1,721,150 research outputs found
Technologies for a miniature LEO satellites telecommunication network
No full textThe aim of this work is to investigate alternative strategies and technical solutions for the realization of low cost telecommunication networks based on miniature satellites. The research is particularly focused on nanosatellites, which represent a class of space vehicles weighing between 1 and 10 kg. Miniature satellites are advantageous as their design and production time is significantly lower than that of traditional satellites; moreover, their reduced mass results in very low production and launch costs, especially if piggyback launches are exploited. However, the reduced onboard resources still prevent the use of miniature satellites for complex or high performance applications. In this work, two strategies have been investigated to cope with the current limitations of miniature satellites.
The first strategy consists of using clusters of small, identical satellites with cooperation capabilities instead of traditional, large satellites, for the realization of telecom constellations. Such architecture implies several advantages; first, by replacing obsolete or damaged units with new ones it is possible to upgrade the system using more advanced technology, or to extend the system lifespan; second, if the amount of small satellites becomes sufficiently large – dozens to hundreds – then economy of scale applies, with significant cost savings. The analysis that was performed shows that such cost savings can sum up to 25% of the cost of constellations based on traditional, monolithic satellites with equivalent performance. Then, the technology gaps preventing the implementation of this strategy have been identified and discussed, the most critical one being the capability to autonomously execute proximity navigation and docking. Thus, as gap-filling technical development, a sensor for relative navigation suitable for autonomous cooperative spacecraft was designed, built and tested. This activity was carried out in the framework of the ARCADE-R2 experiment, which participated to ESA’s Rexus/Bexus programme in 2013.
The second strategy consists of enhancing the communication capabilities of miniature satellites. Optical communication was selected as break-through technology, and the task of precision laser beam pointing was identified as the most critical issue that prevents the use of lasercom terminals onboard miniature satellites. To cope with this, two systems have been proposed and modelled. The first consists of an actively-stabilized platform conceived to provide a stable base to laser pointing systems onboard micro/nano satellites; the second is a coarse pointing system for 3U CubeSats. Both systems are based on the parallel platform configuration, and share many similarities from a technical point of view. Detailed numerical models have been developed and used to preliminary size the needed actuators and sensors. Then, a testbed have been built, which features an excitation stage used to simulate the residual attitude motion of a miniature satellite in LEO and a simplified prototype of the stabilization platform. Laboratory tests have been carried out to validate the models of the system and assess its performance.Lo scopo di questo lavoro è di esplorare strategie alternative e soluzioni tecniche per la realizzazione di reti di telecomunicazioni a basso costo basate su satelliti miniaturizzati. La ricerca si è focalizzata in particolare sui nanosatelliti, che rappresentano una classe di veicoli spaziali di massa compresa tra 1 e 10 kg. I satelliti miniaturizzati sono convenienti perché il tempo richiesto per il loro design e produzione è nettamente inferiore di quello richiesto per satelliti tradizionali; inoltre, la loro massa contenuta implica bassi costi di produzione e lancio, soprattutto se vengono sfruttati lanci piggyback. Tuttavia, le limitate risorse di bordo impediscono al giorno d’oggi l’utilizzo di satelliti miniaturizzati per applicazioni complesse o ad alte prestazioni. In questo studio, due strategie sono state investigate per superare le attuali limitazioni dei satelliti miniaturizzati.
La prima strategia consiste nell’utilizzare flotte di satelliti identici e di piccole dimensioni, dotati di capacità di cooperazione, al posto dei tradizionali satelliti di grandi dimensioni, per la realizzazione di costellazioni per telecomunicazioni. Quest’architettura implica una serie di vantaggi; innanzitutto, sostituendo unità obsolete o danneggiate con unità nuove è possibile aggiornare il sistema con tecnologie più avanzate, o estendere la vita operativa del sistema; inoltre, se il numero totale di piccole unità diventa sufficientemente elevato – decine o centinaia – si può applicare economia di scala, con risparmi significativi. L’analisi che è stata effettuata mostra che tali riduzioni di costo possono ammontare al 25% del costo di una costellazione basata su satelliti tradizionali con prestazioni equivalenti. Successivamente, i limiti tecnologici che impediscono l’implementazione di questa strategia sono stati identificati e discussi, e la capacità di effettuare autonomamente navigazione relativa di prossimità e manovre di docking è stata individuata come la più critica. Per questo, quale tecnologia abilitante, un sensore di navigazione relativa per satelliti autonomi e cooperativi è stato sviluppato e testato. Questa attività si è svolta nell’ambito dell’esperimento ARCADE-R2, che ha partecipato al programma Rexus/Bexus dell’ESA nel 2013.
