Dissertations / Theses on the topic 'On-orbit servicing'

Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2004.
Includes bibliographical references (p. 237-240).
Except for manned servicing operations using the Shuttle, there is no maintenance infrastructure for space systems. The traditional approach is to build in reliability and to replace the system in case of obsolescence or failure. Space systems therefore offer a limited degree of flexibility to adapt to evolving conditions during their long design lifetimes. On-orbit servicing could change this paradigm by providing a physical access to the satellite after it has been deployed. Satellite upgrade appears as a very promising application. On-orbit servicing could offer a broader range of upgrades than current improvements through communication uploads and would be a cheaper alternative to satellite replacement. The attractiveness of on-orbit servicing for satellite upgrade is investigated from a customer point of view. A dynamic framework, based on Real Options and Decision Tree Analysis, is used to account for the value of the flexibility offered by on-orbit servicing. Two case studies are developed: a power upgrade on-board a commercial geosynchronous communication satellite facing an uncertain demand and technology upgrades on a scientific observatory. The power upgrade of a geosynchronous communication satellite is assumed to restore beginning of life power. The model shows that modifying the initial design of the satellite to compensate for power degradation is often preferred to on-orbit servicing because it offers a cheaper and less risky alternative. On-orbit servicing does not appear attractive in this case because the upgrade has a limited effect on satellite capacity and power degradation is a predictable phenomenon that can be partly overcome by design modifications.
(cont.) Using the unique example of the Hubble Space Telescope servicing missions, the upgrade of the payload instruments and the bus subsystems on-board a scientific observatory is modelled. It is shown that satellite upgrades can significantly increase the utility of the mission, in particular if technology is evolving rapidly. It can be concluded from these two case studies that on-orbit servicing is viable and attractive if the increase in utility due to the upgrade is sufficiently large and if there is no other alternative that can offer a similar increase in utility at a lower cost or lower risk. Potential policy barriers to the acceptance of on-orbit servicing are identified and candidate policies are proposed to promote and enable the development of an on-orbit servicing infrastructure. A government intervention is likely to be necessary to overcome the risk averseness of the space industry and the "chicken and egg" problem arising from the necessity of designing the satellite for serviceability.
by Carole Joppin.
S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.
"June 2005."
Includes bibliographical references (195-197).
The question that this thesis examines is whether traditional monolithic satellite designs have limited the value that the satellite market generates for the space industry. To answer this question, this thesis focuses on the "Value" that satellites generate. By examining the value that satellites offer their operators, this thesis determines if alternative methods of satellite design offer greater value than traditional satellite designs. One alternative method that is examined is on-orbit satellite servicing. On a basic level, on-orbit satellite servicing is the process of providing services to a satellite in orbit, such as: relocation, refueling, repairs, or upgrades. The purpose of this thesis is to describe and support a framework for determining the value of on-orbit satellite servicing. The framework involves examining on-orbit servicing as a competitive market and dividing that market into two sides -the customer and the provider. By examining the customer side of on-orbit servicing, this thesis identifies the reasons a customer would require servicing and thus determines the value that can be delivered to the customer. By determining the point where the value of servicing is zero, the customer's maximum servicing price can be computed.
(cont.) By examining the provider's side of the market, this thesis identifies the different forms of servicing that can fulfill the customer's needs. Based on a provider's forms of servicing, the provider's minimum servicing price can be determined. Finally, by overlaying the maximum servicing price with the minimum servicing price, one can determine if a feasible on-orbit servicing market exists. If any overlap exists, then a feasible range of servicing prices exists and servicing makes sense.Simply put, an overlap represents the case where a customer need exists and a provider has the ability to meet that need - hence a servicing market exists. This thesis concludes with a discussion concerning the development of on-orbit satellite servicing and how this development is not limited solely by economic and technical issues. It is the purpose of this thesis to show that on-orbit satellite servicing provides a means for escape from the traditional approach of satellite design. thereby allowing a paradigm shift towards more valuable design approaches. While some may believe that on-orbit satellite servicing provides a means to sustain current technology trends, it is argued that on-orbit satellite servicing is a disruptive technology.
(cont.) With disruptive technologies come the opportunities for greater value and dramatic change. On-orbit satellite servicing provides the opportunity for a paradigm shift in satellite design that can lead to dramatic new ideas, uses, and valuations of space.
by Andrew Michael Long.
S.M.

