Progetto concettuale, ottimizzazione e modellazione CAD di motore Stirling per applicazioni aerospaziali

Nei decenni passati sono stati svolti numerosi studi su sistemi di generazione di potenza elettrica da applicare al settore spaziale, in particolar modo a satelliti e sonde. Ne sono un esempio le analisi riportate dalla Nasa oppure quelle condotte in paesi come il Giappone dall’agenzia spaziale JAXA. Uno dei sistemi spesso utilizzati per generare potenza elettrica si basa sull’applicazione di motori Stirling accoppiati ad un generatore lineare; la differenza di temperatura necessaria per il funzionamento del motore è ottenuta tramite il calore fornito dai radioisotopi di plutonio 238, mentre il raffreddamento del motore avviene mediante scambio termico con l’ambiente esterno.

An Integrated Transmission-Media Noise Calibration Software For Deep-Space Radio Science Experiments

The thesis describes the implementation of a calibration, format-translation and data conditioning software for radiometric tracking data of deep-space spacecraft. All of the available propagation-media noise rejection techniques available as features in the code are covered in their mathematical formulations, performance and software implementations. Some techniques are retrieved from literature and current state of the art, while other algorithms have been conceived ex novo. All of the three typical deep-space refractive environments (solar plasma, ionosphere, troposphere) are dealt with by employing specific subroutines. Specific attention has been reserved to the GNSS-based tropospheric path delay calibration subroutine, since it is the most bulky module of the software suite, in terms of both the sheer number of lines of code, and development time. The software is currently in its final stage of development and once completed will serve as a pre-processing stage for orbit determination codes. Calibration of transmission-media noise sources in radiometric observables proved to be an essential operation to be performed of radiometric data in order to meet the more and more demanding error budget requirements of modern deep-space missions. A completely autonomous and all-around propagation-media calibration software is a novelty in orbit determination, although standalone codes are currently employed by ESA and NASA. The described S/W is planned to be compatible with the current standards for tropospheric noise calibration used by both these agencies like the AMC, TSAC and ESA IFMS weather data, and it natively works with the Tracking Data Message file format (TDM) adopted by CCSDS as standard aimed to promote and simplify inter-agency collaboration.

Development Of New Toolkits For Orbit Determination Codes For Precise Radio Tracking Experiments

This thesis describes the developments of new models and toolkits for the orbit determination codes to support and improve the precise radio tracking experiments of the Cassini-Huygens mission, an interplanetary mission to study the Saturn system. The core of the orbit determination process is the comparison between observed observables and computed observables. Disturbances in either the observed or computed observables degrades the orbit determination process. Chapter 2 describes a detailed study of the numerical errors in the Doppler observables computed by NASA's ODP and MONTE, and ESA's AMFIN. A mathematical model of the numerical noise was developed and successfully validated analyzing against the Doppler observables computed by the ODP and MONTE, with typical relative errors smaller than 10%. The numerical noise proved to be, in general, an important source of noise in the orbit determination process and, in some conditions, it may becomes the dominant noise source. Three different approaches to reduce the numerical noise were proposed. Chapter 3 describes the development of the multiarc library, which allows to perform a multi-arc orbit determination with MONTE. The library was developed during the analysis of the Cassini radio science gravity experiments of the Saturn's satellite Rhea. Chapter 4 presents the estimation of the Rhea's gravity field obtained from a joint multi-arc analysis of Cassini R1 and R4 fly-bys, describing in details the spacecraft dynamical model used, the data selection and calibration procedure, and the analysis method followed. In particular, the approach of estimating the full unconstrained quadrupole gravity field was followed, obtaining a solution statistically not compatible with the condition of hydrostatic equilibrium. The solution proved to be stable and reliable. The normalized moment of inertia is in the range 0.37-0.4 indicating that Rhea's may be almost homogeneous, or at least characterized by a small degree of differentiation.

Studio e ottimizzazione di un autoturboreattore

Il ritiro dello Space Shuttle dalla vita operativa avvenuto nel 2011 e le iniziative in corso tra NASA ed aziende commerciali hanno dato il via ad una fase di transizione nel volo spaziale umano volta a fornire servizi di trasporto spaziale maggiormente flessibili. Accanto ad iniziative private che sono principalmente volte al trasporto di turisti nello spazio allo scopo di far loro provare per pochi minuti l’ebbrezza dell’assenza di gravita’ (ad esempio Virgin Galactic), anche la Difesa si sta impegnando in questo campo, in particolar modo negli USA. Inoltre è stata firmata a marzo 2014 una lettera d’intenti tra l’Aeronautica militare e l’Ente Nazionale per l’Aviazione Civile (ENAC) per definire i criteri e le modalità per lo sviluppo della cooperazione nel settore del volo suborbitale e dell’aerospazio. L’accordo segue di pochi giorni la firma a Washington di un Memorandum of Cooperation sul medesimo argomento tra la Federal Aviation Administration americana(FAA) e la stessa ENAC, accordo che fa dell’Italia il primo paese europeo scelto dalla FAA statunitense come partner per la collaborazione nel settore del trasporto spaziale.