La seconda strategia consiste nell’aumentare le capacità di telecomunicazione dei satelliti miniaturizzati. La comunicazione ottica è stata selezionata come tecnologia innovativa abilitante, e l’estrema accuratezza di puntamento richiesta da un sistema telecom laser è stata identificata come l’aspetto più critico che impedisce al giorno d’oggi l’utilizzo di terminali ottici a bordo di satelliti miniaturizzati. Per superare questo limite, due dispositivi sono stati proposti e studiati. Il primo consiste in una piattaforma stabilizzata attivamente il cui scopo è fornire una base stabile al sistema di puntamento del laser a bordo di micro/nano satelliti; il secondo consiste in un sistema di coarse pointing per CubeSat 3U. Entrambi i dispositivi si basano sulla configurazione del manipolatore parallelo e sono accomunati da varie somiglianze tecniche. Modelli numerici dettagliati sono stati sviluppati e utilizzati per dimensionare preliminarmente attuatori e sensori. Successivamente, è stato realizzato un sistema di test, composto da uno shaker rotativo, usato per simulare il moto d’assetto residuo di un satellite miniaturizzato in LEO, e da un prototipo semplificato della piattaforma stabilizzata. Test di laboratorio sono stati condotti per validare i modelli numerici e valutare le prestazioni del sistema in via preliminare
A miniature stabilized platform for lasercom terminals on-board nanosatellites
No full textIn the last decade miniature satellites have become attractive due to their inherent advantages: the reduced mass, production cost and time, as well as the low launch cost allow small companies, corporations and universities to access space easily. Moreover, constellations based on miniature satellites for observation, mapping or telecommunication purposes could represent an alternative to systems based on larger platforms, thanks to the further cost reduction due to mass production. However, pico- and nano- satellites still present severe technical limitations which prevent their exploitation for complex or high-performance missions. In particular, the reduced available power and volume restrict up/downlink data rates to a few hundred kbit/s.
To this day, optical links represent the unique viable solution to increase dramatically the communication capabilities of nanosatellites. In fact, only lasercom technology, thanks to the very narrow beam emission, permits to achieve data rates up to some Gbit/s with devices which can fit on a nanosatellite host bus in terms of volume, mass and power consumption. RF systems with comparable performance would inevitably exceed the resources available on such miniature platforms.
However, the extremely stringent pointing accuracy and stability required by optical link terminals are not compatible with the actual and perspective attitude control performance of nanosatellites.
In order to overcome these technical limitations, the authors are developing a miniature actively stabilized platform capable of rejecting the residual bus vibration and provide a small optical link device with a vibration-free base. Its exploitation will allow to relax the requirements on both the attitude control system of the host spacecraft and the pointing system of the optical communication terminal, making the miniaturization of the latter easier. The device consists of a parallel, three rotational degrees of freedom platform controlled by means of three identical actuators based on piezoelectric elements. The active control is required to manage low-frequency vibrations, while high frequency disturbances are rejected by high-stiffness elastic elements. The parallel configuration is chosen for its simplicity, symmetry and overall stiffness.
In this paper, the design of the actively stabilized platform is presented, along with the numerical simulations performed in order to evaluate the system performance
New Optical Communication Capabilities Using Nanosatellites
No full textIn this paper, the benefits derived from the exploitation of nanosatellites for complex telecommunication missions are presented, along with their limitations, and laser technology is identified as a viable solution to dramatically increase the downlink and crosslink capabilities of such miniature platforms. Then, the critical technological issues concerning the integration of an optical telecom terminal on a nanosatellite platform are discussed, considering the perspective advancements in areas such as power generation, propulsion and attitude control. The incompatibility of laser terminals pointing requirements with the current and perspective nanosatellite attitude stability has been identified as the most critical issue to be addressed in order to implement optical links on nanosatellites. A possible solution is presented at the end of the discussion
Economic benefits for LEO telecom constellations due to modular spacecraft architecture
No full textThe realization of future satellites based on the aggregation of modular units offers several advantages compared to the traditional approach, consisting of monolithic, highly customized spacecraft. In fact, the aggregation of multiple, standard, self-consistent units with the capability of cooperation would lead to the realization of platforms with equivalent performance compared to traditional satellites, but with increased fault tolerance and flexibility. Such approach would also lead to a significant increase of the platform lifespan by replacement of malfunctioning, damaged or obsolete units with spare or updated units.
The major drawback of this concept is represented by the increase of inert mass of the single unit, which is inevitable in the process of fragmentation of the monolithic platform, leading to increase of costs. While this is certain for a single satellite, this may not apply if we consider a constellation based on dozens of satellites. If each spacecraft is fragmented in a cluster of modular, standard units, their amount becomes so large that economy of scale can be applied, causing decrease of both costs and production time of the single unit. In addition, the fragmentation approach makes it possible to deploy a reduced capability constellation in a short time simply by launching platforms composed by half of the total units; such initial constellation could be further, gradually expanded by launching additional units.
