Dissertations / Theses on the topic 'Automated Rendezvous and Docking'

On-orbit operations such as refuelling, payload updating, inspection, maintenance, material and crew transfer, modular structures assemblies and in general all those processes requiring the participation of two or more collaborative vehicles are acquiring growing importance in the space-related field, since they allow the development of longer-lifetime missions. To successfully accomplish all these on-orbit servicing operations, the ability to approach and mate with another vehicle is fundamental. Rendezvous strategies, proximity procedures and docking manoeuvres between spacecraft are of utmost importance and new, effective, standard and reliable solutions are needed to ensure further technological developments. Presently, the possibility to create low-cost clusters of vehicles able to share their resources may be exploited thanks to the broadening advent of CubeSat-sized spacecraft, which are conditioning the space market nowadays. In this context, this thesis aims at presenting viable strategies for spacecraft RendezVous and Docking (RVD) manoeuvres exploiting electro-magnetic interactions. Two perspective concepts have been investigated and developed, linked together by the use of CubeSat-size testing platforms. The idea behind the first one, PACMAN (Position and Attitude Control with MAgnetic Navigation) experiment, is to actively exploit magnetic interactions for relative position and attitude control during rendezvous and proximity operations between small-scale spacecraft. PACMAN experiment has been developed within ESA Education Fly Your Thesis! 2017 programme and has been tested in low-gravity conditions during the 68th ESA Parabolic Flight Campaign (PFC) in December 2017. The experiment validation has been accomplished by launching a miniature spacecraft mock-up (1 U CubeSat, the CUBE) and a Free-Floating Target (1 U CubeSat, the FFT) that generates a static magnetic fields towards each other; a set of actively-controlled magnetic coils on board the CUBE, assisted by dedicated localization sensors, are used to control the CUBE attitude and relative position, assuring in this way the accomplishment of the soft-docking manoeuvre. The second one, TED (Tethered Electromagnetic Docking), concerns a novel docking strategy in which a tethered electromagnetic probe is expected to be ejected by a chaser toward a receiving electromagnetic interface mounted on a target spacecraft. The generated magnetic field drives the probe to the target and realizes an automatic alignment between the two interfaces, thus reducing control requirements for close approach manoeuvres as well as the fuel consumption necessary for them. After that, hard-docking can be accomplished by retracting the tether and bringing the two spacecraft in contact.
La capacità di eseguire operazioni di servizio su veicoli in orbita ha riscontrato, negli ultimi anni, un’enorme interesse da parte delle maggiori compagnie e agenzie spaziali internazionali. La necessità di ridurre i costi di produzione, assieme alla possibilità di ottenere sistemi complessi più affidabili e duraturi, ha indirizzato marcatamente il mercato dell’ingegneria aerospaziale verso lo studio di soluzioni innovative per eseguire in orbita operazioni quali rifornimento, aggiornamento e manutenzione di sottositemi, riparazioni di componenti non funzionanti e ispezioni. Le nuove idee e tecnologie in via di sviluppo per eseguire queste operazioni sono percepite come estremamente funzionali e efficienti in termini di costo, in grado di estendere la vita operativa di un satellite e diminuire i costi connessi alla sua completa sostituzione. Attualmente, il tassello mancante per poter procedere efficacemente con questo tipo di procedure, è un sistema automatico di docking che possa costituire un nuovo standard semplice ed affidabile. Gli odierni sistemi di docking, infatti, sono caratterizzati da elevati requisiti di puntamento e necessitano dell’attuazione di precise azioni sul controllo d’assetto in modo da garantire un aggancio sicuro tra i due veicoli coinvolti nella manovra. Questo è dovuto al fatto che tali sistemi di aggancio sono stati progettati quasi unicamente per il trasferimento di equipaggio o di materiali mentre nessuna progettazione, finora, è mai stata prevista per i satelliti commerciali e scientifici. Recentemente, l’avvento dei CubeSat ha fortemente incoraggiato aziende e agenzie del settore aerospaziale ad investire nello sviluppo di dimostratori tecnologici e payload scientifici, grazie alla notevole riduzione nel costo necessario per lanciare in orbita tali veicoli. Lo svantaggio nell’utilizzare questo tipo di piattaforme è principalmente legato ai limiti tecnici intrinseci degli stessi, rappresentati dalle ridotte risorse a disposizione. Ciononostante, gran parte di queste limitazioni sono state superate grazie alla possibilità di scalare i risultati ottenuti ed applicarli a sistemi più grandi. Numerose tecnologie sono già state testate e caratterizzate nello spazio usando moduli CubeSat, ma solo esperimenti marginali sono stati condotti sino ad oggi su sistemi di docking, anche se si sta percependo un cambio di tendenza. Tali sistemi, infatti, permetterebbero l’esecuzione di operazioni di aggancio e sgancio, ampliando enormemente i possibili scenari di missione: sistemi modulari formati da molteplici unità CubeSat potrebbero interagire tra loro creando agglomerati più grandi in grado di condividere le risorse più efficacemente, riorganizzarsi e aggiornarsi autonomamente. Lo scopo di questa ricerca è quello di proporre un nuovo sistema di soft-docking caratterizzato da requisiti meno stringenti per quanto concerne l’accuratezza nel puntamento e nel controllo d’assetto rispetto ai sistemi esistenti. L’idea innovativa alla base dello studio è quella di sfruttare la capacità di auto-allineamento e reciproca attrazione garantita dall’interazione magnetica che si instaura tra due interfacce elettromagnetiche, in modo da facilitare le manovre di prossimità ed aggancio. La trattazione è suddivisa in due parti principali. Nella prima parte viene presentato l’esperimento PACMAN (Position and Attitude Control with MAgnetic Navigation) il quale rappresenta un dimostratore tecnologico di un sistema di docking per piccoli satelliti basato su attuatori magnetici. Tale sistema, sviluppato all'interno del programma ESA Education Fly Your Thesis! 2017, è stato testato in gravità ridotta durante la 68th campagna di voli parabolici ESA a dicembre. La seconda parte si focalizza invece su un nuovo concept, TED (Tethered Electromagnetic Docking), secondo il quale le manovre di close-range rendezvous e docking possono essere realizzate lanciando una sonda elettromagnetica collegata ad un filo da un satellite chaser verso un’interfaccia elettromagnetica montata su di un satellite target. Stabilito il collegamento, tramite il recupero del filo, i due veicoli sono connessi rigidamente concludendo la manovra.

