Trajectory design of a multiple flyby mission to asteroids

In designing the trajectory for a multiple flyby mission to asteroids the choice of the targets is the most challenging problem. This dissertation faces this problem in the framework of the recently issued medium-size mission call (M5) from ESA: CASTAway. Starting from the preliminary work done in [6], this thesis develops a methodology for sequencing the potential targets in a multiple flyby mission. In order to reduce the computational time, the complete database of known small bodies is firstly pruned on the base of heuristic considerations. Using the assumption of small manoeuvres, a chief orbit concept could be used. Thus, two heuristic thresholds are defined in order to exclude non-promising targets given a chief orbit. The sequencing process takes chief orbit and promising targets as inputs and gives a set of candidate sequences. The results of such a process are analysed in the CASTAway framework and the best feasible sequence studied in details.

Estimation of the satellite ephemerides of Saturn using optical navigation pictures of Cassini

The goal of this dissertation thesis is the estimation of the Saturnian satellites ephemerides using optical data of Cassini. In the first part we describe the software employed for the reduction of the images showing its main features and the accuracy that can be achieved comparing the results with published astrometry. Afterwards we describe the orbit determination problem (ODP) with particular focus on the weights selection for the estimation process. The third chapter describes the dynamical model used and the sources of potential errors in the residuals. The model have been validated trying to replicate JPL's published ephemerides SAT365, SAT375, SAT389 and SAT409. The final part investigates the residuals and the estimated ephemerides with particular focus on the giant moon Titan, the only in the solar system with an atmosphere other than the Earth. No astrometry have been retrieved in literature of Titan using optical observables, thus this represents one of the first investigations of the giant.

Task analysis for HMI design. Level of automation study of aircraft navigation functions

Advancements in technology have enabled increasingly sophisticated automation to be introduced into the flight decks of modern aircraft. Generally, this automation was added to accomplish worthy objectives such as reducing flight crew workload, adding additional capability, or increasing fuel economy. Automation is necessary due to the fact that not all of the functions required for mission accomplishment in today’s complex aircraft are within the capabilities of the unaided human operator, who lacks the sensory capacity to detect much of the information required for flight. To a large extent, these objectives have been achieved. Nevertheless, despite all the benefits from the increasing amounts of highly reliable automation, vulnerabilities do exist in flight crew management of automation and Situation Awareness (SA). Issues associated with flight crew management of automation include: • Pilot understanding of automation’s capabilities, limitations, modes, and operating principles and techniques. • Differing pilot decisions about the appropriate automation level to use or whether to turn automation on or off when they get into unusual or emergency situations. • Human-Machine Interfaces (HMIs) are not always easy to use, and this aspect could be problematic when pilots experience high workload situations. • Complex automation interfaces, large differences in automation philosophy and implementation among different aircraft types, and inadequate training also contribute to deficiencies in flight crew understanding of automation.

Estimation of the ephemerides and gravity fields of the Galilean moons through orbit determination of the JUICE mission

Jupiter and its moons are a complex dynamical system that include several phenomenon like tides interactions, moon's librations and resonances. One of the most interesting characteristics of the Jovian system is the presence of the Laplace resonance, where the orbital periods of Ganymede, Europa and Io maintain a 4:2:1 ratio respectively. It is interesting to study the role of the Laplace Resonance in the dynamic of the system, especially regarding the dissipative nature of the tidal interaction between Jupiter and its closest moon, Io. Numerous theories have been proposed regarding the orbital evolution of the Galilean satellites, but they disagree about the amount of dissipation of the system, therefore about the magnitude and the direction of the evolution of the system, mainly because of the lack of experimental data. The future JUICE space mission is a great opportunity to solve this dispute. JUICE is an ESA (European Space Agency) L-class mission (the largest category of missions in the ESA Cosmic Vision) that, at the beginning of 2030, will be inserted in the Jovian system and that will perform several flybys of the Galilean satellites, with the exception of Io. Subsequently, during the last part of the mission, it will orbit around Ganymede for nine months, with a possible extension of the mission. The data that JUICE will collect during the mission will have an exceptional accuracy, allowing to investigate several aspects of the dynamics the system, especially, the evolution of Laplace Resonance of the Galilean moons and its stability. This thesis will focus on the JUICE mission, in particular in the gravity estimation and orbit reconstruction of the Galilean satellites during the Jovian orbital phase using radiometric data. This is accomplished through an orbit determination technique called multi-arc approach, using the JPL's orbit determination software MONTE (Mission-analysis, Operations and Navigation Tool-kit Environment).

