16,092 research outputs found
Luigi Antonio Paolozzi tra l'Amiata a la Val di Chiana
No full textBiography of and tribute to the erudite Luigi Antonio Paolozzi (Chianciano Terme, 1706-1765), cancelliere of the Gran Duchy of Tuscany for Amiata and the Val di Chiana. It aims at highlighting the important role of Paolozzi in the historical context of the period, and reasses its weight. It follows the path of Paolozzi's research as a local historian, in particular as regards his archival research, which he conducted as his moved around for his daily job using first-hand archival sources. This work shows that all that has been written about Chianciano in particular after Paolozzi's work depends on the research done by him, in particular as regards his archival research, and aims at a bet For instance, Paolozzi was the first to study the Mount Amiata abbey, as he was also curator and responsible of the archives of that territory. In this book the relations of Paolozzi to three important coeval figures come to the fore: that with Giovanni Lami, founder and editor of the "Novelle Letterarie", and Domenico Maria Manni and Giovanni Antonio Pecci, Siennese historian author of a story of the Sienna State, ie all the municipalities forming the Siennese Republic
LARES succesfully launched in orbit: satellite and mission description
No full textOn February 13th 2012, the LARES satellite of the Italian Space Agency (ASI) was launched into orbit with the qualification flight of the new VEGA launcher of the European Space Agency (ESA). The payload was released very accurately in the nominal orbit. The name LARES means LAser RElativity Satellite and summarises the objective of the mission and some characteristics of the satellite. It is, in fact, a mission designed to test Einstein's General Relativity Theory (specifically 'frame-dragging' and Lense-Thirring effect). The satellite is passive and covered with optical retroreflectors that send back laser pulses to the emitting ground station. This allows accurate positioning of the satellite, which is important for measuring the very small deviations from Galilei-Newton's laws. In 2008, ASI selected the prime industrial contractor for the LARES system with a heavy involvement of the universities in all phases of the programme, from the design to the construction and testing of the satellite and separation system. The data exploitation phase started immediately after the launch under a new contract between ASI and those universities. Tracking of the satellite is provided by the International Laser Ranging Service. Due to its particular design, LARES is the orbiting object with the highest known mean density in the solar system. In this paper, it is shown that this peculiarity makes it the best proof particle ever manufactured. Design aspects, mission objectives and preliminary data analysis will be also presented
LARES: a New Laser Ranged Satellite for Testing General Relativity
No full textIn this paper the LARES space mission, derived from the LAGEOS III project is described. The objective of this mission is to obtain data useful in the field of fundamental physics and Earth science. Specifically LARES will give important contributions in general relativity, geodesy and geodynamics. The mission concept is to use a proof mass (a small and heavy satellite) to study the gravity field around the Earth. The satellite surface is covered with more than 100 cube corner retroreflectors that allow its tracking by over 40 laser ranging stations on Earth. The satellite design is derived from that one of LAGEOS and therefore it will be based on a well tested technology and design. As a consequence this mission will be very reliable, low-cost and will provide data for at least 35 years
Application of High Temperature Optical Fibers in a Reentry Vehicle
No full textOne of the most demanding environment is the one encountered by reentry vehicles at the impact with the atmosphere. The heat produced can reach few MW/m2 and can raise gas temperature above dissociation and even ionization energy. As a consequence the reentry structure is exposed not only to very high temperature but also to chemical attack by the atmospheric species such as atomic oxygen and nitrogen. Another concern is the surface catalysis. The gaseous species are adsorbed by the solid material that can favor recombination of nitrogen with atomic oxygen. This chemical reaction release a further amount of heat right at the surface of the material. Proper choice of material for the Thermal Protection Systems (TPS) can reduce this last type of reaction. To this aim our group at the Univ. of Rome “La Sapienza” in cooperation with prof. Currie at the Univ. of Maryland is proposing an experiment in order to measure catalytic recombination on several samples of classical and newly proposed materials to use as TPS for reentry vehicles. This experiment should fly on the European Experimental Reentry Testbed (EXPERT). EXPERT is an experimental capsule financed by the European Space Agency (ESA) and lead by the European Space Research and Technology Center (ESTEC). The aim of this capsule is to offer researchers from all over Europe the possibility of performing tests on the reentry environment focusing on topics such as hypersonic fluid dynamics and surface catalysis. Three suborbital flights are planned with the capsule which is designed to be reusable. The Volna decommissioned ballistic missile will be used for launch. Presently more than ten experiments are planned in the EXPERT experiment. In order to select the proper material at least with respect to the catalysis phenomenon one has to observe the species concentrations right close to the surface. To this aim prof. Bruno’s group at the Department of Aeronautical and Mechanical Engineering at “La Sapienza” University and our group at the Department of Aerospace and Astronautical Engineering of the same University are proposing an experiment that will observe those species by using one or more sapphire optical fibers. In fact light collected from the different samples of TPS materials that will be attached at the capsule surface will be analyzed inside the unmanned capsule during reentry. Sapphire has the right characteristics to conduct light also in the ultraviolet region (where some spectral lines of interest are located) as well as very high melting points. During reentry, light coming out from the TPS specimen material will carry information on temperature as well as on the species concentration in the plasma. Presently we are selecting the most appropriate spectrograph, the baseline solution at the moment is a Multi-Channel Spectrograph that will allow the observation of more samples at the same time. The spectrograph will analyze the light captured by the sapphire fibers. Data will be stored on board at a rate of few samples per second per channel. A selection of data is also transferred real time on the ground station in case the soft landing of the capsule will fail.