Access to space is becoming less expensive, which is allowing smaller companies with big ideas, such as on-orbit servicing and repair, to enter into the space industry. On-orbit servicing and repair provides capabilities, such as towing, refueling, inspections, and physical repair, to add additional life to on-orbit satellites by resolving life-limiting issues. On-orbit servicing and repair is technically possible, but there is still one major issue that continues to stifle the on-orbit servicing and repair market -- “satellites are not built with servicing in mind” (Parker, 2015).The on-orbit servicing and repair industry is stagnate due to a challenging conundrum. Potential satellite customers are unwilling to pay for on-orbit servicing or repair until the capability is successfully demonstrated on-orbit. Unfortunately, it is difficult for the industry to prove the capability without customers willing to take a little risk. This “chicken and egg” scenario leaves several satellite manufacturers unwilling to change their satellite architectures and designs to accommodate on-orbit servicing and repair. This paper attempts to show the “how” and the “why” the space industry should change their architectures and designs to enable on-orbit servicing and repair.There are many satellite bus components/consumables, including software, that could fail and shorten a satellite’s life. However, the bus components/consumables that fail the most, batteries, solar arrays, propellant, reaction wheels, and power distribution components, are best suited for on-orbit servicing and repair. These five bus components/consumables, in addition to the satellite as a whole, will require several design changes specific to each bus component, which will drive new or updated requirements for each. Additionally, to increase the effectiveness and efficiency of on-orbit servicing and repair, satellite architectures will require changes, such as an on-orbit depot, on-orbit warehouse, and on-orbit gas tank.The consequence of changing satellite design will affect satellite ground testing. The on-orbit servicing and repair processes, such as rendezvous, docking, and EMI/EMC will require testing between the on-orbit servicer and its customer satellite. The on-orbit servicing and repair capability provides the satellite manufacturer the ability to reduce qualification testing, run-time testing, and burn-in testing. This capability increases the probability that redundancy for these five bus components/consumables is no longer required, which reduces the hardware cost and testing schedule for each satellite. On-orbit servicing and repair creates seven new risks -- do no harm, debris and contamination, on-orbit servicer reliability, politics, cyber security, liability, and unintended consequences -- that must be mitigated.Two simple business cases demonstrate the possible value of this new capability. The business case for Low Earth Orbit (LEO) does not provide a return on investment, because on-orbit servicing and repair in LEO is too difficult and too expensive to justify an investment. On the other hand, the business case for Geosynchronous Orbit (GEO), in two distinct scenarios, does provide a return on investment. Those two scenarios are a beginning of life anomaly, and an extension of life.

Thesis: S.M., 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 153-157).
The development of robust and routine execution of autonomous space-based proximity operations is a critical need for the future of space exploration and space-based business enterprise. One application of this host of activities, which includes rendezvous, capture, and docking, is on-orbit assembly and servicing of spacecraft. It is believed that the maturation of this technology could usher in a new era of space technology featuring modular construction of large spacecraft or habitats for exploration and tourism, assembly of large-aperture space telescopes unconstrained by launch vehicle size, and reconfigurable structures for mission adaptability. Furthermore, this technology could extend to capture and repair high asset spacecraft by replacing modular components, all without the need to risk human lives. This thesis seeks to contribute to the development of this technology by focusing on one of its most critical aspects: robust state estimation between the autonomous agents. Several estimation frameworks exist that can be applied. However, two state estimators were specifically chosen, implemented, verified, and validated for reasons discussed in the text. First, a practical method of implementation of an Unscented Kalman Filter for two active, cooperative, autonomously docking satellites that overcomes latency issues from low frequency vision-based relative-pose measurements is presented. Second, a factor graph based incremental smoothing estimator for the same application is implemented, which can be shown to provide robustness to several failures characteristic of the filtering framework. A detailed analysis enumerating the strengths and weaknesses of the two frameworks is provided, as well as the verification and validation of the two estimators via the SPHERES testbed from both a 3-DOF planar air bearing facility and the playback of data sets collected from the International Space Station 6-DOF test environment.
by William D. Sanchez.
S.M.

This dissertation addresses the design procedure of a docking mechanism for space applications, in particular, on-orbit servicing of cooperative satellites. The mechanism was conceived to comply with the technical specifications of the STRONG mission. The objective of this mission is to deploy satellite platforms using a space tug with electric propulsion. This mission is part of the SAPERE project, which focuses on space exploration and access to space. A docking mechanism is used for recovering the misalignments left by the guidance, navigation, and control system of the servicer satellite when approaching the customer spacecraft. However, most importantly, the mechanism must safely dissipate the energy associated with the relative velocities between the spacecraft upon contact. Five concepts were considered as possible candidates for the docking mechanism: a system based on the Stewart-Gough platform with a position controller, a Stewart-Gough platform with impedance control, a central passive mechanism (probe-drogue), a central active mechanism, and a mechanism equipped with articulated arms. Several trade-off criteria were defined and applied to the concepts. The result of this trade study was the selection of the central passive mechanism as the most balanced solution. This mechanism is composed of a probe and a conical frustum equipped with a socket to capture the probe. It was further developed and tested using mathematical models of the docking maneuver. The results of the simulations showed that the passiveness of the system prevented the docking maneuver from being fully accomplished. Consequently, a second design iteration was performed. In this new iteration, the degrees of freedom of the mechanism were increased by adding two controlled linear axes in series with the degrees of freedom of the preliminary design. The electromechanical actuators and transmissions of this mechanism were selected following the guidelines of The ECSS standards. Also, in this case, numerical models were used to assess the functioning of the docking system. The results produced by these models demonstrated the suitability of the mechanism for completing the docking operation defined by the mission’s specifications. Furthermore, the results also showed the architecture and functioning of the mechanism to be possibly suitable for other cooperative docking operations between small and mid-sized satellites. In addition, the definition of the mechanical details as well as the control architecture led to the complete design of an engineering prototype for laboratory tests. In this regard, the laboratory tests were defined with the scope of verifying the different operating modes of the docking mechanism. The test rig was designed to be equipped with a serial manipulator connected to the female part of the mechanism through a force and torque module. The objective will be to simulate the relative motion between the docking halves using different techniques to generate the trajectory of the manipulator.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.