Modifiche al protocollo di trasporto LTP per migliorarne le prestazioni in presenza di perdite elevate

La presente tesi si pone come obiettivo quello di analizzare il protocollo LTP (in particolare in ION) e proporre dei miglioramenti utili al caso in cui siano presenti perdite elevate. Piu in dettaglio, una prima parte introduttiva motiva l'inefficacia del TCP/IP in ambito interplanetario e introduce l'architettura DTN Bundle Protocol (Cap.1). La tesi prosegue con la descrizione delle specifiche del protocollo LTP (Cap.2), in particolar modo evidenziando come un bundle venga incapsulato in un blocco LTP, come questo sia successivamente diviso in tanti segmenti LTP e come questi vengano successivamente inviati con il protocollo UDP o con un protocollo analogo. Viene quindi presentata un'approfondita analisi delle penalizzazioni dovute alle perdite dei segmenti LTP, sia di tipo dati che di segnalazione (Cap. 3). Quest'analisi permette di dimostrare la criticita degli effetti delle perdite, in particolare per quello che riguarda i segmenti LTP di segnalazione. Mentre in presenza di perdite basse tali effetti hanno in media un impatto minimo sul tempo di consegna di un blocco LTP (quindi del bundle in esso contenuto), in quanto avvengono raramente, in presenza di perdite elevate rappresentano un collo di bottiglia per il tempo di consegna di un blocco LTP. A tal proposito sono state proposte alcune modifiche che permettono di migliorare le prestazioni di LTP (Cap. 4) compatibilmente con le specifiche RFC in modo da garantire l'interoperabilita con le diverse implementazioni del protocollo. Successivamente nel Cap. 5 viene mostrato come sono state implementate le modifiche proposte in ION 3.4.1. Nel capitolo finale (Cap. 6) sono presenti i risultati numerici relativi ad alcuni test preliminari eseguiti confrontando la versione originale del protocollo con le versioni modificate contenenti i miglioramenti proposti. I test sono risultati molto positivi per elevate perdite, confermando cosi la validita dell'analisi e dei miglioramenti introdotti.

DTN discovery and routing: from space applications to terrestrial networks.

L'argomento di questa tesi è l'architettura di rete Delay-/Disruption-Tolerant Networking (DTN), progettata per operare nelle reti “challenged”, dove la suite di protocolli TCP/IP risulta inefficace a causa di lunghi ritardi di propagazione del segnale, interruzioni e disturbi di canale, ecc. Esempi di reti “challenged” variano dalle reti interplanetarie alle Mobile Ad-Hoc Networks (MANETs). Le principali implementazioni dell'architettura DTN sono DTN2, implementazione di riferimento, e ION, sviluppata da NASA JPL per applicazioni spaziali. Una grande differenza tra reti spaziali e terrestri è che nello spazio i movimenti dei nodi sono deterministici, mentre non lo sono per i nodi mobili terrestri, i quali generalmente non conoscono la topologia della rete. Questo ha portato allo sviluppo di diversi algoritmi di routing: deterministici per le reti spaziali e opportunistici per quelle terrestri. NASA JPL ha recentemente deciso di estendere l'ambito di applicazione di ION per supportare anche scenari non deterministici. Durante la tesi, svolta presso NASA JPL, mi sono occupato di argomenti diversi, tutti finalizzati a questo obiettivo. Inizialmente ho testato la nuova implementazione dell'algoritmo IP Neighbor Discovery (IPND) di ION, corretti i bug e prodotta la documentazione ufficiale. Quindi ho contribuito ad integrare il Contact Graph Routing (CGR) di ION nel simulatore DTN “ONE” utilizzando la Java Native Interface (JNI) come ponte tra il codice Java di ONE e il codice C di ION. In particolare ho adattato tutte le librerie di ION necessarie per far funzionare CGR all'interno dell'ambiente di ONE. Infine, dopo aver analizzato un dataset di tracce reali di nodi mobili, ho contribuito a progettare e a sviluppare OCGR, estensione opportunistica del CGR, quindi ne ho curato l'integrazione in ONE. I risultati preliminari sembrano confermare la validità di OCGR che, una volta messo a punto, può diventare un valido concorrente ai più rinomati algoritmi opportunistici.

