Dissertations / Theses on the topic 'Autonomous satellites'

In the world of educational satellites, student teams manually conduct operations daily, sending commands and collecting downlinked data. Educational satellites typically travel in a Low Earth Orbit allowing line of sight communication for approximately thirty minutes each day. This is manageable for student teams as the required manpower is minimal. The international Global Educational Network for Satellite Operations (GENSO), however, promises satellite contact upwards of sixteen hours per day by connecting earth stations all over the world through the Internet. This dramatic increase in satellite communication time is unreasonable for student teams to conduct manual operations and alternatives must be explored. This thesis first introduces a framework for developing different Artificial Intelligences to conduct autonomous satellite operations for CubeSat satellites. Three different implementations are then compared using Cal Poly's CP6 CubeSat and the University of Tokyo's XI-IV CubeSat to determine which method is most effective.

This document describes the design and analysis of the Navigation, Guidance and Control System for the KnightSat project. The purpose for the project is to test and demonstrate new technologies the Air Force would be interested in for research and development. The primary mission of KnightSat is to show how a constellation of satellites can maintain relative position with each other autonomously using the Microwave Electro Thermal (MET) thruster. The secondary mission is to use multiple satellite imagery to obtain 3 dimensional stereo photographs of observable terrain. Formation flying itself has many possible uses for future applications. Selected missions that require imaging or data collection can be more economically accomplished using smaller multiple satellites. The MET thruster is a very efficient, but low thrust alternative that can provide thrust for a very long time, hence provide the low thrust necessary to maintain the satellites at a constant separation. The challenge is to design a working control algorithm to provide the desired output data to be used to command the MET thrusters. The satellites are to maintain a constant relative distance from each other, and use the least amount of fuel possible. If one satellite runs out of fuel before the other, it would render the constellation less useful or useless. Hence, the satellites must use the same amount of fuel in order to maintain an optimal operational duration on orbit.
M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Aerospace Engineering

Master of Science
Department of Electrical and Computer Engineering
William B. Kuhn
With the increasing number of satellites and space debris in all orbits the need for individual satellites to be able to autonomously detect and determine methods to navigate around them is increasing. Even with continued input and control from a ground station, the ability for a satellite to act to save itself from obstacles not visible from ground stations, or if communications were temporarily lost could be key to saving millions of dollars in hardware as well as improving overall performance and operational lifetimes.

The space is experiencing a revolution due to the em ergence of satellite services to satisfy environmental, socio-econom ic, and geo-political demands. Earth Observation satellite systems have become dependable resources for climate monitoring, modern agriculture, and other applications. The 5G incursion in the aerospace domain has promoted the satellites as promising platforms to achieve global coverage, and cope the limitations of ground facilities. These demands can be summarized in two system requirements: (1) increase of data transfer capacity, and (2) decrease of end-to-end com m unications latency. Distributed Satellite Systems have emerged as an effective solution of m ultiple satellites operating simultaneouslyto satisfycommon requirements. Federated Satellite Systems are serious candidates to exploit the potential of distributed architectures by establishing opportunistic collaborations among satellites to share unallocated resources. These collaborations, called federations, allows to conceive the space as a cloud in which satellites leverage from other resources to improve their performance. The successive investigations have been centered on developing novel federation technologies. However, multiple design aspects are still open fields of study, such as the development of communications capabilities to establish these federations. This dissertation contributes to fill this gap bydefining mechanisms to deploy a network infrastructure for this purpose. A networked environment in which satellites are able to establish sporadically, and opportunisticallyfederations has been discussed. This context is called the Internet of Satellites paradigm, and prometes the temporal deployment of inter-satellite networks, composed of heterogeneous satellites. This feature---with satellite motion--­poses a challenge on the definition of end-to-end communications routes composed of intermediate satellites. Areview of current routing protocols from other satellite networks is conducted to identify the ideal protocol for these dynam ic networks. The outcome remarks the need to combine capabilities from different domains to achieve the desired performance. Among them, the capabilityto predict future inter-satellite links becomes crucial to mitigate the fragmentation of the network. With this prem ise in mind, this dissertation presents a predictive protocol that perform s the estimation of these inter-satellite contacts in a distributed manner. This new satellite capability may support the routing protocol by allowing the estimation of future routes as a sequence of satellite contacts over time. The research presented in this dissertation also tackles other questions that remained unanswered: How can satellites be aware of the available resources offered by other satellites? What are the necessary mechanisms to deploy a federation? A software stack with two protocols to deal with this technology gap has been developed. The Opportunistic Service Availability Dissem ination Protocol allows notifying the services that are available in a satellite, while the Federation Deploym ent Control Protocol form alizes the rules to establish and m anage a federation. The application of these protocols considerably enhancded the capabilityof the satellite system to download data, becom ing thus enablers of future satellite m issions. The achieved perform anee has motivated the developm ent of a dedicated system. 11 has been named Federated Satellite Systems Experiment payload, and includes a communications device to create inter-satellite links. This system has been verified in a stratospheric balloon campaign, and integrated in a CubeSat miss ion. This dissertation discusses the results of the campaign, which emphasize the benefits and viabilityof this implementation. We expect that the contributions of this dissertation mayencourage to keep investigating on this inter-satellite communications for satellite federations.
L'espai esta experimentant! una revolució degut a l'aparició de serveis per satèl·lit que satisfan les noves demandes ambientals, socials i geo-polítiques. Els sistemes de satèl·lits per observar la Terra han esdevingut recursos essencials per el control del clima, !'agricultura moderna, i altres aplicacions. L'entrada del 5G en el sector aeroespacial ha promogut els satèl·lits com plataformes per aconseguir una cobertura global. Aquestes necessitats poden ser classificades en dos requeriments de sistema: (1) L'augment de la capacitat per transferir dades, i (2) la reducció de la latència en les comunicacions d'extrem-a-extrem. Els sistemes distribuïts de satèl·lits han esdevingut una solució efectiva amb múltiples satèl·lits essent operats simultàniament per satisfer uns requeriments comuns. Els sistemes federats de satèl·lits són candidats prometedors per explotar el potencial de les arquitectures distribuïdes mitjançant col·laboracions oportunistiques entre satèl·lits per compartir recursos. Aquestes col·laboracions, anomenades federacions, permeten concebre l'espai com un entorn on els satèl·lits poden beneficiar-se dels recursos d'altres per millorar el seu funcionament. Les investigacions s'han central en desenvolupar noves tecnologies per aquestes federacions. No obstant, molts aspectes de disseny encara són punts oberts de recerca, com ara el desenvolupament de protocols de comunicació per establir aquestes federacions. Aquesta tesina contribueix definint mecanismes que permeten desplegar una infraestructura en xarxa per establir federacions. A més a més, es discuteix sobre aquest context interconnectat on els satèl·lits poden establir esporàdicament i oportunísticament les federacions. Aquest escenari s'ha anomenat la Internet dels Satèl·lits, i promou els desplegament temporal de xarxes entre satèl·lits heterogenis. Aquesta característica, amb el moviment dels satèl·lits, suposa un repte en la definició de rutes entre extrems formades per satèl·lits intermitjos. Una revisió de protocols d'enrutament actuals d'altres xarxes de satèl·lits s'ha realitzat per identificar el protocol ideal per aquest tipus de xarxa dinàmica. El resultat remarca la necessitat de combinar capacitats de diferents dom in is per aconseguir el funcionament desitjat. Entre aquestes, la capacitat de preveure futurs enllaços entre satèl·lits esdevé crucial per mitigar la fragmentació de la xarxa. Amb aquesta premissa, aquesta tesina presenta un protocol predictiu que estima aquests contactes entre satèl·lits de forma distribuïda. Aquesta nova capacitat pot complementar el protocol d'enrutament mitjançant l'estimació de futures rutes com seqüències of contactes de satèl·lits a través del temps. La recerca presentada en aquesta tesina també respon altres preguntes que no s'havien res post encara: Com els satèl·lits poden descobrir els recursos disponibles en la xarxa? Quins són els mecanismes necessaris per establir i mantenir una federació? Una pila de protocols per cobrir aquesta necessitat tecnològica ha sigut desenvolupat. El protocol de dispersió de la disponibilitat de serveis oportunístics permet notificar els serveis disponibles en un satèl·lit, mentre que el protocol desplegament i control de federacions s'encarrega d'establir i gestionar les federacions. L'aplicació d'aquests protocols considerablement van realçar la capacita! del sistema de satèl·lit per descarregar dades, esdevenint així potenciadors de futures missions. Aquests resultats han motivat el desenvolupament d'un sistema dedica!, que inclou un dispositiu de comunicacions per crear enllaços entre satèl·lit. Aquest sistema ha estat verifica! en una campanya de globus estratosfèrics, i ha sigut integral en una missió de CubeSats. Aquesta dissertació presenta els resultats de la campanya, els quals emfasitzen els profits i viabilitat d'aquesta implementació.