Includes bibliographical references (p. 115-118).
Reconfiguration is an important characteristic in furthering on-orbit servicing, assembly, and operations. Previous work has focused on large assemblers manipulating small payloads, where the dynamics of the assembler is not significantly changed. This work seeks to identify the impact of reconfiguration on maneuver performance. Reconfiguration is considered in two categories: implementation and application. Implementation of reconfiguration consisted of developing a method for defining and updating a configuration, implementation on the SPHERES testbed, and execution of tests (in simulation and on the International Space Station) to assess the control performance improvement after reconfiguration. Four applications were considered in this work, two hardware applications and two systems applications modeled through simulation. The objective of the SWARM application was to demonstrate autonomous assembly capability through docking and undocking maneuvers. The objective of the SIFFT application was to demonstrate formation reconfiguration capability, through the expansion and rotation of an equilateral triangle of three satellites. The objective of the systems applications was to determine the impact of re-configuration in a larger mission context.
(cont.) One application, Mass Property Update, considered how the choice of method for obtaining the mass property information impacts operations. The other application, Modularity Analysis, considered how the implementation of modularity is driven by the mission objectives. Overall, this work has served to demonstrate the control impact of reconfiguration though implementation on the SPHERES testbed. This implementation was used on two hardware applications to determine the performance of reconfiguration for assembly and formation reconfiguration missions. Also, the impact of reconfiguration has been studied in the broader systems context. The choice of method of mass property update was demonstrated to have an impact on operations, in terms of reliability and mass. Finally, the method incorporation of modularity for purposes of on-orbit servicing and assembly was demonstrated to be driven by mission design parameters.
by Swati Mohan.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, June, 2002.
Includes bibliographical references (leaves 203-214).
A roadmap for a comprehensive treatment of issues of flexibility in system design is developed that addresses the following questions: 1) What are the characteristic features of flexibility in system design? Can one clearly and unambiguously characterize flexibility, and disentangle it from closely related concepts? 2) What drives the need for flexibility in system design, and what are the attributes of an environment in which flexible designs should be sought and fielded? 3) How can one embed flexibility in a system design? 4) What are the trade-offs associated with designing for flexibility? What is the value of flexibility and what are the associated penalties (cost, performance, risk, etc.), if any? These are the fundamental questions around which this thesis revolves. The first part of this work addresses the first two questions: Flexibility of a design is here defined as the property of a system that allows it to respond to changes in its initial objectives and requirements-both in terms of capabilities and attributes-occurring after the system has been fielded, i.e., is in operation, in a timely and cost-effective way. It is argued that flexibility should be sought when: 1) the uncertainty in a system's environment is such that there is a need to mitigate market risks, in the case of a commercial venture, and reduce a design's exposure to uncertainty in its environment, 2) the system's technology base evolves on a time scale considerably shorter than the system's design lifetime, thus requiring a solution for mitigating risks associated with technology obsolescence.
(cont.) In other words, flexibility reduces a design's exposure to uncertainty, and provides a solution for mitigating market risks as well as risks associated with technology obsolescence. One way flexibility manifests its criticality to systems architects is in the specification of the system design lifetime requirement. The second part of this work addresses issues of design lifetime, and ways to provide and value flexibility in the particular case of space systems. First, it is shown that design lifetime is a key requirement in sizing various spacecraft subsystems. Second, spacecraft cost profiles as a function of the design lifetime are established and a cost per operational day metric is introduced. It is found that a cost penalty of 30% to 40% is incurred when designing a spacecraft for fifteen years instead of three years, all else being equal. Also, the cost per operational day decreases monotonically as a function of the spacecraft design lifetime. An augmented perspective on system architecture is proposed (diachronic) that complements traditional views on system architecture (synchronic). It is suggested for example that the system's design lifetime is a fundamental component of system architecture although one cannot see it or touch it. Consequently, cost, utility, and value per unit time metrics are introduced and explored in order to identify optimal design lifetimes for complex systems in general, and space systems in particular. Results show that an optimal design lifetime for space systems exists, even in the case of constant expected revenues per day over the system's lifetime ...
by Joseph Homer Saleh.
Ph.D.