"Earth is a small town with many neighborhoods in a very big universe." The quote of the American Astronaut Ronald John Garan Jr. perfectly summarizes the universal and enduring mankind's interest in exploring the unknown, discovering new worlds, pushing the boundaries of scientific and technical limits further and beyond. More than a half century ago, during a speech delivered at Rice University in Houston, President John F. Kennedy claimed the Moon as the new frontier for the human space exploration. The outstanding achievements of the Apollo mission pushed the research in space across the second part of the last century with new goals, as the permanent presence of the human in space. The evolutionary space program built up around that promise was, to say the least, challenging and involved the development of several revolutionary elements. Due to the significant economic effort required by the Apollo mission, only two elements were realized: the Space Shuttle on one side and the Skylab space station on the other. While the Shuttle remained operative until 2011, Skylab was short-lived and disposed after about six years. Only by joining forces with other international partners, NASA was able to realize a long lasting permanent outpost orbiting around Earth, i.e. the International Space Station (ISS). But again, due to the considerable efforts dedicated to build up the ISS and to keep the Space Shuttle operative, the space race suffered a second setback. Until 2007, when the international community drew up a new visionary program. Moon exploration stepped again into the spotlight to extend and sustain human activities beyond Low Earth Orbit (LEO) towards Mars. The new era of space exploration has begun with the intent of expanding the frontiers of knowledge, capability, and opportunities in space. One of the first milestones is represented by the settlement of the so-called Lunar Orbital Platform-Gateway (LOP-G) by the mid 2020's. The Gateway will serve as a manned outpost in the lunar vicinity to support activities on and around the Moon while also servicing as technological and operational testbed to open the frontier for human exploration of Mars, thanks to the exploitation of key technologies, such as high-power electric propulsion. To sustain the LOP-G and its future visiting crews, the Orion spacecraft is currently under development. However, the usability of the Gateway could be extended if new transportation systems would be available to support the station transferring additional supplies and equipment. In compliance with the current plans to efficiently reduce the number of development and validation economic efforts by designing and exploiting same elements for multiple missions, a reusable, high-power electric space tug, i.e. the Lunar Space Tug (LST), is proposed in this Thesis to support the replenishment of the LOP-G. This innovative transportation system should be flexible enough to be adopted in different phases of the Gateway lifetime and for evolving needs. The LST should be in charge of recovering cargo modules released in Earth proximity and transfer them up to the Gateway performing a low-thrust transfer, before return to its operational orbit, ready for the next delivery mission, envisioning a closed-loop mission profile. A tailored multi-input/multi-output design tool has been developed to obtain the preliminary and detailed design, at component level, of the LST spacecraft for several propulsion subsystem architectures. The impact of adopting this technology on the platform design is investigated with respect to several thruster working points and case studies, each one characterized by different refurbishment needs. Then, the optimal LST configuration able to support the Gateway crew for different resupply needs is selected, performing a trade-off analysis among the design solutions that comply with all mission and system constraints previously defined in order to minimize the spacecraft mass, propellant consumption and overall mission cost. From an operational viewpoint, the LST should significantly rely on the Automated Rendezvous and Docking (ARVD) technology, which has been identified as crucial for the transition of space missions from geocentric architectures to self-sustainable, autonomy and independent. At this end, new Guidance Navigation and Control (GNC) algorithms shall be investigated to allow ARVD maneuvers to become reliable routine. In particular, the control problem encapsulates safety restrictions and performance specification that shall be properly addressed verifying the effectiveness and real-time implementability of innovative control strategies. Thus, a 6 Degrees-of-Freedom (DoF) orbital simulator has been developed to simulate the rotational and translational dynamics of the LST and its target vehicles in both Earth orbit and Lunar proximity. Moreover, to reproduce a realistic simulation environment, uncertainty and disturbance affecting the spacecraft dynamics during the maneuver have been modeled and included in the simulator. For attitude and orbital control, three different Model Predictive Control (MPC) algorithms have been implemented and their performance evaluated in the presence of disturbance and parametric uncertainty. In particular, a sampling-based stochastic MPC algorithm is proposed and the typical binding computational effort required by these type of stochastic algorithms, especially when running on low-performing hardware, has been overcome shifting the intensive computations to the offline phase, thus greatly reducing the online computational cost. To complete the algorithms verification process, all three MPC strategies have been experimentally validated exploiting spacecraft mock-up and running the algorithms on the on-board micro-controller, demonstrating their effectiveness and real-time computational applicability.