Satellite constellations are an increasingly attractive option for many commercial and military applications. They provide a robust and distributed method of accomplishing the goals of expensive monolithic satellites. Among the many challenges that satellite constellations engender (challenges in control, coordination, disposal, and other areas), refueling is of particular interest because of the many methods one can use to refuel a constellation and the lifetime implications on the satellites. The present work presents a methodology for carrying out peer-to-peer refueling maneuvers within a constellation. Peer-to-peer (P2P) refueling can be of great value both in cases where a satellite unexpectedly consumes more fuel than it was alloted, and as part of a mixed refueling strategy that will include an outside tanker bringing fuel to the constellation. Without considering mixed-refueling, we formulate the peer-to-peer refueling problem as an assignment problem that seeks to guarantee that all satellites will have the fuel they need to be functional until the next refueling, while concurrently minimizing the cost in fuel that the refueling maneuvers entail. The assignment problem is then solved via auctions, which, by virtue of their distributed nature, can easily and effectively be implemented on a constellation without jeopardizing any robustness properties. Taking as a given that the P2P assignment problem has been solved, and that it has produced some matching among fuel deficient and fuel sufficient satellites, we then seek to sequence those prescribed maneuvers in the most effective manner. The idea is that while a constellation can be expected to have some redundancy, enough satellites leaving their assigned orbital slots will eventually make it impossible for the constellation to function. To tackle this problem, we define a wide class of operability conditions, and present three algorithms that intelligently schedule the maneuvers. We then briefly show how combining the matching and scheduling problems yields a complete methodology for organizing P2P satellite refueling operations.

In this thesis, we investigate the orbit control strategies of small satellites in Low Earth Orbits (LEO) where the disturbance effects are significant, in particular the nonspherical Earth and atmospheric drag effects. These orbits are not suitable to be controlled by using traditional ground-based control strategies which generally require high-thrust propulsion systems and other expensive resources, both onboard and in the ground segment. In order to react to those disturbances spontaneously and keep a small satellite at a pre-defined station using its limited resources, autonomous orbit control technology needs to be enabled. With the current advances in navigation and propulsion technology, as well as onboard computation systems, the only key issue that needs further investigations for practical implementation of an autonomous orbit operation system is the control algorithm. The orbit control strategies we investigate here are treated separately for each of the orbital control phases, i.e. orbit deployment and acquisition, orbit transfer and orbit maintenance. We present various forms of the solutions of the epicycle motion which allow us to treat each control problem according to the control requirements, nature of perturbations, control time scales and available resources. Although applied in different manners, the optimal low-thrust control scheme is a common aim for all control problems investigated here, as we mainly focus upon applications for low cost small satellites in LEO. The verifications of the strategies proposed in this thesis have been demonstrated not only via computer simulations, but also successfully demonstrated on in-orbit small satellite platforms thanks to an active small satellite programme at Surrey Space Centre. The success of this study is hoped to provide a valuable basis for satellite orbit operations which will involve larger number of satellites with more complex configurations in the future.

Autonomous navigation is the determination of satellites position and velocity vectors onboard the satellite, using the measurements available onboard. The orbital information of a satellite needs to be obtained to support different house keeping operations such as routine tracking for health monitoring, payload data processing and annotation, orbit manoeuver planning, and prediction of intrusion in various sensors' field of view by celestial bodies like Sun, Moon etc. Determination of the satellites orbital parameters is done in a number of ways using a variety of measurements. These measurements may originate from ground based systems as range and range rate measurements, or from another satellite as in the case of GPS (Global Positioning System) and TDUSS (Tracking Data Relay Satellite Systems), or from the same satellite by using sensors like horizon sensor^ sun sensor, star tracker, landmark tracker etc. Depending upon the measurement errors, sampling rates, and adequacy of the estimation scheme, the navigation accuracy can be anywhere in the range of 10m - 10 kms in absolute location. A wide variety of tracking sensors have been proposed in the literature for autonomous navigation. They are broadly classified as (1) Satellite-satellite tracking, (2) Ground- satellite tracking, (3) fully autonomous tracking. Of the various navigation sensors, it may be cost effective to use existing onboard sensors which are well proven in space. Hence, in the current thesis, the Horizon scanner is employed as the primary navigation sensor-. It has been shown in the literature that by using horizon sensors and gyros, a high accuracy pointing of the order of .01 - .03 deg can be achieved in the case of low earth orbits. Motivated by such a fact, the current thesis deals with autonomous orbit determination using measurements from the horizon sensors with the assumption that the attitude is known to the above quoted accuracies. The horizon scanners are mounted on either side of the yaw axis in the pitch yaw plane at an angle of 70 deg with respect to the yaw axis. The Field Of View (FOV) moves about the scanner axis on a cone of 45 deg half cone angle. During each scan, the FOV generates two horizon points, one at the space-Earth entry and the other at the Earth-space exit. The horizon points, therefore, lie• on the edge of the Earth disc seen by the satellite. For a spherical earth, a minimum of three such horizon points are needed to estimate the angular radius and the center of the circular horizon disc. Since a total of four horizon points are available from a pair of scanners, they can be used to extract the satellite-earth distance and direction.These horizon points are corrupted by noise due to uncertainties in the Earth's radiation pattern, detector mechanism, the truncation and roundoff errors due to digitisation of the measurements. Owing to the finite spin rate of the scanning mechanism, the measurements are available at discrete time intervals. Thus a filtering algorithm with appropriate state dynamics becomes essential to handle the •noise in the measurements, to obtain the best estimate and to propagate the state between the measurements. The orbit of a low earth satellite can be represented by either a state vector (position and velocity vectors in inertial frame) or Keplerian elements. The choice depends upon the available processors, functions and the end use of the estimated orbit information. It is shown in the thesis that position and velocity vectors in inertial frame or the position vector in local reference frame, do result in a simplified, state representation. By using the f and g series method for inertial position and velocity, the state propagation is achieved in linear form. i.e. Xk+1 = AXK where X is the state (position, velocity) and A the state transition matrix derived from 'f' and 'g' series. The configuration of a 3 axis stabilised spacecraft with two horizon scanners is used to simulate the measurements. As a step towards establishing the feasibility of extracting the orbital parameters, the governing equations are formulated to compute the satellite-earth vector from the four horizon points generated by a pair of Horizon Scanners in the presence of measurement noise. Using these derived satellite-earth vectors as measurements, Kalman filter equations are developed, where both the state and measurements equations are linear. Based on simulations, it is shown that a position accuracy of about 2 kms can be achieved. Additionally, the effect of sudden disturbances like substantial slewing of the solar panels prior and after the payload operations are also analysed. It is shown that a relatively simple Low Pass Filter (LPF) in the measurements loop with a cut-off frequency of 10 Wo (Wo = orbital frequency) effectively suppresses the high frequency effects from sudden disturbances which otherwise camouflage the navigational information content of the signal. Then Kalman filter can continue to estimate the orbit with the same kind of accuracy as before without recourse to re-tuning of covariance matrices. Having established the feasibility of extracting the orbit information, the next step is to treat the measurements in its original form, namely, the non-linear form. The entry or exit timing pulses generated by the scanner when multiplied by the scan rate yield entry or exit azimuth angles in the scanner frame of reference, which in turn represents an effective measurement variable. These azimuth angles are obtained as inverse trigonometric functions of the satellite-earth vector. Thus the horizon scanner measurements are non-linear functions of the orbital state. The analytical equations for the horizon points as seen in the body frame are derived, first for a spherical earth case. To account for the oblate shape of the earth, a simple one step correction algorithm is developed to calculate the horizon points. The horizon points calculated from this simple algorithm matches well with the ones from accurate model within a bound of 5%. Since the horizon points (measurements) are non-linear functions of the state, an Extended Kalman Filter (EKF) is employed for state estimation. Through various simulation runs, it is observed that the along track state has got poor observability when the four horizon points are treated as measurements in their original form, as against the derived satellite-earth vector in the earlier strategy. This is also substantiated by means of condition number of the observability matrix. In order to examine this problem in detail, the observability of the three modes such as along-track, radial, and cross-track components (i.e. the local orbit frame of reference) are analysed. This difficulty in observability is obviated when an additional sensor is used in the roll-yaw plane. Subsequently the simulation studies are carried out with two scanners in pitch-yaw plane and one scanner in the roll-yaw plane (ie. a total of 6 horizon points at each time). Based on the simulations, it is shown that the achievable accuracy in absolute position is about 2 kms.- Since the scanner in the roll-yaw plane is susceptible to dazzling by Sun, the effect of data breaks due to sensor inhibition is also analysed. It is further established that such data breaks do not improve the accuracy of the estimates of the along-track component during the transient phase. However, filter does not diverge during this period. Following the analysis of the' filter performance, influence of Earth's oblateness on the measurement model studied. It is observed that the error in horizon points, due to spherical Earth approximation behave like a sinusoid of twice the orbital frequency alongwith a bias of about 0.21° in the case of a 900 kms sun synchronous orbit. The error in the 6 horizon points is shown to give rise to 6 sinusoids. Since the measurement model for a spherical earth is the simplest one, the feasibility of estimating these sinusoids along with the orbital state forms the next part of the thesis. Each sinusoid along with the bias is represented as a 3 state recursive equation in the following form where i refers to the ith sinusoid and T the sampling interval. The augmented or composite state variable X consists of bias, Sine and Cosine components of the sinusoids. The 6 sinusoids together with the three dimensional orbital position vector in local coordinate frame then lead to a 21 state augmented Kalman Filter. With the 21 state filter, observability problems are experienced. Hence the magnetic field strength, which is a function of radial distance as measured by an onboard magnetometer is proposed as additional measurement. Subsequently, on using 6 horizon point measurements and the radial distance measurements obtained from a magnetometer and taking advantage of relationships between sinusoids, it is shown that a ten state filter (ie. 3 local orbital states, one bias and 3 zero mean sinusoids) can effectively function as an onboard orbit filter. The filter performance is investigated for circular as well as low eccentricity orbits. The 10-state filter is shown to exhibit a lag while following the radial component in case of low eccentricity orbits. This deficiency is overcome by introducing two more states, namely the radial velocity and acceleration thus resulting in a 12-state filter. Simulation studies reveal that the 12-state filter performance is very good for low eccentricity orbits. The lag observed in 10-state filter is totally removed. Besides, the 12-state filter is able to follow the changes in orbit due to orbital manoeuvers which are part of orbit acquisition plans for any mission.