L’objectif de cette thèse est de proposer une solution complète basée sur la vision pour permettre la navigation autonome d’un vaisseau de poursuite (S/C) lors d’opérations de proximité dans l’espace de rendez-vous (RDV) avec une cible non coopérative en utilisant une caméra monoculaire visible.Le rendez-vous autonome est une capacité clé pour répondre aux principaux défis de l’ingénierie spatiale, tels que l’enlèvement actif des débris (ADR) et l’entretien en orbite(OOS). L’ADR vise à éliminer les débris spatiaux, dans les régions protégées en orbite basse, qui sont les plus susceptibles d’entraîner des collisions futures et d’alimenter le syndrome de Kessler, augmentant ainsi le risque pour les engins spatiaux opérationnels.L’OOS comprend des services d’inspection, d’entretien, de réparation, d’assemblage, de ravitaillement et de prolongation de la durée de vie des satellites ou structures en orbite.Lors d’un RDV autonome avec une cible non coopérative, c’est-`a-dire une cible qui n’aide pas / n’interagit pas le chasseur dans les opérations d’acquisition, de poursuite et de rendez-vous, le chasseur doit estimer l’état de la cible `a bord de manière autonome.Les opérations de rendez-vous autonomes nécessitent des mesures précises et actualisées de la pose relative (c’est-à-dire la position et l’attitude de la cible), et la combinaison de capteurs de caméra avec des algorithmes de poursuite peut constituer une solution rentable.La recherche a été divisée en trois études principales : le développement d’un algorithme permettant l’acquisition de la pose initiale (c’est-à-dire la détermination de la pose sans aucune connaissance préalable de cette pose aux instants précédents), le développement d’un algorithme de poursuite récursif (c’est-à-dire d’un algorithme qui exploite les informations sur l’état de la cible à l’instant précédent pour calculer la mise à jour de la pose à l’instant actuel), et le développement d’un filtre de navigation intégrant les mesures provenant de différents capteurs et/ou algorithmes, avec différents taux et délais.En ce qui concerne la phase d’acquisition de la pose, un nouvel algorithme de détection a été développé pour permettre une initialisation rapide de la pose. Une approche est proposée pour récupérer entièrement la pose de la cible en utilisant un ensemble d’invariants et de moments géométriques (c’est-à-dire des caractéristiques globales) calculés à partir des images de la silhouette de la cible. Les caractéristiques globales synthétisent le contenu de l’image dans un vecteur de quelques descripteurs qui changent de valeurs en fonction de la pose relative de la cible. Une base de données des caractéristiques globales est pré-calculée hors ligne en utilisant le modèle géométrique de la cible afin de couvrir tout l’espace de la solution. Au moment de l’exécution, les caractéristiques globales sont calculées sur l’image actuelle acquise et comparées avec la base de données. Différents ensembles de caractéristiques globales ont été comparés afin de sélectionner les plus performants,ce qui a permis d’obtenir un algorithme de détection robuste avec une faible charge de calcul
The aim of this thesis is to propose a full vision-based solution to enable autonomousnavigation of a chaser spacecraft (S/C) during close-proximity operations in space rendezvous(RDV) with a non-cooperative target using a visible monocular camera.Autonomous rendezvous is a key capability to answer main challenges in space engineering,such as Active Debris Removal (ADR) and On-Orbit-Servicing (OOS). ADR aimsat removing the space debris, in low-Earth-orbit protected region, that are more likelyto lead to future collision and feed the Kessler syndrome, thus increasing the risk foroperative spacecrafts. OOS includes inspection, maintenance, repair, assembly, refuelingand life extension services to orbiting S/C or structures. During an autonomous RDVwith a non-cooperative target, i.e., a target that does not assist the chaser in acquisition,tracking and rendezvous operations, the chaser must estimate the target’s state on-boardautonomously. Autonomous RDV operations require accurate, up-to-date measurementsof the relative pose (i.e., position and attitude) of the target, and the combination ofcamera sensors with tracking algorithms can provide a cost effective solution.The research has been divided into three main studies: the development of an algorithmenabling the initial pose acquisition (i.e., the determination of the pose without any priorknowledge of the pose of the target at the previous instants), the development of a recursivetracking algorithm (i.e., an algorithm which exploits the information about thestate of the target at the previous instant to compute the pose update at the currentinstant), and the development of a navigation filter integrating the measurements comingfrom different sensor and/or algorithms, with different rates and delays.For what concerns the pose acquisition phase, a novel detection algorithm has been developedto enable fast pose initialization. An approach is proposed to fully retrieve theobject’s pose using a set of invariants and geometric moments (i.e., global features) computedusing the silhouette images of the target. Global features synthesize the content ofthe image in a vector of few descriptors which change values as a function of the targetrelative pose. A database of global features is pre-computed offline using the target geometricalmodel in order to cover all the solution space. At run-time, global features arecomputed on the current acquired image and compared with the database. Different setsof global features have been compared in order to select the more performing, resultingin a robust detection algorithm having a low computational load.Once an initial estimate of the pose is acquired, a recursive tracking algorithm is initialized.The algorithm relies on the detection and matching of the observed silhouettecontours with the 3D geometric model of the target, which is projected into the imageframe using the estimated pose at the previous instant. Then, the summation of the distances between each projected model points and the matched image points is written as a non-linear function of the unknown pose parameters. The minimization of this costfunction enables the estimation of the pose at the current instant. This algorithm providesfast and very accurate measurements of the relative pose of the target. However,as other recursive trackers, it is prone to divergence. Thus, the detection algorithm isrun in parallel to the tacker in order to provide corrected measurements in case of trackerdivergences. The measurements are then integrated into the chaser navigation filter to provide anoptimal and robust estimate. Vision-based navigation algorithms provide only pose measurements

With the alarming proliferation in the population of orbital debris, scientific analysis has indicated a need to perform space debris remediation through active removal of debris and on-orbit satellite servicing. This thesis aims to study the implications of the existing framework of international space law and public international law on space debris remediation. Following a description of the hypothesis and the research methodology, the introductory chapter explains the current state of the debris environment and the consequent need to perform space debris remediation. With that understanding, the economic and technological feasibility for such an endeavour is also assessed. The second chapter addresses the concerns regarding the current definition of a 'space object' and examines the requirement for the adoption of a separate legal definition of space debris to facilitate space debris remediation activities. The key question of legitimate exercise of jurisdiction and control over space objects, in the realm of space debris remediation, along with contentious issues such as transfer of ownership and/or registry of space objects are discussed in the third chapter. The fourth chapter elaborates on the related responsibility and liability considerations linked to remediation activities in outer space. The final chapter contains a summary of the important conclusions from the earlier chapters and presents some overall observations on the entire analysis.