Esta tese tem como objetivo apresentar uma solução para o problema de RVD/B (encontro e acoplamento/atracação) entre duas espaçonaves, perseguidora e alvo, em órbita. Depois de uma breve revisão da literatura para contextualizar este trabalho, apresentam-se as estratégias de aproximação, as técnicas de sincronização de órbita e atitude, e a técnica de aproximação de proximidade, sendo suportadas por dois sistemas de equações diferenciais para os movimentos translacional e rotacional das espaçonaves. Duas configurações são consideradas para a espaçonave robótica perseguidora: uma, quando o manipulador robótico, nela incorporado, estiver inerte, e a outra, quando o manipulador robótico estiver em ação. Na primeira configuração, a formulação newtoniana é usada para obter as equações da dinâmica de translação de Hill-Clohessy-Wiltshire, e o movimento de atitude é determinado pelas equações de Euler. Estes dois sistemas de equações obtidos acima permitem conduzir o perseguidor até o espaço de trabalho de atracação do alvo. Na segunda configuração, a formulação de Lagrange, para quase-coordenadas e para coordenadas generalizadas, fornece as equações do movimento do manipulador robótico para a atracação no alvo. No equacionamento e na simulação numérica das aberturas do manipulador robótico, reside a originalidade da tese. As simulações computacionais da dinâmica de ambas as configurações foram implementadas utilizando-se o pacote de software MatLab.
In this thesis strategies to solve the problem of the RVD/B (RendezVous and Docking/Berthing) orbital operations are studied. In a brief review of the literature, the strategies of approximation, the techniques for orbit and attitude synchronization, and the technique for the close proximity approximation are presented, all of them supported by two systems of differential equations for the translational and rotational motion of both spacecrafts. Two configurations are considered for the chaser: one when the robotic manipulator of the chaser is inert, and a second one when the robotic manipulator is in action. In the first configuration the Newtonian formulation is used to obtain the equations of Hill-Clohessy-Klein for the translational dynamics, while the attitude motion is determined by Eulers equations. These two systems of differential equations allow to guide the chaser up to the point for berthing the target. In the second configuration, the Lagrangian formulation for quasi-coordinates and generalized coordinates supplies the equations for the motion of the robotic manipulator when berthing the target. These latter equations and their numerical simulation of berthing the target are the original part of this thesis. The computational simulations of the dynamics are carried out by use of the software MatLab.

This paper presents a study on spacecraftRendezvous and Docking (RvD) through a comprehensiveliterature review, in addition to investigate the main phases andpossible control methods during the space rendezvous and docking.It presents a study of different energy efficient far rangerendezvous (e.g. Hoffman, bi-elliptic, phasing maneuver etc.). Aset of formation flying models (i.e. relative navigation) for twospacecraft operating in close proximity are examined. Oneapproach to depict the relative orbit’s dynamics model for closeproximity operations is to mathematically express it by thenonlinear equations of relative motion (NERM), that present thehighest accuracy and are valid for all types of orbit eccentricitiesand separations. Another approach is the Hill-Clohessy-Wiltshire(HCW). This method is only valid for two conditions, when thetarget satellite orbit is near circular and the distance between thechaser and target is small. The dynamics models in this paperdescribe the spacecraft formation flying in both unperturbed andperturbed environment, where only the Earth oblatenessperturbations are being treated.Furthermore, this paper presents a design of a control, guidance,and navigation (GNC) based on the aforementioned dynamicmodel. This will enable the chaser satellite to autonomouslyapproach towards the target satellite during the close proximitynavigation using some control techniques such Linear QuadraticRegulation (LQR) and Linear Quadratic Gaussian (LQG). Thesecontrol techniques aim to reduce both the duration and the ΔVcost of the entire mission.
