Multiple-Sliding-Surface Guidance and Control for Terminal Atmospheric Reentry and Precise Landing

The development of an effective guidance and attitude control architecture for terminal descent and landing represents a crucial issue for the design of reusable vehicles capable of performing a safe atmospheric planetary entry. The sliding mode control represents a nonlinear technique able to generate an effective real-time closed-loop guidance law, even in the presence of challenging contingencies. This work proposes a multiple sliding-surface guidance control law that is able to drive a lifting vehicle toward safe landing conditions, associated with a desired downrange, crossrange, runway heading, and final vertical velocity at touchdown, even starting from challenging initial conditions. The time derivatives of the lift coefficient and the bank angle are used as the control inputs, whereas the sliding surfaces are defined so that these two inputs are involved simultaneously in the lateral and the vertical guidance. The commanded attitude is pursued by the attitude control system, which employs a feedback nonlinear control law that enjoys quasi-global stability properties. Effectiveness and accuracy of the guidance and control strategy at hand are proven numerically by means of a Monte Carlo campaign, in the presence of stochastic wind and large dispersions on the initial conditions

Classici contro

Come nell’antico teatro di Dioniso ad Atene, davanti ai cittadini, i Classici contro ci parlano di democrazia, demagogia, populismo, comunicazione, tirannide, libertà di parola, identità, xenofobia, giustizia, corruzione: con i miti e con le storie, senza nessuna mitizzazione. Tutto ciò che oggi è un problema o un’inquietudine. Attraverso un passo, un’idea, un insieme di parole esemplari, con l’evidenza della performance a teatro e il rigore della filologia i classici antichi agiscono in una sequenza di voci e di figure che ci spiegano qualcosa di noi dal loro speciale punto di vista

A revisited and general Kane’s formulation applied to very flexible multibody spacecraft

Abstract. Current space missions require predicting the spacecraft dynamics with considerable reliability. Among the various components of a spacecraft, subsystems like payload, structures, and power depend heavily on the dynamic behavior of the satellite during its operational life. Therefore, to ensure that the results obtained through numerical simulations correspond to the actual behavior, an accurate dynamical model must be developed. In this context, an implementation of Kane’s method is presented to derive the dynamical equations of a spacecraft composed of both rigid and flexible bodies connected via joints in tree topology. Starting from the kinematics of two generic interconnected bodies, a systematic approach is derived and the recursive structure of the equations is investigated. The Kane’s formulation allows a relatively simple derivation of the equation of motion while obtaining the minimum set of differential equations, which implies lower computational time. On the other hand, this formulation excludes reaction forces and torques from the dynamical equations. Nevertheless, in this work a strategy to compute them a posteriori without further numerical integrations is presented. Flexibility is introduced through the standard modal decomposition technique, so that modal shapes obtained by FEA software can be directly utilized to characterize the elastic motion of the flexible bodies. A spacecraft composed of a rigid bus and several flexible appendages is modeled and numerical simulations point out that this systematic method is very effective for this illustrative example

Numerical solution of a pursuit-evasion differential game involving two spacecraft in low earth orbit

This paper considers a spacecraft pursuit-evasion problem taking place in low earth orbit. The problem is formulated as a zero-sum differential game in which there are two players, a pursuing spacecraft that attempts to minimize a payoff, and an evading spacecraft that attempts to maximize the same payoff. We introduce two associated optimal control problems and show that a saddle point for the differential game exists if and only if the two optimal control problems have the same optimal value. Then, on the basis of this result, we propose two computational methods for determining a saddle point solution: a semi-direct control parameterization method (SDCP method), which is based on a piecewise-constant control approximation scheme, and a hybrid method, which combines the new SDCP method with the multiple shooting method. Simulation results show that the proposed SDCP and hybrid methodsare superior to the semi-direct collocation nonlinear programming method (SDCNLP method), which is widely used to solve pursuit-evasion problems in the aerospace field

Eteokles in Spain? On Brecht’s Mein Bruder war ein Flieger

One of Bertolt Brecht’s most famous poems, Mein Bruder war ein Flieger, is often invoked as a manifesto for pacifist ideals, but some essential questions (who is the lyric I? what is the literal meaning of the poem?) have hardly received any attention. By evoking the poem’s nature as a Kinderlied, the context of its first publication, and its relationship with Brecht’s play Die Gewehre der Frau Carrar, this article tentatively identifies the source of its final pointe in a famous passage of Aeschylus’ Seven against Thebes, thereby suggesting—on the basis of textual comparisons—an example of far-reaching, ideological Antikerezeption in Brecht’s oeuvre, working all the way down to his Kalendergeschichten and to his Antigone

Abbracciare Dafne. L'uomo e l'ambiente tra Omero e il futuro prossimo

Il futuro prossimo è arrivato. La natura, che è madre e matrigna, che è nostra casa e nostro orizzonte, ci pone dinanzi alla hybris dell’uomo e ci interroga. È tempo di medi- tare insieme su tutto questo e di provare a costruire un mondo secondo idee altre. Di qui proviamo a ricominciare: con le idee, le parole e le immagini che ci vengono da tremila anni di pensieri e di esperienze, cer- chiamo di capire qualcosa in più di ciò che sta accadendo. La responsabilità è nostra, nostra l’arroganza e nostro il pericolo. È il tempo di una nuova coscienza civile. Con Omero, con Esiodo o con Esopo, con Virgilio o con Ovidio cominciamo a rimettere gli al- beri, gli animali, il vento, il mare e la terra al centro del mondo, a ridare loro la voce. La poesia, le lettere, la filosofia, le arti insieme alla scienza sono la via per costruire un im- maginario collettivo diverso

Ascent Trajectory Optimization and Neighboring Optimal Guidance of Multistage Launch Vehicles

Multistage launch vehicles are employed to place spacecraft and satellites in their operational orbits. If the rocket aerodynamics and propulsion are modeled appropriately, optimization of their ascent trajectory consists in determining the coast duration and the thrust time history that maximize the final mass at injection. This research derives all the necessary conditions for ascent path optimization of a multistage launch vehicle. With reference to an existing rocket, the indirect heuristic method is then applied, for the numerical determination of the overall ascent trajectory. An effective approach is used with the intent of satisfying the path constraint related to the maximum dynamical pressure in the atmospheric phase. Then, the recently introduced, implicit-type variable-time-domain neighboring optimal guidance is applied to the upper stage powered arc, for the purpose of obtaining the corrective control actions in the presence of nonnominal flight conditions. The guidance approach at hand, based on the second-order analytical conditions for optimality, proves to be rather effective (in terms of propellant budget), and guarantees very accurate orbit injection in spite of perturbations