Es defineix un satèl·lit d'òrbita baixa aquell que es troba a una alçada de fins a 2000 km per sobre de la superfície de la Terra. Degut al ràpid decaïment dels objectes propers a la superfície degut al fregament atmosfèric, s'accepta que l'alçada típica per un LEO esta entre 200 i 2000 km.
Aquesta rang d'alçades fa que els LEO siguin utilitzats per un ampli rang d'aplicacions, com a repetidors de comunicacions, sensors remots, determinació gravimètrica i magnetomètrica, altimetria oceànica, determinació atmosfèrica i en operacions de Search and Rescue (Cerca i rescat). El seu posicionament precís és de gran importància per a poder complir correctament amb els seus objectius. En aquest sentit, una gran quantitat de satèl·lits LEO tenen un receptor GPS, que permet fer mesures GPS durant tot el seu recorregut al voltant de la Terra. Aquestes mesures poden ser utilitzades per determinar la trajectòria del satèl·lit. Aquesta operació es fa normalment a terra, després que el satèl·lit hagi transmès totes les mesures que ha pres. La capacitat de fer aquest posicionament en temps real a bord del satèl·lit és una necessitat per algunes aplicacions. El posicionament autònom es molt diferent del que es pot fer a terra, ja que el processador del satèl·lit te grans limitacions en recursos computacionals, per tant els complexos models i càlculs fets en un ordinador normal a terra, son completament excessius per un ordinador espacial. A més, alguns dels models utilitzats en l'estimació de la trajectòria necessiten dades addicionals (com activitat solar, o paràmetres de rotació de la Terra) que no son disponibles en temps real, per tant s'han de fer algunes aproximacions per tal de no necessitar cap d'aquestes dades. Aquesta tesis estudiarà la navegació autònoma amb GPS de satèl·lits LEO, tendència que esta incrementant la seva importància per les aplicacions tan científiques com tecnològiques que se'n poden derivar. La tesi desenvoluparà nous algoritmes i mètodes per obtenir una posició acurada i continua per LEOs. S'han cobert diferent aspectes:
· Mitigació de multipath e interferències. Les reflexions de senyals GPS en l'estructura del satèl·lit crea una distorsió que afecta la distància mesurada. La repetibilitat d'aquests efectes en relació amb l'orientació del satèl·lit pot ser utilitzat per a mitigar el seu impacte en la solució de navegació. S'han desenvolupat tècniques de mitigació de multipath i interferències per receptors d'una i de dos freqüències.
· Models dinàmics de forces. L'alta predictibilitat de la trajectòria d'objectes orbitant la Terra pot ser utilitzat en sinergia amb el GPS per a aconseguir solucions més precises que fent servir únicament GPS. Això s'utilitza normalment en estratègies en postprocess, però te grans requeriments computacionals, i necessita paràmetres no disponibles en temps real. La simplificació d'aquests models, i la supressió de paràmetres no disponibles es necessari per poder aplicar aquesta tècnica de processat en condicions de temps real.
· Maniobres. Els cossos en òrbita al voltant de la Terra no segueixen una trajectòria perfectament predeible. Hi han petites pertorbacions que modifiquen la seva trajectòria a llarg termini, i a més, el fregament atmosfèric frena poc a poc al satèl·lit, disminuint la seva alçada. Això fa necessari una correcció periòdica de la seva trajectòria, realitzat amb petits impulsos del sistema de propulsió del satèl·lit en lo que s'anomena una maniobra. Quan un satèl·lit es troba en una maniobra, deixa de seguir els models de caiguda lliure, per tant la maniobra s'ha de tenir en conte en l'estimació del filtre.
Tots els algoritmes i mètodes dissenyats han sigut testejats amb dades reals de diferents missions: SAC-C, CHAMP, JASON-1 i GRACE. S'han fet servir diversos tests cobrint diferents opcions de parametrització per tal d'avaluar el seu comportament.
Se define un satélite de órbita baja aquel que se encuentra en una altura de hasta 2000 km sobre la superficie terrestre. Debido al rápido decaimiento de los objetos cercanos a la superficie debido al fregamiento atmosférico se acepta que la altura típica para un LEO se sitúa entre 200 y 2000 km.
Este rango de alturas hace que los LEO sean utilizados para un amplio rango de aplicaciones como repetidores de comunicaciones, sensores remotos, determinación gravimétrica y magnetométrica, altimetría oceánica, determinación atmosférica y en operaciones de Search and Rescue (Búsqueda y rescate). Su posicionamiento preciso es de gran importancia para poder cumplir correctamente con sus objetivos. En este sentido, una gran cantidad de satélites LEO disponen de un receptor GPS, que permite realizar medidas GPS durante todo su recorrido alrededor de la Tierra. Estas medidas puede ser utilizadas para determinar la trayectoria del satélite. Esta operación se suele realizar en tierra, después que el satélite haya retransmitido todas las medidas que ha tomado. La capacidad de hacer este posicionamiento en tiempo real a bordo del satélite es una necesidad para algunas aplicaciones. El posicionamiento autónomo es muy diferente al que se puede realizar en tierra, ya que los procesadores de satélites tienen limitaciones en recursos computacionales, y por tanto los complejos modelos y cálculos realizados en un ordenador normal en tierra son excesivos para un ordenador espacial. Además, algunos de los modelos utilizados en la estimación de la trayectoria necesitan datos adicionales (como actividad solar, o parámetros de rotación de la Tierra) que no están disponibles en tiempo real, por lo que hay que realizar algunas aproximaciones para no necesitar ninguno de estos datos. Esta tesis estudiará la navegación autónoma mediante GPS en satélites LEO, tendencia que esta aumentando su importancia por las aplicaciones tanto científicas como tecnológicas que se pueden derivar. La tesis desarrollara nuevos algoritmos y métodos para obtener una posición precisa y continua para LEOs. Se han cubierto diferentes aspectos:
· Mitigación de multipath e interferencias. Las reflexiones de las señales GPS en la estructura del satélite crea una distorsión que afecta la distancia medida. La repetibilidad de estos efectos en relación con la orientación del satélite puede ser utilizado para mitigar su impacto en la solución de navegación. Se han desarrollado técnicas de mitigación de multipath e interferencias para receptores de una o dos frecuencias.
· Modelos dinámicos de fuerzas. La trayectoria de objetos orbitando la Tierra es muy predecible, lo cual puede ser usado en sinergia con GPS para conseguir posiciones más precisas que usando solo GPS. Esto se utiliza normalmente en estrategias en postproceso, pero tiene grandes necesidades computacionales, y requiere de parámetros no disponibles en tiempo real. La simplificación de estos modelos, y la supresión e esos parámetros es necesario para poder aplicar esta técnica de procesado en condiciones de tiempo real.
· Maniobras. Los cuerpos en órbita alrededor de la Tierra no siguen una trayectoria perfectamente predecible. Hay pequeñas perturbaciones que modifican su trayectoria a largo plazo. Además el fregamiento atmosférico frena poco a poco el satélite, reduciendo su altura. Esto hace que sea necesaria una corrección periódica de su trayectoria, realizado en pequeños impulsos por el sistema de propulsión del satélite en lo que se llama una maniobra. Cuando un satélite realiza una maniobra deja de comportarse según los modelos de caida libre, por tanto su maniobra se ha de tener en cuenta en la estimación del filtro. Todos los algoritmos y métodos diseñados han sido testeados con datos reales de diferentes misiones: SAC-C, CHAMP, JASON-1 y GRACE. Se han realizado un amplio abanico de tests cubriendo diferentes opciones de parametrización para evaluar su comportamiento.
Satellites in low Earth orbits (LEO) are generally defined to be up to an altitude of 2000 km above Earth's surface and given the rapid decay of objects on the lower altitude range due to atmospheric drag, it is commonly accepted that a typical LEO height lies between 200 and 2000 km. This altitude range makes LEO satellites useful for a wide range of applications such as communication transponders, remote sensing, gravimetric and magnetometric sounding, ocean altimetry, atmospheric retrieval and Search and Rescue alarm operations. Its accurate positioning is of great importance in the successful accomplishment of their objectives. In this sense, most LEO satellites have a GPS receiver, which allows to collect GPS measurements in its full revolution around the Earth. These measures can be used to precisely estimate the trajectory of the spacecraft. This operation is normally done on ground, after the satellite was able to downlink all the data it collected. The capacity to do this positioning in real-time onboard the satellite is a necessity for some of the applications, and would also allow a faster science product delivery.
This autonomous positioning is very different that the one that can be done on ground, as the satellite processor has large limitations in computational resources, so the complex models and calculus done in a normal computer on ground are completely unaffordable for the onboard processor. Besides, some of the models used in the trajectory estimation need some additional data (such as solar activity, or Earth rotation parameters) that are not available in real-time, so some approximations must be done to cope with these lack of data. This thesis will deepen into the study of autonomous GPS navigation of LEO satellites, a trend that is increasing its importance for their applications in both science and technological fields. It will develop new algorithms and methods in order to provide accurate and continuous positions for the satellites. Different aspects have been covered:
· Multipath and interference mitigation. Reflections of GPS signals in the spacecraft structure cause a distress that affects the measured distance. On the other hand, some spacecraft have more than one GPS antenna on its payload. This creates a cross-talk interference that also affects the measures. The repeatability of these effects in relation to the attitude of the spacecraft can be used to mitigate its impact into the final navigation solution. Multipath mitigation techniques have been developed for both single- and dual-frequency receivers.
· Dynamic force models. The high predictability of the trajectory of Earth orbiters is used in conjunction to GPS measurements to provide a more accurate solution than GPS standalone positions. This is a widely used technique in postprocessing strategies, but has high computational requirements and needs parameters not available in real-time. The simplifications of these models, along with the suppression of the parameters not available in an onboard environment is necessary to use these kind of positioning by a satellite processing in real-time conditions.
· Maneuver handling. Earth orbiters do not follow a fully predictable orbit, some low-order perturbations modifies its trajectory on the long term, and atmospheric drag slowly brakes the satellite, decreasing its altitude. This makes necessary a periodic correction of its trajectory.
This is done by short impulses produced by the satellite propulsion systems in what is called a maneuver. When a spacecraft is in a maneuver, it no longer follows the free-flight dynamic models, so this should be taken into account in the estimation filter. All the algorithms and methods have been tested with real data from different missions: SAC-C, CHAMP, JASON-1 and GRACE. Several test cases covering a wide range of days and parametrization options have been done in order to assess its performance.