In this work, the economic benefits deriving from the adoption of a modular design applied to LEO telecom constellations is analysed. The overall cost of constellations based on monolithic satellites and modular platforms with equivalent telecom capabilities and performance are compared, considering different constellation architectures and reference monolithic satellites. For each architecture, the mass of the monolithic satellite is determined exploiting historical data, as well as the mass of the modular units as a function of the number of units the monolithic satellite is fragmented. Then, the overall cost of the fragmented platforms is calculated using cost estimating relationships (CERs) and compared to the cost of the monolithic satellites. The analysis shows that in most of cases there is a fractioned configuration that significantly reduces the cost of the whole constellation
Multivalent Glycocalixarenes
No full textWe herein briefly introduce the potentials of glycocalixarene as multivalent ligands. Their ability to inhibit specific proteins or to stimulate the immuno response, in fact, discloses the important role they might play in bionanotechnology and in nanomedicine. Nella presente rassegna vengono brevemente presentate le potenzialità dei glicocalixareni come leganti multivalenti. La loro capacità di inibire specifiche proteine o stimolare la risposta immunitaria mette in luce l’importante ruolo che questi leganti possono avere nel campo delle bionanotecnologie e della nanomedicina
Biomimetic Macrocyclic Receptors for Carboxylate Anion Recognition
No full textCarboxylate anions are ubiquitous in nature and are
involved in several biological processes. For example,
the carboxylate group of the D-alanyl-D-alanine terminal
part of the cell wall peptidoglycan is selectively recognized
by the binding pocket of vancomycin-type antibiotics,[1]
di- and tricarboxylates are involved in several metabolic
processes,[2] and other carboxylate anions are known to be
substrates or inhibitors of enzymes.[3] Moreover, chiral propionic
acid derivatives are widely used in therapy as nonsteroidal
anti-inflammatory drugs[4] and carboxylate polyanions
can form well-ordered self-assembled structures
when mixed with complementary polycations or hydrogen
bonding donor groups.[5] For all these reasons the synthesis
of biomimetic receptors for carboxylate anions have been
recently pursued in supramolecular chemistry,[6–8] with
the aim of obtaining 1) useful models of the biological
processes, 2) biologically active molecules, 3) selective
chemosensors, and 4) selective separation systems.
The objective of this article is to highlight the most
successful approaches followed in the design and synthesis
of biomimetic receptors for carboxylate anion recognition,
with major emphasis on the results achieved in
the last 5 years with macrocyclic compounds, and on our
own work
Special issue of Supramolecular Chemistry honouring Professor Rocco Ungaro
No full textIt is really a great pleasure and a privilege for us to
introduce this special issue of Supramolecular Chemistry,
which is dedicated to our esteemed mentor, Prof. Rocco
Ungaro, on the occasion of his 70th birthday
Multivalent and Multifunctional Calixarenes in Bionanotechnology
Full text linkThe key features of calixarene derivatives as multivalent ligands for biomacromolecules and as multifunctional catalysts are reviewed herein. The ease of functionalization and the possibility to control the regio- and stereochemical disposition of multiple ligating units around a central core allow to obtain ligands with high affinity and selectivity especially for proteins and nucleic acids. The hydrophilic/lipophilic character can also be finely tuned, allowing to obtain monomeric hybrid derivatives or amphiphiles able to self-assemble alone or in co-formulation with lipids to give nanoparticles and liposomes that incorporate calixarenes. The knowledge acquired up to now sheds light on the future applications of calixarenes in bionanotechnology and nanomedicine
Multivalent glycocalixarenes for recognition of biological macromolecules: glycocalyx mimics capable of multitasking
No full textThe glycoside cluster effect, a special case of multivalency involving carbohydrates, is a powerful tool exploited by Nature to make relatively weak interactions stronger and more specific. Organic and supramolecular chemists have been applying this concept and are devising a plethora of neo-glycoconjugates which can interfere with a series of pathological events such as infections due to viruses and bacteria, tumour progression and migration, and inflammation processes. In the present Tutorial Review, we will illustrate the factors that make calixarenes, the cyclic oligomers obtained by the condensation of phenols/resorcinols and aldehydes, unique scaffolds for the construction of multivalent glycosylated ligands, individually analysing how structural parameters such as the size, valency, conformation, self-assembling behaviour of the macrocycle and especially the topology of the saccharide presentation in space influence the biological properties. We will not only survey the most significant results obtained to date in the inhibition of carbohydrate binding proteins (lectins), but we will also try to paint a picture of the potential that multivalent glycocalixarenes might have in bionanotechnology and nanomedicine, that are especially related to their combined ability to load cargo and to specifically deliver that cargo to target cells
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