I denna rapport utreds olika faser avrymdfarkosters rendezvous och docknings manövrar (RvD) samtundersöks en rad matematiska modeller för formationsflygning,nämligen de icke-linjära ekvationerna av relativ rörelse (NERM)och Hill-Clohessy-Wiltshire-ekvationer (HCW). Dessa dynamiskasystemmodeller beskriver formationsflygningen i både ostörd ochstörd omgivning. Vidare undersöks alternativa reglermetoder ochen filtreringsmetod såsom Linjär Kvadratisk Regulator (LQR),Linjär Kvadratisk Gaussisk (LQG) och utökad Kalman filtrering(EKF), för att reducera både tid och ΔV-kostnaden för hela rymduppdraget.Målen med dessa reglermetoder är att rymdfarkostensjälvständigt skall kunna utföra rendezvous och dockning.

The purpose of this bachelor thesis was to discover howan articulated vehicle can park itself using a pre-definedparking path with a combination of ultrasonic sensors aswell as a rotary angle sensor.The project was divided into two parts: constructing asmall scale demonstrator and the software controlling thedemonstrator. The demonstrator was constructed from offthe-shelf components and custom parts. The truck was designedbased on a rear wheel driven truck with Ackermannsteering. The localization of a parking spot and measuringother distances was done with ultrasonic sensors and thehitch angle was measured by a rotary angle sensor.The performance of the demonstrator was evaluated bymeasuring the trailers angle difference from the center lineof the parking spot.The performance was deemed to be reasonably goodwith successful parkings in 8 out of 10 attempts.
Kandidatarbetet syftar till att undersöka hur ett ledatfordon kan parkera sig självt efter en förbestämd parkeringsruttmed en kombination av flera ultraljudssensorersamt en vinkelgivare.Projektet består av två delar; konstruktion av ett miniatyrfordonsamt mjukvaran som styr fordonet. Fordonettillverkades från butiksköpta komponenter och skräddarsyddadelar. Lastbilens design var baserad p°a en bakhjulsdrivenAckermannstyrd lastbil. Identifieringen av en parkeringsplatssamt avståndsmätning hanterades av ultraljudssensoreroch hitch vinkeln mättes av en vinkelgivare.Miniatyrfordonets prestanda utvärderades genom attmäta släpets vinkelskillnad från centerlinjen av parkeringsplatsen.Prestandan ansågs att vara tillräckligt god med lyckadeparkeringar i 8 av 10 tester.

The purpose of this bachelor thesis was to discover how an articulated vehicle can park itself using a pre-defined parking path with a combination of ultrasonic sensors as well as a rotary angle sensor. The project was divided into two parts: constructing a small scale demonstrator and the software controlling the demonstrator. The demonstrator was constructed from offthe- shelf components and custom parts. The truck was designed based on a rear wheel driven truck with Ackermann steering. The localization of a parking spot and measuring other distances was done with ultrasonic sensors and the hitch angle was measured by a rotary angle sensor. The performance of the demonstrator was evaluated by measuring the trailers angle difference from the center line of the parking spot. The performance was deemed to be reasonably good with successful parkings in 8 out of 10 attempts.
Kandidatarbetet syftar till att undersöka hur ett ledat fordon kan parkera sig självt efter en förbestämd parkeringsrutt med en kombination av flera ultraljudssensorer samt en vinkelgivare. Projektet består av två delar; konstruktion av ett miniatyrfordon samt mjukvaran som styr fordonet. Fordonet tillverkades från butiksköpta komponenter och skräddarsydda delar. Lastbilens design var baserad på en bakhjulsdriven Ackermannstyrd lastbil. Identifieringen av en parkeringsplats samt avståndsmätning hanterades av ultraljudssensorer och hitch vinkeln mättes av en vinkelgivare. Miniatyrfordonets prestanda utvärderades genom att mäta släpets vinkelskillnad från centerlinjen av parkeringsplatsen. Prestandan ansågs att vara tillräckligt god med lyckade parkeringar i 8 av 10 tester.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 189-194).
As efforts to expand humanity's presence in space continue to increase, a need for spacecraft to autonomously perform in-space close proximity maneuvers without a human operator increases, as well. Such in-space close proximity maneuvers include active debris removal, satellite servicing, and in-space assembly. Active debris removal will facilitate the continued use and access to low Earth orbit, mitigating the exponential debris growth occurring due to decrepit satellites and rocket bodies colliding. Satellite servicing will provide the capability to repair and refurbish spacecraft, elongating the lifetime of valuable assets both locally orbiting Earth and on routes further out in the solar system. In-space assembly is the means by which large space structures are developed in orbit. Currently, such feats occur with the help of astronauts and robotic arms (i.e. the continued development of the International Space Station). However, for increased benefit, in-space assembly must occur autonomously, without a human in-the-loop, in order to create large structures in locations unideal for humans or with a non-negligible communication latency. These three reference missions need the software enabling autonomous rendezvous and docking to reach a technical readiness level to be employed with confidence. In-space close proximity maneuvers share a standard sequence of events described in this thesis. The focus of this thesis address the terminal approach trajectory to soft docking, the contact dynamics of docking between two spacecraft, the optimization of the detumble procedure to bring the Target to stabilization, and adaptive control techniques to handle uncertainties in spacecraft knowledge. The software developed in support of these subproblems is included in the appendices and is largely based on implementation with the Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) platform or with the characteristics of SPHERES considered.
by Hailee Elida Hettrick.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 251-267).