L'estimation de la pose (position et l'attitude) en temps réel est une fonction clé pour les véhicules autonomes routiers. Cette thèse vise à étudier des systèmes de localisation pour ces véhicules en utilisant des capteurs automobiles à faible coût. Trois types de capteurs sont considérés : des capteurs à l'estime qui existent déjà dans les automobiles modernes, des récepteurs GNSS mono-fréquence avec antenne patch et une caméra de détection de la voie regardant vers l’avant. Les cartes très précises sont également des composants clés pour la navigation des véhicules autonomes. Dans ce travail, une carte de marquage de voies avec une précision de l’ordre du décimètre est considérée. Le problème de la localisation est étudié dans un repère de travail local Est-Nord-Haut. En effet, les sorties du système de localisation sont utilisées en temps réel comme entrées dans un planificateur de trajectoire et un contrôleur de mouvement pour faire en sorte qu’un véhicule soit capable d'évoluer au volant de façon autonome à faible vitesse avec personne à bord. Ceci permet de développer des applications de voiturier autonome aussi appelées « valet de parking ». L'utilisation d'une caméra de détection de voie rend possible l’exploitation des informations de marquage de voie stockées dans une carte géoréférencée. Un module de détection de marquage détecte la voie hôte du véhicule et fournit la distance latérale entre le marquage de voie détecté et le véhicule. La caméra est également capable d'identifier le type des marquages détectés au sol (par exemple, de type continu ou pointillé). Comme la caméra donne des mesures relatives, une étape importante consiste à relier les mesures à l'état du véhicule. Un modèle d'observation raffiné de la caméra est proposé. Il exprime les mesures métriques de la caméra en fonction du vecteur d'état du véhicule et des paramètres des marquages au sol détectés. Cependant, l'utilisation seule d'une caméra a des limites. Par exemple, les marquages des voies peuvent être absents dans certaines parties de la zone de navigation et la caméra ne parvient pas toujours à détecter les marquages au sol, en particulier, dans les zones d’intersection. Un récepteur GNSS, qui est obligatoire pour le démarrage à froid, peut également être utilisé en continu dans le système de localisation multi-capteur du fait qu’il permet de compenser la dérive de l’estime. Les erreurs de positionnement GNSS ne peuvent pas être modélisées simplement comme des bruits blancs, en particulier avec des récepteurs mono-fréquence à faible coût travaillant de manière autonome, en raison des perturbations atmosphériques sur les signaux des satellites et les erreurs d’orbites. Un récepteur GNSS peut également être affecté par de fortes perturbations locales qui sont principalement dues aux multi-trajets. Cette thèse étudie des modèles formeurs de biais d’erreur GNSS qui sont utilisés dans le solveur de localisation en augmentant le vecteur d'état. Une variation brutale due à multi-trajet est considérée comme une valeur aberrante qui doit être rejetée par le filtre. Selon le flux d'informations entre le récepteur GNSS et les autres composants du système de localisation, les architectures de fusion de données sont communément appelées « couplage lâche » (positions et vitesses GNSS) ou « couplage serré » (pseudo-distance et Doppler sur les satellites en vue). Cette thèse étudie les deux approches. En particulier, une approche invariante selon la route est proposée pour gérer une modélisation raffinée de l'erreur GNSS dans l'approche par couplage lâche puisque la caméra ne peut améliorer la performance de localisation que dans la direction latérale de la route
Estimating the pose (position and attitude) in real-time is a key function for road autonomous vehicles. This thesis aims at studying vehicle localization performance using low cost automotive sensors. Three kinds of sensors are considered : dead reckoning (DR) sensors that already exist in modern vehicles, mono-frequency GNSS (Global navigation satellite system) receivers with patch antennas and a frontlooking lane detection camera. Highly accurate maps enhanced with road features are also key components for autonomous vehicle navigation. In this work, a lane marking map with decimeter-level accuracy is considered. The localization problem is studied in a local East-North-Up (ENU) working frame. Indeed, the localization outputs are used in real-time as inputs to a path planner and a motion generator to make a valet vehicle able to drive autonomously at low speed with nobody on-board the car. The use of a lane detection camera makes possible to exploit lane marking information stored in the georeferenced map. A lane marking detection module detects the vehicle’s host lane and provides the lateral distance between the detected lane marking and the vehicle. The camera is also able to identify the type of the detected lane markings (e.g., solid or dashed). Since the camera gives relative measurements, the important step is to link the measures with the vehicle’s state. A refined camera observation model is proposed. It expresses the camera metric measurements as a function of the vehicle’s state vector and the parameters of the detected lane markings. However, the use of a camera alone has some limitations. For example, lane markings can be missing in some parts of the navigation area and the camera sometimes fails to detect the lane markings in particular at cross-roads. GNSS, which is mandatory for cold start initialization, can be used also continuously in the multi-sensor localization system as done often when GNSS compensates for the DR drift. GNSS positioning errors can’t be modeled as white noises in particular with low cost mono-frequency receivers working in a standalone way, due to the unknown delays when the satellites signals cross the atmosphere and real-time satellites orbits errors. GNSS can also be affected by strong biases which are mainly due to multipath effect. This thesis studies GNSS biases shaping models that are used in the localization solver by augmenting the state vector. An abrupt bias due to multipath is seen as an outlier that has to be rejected by the filter. Depending on the information flows between the GNSS receiver and the other components of the localization system, data-fusion architectures are commonly referred to as loosely coupled (GNSS fixes and velocities) and tightly coupled (raw pseudoranges and Dopplers for the satellites in view). This thesis investigates both approaches. In particular, a road-invariant approach is proposed to handle a refined modeling of the GNSS error in the loosely coupled approach since the camera can only improve the localization performance in the lateral direction of the road. Finally, this research discusses some map-matching issues for instance when the uncertainty domain of the vehicle state becomes large if the camera is blind. It is challenging in this case to distinguish between different lanes when the camera retrieves lane marking measurements.As many outdoor experiments have been carried out with equipped vehicles, every problem addressed in this thesis is evaluated with real data. The different studied approaches that perform the data fusion of DR, GNSS, camera and lane marking map are compared and several conclusions are drawn on the fusion architecture choice