Avec la prolifération alarmante du nombre de débris orbitaux, des études scientifiques ont montré la nécessité d'effectuer un nettoyage des débris spatiaux, par le biais de la suppression effective de ces débris ainsi que la mise en place d'un système orbital de « service » aux satellites. Cette thèse vise à étudier les effets du cadre actuel du droit spatial international et du droit international public, sur la gestion du problème des débris spatiaux. Après une description du postulat et de la méthodologie de recherche, le chapitre introductif (chapitre I) explique l'état actuel de l'environnement des débris spatiaux et la nécessité d'éliminer ces débris. Dans ce contexte, la faisabilité économique et technique d'une telle entreprise est évaluée au chapitre II. Le chapitre III traite des questions liées à la définition actuelle d'«objet spatial» et examine les conditions de l'adoption d'une définition juridique distincte pour les débris spatiaux, afin de faciliter les activités de nettoyage afférentes. La question essentielle de l'exercice légitime de la juridiction et du contrôle des objets spatiaux, s'agissant de leur nettoyage, ainsi que les sujets controversés tels que le transfert de propriété et/ou l'enregistrement des objets spatiaux, sont examinés dans le chapitre IV. Le chapitre V entre dans le détail des réflexions sur la responsabilité liée aux activités de dépollution dans l'espace. La section finale (chapitre VI) comprend un résumé des conclusions importantes des chapitres précédents, et présente quelques observations générales sur toute l'analyse.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 175-181).
The Hubble Space Telescope has demonstrated that on-orbit servicing can provide significant benefits for scientific space programs. Specifically, servicing missions can replace failed components to keep spacecraft operational, and can upgrade onboard components to improve spacecraft performance. Hubble was able to capture these benefits because it was designed to be serviceable; however, many other programs have excluded serviceability from the design due to cost considerations. Often, the value of serviceability cannot be quantitatively justified. This thesis develops a framework to determine the value of including serviceability in a space telescope. Various principles to evaluate serviceability are proposed throughout the literature, and this thesis incorporates three main principles to construct the framework. First, the costs and benefits of servicing are separated so that the "cost" of servicing is expressed as the maximum price the customer is willing to pay. Second, the value of serviceability will be determined by comparing a telescope servicing program to a telescope replacement program. Third, the value of flexibility provided by servicing is analyzed by a Monte-Carlo simulation and decision rule analysis. A case study was performed to demonstrate how the framework is used, using representative data from Hubble. For a simple space telescope, the case study calculated the increase in science return gained by servicing and the maximum price for servicing missions. The case study illustrated an important trade between science return and risk of telescope downtime. Finally, the principles and techniques used in this framework are more generally applicable to non-revenue generating spacecraft.
by Mark Baldesarra.
S.M.

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.