Effects of Accelerated Hygroscopic Ageing on Interlaminar Shear Strength and Glass Transition Temperature of CFRP

This study, which is undertaken in cooperation with Riba-COMPOSITES, investigates the effects of hygroscopic ageing on the Interlaminar Shear Strength and Glass Transition Temperature of short-beams made of carbon fibre reinforced polymer (CFRP) composites provided by two different vendors. The materials have the same weave pattern but differ in the epoxy resin formulation. The tests are done in accordance with ASTM. Accelerated ageing techniques are carried out by immersion of the specimens in deionized water at 70°C for different periods of time, developing different degrees of ageing. The results of the tests confirm that hygroscopic ageing causes a loss of properties and a depression of the glass transition temperature in both the materials. However, since one of the two materials shows more constant property degradation, its behaviour in service conditions should be more easily predictable.

Vibro-acoustic analysis of additively manufactured acoustic metamaterials

In the last decade it emerged the interest in new types of acoustic insulating materials, called acoustic metamaterials. These materials are composed by a host and inclusions and are arranged periodically or non-periodically in sub-wavelength elements called meta-atoms. Their inclusions and internal geometries can be manipulated to tailor the acoustic properties, reducing weight, and increasing at the same time their efficiency. Thanks to the high absorbing characteristics that they can achieve, their usage is of particularly interest as material of the core in sandwich panels of aerospace structures to reduce vibrations and noise inside passengers aircraft’s cabin. In addition, since the low frequency signals are difficult to be damped with conventional materials, their usage can guarantee a high transmission loss at low frequencies, obtaining a positive benefit on passengers’ comfort. The performances and efficiency of these materials are enhanced thanks to the new additive manufacturing techniques opposed to the conventional ones uncapable to pro- duce such complex internal geometries. The aim of this work is to study, produce and redesign micro-perforated sandwich panels of a literature case study to achieve high performances in the low frequency range, e.g., below 2000 Hz. Some geometrical parameters, such as perforation ratio and diameter of holes, were considered to realize different models and see the differences in the sound transmission loss. The models were produced by means of Fused Deposition Modelling using an Acrylonitrile Butadiene Styrene (ABS Plus p430) material on a commercial additive manufacturing system. Finally, the frequency response analysis was carried out with Mul2 software, based on the Carrera’s Unified Formulation (CUF) to understand the acoustic and structural properties of the material employed, analyzing the plates’ displacements and the TL results.

Study of the rotational state of Titan using radio tracking data of the Dragonfly mission

Our solar system contains an impressive amount of celestial bodies. For example Saturn posses a huge variety of natural satellites, the diversity in size and physical proprieties of which might amaze imagination. The observational data gathered in 30 years range of deep space missions revealed, that some of these bodies can hide subsurface oceans under their crust. The water, as we know, serves as a fundamental base for a possible appearance of life. This statement is quite exited for the scientific society and serves as a reason for studying so called ”ocean worlds”. In order to detect the celestial bodies with the hidden subsurface ocean, one of the key aspects is the study of their rotational state, which is strongly coupled with the body internal structure. It can be done through the various techniques mentioned in Chapter 1. The main goal of the thesis is the study of rotational state of Titan, whose interior structure expectedly contains liquid ocean layer under its icy crust. Titan is the largest moon of Saturn and it is the second largest moon in the solar system in general. This natural satellite is of particular scientific interest, because it is one of a kind which has substantial atmosphere. The present work was done using radio tracking data of the Dragonfly mission which is one of the next NASA’s missions destined for Titan selected as a part of the New Frontiers Program in 2019. The detailed characteristic of the Dragonfly regarding the landing site and mission lifetime was reported in Chapter 2. The radio-tracking communication link from Titan side was performed using Dragonfly X band transponder according to the schedule tracking opportunity. From Earth side according to the mission, Deep Space Station 25 which is a part of NASA’s Deep Space Network was considered. Only Doppler data was used for studying Titan rotational state, even though there are other reliable techniques described in Chapter 3, that in general could be implemented.