La mission pierre angulaire de l'ESA, Gaia, doit bâtir un catalogue d'étoiles limité seulement par leurs magnitudes. Ce milliard d'objets doivent être détectés à bord en temps réel pour pouvoir être observés et les exigences scientifiques et techniques font de ce problème un défi d'ingénierie. Nous avons élaboré un prototype pour estimer les performances accessibles et servir au dimensionnement de l'électronique à bord (TDA PDHE). Il s'appuie sur une séquence de quatre tâches: la calibration des données issues des CCDs, l'estimation du fond de ciel, l'identification des objets et, enfin, leur caractérisation pour commander les observations elles-mêmes. Bien qu'inspirée par des études antérieures (APM, Sextractor), cette approche a été intégralement révisée et adaptée aux spécificités de Gaia. Suite aux recommandations du TDA PDHE, une implémentation mixte est proposée qui traite les volumes de données importants et soumis aux contraintes de temps-réel « dures » avec de l'électronique dédiée (FPGA) et réalise les traitements complexes ou variables via du logiciel. Cette partition correspond aussi à subdiviser les opérations précédentes en un domaine pixel et un domaine objet. Notre démonstrateur montre que les attentes scientifiques sont satisfaites en termes de complétude, de précision et de robustesse à la diversité des configurations. Techniquement parlant, notre pipeline, optimisé quant à la surface et la consommation électrique, permet l'identification d'une technologie cible. Notre modèle n'a pas été retenu pour les phases industrielles de Gaia mais, outre son utilité avérée dans le projet, représente une R&D pour la génération de satellites à venir
ESA's cornerstone mission Gaia aims at building a star catalogue limited only by their magnitudes. The expected billion objects must be detected on board in real-time before they can be observed and the scientific and technical requirements make this an engineering challenge. We have devised a prototype to assess achievable performances and assist in sizing the on-board electronics (PDHE TDA). It is based on a sequence of four tasks: calibrating the incoming data from the CCDs, estimating the sky background, identifying the objects and, finally, characterising them to command subsequent observations. Although inspired by previous similar studies (APM, Sextractor), this approach has been thoroughly revisited and finely adapted to Gaia. Following the recommendations of the PDHE TDA, a mixed implementation is proposed which deals with the important data flow and the hard real-time constraints in hardware (FPGA) and entrusts more complex or variable processing to software. The segmentation also corresponds to subdividing the previous operations in pixel-based and object-based domains. Our demonstrator shows that the scientific specifications are met in terms of completeness, of precision and of robustness to the variety of observing conditions while, technically speaking, our pipeline, optimised for area and power consumption, allows for identifying a target technology. Our model has not been retained for the industrial phases of Gaia but, beside it recognised usefulness in the project, represents R&D for the forthcoming generation of satellites

Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, September 2002.
Thesis advisor(s): Michael G. Spencer, Brij N. Agrawal. Includes bibliographical references (p. 83). Also available online.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2003.
Includes bibliographical references (leaves 237-240).
by Joshua B. McConnell.
S.M.

Motivée par les besoins du domaine spatial en termes de diagnostic embarqué et d’autonomie, cette thèse s’intéresse aux problèmes de diagnostic, de diagnosticabilité et de diagnostic actif des systèmes hybrides. Un formalisme hybride est proposé pour représenter les deux dynamiques, continues et discrètes, du système. En s’appuyant sur ce modèle, une approche de diagnostic passif est proposée en mariant les techniques des systèmes à événements discrets et des systèmes continus. Un cadre formel pour la diagnosticabilité des systèmes hybrides a également été établi proposant des définitions et des critères pour la diagnosticabilité hybride. Suite à un diagnostic passif ambigu, le diagnostic actif est nécessaire afin de désambiguïser l’état du système. Cette thèse propose donc une approche de diagnostic actif, qui partant d’un état de croyance incertain, fait appel aux propriétés de diagnosticabilité du système pour déterminer la configuration où les fautes peuvent être discriminées. Une nouvelle machine à états finis appelée diagnostiqueur actif est introduite permettant de formaliser le diagnostic actif comme un problème de planification conditionnelle. Un algorithme d’exploration de graphes ET-OU est proposé pour calculer les plans de diagnostic actif. Finalement, l’approche de diagnostic a été testée sur le Système de Contrôle d’Attitude (SCA) d’un satellite de Thales Alenia Space. Le module de diagnostic a été intégré dans la boucle fermée de commande. Des scénarios de faute ont été testés donnant des résultats très satisfaisants
Motivated by the requirements of the space domain in terms of on-board diagnosis and autonomy, this thesis addresses the problems of diagnosis, diagnosability and active diagnosis of hybrid systems. Supported by a hybrid modeling framework, a passive approach for model-based diagnosis mixing discrete-event and continuous techniques is proposed. The same hybrid model is used to define the diagnosability property for hybrid systems and diagnosability criteria are derived. When the diagnosis provided by the passive diagnosis approach is ambiguous, active diagnosis is needed. This work provides a method for performing such active diagnosis. Starting with an ambiguous belief state, the method calls for diagnosability analysis results to determine a new system configuration in which fault candidates can be discriminated. Based on a new finite state machine called the diagnoser, the active diagnosis is formulated as a conditional planning problem and an AND-OR graph exploration algorithm is proposed to determine active diagnosis plans. Finally, the diagnosis approach is tested on the Attitude Control System (ACS) of a satellite simulator provided by Thales Alenia Space. The diagnosis module is successfully tested on several fault scenarios and the obtained results are reported

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009.
Autonomous rendezvouz and docking is seen as an enabling technology. It allows, among others, the construction of larger space platforms in-orbit and also provides a means for the in-orbit servicing of space vehicles. In this thesis a docking sequence is proposed and tested in both simulation and practice. This therefore also requires the design and construction of a test platform. A model hovercraft is used to emulate the chaser satellite in a 2-dimensional plane as it moves relatively frictionlessly. The hovercraft is also equipped with a single camera (monocular vision) that is used as the main sensor to estimate the target’s pose (relative position and orientation). An imitation of a target satellite was made and equipped with light markers that are used by the chaser’s camera sensor. The position of the target’s lights in the image is used to determine the target’s pose using a modified version ofMalan’s Extended Kalman Filter [20]. This information is then used during the docking sequence. This thesis successfully demonstrated the autonomous and reliable identification of the target’s lights in the image, and the autonomous docking of a satellite pair using monocular camera vision in both simulation and emulation.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada
The Extreme Ultraviolet Explorer (EUVE) satellite was designed to operate with the Tracking and Data Relay Satellite System (TDRSS) and Deep Space Network (DSN). NASA, the Jet Propulsion Laboratory and the Center for EUV Astrophysics have been evaluating a commercially available ground station already used for NASA's Low Earth Orbit (LEO) weather satellites. This ground station will be used in a network of unattended, autonomous ground stations for telemetry reception, processing, and routing of data over a commercial, secure data line. Plans call for EUVE to be the initial network user. This network will be designed to support many TDRSS/DSN compatible missions. It will open an era of commercial, low-cost, autonomous ground station networks. The network will be capable of supporting current and future NASA scientific missions, and NASA's LEO and geostationary weather satellites. Additionally, it could support future, commercial communication satellites in low, and possibly medium, Earth orbit. The combination of an autonomous ground station and an autonomous telemetry monitoring system will allow reduction in personnel. The EUVE Science Operations Center has already reduced console work from three shifts to one by use of autonomous telemetry monitoring software.