Rendezvous and docking missions have been a mainstay of space exploration from the Apollo program through present day operations with the International Space Station. There remains a growing interest in several mission types that not only rely on rendezvous and docking, but also rely on maneuvering spacecraft once docked. For example, there is active interest in orbital debris removal, on-orbit assembly, on-orbit refueling, and on-orbit servicing and repair missions. As these missions become more and more popular, the number of rendezvous and docking class operations will increase dramatically. Current methods focus on performing rendezvous and docking to very well-known targets and in very well-known conditions. Inherent to these new mission types, however, is an increasing element of uncertainty to which new guidance and control architectures will need to be robust. As guidance and control techniques become more robust, a corresponding tradeoff in performance can typically be experienced. This thesis attempts to address the uncertainties in rendezvous and docking operations while maintaining a probabilistically optimal level of performance. There are two main focuses in the thesis: spacecraft trajectory optimization and reference-tracking controller selection. With respect to trajectory optimization, the goal is to nd probabilistically optimal trajectories given large uncertainties in mission critical parameters, such as knowledge of an obstacle's position, while knowing that the trajectory is able to be replanned onboard the spacecraft when higher precision information is obtained. This baseline optimal trajectory and subsequently replanned trajectories are then followed by an optimally determined set of reference-tracking controllers. These controllers are selected and scheduled throughout the phases of the mission based on the probabilistically expected performance in the presence of noise and uncertain parameters. This process is explored through its implementation on a generic problem setup for rendezvous, docking, and joint maneuvering. Results specfic to this problem and associated analysis motivate the use of probabilistic planning in future space missions. Specically, the thesis shows that fuel and tracking performance can be improved if multi-stage missions are planned continuously through phase transitions and without the use of waypoints. Furthermore, under the presence of large uncertainties, the techniques in this thesis produce better expected fuel and tracking performance than traditional trajectory planning and controller selection methods.
by Christopher Michael Jewison.
Ph. D.

This thesis proposes a hybrid control strategy to solve the problem of rendezvous, proximity operations, and docking of an autonomous spacecraft in 3-dimensional space. Due to the different constraints and tasks to perform, a hybrid systems approach is implemented to solve the problem in three phases: 1. rendezvous; 2. docking phase; 3. docked phase; with range and angle measurements. A supervisor that robustly coordinates the individual controllers and induces robust semiglobal asymptotic stability is proposed. This thesis also includes designs of these individual controllers that solve the appropriate control problems for the individual phases. Numerical results for both the nominal and perturbed case validate the hybrid control strategy for the spacecraft close-proximity mission.

Neste trabalho foram analisadas as possibilidades de se viabilizar computacionalmente a implementação de manobras de rendezvous (encontro) e docking (acoplamento) espacial entre o Satélite de Reentrada Atmosférica (SARA) e um segmento orbital permanente. Mais especificamente, foram levantadas as necessidades de software e os algoritmos de vôo que devem ser desenvolvidos para procedimentos desse tipo. Além das revisões sobre as abordagens de procedimentos e tecnologias envolvendo este tipo de manobra, foi desenvolvida uma arquitetura de simulação constituída por um ambiente virtual distribuído, capaz de fornecer simulação integrada em tempo quase-real, juntamente com outro ambiente de controle e monitoramento implementado em linguagem interpretada para facilitar sua utilização como uma ferramenta de software para engenharia de sistemas e engenharia de software espaciais. Com base neste ambiente virtual de simulação, foram também desenvolvidos algoritmos que simulam a lógica embarcada em cada veículo atuante no cenário e também as rotinas de operação remota e monitoramento existentes nas estações de rastreio em solo. Esta metodologia de comunicação entre dois ambientes simulados é capaz de executar um cenário de simulação de forma totalmente interativa e de fácil entendimento para o usuário, pois são geradas saídas gráficas em 3-D exibindo toda a evolução durante sua execução. Os resultados mostraram que o desenvolvimento de cenários de rendezvous e docking dentro deste tipo de arquitetura tornam as análises de procedimentos de software embarcado mais precisas e dinâmicas, sem a necessidade do desenvolvimento de simuladores ou ambientes virtuais a partir do início. Todos esses conceitos foram relacionados às suas respectivas aplicações dentro do Projeto SARA, correspondendo ao princípio de desenvolvimento de um protótipo de software embarcado a ser implementado nos subsistemas computacionais de bordo dos veículos da missão que irão executar as referidas manobras.
