1,721,028 research outputs found
Development of a Miniaturized Electric Propulsion System for the E-Sail Project
No full textThe Electric Sail (E-Sail) is an innovative space propulsion concept relying on the solar wind momentum for producing thrust through the interaction of solar wind protons with a number of very long, electrically charged tethers. With such long wires, centrifugal force alone is not sufficient to ensure complete deployment of the assembly. Therefore, small thrusters are needed to increase/decrease the angular velocity and, accordingly, determine centrifugal force during tether deployment. In consideration of the stringent requirements of E-Sail, a variant of the Field Emission Electric Propulsion (FEEP) system has been selected, based on the use of ionic liquids as propellant, instead of alkali metals. This paper discusses the unique challenges posed by the development of the E-Sail Remote Unit thruster system. The envisaged simplified ionic liquid FEEP has a large potential for utilization on a variety of micro- and nano- satellite platforms, from Cubesats to Earth observation small satellites, to future scientific mission
High Power Electric Propulsion for a Flexible Space Exploration Architecture
No full textAn affordable architecture for future space exploration programmes is outlined in this study. Following the key guidelines of the flexible path approach, the increased capability in space operations gained with the ISS programme and the advances in efficient in-space transportation systems, the architecture proposed is indented to be the steppingstone to the next generation space missions. The time horizon envisaged is the next six decades and to cope with this timeframe, solar electric propulsion and inflatable modules are chosen as the key building blocks of the architecture proposed.
Instead of sizing a single spacecraft, the architecture presents the key building blocks that represent the enabling technologies for the future exploration pathways envisaged. The exploration of the near Earth region, the Moon next, asteroid next and Mars next scenarios are considered, and analyzed. The main elements are sized and a preliminary mission analysis to assess the performance of the architecture is carried out in this study
Joint Trajectory and Energy Management Simulation of Low Thrust Missions
No full textSpacecraft equipped with electric propulsion systems need an accurate monitoring of on-board available energy. The high power-to-thrust ratios typical of these propulsive systems and their long thrusting periods cause a major demand of electrical power, so that the use of electric propulsion strongly influence the management of on-board resources. The strong interaction among power generation, energy storage and propulsion is evident considering that both the energy availability and the power required by the main subsystems affect the spacecraft thrusting capabilities. Thus, it is clear that these aspects must be considered jointly even in preliminary mission analysis. The integrated simulator here presented, SATSLab, is conceived to support preliminary mission analysis considering the coupling of on-board available energy and attitude-orbital dynamics in electric propulsion equipped missions. In this paper a brief overview of the STASLab software package is given. Examples of relevant mission scenarios are presented, highlighting the simulator capability to reveal non-trivial features of the energy-trajectory interplay
Electric Propulsion Options for Cubesats
No full textThe CubeSat platform is presently well established as a standard building block for nano-satellites and presents a large potential for a number of applications, particularly in its 3U (or larger) version. The aim of this study is to investigate the possibilities offered by the implementation of Electric Propulsion (EP) on CubeSat platforms and to analyse the relative advantages of several current EP technologies with respect to specific constraints of such minimal spacecraft. We focus on devices requiring limited power and with small mass and size, yet performing at relatively high specific impulse, such as Hall Effect Thrusters, Field Emission Electric Propulsion, Pulsed Plasma Thrusters and resistojets. Performance analysis is performed first analytically, then by direct simulation of representative mission profiles on Alta's SATSLAB simulator, whereby the coupled effect of orbit, attitude and onboard energy management is accounted for. We show that performance of CubeSats is significantly enhanced by a properly chosen EP system, extending the operational envelope to include manoeuvres such as residual drag compensation, change of orbital altitude and plane inclination, and rephasing in constellations, resulting in additional mission profile flexibility. New mission classes, enabled by the unique combination of CubeSat's tiny mass and EP manoeuvring capability, are outlined and discussed
Ionic Liquid FEEP: Recent Experimental Results
No full textThe ionic liquid FEEP (IL-FEEP) is new, simplified version of the field emission thruster where the alkali metal propellant is replaced by an ionic liquid. Development of the IL-FEEP thruster is based on the heritage of the cesium FEEP and is currently funded by ESA and EU programmes. This paper presents the results of a recent experimental campaign aimed at assessing the performance of a novel linear slit FEEP emitter fed with a ionic liquid propellant. Tests were done on a newly designed, 8-mm slit FEEP emitter made of glass, fed with EMI-BF4. The test setup allowed for continuous monitoring of the thruster electrical parameters, as well as for direct scanning of the exhaust beam profiles using electrostatic wire probes. The test results essentially validate the possibility to operate the linear slit FEEP emitter with ionic liquid propellant in pure ionic mode and confirm that the glass emitter is suited for operation with the selected propellant. Experimental results show very regular and repeatable performance in positive mode, while operation in negative polarity showed some irregularities in beam profiles. Thruster performance in a later test in alternate polarity mode was remarkably stable over a very long period, in spite of the predominance of positive mode firing that could have affected the propellant composition in the reservoir due to electrochemical degradation. Alternate polarity is therefore regarded as a promising operating mode for the simplified FEEP thruster
Mosaici con rappresentazioni mitologiche nel Norico e in Pannonia. Alcune osservazioni su Teseo e Bellerofonte
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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