La complexité des missions spatiales a augmenté de façon exponentielle, avec des exigences croissantes en matière de performance, de précision et de robustesse. Cette évolution est due à la fois aux progrès technologiques et à la nécessité de satisfaire de nouveaux défis, tels que les satellites en rotation (spinnés), l'assemblage en orbite et le service en orbite. Ces missions nécessitent l'intégration de systèmes mécaniques complexes, notamment des réservoirs de carburant liquide et ballotant, des systèmes de pointage précis et des structures flexibles qui présentent généralement des modes à basse fréquence, proches en fréquence et peu amortis. À mesure que les engins spatiaux deviennent plus modulaires avec plusieurs composants interconnectés tels que les antennes et les charges utiles, il est essentiel de modéliser et de contrôler avec précision ces systèmes multicorps complexes. Les interactions entre les structures flexibles et les systèmes de contrôle peuvent avoir un impact significatif sur les tâches critiques telles que le contrôle de l'attitude et la précision du pointage. Il est donc essentiel de prendre en compte les dynamiques couplées et les perturbations externes pour garantir le succès de la mission.Afin de résoudre ces problèmes, cette thèse présente une approche unifiée de la modélisation et du contrôle des systèmes multicorps flexibles dans les missions spatiales. Elle utilise des modèles de représentation fractionnaire linéaire (LFR) pour capturer efficacement la dynamique complexe et les incertitudes inhérentes à ces scénarios. La recherche commence par la dérivation d'un modèle LFR pour une poutre extsc{Euler}- extsc{Bernoulli} flexible et en rotation, prenant en compte les forces centrifuges et leur dépendance par rapport à la vitesse angulaire. Ce modèle à six degrés de liberté (DOFs) intègre les dynamiques de flexion, de traction et de torsion et est conçu pour être compatible avec l'approche des ports à deux entrées et deux sorties (TITOP), permettant de modéliser des systèmes multicorps complexes. Ce manuscrit présente également un modèle multicorps pour un scénario de mission de vaisseau spatial en rotation, suivi de la conception d'un système de contrôle.La thèse étend l'application des modèles LFR à une mission de service en orbite, en se concentrant sur le contrôle robuste de la dynamique d'attitude malgré les incertitudes et les paramètres variables du système. Une nouvelle approche de modélisation pour le mécanisme d'amarrage est introduite pour prendre en compte les propriétés dynamiques de rigidité et d'amortissement de la chaîne cinématique en boucle fermée formée par le véhicule chasseur et le véhicule cible. Un système de contrôle par rétroaction assurant une stabilité et des performances robustes pendant toutes les phases de la mission est proposé et validé par une analyse structurée des valeurs singulières.A partir de ces éléments, la thèse développe finalement une méthodologie complète pour la modélisation d'une mission d'assemblage en orbite impliquant un robot à bras multiples construisant une grande structure flexible. Ce travail aborde également la dynamique de couplage entre le robot et la structure évolutive tout en considérant les changements significatifs d'inertie et de flexibilité au cours du processus d'assemblage. Un algorithme d'optimisation de planification de tâches est finalement proposé pour assurer des opérations robotiques stables et efficaces, mettant en évidence l'efficacité de l'approche de modélisation basée sur la représentation LFR
Space missions have grown exponentially in complexity, with increasing demands for performance, precision and robustness. This evolution is driven by both technological advancements and the need for spacecraft to support diverse mission objectives, such as spinning spacecraft, on-orbit assembly and on-orbit servicing. These missions require the integration of large and complex designs, including dynamic fuel tanks, precise pointing systems and flexible structures that typically exhibit low-frequency, closely spaced and poorly damped modes. As spacecraft become more modular with multiple interconnected components like antennas and payloads, accurately modeling and controlling these complex multibody systems is crucial. The interactions between flexible structures and control systems can significantly impact mission-critical tasks such as attitude control and pointing accuracy, making it essential to address the coupled dynamics and external disturbances to ensure successful mission outcomes.In order to tackle these problems, this thesis presents a unified approach to the modeling and control of flexible multibody systems in space missions. It utilizes linear fractional representation (LFR) models to effectively capture the complex dynamics and uncertainties inherent in these scenarios. The research begins with the derivation of an LFR model for a flexible and spinning extsc{Euler}- extsc{Bernoulli} beam, fully accounting for centrifugal forces and their dependence on the angular velocity. This six degrees of freedom model integrates bending, traction and torsion dynamics and is designed to be compatible with the Two-Input-Two-Output Ports (TITOP) approach, enabling the modeling of complex multibody systems. This manuscript also introduces a multibody model for a spinning spacecraft mission scenario, followed by the design of a control system.The thesis further extends the application of LFR models to an on-orbit servicing mission, focusing on the robust control of attitude dynamics despite uncertainties and varying system parameters. A novel modeling approach for a docking mechanism is introduced, capturing the dynamic stiffness and damping properties of the closed-loop kinematic chain formed by the chaser and target spacecraft. The design of a feedback control system ensuring robust stability and performance across all mission phases is proposed, validated through structured singular value analysis.Building on this foundation, the thesis finally develops a comprehensive methodology for modeling an on-orbit assembly mission involving a multi-arm robot constructing a large flexible structure. This work also addresses the coupling dynamics between the robot and the evolving structure while considering significant changes in inertia and flexibility during the assembly process. A path optimization algorithm is ultimately proposed to ensure stable and efficient robotic operations, highlighting the effectiveness of the LFR-based modeling approach

Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Panagiotis Tsiotras; Committee Member: Eric Feron; Committee Member: Joseph Saleh; Committee Member: Ryan Russell; Committee Member: William Cook