In this work, it was analysed the possibilities of becoming computationally viable the space rendezvous and docking maneuvers implementation between the recoverable SARA satellite and another permanent orbital segment. More specifically, the software needs and the flight algorithms that have to be developed to accomplish procedures like this were raised. Besides the reviews about procedures and technologies approaches involving that kind of maneuver, it was also developed a simulation architecture made by a distributed virtual environment, capable to supply integrated simulation in near real time, together with another environment for controlling and monitoring which was implemented by interpreted language, in order to ease its using as a software tool for space engineers and space software engineers. Based on that virtual simulation environment, it was also developed some algorithms that simulate the embedded logic in each vehicle acting on the scenario and also the remote operation and monitoring routines that reside on tracking ground stations. That communication methodology between two simulated environments is capable to run a simulation scenario in a totally interactive way and easy understanding to the user, because 3-D graphical outputs are generated showing all the simulation execution evolution. The results showed that the rendezvous and docking scenario development inside that kind of architecture turns the embedded software procedure analysis more precise and dymanic, without the need to develop simulators or virtual environments from scratch. All of those subjects were related to their respective applications within the SARA Project, addressing to the development principles of an embedded software prototype to be implemented onboard the mission vehicles computational subsystems that will accomplish the referred maneuvers.

Unmanned underwater vehicles (UUV) are receiving increased attention for both military and civilian applications. For example, UUVs were deployed in the war against Iraq for mine counter measure missions and are becoming a necessary tool in the deep sea mining industry. If UUVs were able to dock while submerged, it would greatly increase their efficiency, as well as reduce the cost involved in their deployment and recovery. The ability to both operate and dock in a submerged state would also provide the UUV a degree of stealth. A future application where UUVs would prove a valuable asset is for harbor control where stealth is an essential quality. A submerged docking bay would enable the UUV to both upload completed mission data and download new mission objectives while recharging its batteries. To succeed in this endeavor, a control system capable of guiding the UUV safely into an underwater docking bay is required. This thesis describes the development of two different control algorithms, a fuzzy controller and a Linear Quadratic Regulator (LQR). For simulation purposes, a 3D model of a small UUV is generated using ADAMS/view software. Another model is generated in Simulink/MATLAB using the equations of motions for the UUV, yielding faster and more numerically stable simulations. Both models are including the effects of water drag and have vertical and horizontal rudders and thruster inputs. The controllers are built using Simulink/MATLAB and the simulations are run either using Simulink/MATLAB entirely or in co-simulation mode with ADAMS, enabling a more graphic representation of the results. The UUV chosen for this thesis is called REMUS and is developed by Woods Hole Oceanographic Institute. It measures 1.6 m and weighs 37 kg. Included in this work is a thorough analysis of both controllers including key results enabling a comparison of the two controllers performance. A number of requirements were set up for the controllers and except for water current disturbances, both controllers met their requirements. When off course the presented LQR is able to steer the UUV back on course more quickly and smoothly than the Fuzzy controller. The conclusion of this thesis when combining all characteristics of the different controllers’ performance is that the LQR is the natural choice of controller for autonomous underwater docking of an UUV. The research described in this thesis has the potential to further increase the efficiency of UUVs by enabling underwater docking. The ultimate future work would naturally be to test the described controllers on the REMUS in a test tank to verify the results presented in this thesis.

The increasing number of human objects in space has laid the foundation of a novel class of orbital missions for servicing and maintenance. The main goal of this thesis is the development, building and testing of a robotic manipulator for the simulation of orbital maneuvers, with particular attention to Active Debris Removal (ADR) and On-Orbit Servicing (OOS). There are currently very few ways to reproduce microgravity in a non-orbital environment: among the main techniques, it is worth mentioning parabolic flights, pool simulations and robotic facilities. Parabolic flights allow to reproduce orbital conditions quite faithfully, but simulation conditions are very constraining. Pool simulations, on the other hand, have fewer constrictions in terms of cost, but the drag induced by the water negatively affects the simulated microgravity. Robotic facilities, finally, permit to reproduce indirectly (that is, with an appropriate control system) the physics of microgravity. State of the art on 3D robotic simulations is nowadays limited to industrial robots facilities, that bear conspicuous costs, both in terms of hardware and maintenance. This project proposes a viable alternative to these costly structures. Through dedicated algorithms, the system is able to compute in real time the consequences of these contacts in terms of trajectory modifications, which are then fed to the hardware in the loop (HIL) control system. Moreover, the governing software can be commanded to perform active maneuvers and relocations: as a consequence, the manipulator can be used as the testing bench not only for orbital servicing operations but also for attitude control systems, providing a faithful, real-time simulation of the zero-gravity behavior. Furthermore, with the aid of dynamic scaling laws, the potentialities of the facility can be exponentially increased: the simulation environment is not longer bounded to be as big as the robot workspace, but could be several orders of magnitude bigger, allowing for the reproduction of otherwise preposterous scenarios. The thesis describes the detailed mechanical design of the facility, corroborated by structural modeling, static and vibrational finite element verification. A strategy for the simulation of impedance-matched contacts is presented and an analytical control analysis defines the set of allowable inertial properties of the simulated entities. Focusing on the simulation scenarios, an innovative information theoretic approach for simultaneous localization and docking has been designed and applied for the first time to a 3D rendezvous scenario. Finally, in order to instrument the facility’s end effector with a consistent sensor suite, the design and manufacturing of an innovative Sun sensor is proposed.
