101,929 research outputs found
Jurassic paleogeographic reconstruction and Cenozoic tectonic evolution of the Lucretili and Sabini Mountains (central Italy), new data and interpretations
No full textThe study area is located in the central Apennines (Italy), between the Lucretili and the southern Sabini Mountains. The stratigraphic and structural data collected in the field resulted in a paleogeographic reconstruction of the Sabina domain that is comparable with the paleogeography of the Umbria-Marche domain, in which the Jurassic horsts are spaced by a distance of about ten kilometers. The structural analysis of fault planes allowed to reconstruct the Tertiary tectonic evolution of the sector, which was affected by five kinematic phases. A first compressional phase, with NE-SW maximum compression, was followed by a second compressional phase with WNWESE maximum compression. The polyphasic compressional phase affected this sector during the late Miocene-early Pliocene, it is due to the convergence between the African plate and the European plate. The compression was followed by a minor strike-slip tectonic phase. Compressional and strike slip structures were then affected by an extensional phase, subsequent to the early Pliocene, with NE-SW minimum compression. The extensional phase is due to the roll-back of the Adria slab. Finally a new Pleistocene strike-slip phase affected the study area and it can be related to the stress due to the effect of the Mesozoic rifting on the lithosphere, in terms of subductibility
Approach to Technology Prioritization In Support Of Moon Initiatives In The Framework Of ESA Exploration Technology Roadmaps
No full textExploration technology roadmaps have been developed by ESA in the past few years and the latest edition has been released in 2015. Scope of these technology roadmaps, elaborated in consultation with the different ESA stakeholders (e.g. European Industries and Research Entities), is to provide a powerful tool for strategic, programmatic and technical decisions in support of the European role within an International Space Exploration context. In the context of preparation for possible future European Moon exploration initiatives, the technology roadmaps have been used to highlight the role of technology within Missions, Building Blocks and Operational Capabilities of relevance. In particular, as part of reference missions to the Moon that would fit in the time frame 2020 to 2030, ESA has addressed the definition of lunar surface exploration missions in line with its space exploration strategy, with the common mission goals of returning samples from the Moon and Mars and expanding human presence to these destinations in a step-wise approach. The roadmaps for the procurement of technologies required for the first mission elements of the above strategy have been elaborated through their main building blocks, i.e. Visual navigation, Hazard detection and avoidance; Sample acquisition, processing and containment system; Surface mobility elements; Tele-robotic and autonomous control systems; and Storable propulsion modules and equipment. Technology prioritization methodologies have been developed in support of the ESA Exploration Technology Roadmaps, in order to provide logical and quantitative instruments to verify choices of prioritization that can be carried out on the basis of important, but non-quantitative factors. These methodologies that are thoroughly described in the paper proceed through subsequent steps. First technology prioritization’s criteria are selected; then decision trees are developed to highlight all feasible paths of combination of technology prioritization’s criteria and to assess the final achievement of each path, i.e. the cost-effectiveness. The risk associated to each path is also evaluated. In the second part of the paper, these prioritization methodologies have been applied to some of the building blocks of relevance for the mission concepts under evaluation at ESA (such as Tele-robotic and autonomous control systems; Storable propulsion modules and equipment) and the results are presented to highlight the approach for an effective TRL increase. Eventually main conclusions are drawn
Technology RoadmappIng Strategy, TRIS: Methodology and tool for technology roadmaps for hypersonic and re-entry space transportation systems
No full textThis paper describes the methodology developed by Politecnico di Torino in support to the elaboration of hypersonic and re-entry space transportation systems roadmaps, currently on going at ESA. TRIS (Technology RoadmappIng Strategy) is here presented as a collection of algorithms leading the stakeholders from the selection of a set of elements (e.g. the technologies) up to the generation of their incremental paths towards a final target (e.g. Technology Readiness Level (TRL) 8). In particular this paper focuses on the generation and update of technology roadmaps for hypersonic and re-entry systems. In particular, the Intermediate eXperimental Vehicle (IXV) experiment is presented as validation case study, allowing the comparison of the TRL increase path suggested by the proposed methodology and the decisions that were taken at the time of the IXV mission planning
A Flight Demonstration of FEEP: Electric Thrusters for Microgravity Laboratories and Drag-Free Spacecraft
No full textThe scientific community's recent interest in Field Emission Electric Propulsion for drag-free spacecraft represents a major breakthrough for this technology. While FEEP was traditionally intended as a candidate for the attitude control and fine pointing of small satellites, i.e., for mN level thrust missions, this new, previously unforeseen application opportunity is due to its capabilities in the very low thrust range (about 1 μN). A major project such as LISA, presently a candidate for the next cornerstone in Horizon 2000, features FEEP as a mission-enabling technology. Several other concepts have been proposed, ranging from AU baselength interferometry, to a spaceborne constellation of antennas for syntetic aperture radiometry to be used for high accuracy weather forecasting, to noiseless microgravity laboratories. A recent proposal to the Italian Space Agency highlights the benefits of adopting a Field Emission Electric Propulsion system for a Flight Experiment on the Equivalence Principle (FEEP2).