Comparing satellite and ground-based observations of paroxysmal degassing events at Etna volcano, Italy

Mount Etna, Italy, is one of the most active volcanoes in the world, and is also regarded as one of the strongest volcanic sources of sulfur dioxide (SO2) emissions to the atmosphere. Since October 2004, an automated ultraviolet (UV) spectrometer network (FLAME) has provided ground-based SO2 measurements with high temporal resolution, providing an opportunity to validate satellite SO2 measurements at Etna. The Ozone Monitoring Instrument (OMI) on the NASA Aura satellite, which makes global daily measurements of trace gases in the atmosphere, was used to compare SO2 amount released by the volcano during paroxysmal lava-fountaining events from 2004 to present. We present the first comparison between SO2 emission rates and SO2 burdens obtained by the OMI transect technique and OMI Normalized Cloud-Mass (NCM) technique and the ground-based FLAME Mini-DOAS measurements. In spite of a good data set from the FLAME network, finding coincident OMI and FLAME measurements proved challenging and only one paroxysmal event provided a good validation for OMI. Another goal of this work was to assess the efficacy of the FLAME network in capturing paroxysmal SO2 emissions from Etna, given that the FLAME network is only operational during daylight hours and some paroxysms occur at night. OMI measurements are advantageous since SO2 emissions from nighttime paroxysms can often be quantified on the following day, providing improved constraints on Etna’s SO2 budget.

EXPLORATION OF THE MTSAT2 SATELLITE CAPABILITIES FOR REAL TIME DETECTION AND CHARACTERIZATION OF VOLCANIC EMISSIONS

In this report, we attempt to define the capabilities of the infrared satellite remote sensor, Multifunctional Transport Satellite-2 (MTSAT-2) (i.e. a geosynchronous instrument), in characterizing volcanic eruptive behavior in the highly active region of Indonesia. Sulfur dioxide data from NASA's Ozone Monitoring Instrument (OMI) (i.e. a polar orbiting instrument) are presented here for validation of the processes interpreted using the thermal infrared datasets. Data provided from two case studies are analyzed specifically for eruptive products producing large thermal anomalies (i.e. lava flows, lava domes, etc.), volcanic ash and SO2 clouds; three distinctly characteristic and abundant volcanic emissions. Two primary methods used for detection of heat signatures are used and compared in this report including, single-channel thermal radiance (4-µm) and the normalized thermal index (NTI) algorithm. For automated purposes, fixed thresholds must be determined for these methods. A base minimum detection limit (MDL) for single-channel thermal radiance of 2.30E+05 Wm- 2sr-1m-1 and -0.925 for NTI generate false alarm rates of 35.78% and 34.16%, respectively. A spatial comparison method, developed here specifically for use in Indonesia and used as a second parameter for detection, is implemented to address the high false alarm rate. For the single-channel thermal radiance method, the utilization of the spatial comparison method eliminated 100% of the false alarms while maintaining every true anomaly. The NTI algorithm showed similar results with only 2 false alarms remaining. No definitive difference is observed between the two thermal detection methods for automated use; however, the single-channel thermal radiance method coupled with the SO2 mass abundance data can be used to interpret volcanic processes including the identification of lava dome activity at Sinabung as well as the mechanism for the dome emplacement (i.e. endogenous or exogenous). Only one technique, the brightness temperature difference (BTD) method, is used for the detection of ash. Trends of ash area, water/ice area, and their respective concentrations yield interpretations of increased ice formation, aggregation, and sedimentation processes that only a high-temporal resolution instrument like the MTSAT-2 can analyze. A conceptual model of a secondary zone of aggregation occurring in the migrating Kelut ash cloud, which decreases the distal fine-ash component and hazards to flight paths, is presented in this report. Unfortunately, SO2 data was unable to definitively reinforce the concept of a secondary zone of aggregation due to the lack of a sufficient temporal resolution. However, a detailed study of the Kelut SO2 cloud is used to determine that there was no climatic impacts generated from this eruption due to the atmospheric residence times and e-folding rate of ~14 days for the SO2. This report applies the complementary assets offered by utilizing a high-temporal and a high-spatial resolution satellite, and it demonstrates that these two instruments can provide unparalleled observations of dynamic volcanic processes.