Il crescente numero di oggetti umani nello spazio ha posto le basi per una nuova classe di missioni orbitali per l'assistenza e la manutenzione. L'obiettivo principale di questa tesi è lo sviluppo, la costruzione e la verifica sperimentale di un manipolatore robotico per la simulazione di manovre orbitali, con particolare attenzione alla rimozione di detriti (ADR) e la manutenzione in orbita (OOS). Allo stato dell'arte, sono poche le modalità utilizzate per la riproduzione della microgravità in un ambiente non-orbitale: fra le tecniche principali, vale la pena ricordare voli parabolici, simulazioni in piscina e simulatori robotici. I voli parabolici consentono di riprodurre le condizioni orbitali abbastanza fedelmente, ma le condizioni di simulazione sono pesantemente vincolanti. Le simulazioni in piscina, d'altra parte, hanno meno costrizioni in termini di costo, ma la resistenza indotta dall'acqua influisce negativamente sulla qualità della microgravità simulata. Gli impianti robotizzati, infine, permettono di riprodurre indirettamente (cioè attraverso un adeguato sistema di controllo) la fisica della microgravità. Lo stato dell'arte sulle simulazioni robotiche 3D è oggi limitato a robot industriali, caratterizzati da notevoli costi sia in termini di hardware che di manutenzione. Questo progetto propone un'alternativa a queste strutture: attraverso algoritmi dedicati, il sistema è in grado di calcolare in tempo reale le conseguenze dei contatti tramite le opportune modifiche alla traiettoria, che vengono poi fornite al sistema di controllo "hardware in the loop" (HIL). Inoltre, il software può essere comandato per eseguire manovre attive e di "relocation": di conseguenza, il manipolatore può essere utilizzato come test-bed non solo per operazioni di manutenzione orbitale, ma anche per sistemi di controllo di assetto, fornendo una fedele simulazione in tempo reale del rispettivo comportamento in assenza di gravità. La tesi descrive la progettazione meccanica dettagliata della struttura, corroborata dalla rispettiva modellazione strutturale, e dalla verifica agli elementi finiti delle prestazioni statiche e vibrazionali. Viene successivamente presentata una strategia per la simulazione di contatti tramite il matching tra le impedenze e un controllore dedicato definisce l'insieme delle proprietà inerziali simulabili tramite la struttura. Concentrandosi sugli scenari di simulazione, viene poi presentato un innovativo approccio SLAM (simultaneous localization and mapping) che utilizza metodi stocastici per il design di traiettorie di ispezione e riconoscimento markers applicato ad un task di rendez-vous 3D. Infine, con l'obiettivo di fornire una sensor-suite capace di stimare in real-time l'assetto dell'end-effector, viene descritto un innovativo sensore di Sole miniaturizzato. Ne vengono discusse la progettazione e la fabbricazione, corroborate dalle necessarie verifiche sperimentali.

This dissertation develops the visual pursuit method for air-to-air tracking and rendezvous of unmanned aircraft systems. It also shows the development of vector-field and proportional-integral methods for controlling UAS flight in formation with other aircraft. The visual pursuit method is a nonlinear guidance method that uses vision-based line of sight angles as inputs to the algorithm that produces pitch rate, bank angle and airspeed commands for the autopilot to use in aircraft control. The method is shown to be convergent about the center of the camera image frame and to be stable in the sense of Lyapunov. In the lateral direction, the guidance method is optimized to balance the pursuit heading with respect to the prevailing wind and the location of the target on the image plane to improve tracking performance in high winds and reduce bank angle effort. In both simulation and flight experimentation, visual pursuit is shown to be effective in providing flight guidance in strong winds. Visual pursuit is also shown to be effective in guiding the seeker while performing aerial docking with a towed aerial drogue. Flight trials demonstrated the ability to guide to within a few meters of the drogue. Further research developed a method to improve docking performance by artificially increasing the length of the line of sight vector at close range to the target to prevent flight control saturation. This improvement to visual pursuit was shown to be an effective method for providing guidance during aerial docking simulations. An analysis of the visual pursuit method is provided using the method of adjoints to evaluate the effects of airspeed, closing velocity, system time constant, sensor delay and target motion on docking performance. A method for predicting docking accuracy is developed and shown to be useful for predicting docking performance for small and large unmanned aircraft systems.