Un environnement spatial naturel hostile, les systèmes spatiaux de télédétection traditionnels,monolithiques et téléopérés depuis le sol, demeurent vulnérables face à un nombre croissant de menaces émergentes issues de l’environnement spatial artificiel (armes antisatellites,débris). Plutôt que de chercher à protéger physiquement les satellites, nous proposons d’adopter une stratégie fondée sur le concept de résilience, qui traduit la capacité d’un système à poursuivre sa mission face à des aléas imprévisibles, fût-ce en mode dégradé. En nous appuyant sur de récentes innovations dans les technologies spatiales, nous nous sommes intéressés à la conception et à l’évaluation d’architectures système fondées sur la mise en réseau de constellations de microsatellites hétérogènes, autonomes et communicants.Afin d’étudier de telles architectures, appelées réseaux de constellations autonomes (RCA),nous proposons une approche de modélisation ainsi qu’un outil de simulation à base de réseaux de Petri imbriqués. Grâce à des métriques issues des réseaux de télécommunication ainsi que des systèmes multiagents, nous avons évalué les RCA au travers de leurs performances opérationnelles et de leurs capacités de communication, nominales puis dans divers modes dégradés. Du point de vue de la résilience, les résultats présentés mettent en évidence l’intérêt de disposer de réseaux de communication denses et de modules de reconfiguration autonomes embarqués au sein même des satellites
Although Earth observation space systems are designed with strong safety requirements due to an hostile natural space environment, they remain vulnerable to an increasing range of emerging space threats such as antisatellite weapons or orbital debris. Instead of a physical protection of these monolithic and remote-controlled assets, we propose a design strategy based on the concept of resilience which is the ability of a system to maintain an acceptable level of performance in the presence of unforeseeable disturbance.Thanks to the latest space technology innovations, we devised new system architectures composed of networked constellations of heterogeneous and autonomous interacting microsatellites. We decided to model these architectures, called autonomous networked constellations (RCA in French), thanks to Petri nets, and more specifically their nets-within-nets variant. Using telecommunication and multiagent metrics, we assessed different RCA configurations through their operational performance and communicability, for nominal as wellas degraded modes. From the resilience point of view, we present quantitative results that point out the benefits of dense space networks and embedded autonomous reconfiguration modules

Future spacecraft missions are trending towards the use of distributed systems or fractionated spacecraft. Initiatives such as DARPA's System F6 are encouraging the satellite community to explore the realm of collaborative spacecraft teams in order to achieve lower cost, lower risk, and greater data value over the conventional monoliths in LEO today. Extensive research has been and is being conducted indicating the advantages of distributed spacecraft systems in terms of both capability and cost. Enabling collaborative behaviors among teams or formations of pico-satellites requires technology development in several subsystem areas including attitude determination and control subsystems, orbit determination and maintenance capabilities, as well as a means to maintain accurate knowledge of team members' position and attitude. All of these technology developments desire improvements (more specifically, decreases) in mass and power requirements in order to fit on pico-satellite platforms such as the CubeSat. In this thesis a solution for the last technology development area aforementioned is presented. Accurate knowledge of each spacecraft's state in a formation, beyond improving collision avoidance, provides a means to best schedule sensor data gathering, thereby increasing power budget efficiency. Our solution is composed of multiple software and hardware components. First, finely-tuned flight system software for the maintaining of state knowledge through equations of motion propagation is developed. Additional software, including an extended Kalman filter implementation, and commercially available hardware components provide a means for on-board determination of both orbit and attitude. Lastly, an inter-satellite communication message structure and protocol enable the updating of position and attitude, as required, among team members. This messaging structure additionally provides a means for payload sensor and telemetry data sharing. In order to satisfy the needs of many different missions, the software has the flexibility to vary the limits of accuracy on the knowledge of team member position, velocity, and attitude. Such flexibility provides power savings for simpler applications while still enabling missions with the need of finer accuracy knowledge of the distributed team's state. Simulation results are presented indicating the accuracy and efficiency of formation structure knowledge through incorporation of the described solution. More importantly, results indicate the collaborative module's ability to maintain formation knowledge within bounds prescribed by a user. Simulation has included hardware-in-the-loop setups utilizing an S-band transceiver. Two "satellites" (computers setup with S-band transceivers and running the software components of the collaborative module) are provided GPS inputs comparable to the outputs provided from commercial hardware; this partial hardware-in-the-loop setup demonstrates the overall capabilities of the collaborative module. Details on each component of the module are provided. Although the module is designed with the 3U CubeSat framework as the initial demonstration platform, it is easily extendable onto other small satellite platforms. By using this collaborative module as a base, future work can build upon it with attitude control, orbit or formation control, and additional capabilities with the end goal of achieving autonomous clusters of small spacecraft.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada
In 1998, AlliedSignal Technical Services (ATSC) installed three fully autonomous 13-meter satellite tracking systems for the Integrated Program Office of the National Oceanic and Atmospheric Administration (NOAA) at the Command and Data Acquisition Station near Fairbanks, Alaska. These systems track and command NOAA Polar Orbiting Weather Satellites and Defense Meteorological Satellites. Each tracking system operates for extended periods of time with little intervention other than periodic scheduling contacts. Schedule execution initiates equipment configuration, including establishing the RF communications link to the satellite. Station autonomy is achieved through use of a robust scheduler that permits remote users and the System Administrator to request pass activities for any of the supported missions. Spacecraft in the mission set are scheduled for normal operations according to the priority they have been assigned. Once the scheduler resolves conflicts, it builds a human-readable control script that executes all required support activities. Pass adds or deletes generate new schedule scripts and can be performed in seconds. The systems can be configured to support CCSDS and TDM telemetry processing, but the units installed at Fairbanks required only telemetry and command through-put capabilities. Received telemetry data is buffered on disk-storage for immediate, post-pass playback, and also on tape for long-term archiving purposes. The system can autonomously support up to 20 spacecraft with 5 different configuration setups each. L-Band, S-Band and X-Band frequencies are supported.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada
Employment of the retro-directive technique described in Reference 1 describes a totally Autonomous Ground Station providing hemispheric coverage and continuous tracking. This System establishes communications between the satellite and ground station without human intervention or moving parts. When a satellite is in view, the ground station beacon antenna, using CDMA, enables the desired satellite transmitter and directs its beam to the ground station. The ground station, using the satellite’s transmitted signal, directs it’s receive and transmit arrays to point the ground station beams to the satellite, establishing two-way communications. The process is automatic and provides continuous horizon to horizon tracking.