This thesis addresses visual tracking of a non-cooperative as well as a partially cooperative satellite, to enable close-range rendezvous between a servicer and a target satellite. Visual tracking and estimation of relative motion between a servicer and a target satellite are critical abilities for rendezvous and proximity operation such as repairing and deorbiting. For this purpose, Lidar has been widely employed in cooperative rendezvous and docking missions. Despite its robustness to harsh space illumination, Lidar has high weight and rotating parts and consumes more power, thus undermines the stringent requirements of a satellite design. On the other hand, inexpensive on-board cameras can provide an effective solution, working at a wide range of distances. However, conditions of space lighting are particularly challenging for image based tracking algorithms, because of the direct sunlight exposure, and due to the glossy surface of the satellite that creates strong reflection and image saturation, which leads to difficulties in tracking procedures. In order to address these difficulties, the relevant literature is examined in the fields of computer vision, and satellite rendezvous and docking. Two classes of problems are identified and relevant solutions, implemented on a standard computer are provided. Firstly, in the absence of a geometric model of the satellite, the thesis presents a robust feature-based method with prediction capability in case of insufficient features, relying on a point-wise motion model. Secondly, we employ a robust model-based hierarchical position localization method to handle change of image features along a range of distances, and localize an attitude-controlled (partially cooperative) satellite. Moreover, the thesis presents a pose tracking method addressing ambiguities in edge-matching, and a pose detection algorithm based on appearance model learning. For the validation of the methods, real camera images and ground truth data, generated with a laboratory tet bed similar to space conditions are used. The experimental results indicate that camera based methods provide robust and accurate tracking for the approach of malfunctioning satellites in spite of the difficulties associated with specularities and direct sunlight. Also exceptional lighting conditions associated to the sun angle are discussed, aimed at achieving fully reliable localization system in a certain mission.

Multi-body systems (MSs) are assemblies composed of multiple bodies (either rigid or structurally flexible) connected among each other by means of mechanical joints. In many engineering fields (such as aerospace, aeronautics, robotics, machinery, military weapons and bio-mechanics) a large number of systems (e.g. space robots, aircraft, terrestrial vehicles, industrial machinery, launching systems) can be included in this category. The dynamic characteristics and performance of such complex systems need to be accurately and rapidly analyzed and predicted. Taking this engineering background into consideration, a new branch of study, named as Multi-body Systems Dynamics (MSD), emerged in the 1960s and has become an important research and development area in modern mechanics; it mainly addresses the theoretical modeling, numerical analysis, design optimization and control for complex MSs. The research on dynamics modeling and numerical solving techniques for rigid multi-body systems has relatively matured and perfected through the developments over the past half century. However, for many engineering problems, the rigid multi-body system model cannot meet the requirements in terms of precision. It is then necessary to consider the coupling between the large rigid motions of the MS components and their elastic displacements; thus the study of the dynamics of flexible MSs has gained increasing relevance. The flexible MSD involves many theories and methods, such as continuum mechanics, computational mechanics and nonlinear dynamics, thus implying a higher requirement on the theoretical basis. Robotic on-orbit operations for servicing, repairing or de-orbiting existing satellites are among space mission concepts expected to have a relevant role in a close future. In particular, many studies have been focused on removing significant debris objects from their orbit. While mission designs involving tethers, nets, harpoons or glues are among options studied and analyzed by the scientific and industrial community, the debris removal by means of robotic manipulators seems to be the solution with the longest space experience. In fact, robotic manipulators are now a well-established technology in space applications as they are routinely used for handling and assembling large space modules and for reducing human extravehicular activities on the International Space Station. The operations are generally performed in a tele-operated approach, where the slow motion of the robotic manipulator is controlled by specialized operators on board of the space station or at the ground control center. Grasped objects are usually cooperative, meaning they are capable to re-orient themselves or have appropriate mechanisms for engagement with the end-effectors of the manipulator (i.e. its terminal parts). On the other hand, debris removal missions would target objects which are often non-controlled and lacking specific hooking points. Moreover, there would be a distinctive advantage in terms of cost and reliability to conduct this type of mission profile in a fully autonomous manner, as issues like obstacle avoidance could be more easily managed locally than from a far away control center. Space Manipulator Systems (SMSs) are satellites made of a base platform equipped with one or more robotic arms. A SMS is a floating system because its base is not fixed to the ground like in terrestrial manipulators; therefore, the motion of the robotic arms affects the attitude and position of the base platform and vice versa. This reciprocal influence is denoted as "dynamic coupling" and makes the dynamics modeling and motion planning of a space robot much more complicated than those of fixed-base manipulators. Indeed, SMSs are complex systems whose dynamics modeling requires appropriate theoretical and mathematical tools. The growing importance SMSs are acquiring is due to their operational ductility as they are able to perform complicated tasks such as repairing, refueling, re-orbiting spacecraft, assembling articulated space structures and cleaning up the increasing amount of space debris. SMSs have also been employed in several rendezvous and docking missions. They have also been the object of many studies which verified the possibility to extend the operational life of commercial and scientific satellites by using an automated servicing spacecraft dedicated to repair, refuel and/or manage their failures (e.g. DARPA's Orbital Express and JAXA's ETS VII). Furthermore, Active Debris Removal (ADR) via robotic systems is one of the main concerns governments and space agencies have been facing in the last years. As a result, the grasping and post-grasping operations on non-cooperative objects are still open research areas facing many technical challenges: the target object identification by means of passive or active optical techniques, the estimation of its kinematic state, the design of dexterous robotic manipulators and end-effectors, the multi-body dynamics analysis, the selection of approaching and grasping maneuvers and the post-grasping mission planning are the main open research challenges in this field. The missions involving the use of SMSs are usually characterized by the following typical phases: 1. Orbital approach; 2. Rendez-vous; 3. Robotic arm(s) deployment; 4. Pre-grasping; 5. Grasping and post-grasping operations. This thesis project will focus on the last three. The manuscript is structured as follows: Chapter 1 presents the derivation of a multi-body system dynamics equations further developing them to reach their Kane's formulation; Chapter 2 investigates two different approaches (Particle Swarm Optimization and Machine Learning) dealing with a space manipulator deployment maneuver; Chapter 3 addresses the design of a combined Impedance+PD controller capable of accomplishing the pre-grasping phase goals and Chapter 4 is dedicated to the dynamic modeling of the closed-loop kinematic chain formed by the manipulator and the grasped target object and to the synthesis of a Jacobian Transpose+PD controller for a post-grasping docking maneuver. Finally, the concluding remarks summarize the overall thesis contribution.