A Surface Displacement Analysis for Volcan Pacaya from October 2001 through March 2013 by Means of 3-D Modeling of Precise Position GPS Data

Volcán Pacaya is one of three currently active volcanoes in Guatemala. Volcanic activity originates from the local tectonic subduction of the Cocos plate beneath the Caribbean plate along the Pacific Guatemalan coast. Pacaya is characterized by generally strombolian type activity with occasional larger vulcanian type eruptions approximately every ten years. One particularly large eruption occurred on May 27, 2010. Using GPS data collected for approximately 8 years before this eruption and data from an additional three years of collection afterwards, surface movement covering the period of the eruption can be measured and used as a tool to help understand activity at the volcano. Initial positions were obtained from raw data using the Automatic Precise Positioning Service provided by the NASA Jet Propulsion Laboratory. Forward modeling of observed 3-D displacements for three time periods (before, covering and after the May 2010 eruption) revealed that a plausible source for deformation is related to a vertical dike or planar surface trending NNW-SSE through the cone. For three distinct time periods the best fitting models describe deformation of the volcano: 0.45 right lateral movement and 0.55 m tensile opening along the dike mentioned above from October 2001 through January 2009 (pre-eruption); 0.55 m left lateral slip along the dike mentioned above for the period from January 2009 and January 2011 (covering the eruption); -0.025 m dip slip along the dike for the period from January 2011 through March 2013 (post-eruption). In all bestfit models the dike is oriented with a 75° westward dip. These data have respective RMS misfit values of 5.49 cm, 12.38 cm and 6.90 cm for each modeled period. During the time period that includes the eruption the volcano most likely experienced a combination of slip and inflation below the edifice which created a large scar at the surface down the northern flank of the volcano. All models that a dipping dike may be experiencing a combination of inflation and oblique slip below the edifice which augments the possibility of a westward collapse in the future.

GROUND-BASED AND SATELLITE REMOTE SENSING OF PAROXYSMAL ERUPTIONS AT ETNA VOLCANO, 2011-2012.

Mt Etna's activity has increased during the last decade with a tendency towards more explosive eruptions that produce paroxysmal lava fountains. From January 2011 to April 2012, 25 lava fountaining episodes took place at Etna's New South-East Crater (NSEC). Improved understanding of the mechanism driving these explosive basaltic eruptions is needed to reduce volcanic hazards. This type of activity produces high sulfur dioxide (SO2) emissions, associated with lava flows and ash fall-out, but to date the SO2 emissions associated with Etna's lava fountains have been poorly constrained. The Ultraviolet (UV) Ozone Monitoring Instrument (OMI) on NASA's Aura satellite and the Atmospheric Infrared Sounder (AIRS) on Aqua were used to measure the SO2 loadings. Ground-based data from the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC) L-band Doppler radar, VOLDORAD 2B, used in collaboration with the Italian National Institute of Geophysics and Volcanology in Catania (INGV-CT), also detected the associated ash plumes, giving precise timing and duration for the lava fountains. This study resulted in the first detailed analysis of the OMI and AIRS SO2 data for Etna's lava fountains during the 2011-2012 eruptive cycle. The HYSPLIT trajectory model is used to constrain the altitude of the observed SO2 clouds, and results show that the SO2 emission usually coincided with the lava fountain peak intensity as detected by VOLDORAD. The UV OMI and IR AIRS SO2 retrievals permit quantification of the SO2 loss rate in the volcanic SO2 clouds, many of which were tracked for several days after emission. A first attempt to quantitatively validate AIRS SO2 retrievals with OMI data revealed a good correlation for high altitude SO2 clouds. Using estimates of the emitted SO2 at the time each paroxysm, we observe a correlation with the inter-paroxysm repose time. We therefore suggest that our data set supports the collapsing foam (CF) model [1] as driving mechanism for the paroxysmal events at the NSEC. Using VOLDORAD-based estimates of the erupted magma mass, we observe a large excess of SO2 in the eruption clouds. Satellite measurements indicate that SO2 emissions from Etnean lava fountains can reach the lower stratosphere and hence could pose a hazard to aviation. [1] Parfitt E.A (2004). A discussion of the mechanisms of explosive basaltic eruptions. J. Volcanol. Geotherm. Res. 134, 77-107.

The Amplifier - v. 8, no. 7

In this issue...Magma Yearbook, Marvin Senne, Continental Oil Company, NASA, Circle K Club, Mine Rescue training, Walter Mitty, International Club, Stu Stadler

The Amplifier - v. 9, no. 6

In this issue...Faculty Women's Club, Engineering week, ARMCO, Uuno Sahinen, NASA, MSM library, Flying Club, weightlifting, intramural sports, Theta Tau