Another area of interest for optical fiber in a spacecraft is the structural health monitoring for reusable launch vehicles. Soon after the Apollo program, based on expendable rockets and capsules, NASA started a new approach that was intended to reduce cost of access to space to manned missions. That lead in about ten years to the space shuttle whose reliability was proven to be not as high as expected. After the second disaster one has to recognize that the Russian Soyuz launch vehicle is more reliable and cost effective than the US Space Transportation System (STS). That is not surprising since, in spite of the not optimized launch vehicle design (Russian Soyuz is more than 30 years old) it has a very well proven activity (more than 1000 successful launches). However before the Columbia disaster NASA was already thinking to a future generation of reusable launch vehicles that could lead to a reduction of cost a factor of 10 in the mid term and a factor of 100 in the long term. To contribute to achieve such a goal the reduction of personnel used for maintenance and operation is required and consequently several health monitoring systems are envisaged. The most credited hypothesis for the Columbia disaster is the failure on a Thermal Protection System (TPS) on the leading edge of the wing of the Shuttle which is made of Carbon/Carbon. A health monitoring system on the TPS could have prevented such a disaster or at least could have given the opportunity to attempt a rescue of the crew while in orbit, if the failure was detected right at the beginning of the mission. Recently our group in cooperation with a group at the Department of Chemical Engineering, Materials, Row Materials and Metallurgy has been working on preliminary tests aimed to verify the feasibility of such a system. In Ref. [1] we have used telecommunication optical fibers with polyimide coating in an embedding test with a thermal spraying technique called HP/HVOF. CERMET particles (NiCr-WC based powder, and NiCrBFeSi) were partly melted and projected at high speed towards the target constituted by an aluminium plate with the fiber blocked on its surface by a lamination procedure. The embedding process was proven feasible even if in this preliminary study optical transmission tests were only partially successful since, some fibers were damaged. In Ref. [2] first tests with sapphire fibers were performed. Specifically a copper alloy was cast over the special fiber and an interferometric set-up was prepared using the embedded fiber. Only the speckle pattern has been observed at that time while the actual interferometric tests were left for future applications. Also in the paper was presented a test concerning the embedding of a sapphire fiber into very high temperature ceramics using the Self-propagating High-temperature Synthesis (SHS) technique. The method involves self-propagating reaction fronts that are induced by a laser pulse. The wavefront moves at a relatively high speed and at temperatures that can be higher than 3000 C. In the paper a small cylindrical sample of ZrB2 was prepared. The results were promising but not satisfactory, the fiber was almost destroyed. In Fig. 1 is reported a SEM micrograph showing the fiber decomposed into several filaments oriented in different directions. We realized that the fiber was subjected to a very severe environment in terms of temperature and mechanical stresses. For that reason a further step was required: to protect the fiber with a thick metallic coating capable of providing a high heat capacity and a higher strength. Electrowinning technique is the best candidate for providing such a protection. In order to use this technique a thin coating of metallic material has to be previously deposited using Physical Vapor Deposition (PVD). When used on a fiber laying on a metallic substrate, electrowinning provided an excellent means to block the fiber in place [3], before a plasma spray technique could be used [4]. Currently we are experimenting the embedding of sapphire optical fibers into superalloy. Specifically the alloy used is an Inconel with nominal composition: 74.92% Ni, 15.50% Cr, 8.00% Fe, 1.00%Al, 0.50% Ti and 0.08% C. A centrifugal induction furnace with graphite crucible was used to cast the abovementioned alloy over the fiber. The casting has been performed in a protective argon atmosphere. In Fig. 2 one can recognize the sample of superalloy with the embedded optical fiber. The first attempts were not successful because the flow of the molten metal broke the fiber. For that reason the fiber has been protected with a Ni-Co alloy using electrowinning as performed previously in Ref. [5]. In Fig. 2 one can easily recognize the presence of the coating on the fiber. In Fig. 3 is reported the SEM micrograph of a longitudinal section of a specimen manufactured previously with the same technique. The fiber metal interface is quite satisfactory. Optical transmission tests on the embedded fiber were conducted on a transversal section of a polished metallographic specimen. In spite of the poor optical quality of the fiber used the result was quite satisfactory
Recent Researches on Fibre Optic Smart Structures in Italy and Future Trends in Europe
No full textIn this paper recent developments on the embedding of optical fibres into polymeric composites and metal alloys, performed by research groups in Italy will be reviewed. The types of measurements performed with sensorless embedded optical fibres will be outlined. An application related to an intelligent thermal protection system for space vehicles, based on optical fibres will be briefly addressed. Development of sensors for smart manufacturing, the realization of Bragg gratings and relevant interrogation systems will also be considered. Some projects approved by the European union will be also mentioned
A space Debris Monitoring System for the ISS Based on Optical fibers
No full textThe purpose of the paper is to study the realization of panels with
embedded optical fibers to show the feasibility of:
i) an integrated health monitoring system for aerospace structural components,
ii) an integrated modal parameteridentification system for aerospace structural components,
iii) a space debris monitoring system.
