1,721,209 research outputs found
Effects of Discrete Thrust Levels on the Trajectory Design of the BIT-3 RF Ion Thruster-Equipped CubeSat
No full textThe use of continuous-thrust propulsion systems allows spacecraft to cover complex space trajectories and to complete missions that would be difficult using chemical thrusters. Among the continuous-thrust propulsion systems proposed in recent decades, solar electric thrusters occupy an important position thanks to the maturity reached by this technology. Technological advances in the miniaturization of spacecraft components allow an electric thruster to be installed even in a small and standardized vehicle such as a CubeSat. In this context, the BIT-3 RF ion thruster is an interesting option that has been recently employed in some space missions for the study of the lunar surface. In the recent literature, the performance of a CubeSat equipped with a propulsion system based on the BIT-3 has been studied considering a simplified model in which the thrust magnitude has a fixed value or varies continuously within a prescribed range. However, the operating levels of a BIT-3 are finite in number. This paper studies the transfer performance of a BIT-3-propelled CubeSat considering the actual operating levels that can be provided by such a thruster. The work analyzes the optimal transfer towards asteroid 2000 SG344 when the electric power is obtained through solar arrays
I sistemi di copertura in Messapia nella fase arcaica. Contributo allo studio dell'edilizia domestica
No full textIl lavoro affronta la problematica dei sistemi di copertura in messapia in età arcaica. Dopo una preliminare storia della ricerca nel settore ed un inquadramento metodologico dello studio si analizzano i materiali di copertura di s. Vito dei Normanni (BR) e di Cavallino (LE). Le recenti indagini archeologiche nei due siti hanno offerto nuovi dati sull'architettura ed il modo di abitare in età arcaica. A Cavallino è stato individuato un sistema di copertura sul modello laconico con l'impiego di soli coppi disposti alternativamente. A s. Vito dei Normanni la copertura degli edifici è più complessa. I tetti disponevano di tegole piatte con alette laterali rialzate e coppi utilizzati come coprigiunti tra le commettiture. In questo sito, lo studio analitico dei crolli durante lo scavo archeologico ha permesso di ricostruire la tecnica costruttiva dell'alzato ed i materiali impiegati. E' stato possibile individuare anche una prima forma di decorazione architettonica. I dati archeologici hanno consentito l'elaborazione di una ricostruzione grafica del grande edificio di s. Vito dei Normanni.
Il lavoro è completato da un'appendice sull'architettura rurale salentina, valido modello di confronto per lo studio delle soluzioni architettoniche. Un paragrafo affronta il problema delle incisioni su tegole e coppi chiarendo come spesso si tratti di semplici marche da montaggio.Analysis of roofs in messapia in archaic period. after a preliminary history of researches in the field and of methodology's discussion, the author examines the architectural material from san vito dei normanni (Br) and Cavallino (LE)
Warm start for optimal transfer between close circular orbits with first generation E-sail
No full textThe Electric Solar Wind Sail (E-sail) is a propellantless propulsion system for deep space navigation that exploits the dynamic pressure of the solar wind to generate thrust using a web of long, conducting tethers. The heliocentric trajectory of an E-sail-based spacecraft in a classic transfer between two Keplerian orbits is usually analyzed, in an optimal framework, by minimizing the total flight time. This paper discusses an analytical, approximate procedure for solving the two-point boundary value problem associated with the trajectory optimization process in a heliocentric, two-dimensional scenario involving a first-generation E-sail. The procedure is applied in a typical transfer between two coplanar circular orbits whose (assigned) radii are sufficiently close to each other. Paralleling the approach proposed in the recent literature, the mathematical model presented in this paper discusses a set of analytical equations that give an accurate approximation of both the minimum flight time and the (unknowns) initial adjoint variables. The paper also analyzes a set of mission applications, which involve interplanetary transfers to some near-Earth asteroids whose orbits have a very small value of both eccentricity and inclination
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
Fuel-Optimal, Power-Limited Rendezvous with Variable Thruster Efficiency
No full textThe problem of minimum-fuel, time-fixed, three-dimensional rendezvous for a solar electric propulsion spacecraft
is discussed. The problem is solved via an indirect approach. The formulation takes into account both a
variable bounded specific impulse and a variable thruster efficiency and permits us to manage solutions with coast
arcs. The thruster efficiency is assumed to vary with the specific impulse through a polynomial approximation. The
optimal specific impulse control law is found to depend on the instantaneous values of the primer vector modulus, the spacecraft mass, the mass costate, and the thruster model. Optimal interplanetary trajectories toward Mars are discussed. It is shown that the inclusion of a variable efficiency thruster model has important effects on fuel
consumption. In particular, the classic constant efficiency thruster model overestimates the final spacecraft mass
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