Characterization of Mars rotational dynamics from Doppler tracking of the InSight lander

In the last decades the evolution of radio science has made it possible to infer the atmosphere composition, the surface and the internal structure of the planets. Since the arrival of the first landers on Mars it was possible to make accurate measurements of the dynamics of this planet; in this thesis we will focus on InSight, considering the data disclosed by the JPL relative to the period from November 26th, 2018 to August 15th, 2021. In particular, the Doppler and Range measurements conducted by the RISE (Rotation and Interior Structure Experiment) will be analyzed. Since the accuracy of these measurements was improved significantly the effects due to the atmosphere of Mars might be measured so it should thus be possible to obtain a better estimate of the parameters characterizing the rotational dynamic of Mars. A large part of this study will therefore be dedicated to the study, modeling, implementation and analysis of the atmosphere of Mars, in both its components: troposphere and ionosphere. Once the complete model of Mars had been built, i.e. including the atmosphere, it was then possible to analyze the residuals, obtained between the data of the measurements carried out and the values predicted by the developed model, in order to obtain an estimate of the rotational dynamic of Mars.

Design of compliant mechanisms and their application to morphing wing technology

This thesis describes a study conducted for the development of a new approach for the design of compliant mechanisms. Currently compliant mechanisms are based on a 2.5D design method. The applications for which compliant mechanisms can be used this way, is limited. The proposed research suggests to use a 3D approach for the design of CM’s, to better exploit its useful properties. To test the viability of this method, a practical application was chosen. The selected application is related to morphing wings. During this project a working prototype of a variable sweep and variable AoA system was designed and made for an SUAV. A compliant hinge allows the system to achieve two DOF. This hinge has been designed using the proposed 3D design approach. To validate the capabilities of the design, two methods were used. One of these methods was by simulation. By using analysis software, a basic idea could be provided of the stress and deformation of the designed mechanism. The second validation was done by means of AM. Using FDM and material jetting technologies, several prototypes were manufactured. The result of the first model showed that the DOF could be achieved. Models manufactured using material jetting technology, proved that the designed model could provide the desired motion and exploit the positive characteristics of CM. The system could be manufactured successfully in one part. Being able to produce the system in one part makes the need for an extensive assembly process redundant. This improves its structural quality. The materials chosen for the prototypes were PLA, VeroGray and Rigur. The material properties were suboptimal for its final purpose, but successful results were obtained. The prototypes proved tough and were able to provide the desired motion. This proves that the proposed design method can be a useful tool for the design of improved CM’s. Furthermore, the variable sweep & AoA system could be used to boost the flight performance of SUAV’s.

Experimental characterization of a planar jet by hot-wire anemometry

The study of turbulence is also nowadays a problem that does not have solution from the mathematical point of view due to the lack of solution to link the mean part of the flow with the fluctuating one. To solve this problem, in the CICLoPE laboratory of Predappio, experiments on different type of jets are performed in order to derive a closure model able to close our mathematical model. One of the most interesting type of jet that could be studied is the planar turbulent free jet which is a two dimensional canonical jet characterized by the self-similarity condition of the velocity profiles. To study this particular jet, a new facility was built. The aim of this project is to characterize the jet at different distances from the nozzle exit, for different values of Reynolds number, to demonstrate that the self-similarity condition is respected. To do that, the evaluation of quantities such as spreading rate, centerline velocity decay and relation between fluctuations and mean part of the flow has to be obtain. All these parameters could be detected thanks to the use of single and X hot-wire anemometry with which it is possible to analyzed the fluctuating behaviour of the flow by associating to an electric signal a physical variable expressed in terms of velocity. To justify the data obtain by the measures, a comparison with results coming from the literature has to be shown.

Neural Network Based UAV Fault Tolerant Control with Aerodynamic Disturbance Estimation and Compensation

In this thesis, the problem of controlling a quadrotor UAV is considered. It is done by presenting an original control system, designed as a combination of Neural Networks and Disturbance Observer, using a composite learning approach for a system of the second order, which is a novel methodology in literature. After a brief introduction about the quadrotors, the concepts needed to understand the controller are presented, such as the main notions of advanced control, the basic structure and design of a Neural Network, the modeling of a quadrotor and its dynamics. The full simulator, developed on the MATLAB Simulink environment, used throughout the whole thesis, is also shown. For the guidance and control purposes, a Sliding Mode Controller, used as a reference, it is firstly introduced, and its theory and implementation on the simulator are illustrated. Finally the original controller is introduced, through its novel formulation, and implementation on the model. The effectiveness and robustness of the two controllers are then proven by extensive simulations in all different conditions of external disturbance and faults.