As far as the concept is concerned, FEEP is a thoroughly proven technology. Tests in space simulators were extensively carried out at both the Electric Propulsion Laboratory of ESTEC and at Centrospazio, covering all of the thruster’s subsystems (ion emitter, propellant feeding system, neutralizer, power electronics). The basic hardware is ready to undergo a flight demonstration. This would open the way to several applications in each of three major areas: first, scientific spacecraft for fundamental physics, requiring unprecedented high performance drag-free controllers; second, microgravity laboratories; third, small satellites with accurate orbit and attitude control capabilities.
This paper summarizes the state of the art of FEEP technology and outlines the technical characteristics of the hardware for a flight experiment. The feasibility of a low cost flight demonstration is discussed and a proposed approach for a dedicated spacecraft, based on a commercially available microsatellite bus, is presented
Deep space transportation enhanced by 20 kW-Class Hall Thrusters
No full textDeep space is the new frontier for human exploration, with Moon and Mars identified as fundamental targets. Improving in-space transportation capabilities has been recognized as one of the critical enabler for sustainable and affordable space programs in Earth proximity and beyond. Envisioning the presence of future deep space infrastructures, cargo transferring becomes a major issue that can benefit from improvements in in-space propulsion technology. Electric propulsion could represent the turning point, thanks to the combination of new system architectures and technology advancements, e.g. cluster architecture and magnetic shielding, and improved capability of on-board power generation. High-power Hall Thrusters are considered the most promising solution for future space exploration, thanks to a favourable thrust to power ratio, higher than Gridded Ion Engines. Reusable platforms, based on Hall Thrusters, could represent a valid alternative to chemical-propelled spacecraft. These systems could be exploited to support human presence in deep space, delivering life support items and providing on-orbit servicing capabilities. In this paper, the typical mission analysis tools have been exploited to analyse the selected scenarios. The analysis highlights possible advantages achievable adopting high-power Hall Thrusters on board reusable platforms. Since the design of these spacecraft envisions the adoption of a 20 kW-class Hall Thruster string, the mass and power budgets are obtained for those subsystems that are most affected by this critical technology. Then, the feasibility of each scenario is assessed considering the needs defined not only by the traffic plan, in terms of loading/unloading cargo and transfer duration, but also by the peculiar mission and physical constraints. Last, the different platform design solutions are compared with respect to their electric propulsion configurations, in order to identify the possible commonalities in terms of architecture and technology, in line with the current trend of modularity and affordability
Development of Green Hydrogen Peroxide Monopropellant Rocket Engines and Testing of Advanced Catalytic Beds
No full textWith the financial support of the European Space Agency, Alta S.p.A. in Italy and DELTACAT Ltd. in the United Kingdom are conducting a joint study on the development of two hydrogen peroxide monopropellant thruster prototypes (5 and 25 N vacuum thrust) using advanced catalytic beds. The present article illustrates the results of recent tests on the developed catalysts and the main aspects of the thruster design as well as of the technique used for quantitative determination of the observed decomposition rates. Preliminary results indicate that platinum deposited on a γ−alumina substrate yields the best performance with respect to the other solutions under consideration
Experimental Characterization of a 5 N Hydrogen Peroxide Monopropellant Thruster Prototype
No full textIn the framework of the LET-SME program funded by the European Space Agency, ALTA S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) jointly investigated the use of advanced catalytic beds on ceramic supports as a cost-effective alternative to metal screen reactors for the decomposition of high-concentration hydrogen peroxide in small monopropellant rockets. To this purpose ALTA S.p.A. designed and realized a reconfigurable test bench for the characterization of the operation and propulsive performance of small rocket thrusters. The present paper illustrates the experimental campaign carried out on a 5 N thruster prototype operating with two platinum catalysts on g− alumina supporting spheres, especially developed by ALTA in collaboration with the Chemistry and Industrial Chemistry Department of Pisa University, Italy. The results indicated that Pt/Al2 O3 is an effective catalyst combination for the decomposition of 87.5% propellant grade hydrogen peroxide, with good stability and performance comparable to silver screen beds of equal geometric envelope and operational conditions. Incomplete hydrogen peroxide decomposition and the onset of flow oscillations in the reactor were observed at the tested levels of bed loading, residence time and flow pressure. Thermal stresses due to the large temperature gradients occurring during the decomposition of high grade hydrogen peroxide (87.5% by weight) caused the ceramic pellets to break and the progressive occlusion of the bed. Based on the analysis of the test results, several ways to overcome these problems in future investigations have been tentatively identified, together with the necessary modifications to the present experimental set-up
The chemical advantage of sulfur over selenium: controlling the switching-in-function of the moonlighting behaviour of Peroxiredoxin.
No full textCrystal structure of Plasmodium falciparum thioredoxin reductase, a validated drug target.
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