Satellite imagery has become an essential resource for environmental, humanitarian, and industrial endeavours. As a means to satisfy the requirements of new applications and user needs, novel Earth Observation (EO) systems are exploring the suitability of Distributed Satellite Systems (DSS) in which multiple observation assets concurrently sense the Earth. Given the temporal and spatial resolution requirements of EO products, DSS are often envisioned as large-scale systems with multiple sensing capabilities operating in a networked manner. Enabled by the consolidation of small satellite platforms and fostered by the emerging capabilities of distributed systems, these new architectures pose multiple design and operational challenges. Two of them are the main pillars of this research, namely, the conception of decision-support tools to assist the architecting process of a DSS, and the design of autonomous operational frameworks based on decentralised, on-board decision-making. The first part of this dissertation addresses the architecting of heterogeneous, networked DSS architectures that hybridise small satellite platforms with traditional EO assets. We present a generic design-oriented optimisation framework based on tradespace exploration methodologies. The goals of this framework are twofold: to select the most optimal constellation design; and to facilitate the identification of design trends, unfeasible regions, and tensions among architectural attributes. Oftentimes in EO DSS, system requirements and stakeholder preferences are not only articulated through functional attributes (i.e. resolution, revisit time, etc.) or monetary constraints, but also through qualitative traits such as flexibility, evolvability, robustness, or resiliency, amongst others. In line with that, the architecting framework defines a single figure of merit that aggregates quantitative attributes and qualitative ones-the so-called ilities of a system. With that, designers can steer the design of DSS both in terms of performance or cost, and in terms of their high-level characteristics. The application of this optimisation framework has been illustrated in two timely use-cases identified in the context of the EU-funded ONION project: a system that measures ocean and ice parameters in Polar regions to facilitate weather forecast and off-shore operations; and a system that provides agricultural variables crucial for global management of water stress, crop state, and draughts. The analysis of architectural features facilitated a comprehensive understanding of the functional and operational characteristics of DSS. With that, this thesis continues to delve into the design of DSS by focusing on one particular functional trait: autonomy. The minimisation of human-operator intervention has been traditionally sought in other space systems and can be especially critical for large-scale, structurally dynamic, heterogeneous DSS. In DSS, autonomy is expected to cope with the likely inability to operate very large-scale systems in a centralised manner, to improve the science return, and to leverage many of their emerging capabilities (e.g. tolerance to failures, adaptability to changing structures and user needs, responsiveness). We propose an autonomous operational framework that provides decentralised decision-making capabilities to DSS by means of local reasoning and individual resource allocation, and satellite-to-satellite interactions. In contrast to previous works, the autonomous decision-making framework is evaluated in this dissertation for generic constellation designs the goal of which is to minimise global revisit times. As part of the characterisation of our solution, we stressed the implications that autonomous operations can have upon satellite platforms with stringent resource constraints (e.g. power, memory, communications capabilities) and evaluated the behaviour of the solution for a large-scale DSS composed of 117 CubeSat-like satellite units.
La imatgeria per satèl·lit ha esdevingut un recurs essencial per assolir tasques ambientals, humanitàries o industrials. Per tal de satisfer els requeriments de les noves aplicacions i usuaris, els sistemes d’observació de la Terra (OT) estan explorant la idoneïtat dels Sistemes de Satèl·lit Distribuïts (SSD), on múltiples observatoris espacials mesuren el planeta simultàniament. Degut al les resolucions temporals i espacials requerides, els SSD sovint es conceben com sistemes de gran escala que operen en xarxa. Aquestes noves arquitectures promouen les capacitats emergents dels sistemes distribuïts i, tot i que són possibles gràcies a l’acceptació de les plataformes de satèl·lits petits, encara presenten molts reptes en quant al disseny i operacions. Dos d’ells són els pilars principals d’aquesta tesi, en concret, la concepció d’eines de suport a la presa de decisions pel disseny de SSD, i la definició d’operacions autònomes basades en gestió descentralitzada a bord dels satèl·lits. La primera part d’aquesta dissertació es centra en el disseny arquitectural de SSD heterogenis i en xarxa, imbricant tecnologies de petits satèl·lits amb actius tradicionals. Es presenta un entorn d’optimització orientat al disseny basat en metodologies d’exploració i comparació de solucions. Els objectius d’aquest entorn són: la selecció el disseny de constel·lació més òptim; i facilitar la identificació de tendències de disseny, regions d’incompatibilitat, i tensions entre atributs arquitecturals. Sovint en els SSD d’OT, els requeriments del sistema i l’expressió de prioritats no només s’articulen en quant als atributs funcionals o les restriccions monetàries, sinó també a través de les característiques qualitatives com la flexibilitat, l’evolucionabilitat, la robustesa, o la resiliència, entre d’altres. En línia amb això, l’entorn d’optimització defineix una única figura de mèrit que agrega rendiment, cost i atributs qualitatius. Així l’equip de disseny pot influir en les solucions del procés d’optimització tant en els aspectes quantitatius, com en les característiques dalt nivell. L’aplicació d’aquest entorn d’optimització s’il·lustra en dos casos d’ús actuals identificats en context del projecte europeu ONION: un sistema que mesura paràmetres de l’oceà i gel als pols per millorar la predicció meteorològica i les operacions marines; i un sistema que obté mesures agronòmiques vitals per la gestió global de l’aigua, l’estimació d’estat dels cultius, i la gestió de sequeres. L’anàlisi de propietats arquitecturals ha permès copsar de manera exhaustiva les característiques funcionals i operacionals d’aquests sistemes. Amb això, la tesi ha seguit aprofundint en el disseny de SSD centrant-se, particularment, en un tret funcional: l’autonomia. Minimitzar la intervenció de l’operador humà és comú en altres sistemes espacials i podria ser especialment crític pels SSD de gran escala, d’estructura dinàmica i heterogenis. En els SSD s’espera que l’autonomia solucioni la possible incapacitat d’operar sistemes de gran escala de forma centralitzada, que millori el retorn científic i que n’apuntali les seves propietats emergents (e.g. tolerància a errors, adaptabilitat a canvis estructural i de necessitats d’usuari, capacitat de resposta). Es proposa un sistema d’operacions autònomes que atorga la capacitat de gestionar els sistemes de forma descentralitzada, a través del raonament local, l’assignació individual de recursos, i les interaccions satèl·lit-a-satèl·lit. Al contrari que treballs anteriors, la presa de decisions autònoma s’avalua per constel·lacions que tenen com a objectius de missió la minimització del temps de revisita global.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California
A strategy for addressing the complexity of problem identification and notification by autonomous telemetry monitoring software is discussed. The Extreme Ultraviolet Explorer (EUVE) satellite's science operations center (ESOC) is completing a transition to autonomous operations. Originally staffed by two people, twenty-four hours every day, the ESOC is nearing the end of a phased transition to unstaffed monitoring of the science payload health. To develop criteria for the implementation of autonomous operations we first identified and analyzed potential risk areas. These risk areas were then considered in light of a fully staffed operations model, and in several reduced staffing models. By understanding the accepted risk in the nominal, fully staffed model, we could define what criteria to use in comparing the effectiveness of reduced staff models. The state of the scientific instrument package for EUVE is evaluated by a rule-based telemetry processing software package. In the fully automated implementation, anomalous states are characterized in three tiers: critical to immediate instrument health and safety, non-critical to immediate instrument health and safety, and affecting science data only. Each state requires specific action on the part of the engineering staff, and the response time is determined by the tier. The strategy for implementing this prioritized, autonomous instrument monitoring and paging system is presented. We have experienced a variety of problems in our implementation of this strategy, many of which we have overcome. Problems addressed include: dealing with data dropouts, determining if instrument knowledge is current, reducing the number of times personnel are paged for a single problem, prohibiting redundant notification of known problems, delaying notification of problems for instrument states that do not jeopardize the immediate health of the instrument, assuring a response to problems in a timely manner by engineering staff, and communicating problems and response status among responsible personnel.

Multi-platform swarm/cluster missions are an attractive prospect for improved science return as they provide a natural capability for temporal, spatial and signal separation with further engineering and economic advantages. As spacecraft numbers increase and/or the round-trip communications delay from Earth lengthens, the traditional "remotely-controlled" approach begins to break down. It is therefore essential to push the management of the spacecraft into the space segment. In other words, to make spacecraft more autonomous - if the desired goal of missions involving satellite swarms is to be realised. An autonomous group of spacecraft requires coordination, but standard terrestrial paradigms such as negotiation, require high levels of inter-spacecraft communication and on-board computation power, both of which are nontrivial in space (especially in the context of smaller nanosatellites platforms). This research therefore introduces the principles of stigmergy as a novel method for coordinating a cluster. Stigmergy is an agent-based, behavioural approach that allows for infrequent communication with decisions based on local information. Supervisors/ ground stations occasionally adjust parameters and disseminate a common feedforward and feedback environment that is used for local decisions and indirect coordination. Such an autonomous group of spacecraft can be considered as an emergent system, with the top-level group behaviour emerging from the local low-level behaviours of the individuals. Analysis is presented for a number of scenarios with performance evaluated in terms of intuitive behaviours: greedy, considerate, proactive and obstinate, which are mathematically defined. This reveals that effectiveness can be steadily improved by making the behaviours more "self-aware". The inherent suitability of the stigmergy solution for spacecraft swarm coordination is demonstrated by considering its three major benefits the first of which is scalability. Stigmergy is the mechanism used to coordinate hundreds of thousands of individuals in insect colonies. Hence it can cope in missions involving large numbers of spacecraft (demonstration of its application to up to 18 spacecraft in this work) unlike other distributed planning approaches that consider only a handful. Moreover the system is hierarchical which further helps to free the ground station from the micromanagement of individual spacecraft that is essential for remote cluster missions. All this is achievable without direct coordination, which would require the need for intersatellite links, that may well be costly on nanospacecraft platforms. The second major benefit is the ability to cope with dynamic problems. Large numbers of spacecraft will always introduce some degree of chaos and dynamism to the problem. lbis is exacerbated by the fact that tasks and/or spacecraft may fail at any time. The current planning approaches would require replanning to alleviate this, which can be highly costly and slow to respond. This work shows that the self organisation of the system brings inherent resilience. Spacecraft can then easily cope with uncertainty; can reconfigure based on spacecraft failure; can cope with changing mission goals and bursts of unexpected tasks into the system - all without additional overhead. The third major benefit is that only simple algorithms are needed which is essential for low-power nanospacecraft. In essence, the spacecraft needs only to maintain a local behaviour without interacting with others. In this thesis we describe in detail exactly what an on board "behaviour" is and how evaluation of its appropriateness for different goals is studied. This continuous search for a changing optimal behaviour is performed using a genetic algorithm, which is a challenging problem posing difficulties for existing operators. The search problem is explored analytically using Markov chains, leading to the development of a new family of distribution replacement operators. These operators have the unique ability to explicitly (rather than probabilistically) control the population diversity in fitness (rather than genome) space, which translates into improved performance. Finally this thesis concludes by considering three case studies. The first shows the implementation of the algorithms on realistic nanospacecraft flight hardware, demonstrating that the system could feasibly be deployed, even with currently available nanospacecraft platform technologies. The second demonstrates hierarchical load balancing of the cluster to maintain even power usage. Finally the third case study shows how the system can operate well on more realistic multidimensional resource spaces.

International Telemetering Conference Proceedings / October 28-31, 1985 / Riviera Hotel, Las Vegas, Nevada
Autonomous operation is rapidly becoming a requirement for most new spacecraft systems. An autonomous spacecraft greatly simplifies the ground station processing and monitoring requirements, freeing ground station capabilities for other important tasks. The T2C2 (Telemetry, Timing, Command and Control) System has been conceived and architected to facilitate spacecraft autonomy. The T2C2 architecture is ideally suited for onboard closed-loop control, redundancy management, housekeeping and other autonomous functions. This paper provides an overview of the T2C2 architecture and its applications in the design and implementation of an autonomous spacecraft.