The last point has been the object of an informal presentation at the
workshop meeting on the scientific exploitation of the International
Space Station (ISS). The idea is that one of exposing a plate with
embedded optical fiber sensors, either made of isotropic (aluminum alloy) or anisotropic (composite laminate) materials to the space environment around the space station.
Space debris monitoring is one of the major concerns for the aerospace community because the debris population is the ever increasing and might endanger all future space activities. Once exceeded a certain threshold a chain reaction of impacts that generates more and more debris of smaller dimensions could inhibit any safe space mission. For this reason many studies are in progress to estimate the debris population and its evolution. To this end computer codes have been developed.
These propagators assume an initial debris distribution which is indeed
not well known for particles smaller than about 5cm. A plate with an embedded sensing system exposed to the space environment could give information on impact frequency, discriminate between single impacts or impacts from a group of particles, direction, intensity, and impact location. This last aspect even if hard to accomplish on the basis of the time delay signals caused by the interaction of ultrasonic elastic waves with the sensors could be tackled and could be usefully employed to determine the correspondence between the impact information described above and the chemical composition of the debris, this last one obtained after recovery of the plate. Chemical analysis can in fact be useful to distinguish between artificial debris and natural meteoroids.
For this particular application it is not necessarily required a metallic
plate but this one seems to offer many advantages over the polymeric composite one:
i) the know-how acquired in the embedding process could be used also for
the structural parts of space habitat, space structures, some of the
shields used in the space debris bumper assembly; ii) easier modeling of
elastic wave propagation in isotropic material, iii) metallic materials are
prone to permanent deformation due to impact that can be measured at any
time after the event.
Let us now turn to the reasons why optical fibers are being considered
in this study.
Fiber optic and fiber optic sensors can be used as a very attractive
sensing system because of the many advantages they offer with respect to
conventional sensors. Most optical fibers, including the very common silica
based optical fibers are very thin (125 - 155 microns in diameter), flexible
(curvature radius lower than 0.01m), immune to electromagnetic and
radio-frequency interference and non-conductive. This last aspect is essential when one thinks about embedding the optical fiber into a metallic material.
As a further advantage one can think of the fiber (or chosen sections of it
if you use the so-called intrinsic sensors) as both the sensing element and
the transmission cable. By measuring variations of amplitude, wavelength,
phase or polarization of the light due to environmental effects one can
obtain information of almost any kind of physical property such as strain,
stress, temperature, pressure. Due also to their small dimensions, their
relatively high melting temperature and their very low transmission loss,
optical fibers are very good candidate for being embedded into metallic
materials with not very high melting temperature. Aluminum alloys for
aerospace applications are for instance a very good choice.
The possibility of embedding can suggest to use the optical fiber system
not only during operation but also to monitor manufacturing parameters during forming, important for instance during the curing cycle of polymeric
composites but also for metallic casting and subsequent thermal treatment. An embedded fiber optic system could be the sensing part of a more complex smart structure that is capable of reacting to the sensed environment. But it can work independently from the acting system with a negligible amount of energy and without complex control algorithms and hardware. Considering that optical fiber strain gauges have usually much greater frequency response than their electrical counterpart they can measure both static and dynamic structural response. A structure with an embedded fiber optic network can give therefore actual information of its dynamic properties and its evolution in time due to environmental effects. Consequently fiber optic sensors can also be used to identify the dynamic properties of a space structure or of space habitat under its actual operating conditions, that are very difficult to simulate with ground tests where air and gravity can play a not negligible role
Testing general relativity with a high-density satellite
Get PDFThe Laser Relativity Satellite is built from a specifically chosen, dense tungsten alloy and is covered with laser retroreflectors to test general relativity and fundamental physics
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