Development of iodine and air chemistry models for the simulation of plasma in Helicon Plasma Thrusters

The aim of this work is to analyse the chemistry models of low pressure Helicon discharges fed with iodine and air. In particular the focus of this research is to understand the plasma dynamics in order to predict propulsive performances of iodine and air-breathing Helicon Plasma Thrusters. The two systems have been simulated and analysed with the use of global models, i.e. a 0 dimensional tool to solve the set of governing equations by assuming that all quantities are volume averaged. Furthermore, some strategies have been implemented to improve the accuracy of this approach. A verification have been accomplished on the global models for both iodine and air, comparing results against simulations taken from literature. Moreover, the iodine global model has been validated against the experimental measurements of REGULUS, an helicon plasma thruster developed by the Italian company T4i, with a good agreement. From the analysis of iodine model, it has been found a significantly higher density for atomic positive ions with respect to molecular ions. Negative ions, instead, have shown to have negligible effect on the propulsive results. Also, the influence of reactions between heavy particles has been analysed with the global model. Results have demonstrated that, in the iodine case, chemistry is almost entirely affected by electronic collisions. For what concerns air-breathing results, it has been investigated the effects of the orbital height on propulsive performances. In particular, the global model has shown that at lower height, the values of thrust and specific impulse are lower due a change in atmosphere concentration. Finally, the iodine chemistry model has been introduced in the fluid code 3D-VIRTUS in order to preliminary assess the plasma properties of a Helicon discharge chamber for electric propulsion.

Fractional Order Modeling and Control of a Flexible Satellite

Researchers have engrossed fractional-order modeling because of its ability to capture phenomena that are nearly impossible to describe owing to its long-term memory and inherited properties. Motivated by the research in fractional modeling, a fractional-order prototype for a flexible satellite whose dynamics are governed by fractional differential equations is proposed for the first time. These relations are derived using fractional attitude dynamic description of rigid body simultaneously coupled with the fractional Lagrange equation that governs the vibration of the appendages. Two attitude controls are designed in the presence of the faults and uncertainties of the system. The first is the fractional-order feedback linearization controller, in which the stability of the internal dynamics of the system is proved. The second is the fractional-order sliding mode control, whose asymptotic stability is demonstrated using the quadratic Lyapunov function. Several nonlinear simulations are implemented to analyze the performance of the proposed controllers.

Upper-Limb Exoskeleton Design for Firefighter

Every day, firefighters are involved in emergency response tasks, which are both physically and psychologically exhausting. According to the National Fire Protection Association (NFPA), the number of firefighters who are injured or die while performing their job is incredibly high. When firefighters are injured, they must follow a rehabilitation therapy program to physically recover and depending on the severity of their injuries they may not fully recuperate at all. If they sustain a permanent injury that they cannot recover from, they may be out of work for the rest of their career. This research focuses on studying and developing a special device, known as an exoskeleton, aimed at assisting and preventing potential injuries among firefighters. Nowadays, the usage of human exoskeletons is becoming more common in a variety of fields. In fact, it is currently being researched and developed for soldiers, athletes, and critical care patients around the world. Most of the existing exoskeletons have been developed for the assistance of the lower human body. The research that I have done in my thesis instead relates to mobility of the upper body. Many of the existing exoskeletons have been analyzed and compared to each other and the human body, such as the study of human arm parts and their movements around three principal joints: shoulder, elbow, and wrist. The correct design of the shoulder exoskeleton join is still a big challenge for designers because of the complexity of biomechanical human movements. The exoskeleton must fit perfectly to the human body, otherwise it could be harmful for both the recovery and the safety of the user. The goal of this thesis is to design an upper-body arm exoskeleton worn by firefighters and develop and test a PID control system to prevent the risk of injuries while performing their job.

Root cause analysis applied to a finite element model's refinement of a negative stiffness structure

Negative Stiffness Structures are mechanical systems that require a decrease in the applied force to generate an increase in displacement. They are structures that possess special characteristics such as snap-through and bi-stability. All of these features make them particularly suitable for different applications, such as shock-absorption, vibration isolation and damping. From this point of view, they have risen awareness of their characteristics and, in order to match them to the application needed, a numerical simulation is of great interest. In this regard, this thesis is a continuation of previous studies in a circular negative stiffness structure and aims at refine the numerical model by presenting a new solution. To that end, an investigation procedure is needed. Amongst all of the methods available, root cause analysis was the chosen one to perform the investigation since it provides a clear view of the problem under analysis and a categorization of all the causes behind it. As a result of the cause-effect analysis, the main causes that have influence on the numerical results were obtained. Once all of the causes were listed, solutions to them were proposed and it led to a new numerical model. The numerical model proposed was of nonlinear type of analysis with hexagonal elements and a hyperelastic material model. The results were analyzed through force-displacement curves, allowing for the visualization of the structure’s energy recovery. When compared to the results obtained from the experimental part, it is evident that the trend is similar and the negative stiffness behaviour is present.