The prediction of a protein-ligand interaction when the interaction site is known is a relatively simple task. The greater challenge is to be able to predict both the mode and location of the interaction, preferably in the absence of any information other than the structures of the molecules themselves. A 'blind' docking approach, using an iterative genetic algorithm, challenged large areas of the target proteins in order to determine the mode and location of ligand interaction. Progressively complex systems were analysed commencing with small and large rigid ligands, followed by small flexible ligands and finally complex flexible ligands interacting with a viral capsid protein that lacked a classically defined binding site. Manual screening methods and a post-processing algorithm were developed for the examination of the output from flexible ligand docking simulations. A database of annotated three-dimensional structures was also produced in an effort to identify potential interaction sites. Both the mode and location of interactions involving rigid ligands were predicted with a high degree of confidence. Interactions involving flexible ligands were predicted with a confidence that was inversely proportional to ligand flexibility, to the extent that interaction sites were initially unidentifiable in the simulations examining greatest flexibility. Application of the post-processing algorithm identified flexible ligand binding sites with good correlation to experimentally determined results. Recent developments in automated docking procedures have lessened the impact of ligand flexibility when the intended binding site is known, but it becomes of paramount importance when attempting to determine the location of an interaction on a protein surface. Supplementary information will often be required to identify binding sites that are not classically defined by cavities or depressions on the protein surface. The development of a post-processing algorithm and an annotated structure database will help to identify these sites and allow for more focussed interaction prediction.

An autonomous mission manager is being developed for use on CubeSats to perform proximity operations with other vehicles. The mission manager software is designed to run in real-time on a microprocessor used on a CubeSat. A simulation tool was developed that provides orbital dynamics and sensor measurements to test the mission manager software. A scenario was developed to demonstrate the control of a spacecraft from 1 km to 1 m to a target vehicle. Two small satellites were simulated in near-circular orbits around Earth at an approximate 400 km altitude. Each satellite is incorporated with simulated sensors and a Kalman filter. The simulation tool includes models for accelerometers and Global Positioning System receivers. Noise corruption is added to the modeled sensors to simulate imperfect knowledge. The simulation environment is capable of modeling Earth as a spherical or non-spherical body with spherical gravitational harmonics. Simulation parameters, such as the vehicle's initial states, Earth gravity model, and sensor noise are easily changed without recompiling the program through a simulation input file.
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Automated spacecraft docking is a concept of operations with several important potential applications. One application that has received a great deal of attention recently is that of an automated docking capable unmanned re-supply spacecraft. In addition to being useful for re-supplying orbiting space stations, automated shuttles would also greatly facilitate the manned exploration of nearby space objects, including the Moon, near-Earth asteroids, or Mars. These vehicles would allow for longer duration human missions than otherwise possible and could even accelerate human colonization of other worlds. This thesis develops an optimal docking controller for an automated docking capable spacecraft. An innovative vision-based relative navigation system called VisNav is used to provide real-time relative position and orientation estimates, while a Kalman post-filter generates relative velocity and angular rate estimates from the VisNav output. The controller's performance robustness is evaluated in a closed-loop automated spacecraft docking simulation of a scenario in circular lunar orbit. The simulation uses realistic dynamical models of the two vehicles, both based on the European Automated Transfer Vehicle. A high-fidelity model of the VisNav sensor adds realism to the simulated relative navigation measurements. The docking controller's performance is evaluated in the presence of measurement noise, with the cases of sensor noise only, vehicle mass errors plus sensor noise, errors in vehicle moments of inertia plus sensor noise, initial starting position errors plus sensor noise, and initial relative attitude errors plus sensor noise each being considered. It was found that for the chosen cases and docking scenario, the final controller was robust to both types of mass property modeling errors, as well as both types of initial condition modeling errors, even in the presence of sensor noise. The VisNav system was found to perform satisfactorily in all test cases, with excellent estimate error convergence characteristics for the scenario considered. These results demonstrate preliminary feasibility of the presented docking system, including VisNav, for space-based automated docking applications.

Though the Aerospace industry is moving towards small satellites and smaller sensor technologies, sensors used for close-proximity operations are generally cost (and often size and power) prohibitive for University-class satellites. Given the need for low-cost, low-mass solutions for close-proximity relative navigation sensors, this research analyzed the expected errors due to near-field effects using a coarse sun sensor as part of a 6-degree-of-freedom (6-dof) solution. To characterize these near-field effects, a test bed (Characterization Test Apparatus or CTA) was proposed, its design presented, and the design stage uncertainty analysis of the CTA performed. A candidate coarse sun sensor (NorthStarTM) was chosen for testing, and a mathematical model of the sensor’s functionality was derived. Using a Gaussian Least Squares Differential Correction (GLSDC) algorithm, the model parameters were estimated and a comparison between simulated NorthStarTM measurements and model estimates was performed. Results indicate the CTA is capable of resolving the near-field errors. Additionally, this research found no apparent show stoppers for using coarse sun sensors for 6-dof solutions.