumptions have been introduced in order to make the mathematical problem tractable, to reduce the simulation time and guarantee a thorough parametric investigation of the mission performance. The analysis performed in this chapter is useful to obtain a first order estimate of the mission requirements as a function of the specific thruster characteristics
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