Spacecraft (S/C) docking is the last and most challenging phase in the contact closure of two separately flying S/C. The design and testing of S/C docking missions using software-multibody simulations need to be complemented by Hardware-In-The-Loop (HIL) simulation using the real docking hardware. The docking software multibody simulation is challenged by the proper modeling of contact forces, whereas the HIL docking simulation is challenged by proper inclusion of the real contact forces. Existing docking HIL simulators ignore back-reaction force modeling due to the large S/C sizes, or use compliance devices to reduce impact, which alters the actual contact force. This dissertation aims to design a docking HIL testbed to verify docking contact dynamics for small and rigid satellites by simulating the real contact forces without artificial compliance. HIL simulations of docking contact dynamics are challenged mainly by: I. HIL simulation quality: quality of realistic contact dynamics simulation relies fundamentally on the quality of HIL testbed actuation and sensing instrumentation (non-instantaneous, time delays, see Fig. 1) II. HIL testbed design: HIL design optimization requires a justified HIL performance prediction, based on a representative HIL testbed simulation (Fig. 2), where appropriate simulation of contact dynamics is the most difficult and sophisticated task. The goal of this dissertation is to carry out a systematic investigation of the technically possible HIL docking contact dynamics simulation performances, in order to define an appropriate approach for testing of docking contact dynamics of small and rigid satellites without compliance and using HIL simulation. In addition, based on the investigations, the software simulation results shall be validated using an experimental HIL setup. To achieve that, multibody dynamics models of docking S/C were built, after carrying out an extensive contact dynamics research to select the most representative contact model. Furthermore, performance analysis models of the HIL testbed were built. In the dissertation, a detailed parametric analysis was carried out on the available models’ design-spaces (e.g., spacecraft, HIL testbed building-blocks and contact dynamics), to study their impacts on the HIL fidelity and errors (see Fig. 1). This was done using a generic HIL design-tool, which was developed within this work. The results were then used to identify the technical requirements of an experimental 1-Degree-of-Freedom (DOF) HIL testbed, which was conceived, designed, implemented and finally utilized to test and validate the selected docking contact dynamics model. The results of this work showed that the generic multibody-dynamics spacecraft docking model is a practical tool to model, study and analyze docking missions, to identify the properties of successful and failed docking scenarios before it takes place in space. Likewise, the 'Generic HIL Testbed Framework Analysis Tool' is an effective tool for carrying out performance analysis of HIL testbed design, which allows to estimate the testbed’s fidelity and predict HIL errors. Moreover, the results showed that in order to build a 6DOF HIL docking testbed without compliance, it is important to study and analyze the errors’s sources in an impact and compensate for them. Otherwise, the required figure-of-merits of the instruments of the HIL testbed would be extremely challenging to be realized. In addition, the results of the experimental HIL simulation (i.e., real impacts between various specimen) serve as a useful contribution to the advancement of contact dynamics modeling.

The Canadian Nanosatellite Advanced Propulsion System is a liquefied cold-gas thruster system that provides propulsive capabilities to CanX-4/-5, the Canadian Advanced Nanospace eXperiment 4 and 5. With a launch date of early 2014, CanX-4/-5's primary mission objective is to demonstrate precise autonomous formation flight of nanosatellites in low Earth orbit. The high-level CanX-4/-5 mission and system architecture is described. The final design and assembly of the propulsion system is presented along with the lessons learned. A high-level test plan provides a roadmap of the testing required to qualify the propulsion system for flight. The setup and execution of these tests, as well as the analyses of the results found therein, are discussed in detail.