La collecte d’informations et leur transmission au travers d’un réseau de communications peut être effectuée par des réseaux de capteurs autonomes ainsi que par des satellites d’observation. L’utilisation conjointe de ces réseaux fournirait des données complémentaires et permettrait à l’Humanité de pérenniser son avenir en comprenant les mécanismes du monde qui l’entoure. Ces dernières années, le secteur spatial a montré une volonté d’unifier et de faciliter la réutilisation des développements réalisés avec la création de filières de plateformes multi-missions ainsi que la définition de protocoles applicables à différents contextes. L’objectif de cette thèse est d’étudier les caractéristiques des différentes technologies d’observation afin d’en exploiter les points communs. À ces fins, nous nous intéressons aux technologies et aux architectures utilisées dans de tels contextes. Nous proposons alors une architecture de réseau répondant aux contraintes des systèmes les plus communément utilisés dans un tel cadre. Les principales contraintes des scénarios d’observation sont liées à la forte intermittence des liens et donc au manque de connexité du réseau. Nous nous orientons donc vers une solution ayant recours au concept de réseaux tolérants au délai. Dans un tel contexte, l’existence d’une route entre la source et la destination n’est pas garantie. C’est pourquoi les protocoles de communication utilisés propagent généralement plusieurs exemplaires d’un même message vers plusieurs entités afin d’augmenter le taux de délivrance. Nous avons souhaité diminuer l’utilisation des ressources du réseau tout en conservant des performances similaires afin d’augmenter l’efficacité du réseau. Après avoir proposé une architecture commune, nous nous sommes focalisés sur les spécificités des différents segments de notre réseau afin de répondre localement à ces problèmes. Pour le segment satellite, nous nous sommes plus spécialement concentrés sur les techniques de gestion de mémoire. Nous considérons un satellite défilant avec une mémoire embarquée limitée, collectant des données en provenance de passerelles. Il s’agit alors de sélectionner les messages les plus urgents quitte à déposer sur une autre passerelle les messages moins contraints. Sur le réseau de capteurs terrestre, nous nous sommes focalisés sur la diminution de l’utilisation des ressources du réseau. Pour cela nous avons utilisé l’historique des rencontres entre les nœuds et analysé l’influence de la quantité de mémoire allouée aux accusés de réception sur les performances du réseau. Nous sommes parvenus à atteindre des performances supérieures aux solutions existantes à moindre frais. Les solutions proposées peuvent être mises en œuvre et appliquées dans différents contextes applicatifs.

The costs in satellite operations are generally not negligible, especially for longterm missions. An alternative to lower costs is to increase the level of automation in procedures whenever possible. This thesis proposes a dynamic and autonomous approach to small satellite ground station networks aimed at minimizing these operational costs. The proposed solution is called the ADSGS (Autonomous and Dynamic System Ground Station) and is a middleware with hardware and software components to operate in a distributed network environment of ground stations. In this work the SATNet network was considered as currently it lacks an allocation component with the characteristics of dynamism and autonomy. In ADSGS this is provided through the use of artificial intelligence in a rule-based expert system. In the proposal, an ADSGS network agent operates autonomously and dynamically on the SATNet network where the associated station components are managed. The ADSGS agent uses an adapted version of the Hungarian Algorithm for combinatorial optimization of allocation problems and responds to events such as service interruption. The proposed hardware component uses COTS and Software Defined Radio (SDR) technology while the software component uses packages such as Orbitron, ProEst, the SINTA expert system, among others. UML modeling is provided to document the software component. A case study is made to illustrate the main features of the ADSGS consisting of a small simulation in MATLAB with STK (Systems Tool Kit) two scenarios of designation (1-to-m and n-to-m) of stations in the SATNet network to satellites by the ADSGS agent.
Os custos nas operações de satélites geralmente não são desprezíveis, especialmente para missões de longa duração. Uma alternativa para baratear custos é aumentar o nível de automação em procedimentos quando for possível. Este trabalho de tese propõe uma abordagem dinâmica e autônoma para operações espaciais em redes de estações terrenas para pequenos satélites que visa minimizar seus custos operacionais. A solução proposta denomina-se ADSGS (Autonomous and Dynamic System Ground Station em Inglês) e é um middleware com componentes de hardware e software para atuação em um ambiente distribuído em uma rede de estações terrenas. Neste trabalho foi adotada a rede SATNet que carece de um componente de alocação com as características de dinamismo e autonomia. No ADSGS isto é oferecido mediante o uso da inteligência artificial em um sistema especialista baseado em regras. Na proposta, um agente de rede da ADSGS atua autônoma e dinamicamente na rede SATNet onde se gerenciam componentes das estações associadas. O agente ADSGS utiliza uma versão estendida do Algoritmo Húngaro para otimização combinatória de problemas de alocação e responder a eventos como interrupção de serviços. O componente de hardware proposto utiliza elementos de hardware COTS e tecnologia SDR (Software Defined Radio) ao passo que o componente de software utiliza pacotes como Orbitron, ProEst, o sistema especialista SINTA, entre outros. A modelagem UML é oferecida para documentar o componente de software. Um estudo de caso é feito para ilustrar as principais funcionalidades do ADSGS consistindo de uma pequena simulação em MATLAB com STK (Systems Tool Kit) e dois cenários de designação (1-to-m e n-to-m) de estações na rede SATNet a satélites pelo agente ADSGS.

With the rising popularity of small satellites, such as CubeSats, many smaller institutions previously incapable of developing and deploying a spacecraft have starting to do so. Institutions with a history of space flight, such as NASA JPL, have begun to put projects on CubeSats that would normally fly on much larger satellites. As a result, the institutions with space flight heritage have begun to port spacecraft software that was previously designed for much larger and more complex satellites to the CubeSat platform. Unfortunately for universities, who are the majority of all institutions devel- oping CubeSats, these ported systems are too large and complex to be a practical control solution. Student teams have a high turnover rate due to graduation and when a student becomes an expert on the control system, they graduate; most students get a maximum of two or three years of experience before graduating. This thesis proposes the Generic Decision Making Framework for Autonomous Systems (GDMFAS) as an accessible, easily extensible, component-based executive system architecture. The architecture is designed for Linux distributions, including the custom Linux distribution used by PolySat, and is implemented using C++. The proposed framework provides much of the same functionality as systems designed for larger satellites in a smaller, more straightforward pack- age, which includes both scheduling and executive components. This thesis also provides validation for the prototype implementation and evaluates the system according to six metrics. The metric analysis for this work is then compared with the metric analyses of previous works.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California
The science payload for NASA's Extreme Ultraviolet Explorer (EUVE) satellite is controlled from the EUVE Science Operations Center (ESOC) at the Center for EUV Astrophysics (CEA), University of California, Berkeley (UCB). The ESOC is in the process of a transition from a single staffed shift to an autonomous, zero-shift, "lights out" science payload operations scenario (a.k.a., 1:0). The purpose of the 1:0 transition is to automate all of the remaining routine, daily, controller telemetry monitoring and associated "shift" work. Building on the ESOC's recent success moving from three-shift to one-shift operations (completed in Feb 1995), the 1:0 transition will further reduce payload operations costs and will be a "proof of concept" for future missions; it is also in line with NASA's goals of "cheaper, faster, better" operations and with its desire to out-source missions like EUVE to academe and industry. This paper describes the 1:0 transition for the EUVE science payload: the purpose, goals, and benefits; the relevant science payload instrument health and safety considerations; the requirements for, and implementation of, the multi-phased approach; a cost/benefit analysis; and the various lessons learned along the way.

There are benefits to the use of internal actuators for rotational maneuvers of small-scale underwater vehicles. Internal actuators are protected from the outside environment by the external pressure hull and will not disturb the surrounding environment during inspection tasks. Additionally, internal actuators do not rely on the relative fluid motion to exert control moments, therefore they are useful at low speed and in hover. This paper describes the design, fabrication and testing of one such autonomously controlled, internally actuated underwater vehicle.

The Internally Actuated, Modular Bodied, Untethered Submersible (IAMBUS) can be used to validate non-linear control strategies using internal actuators. Vehicle attitude control is provided by three orthogonally mounted reaction wheels. The housing is a spherical glass pressure vessel, which contains all of the components, such as actuators, ballast system, power supply, on-board computer and inertial sensor. Since the housing is spherically symmetric, the hydrodynamics of IAMBUS are uncoupled (e.g. a roll maneuver does not impact pitch or yaw). This hull shape enables IAMBUS to be used as a spacecraft attitude dynamics and control simulator with full rotational freedom.
Master of Science

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada
This paper presents the results of a feasibility study undertaken by the University of Salzburg (Austria), investigating the autonomous acquisition of environmental data in a global network. A suggested application which is used as the basis of this paper is a volcano monitoring system which would be able to track the activity of a volcano and act as a disaster warning system. The background Volcano observation data required for such a system is covered, before discussing the concepts for sensor data acquisition, storage and processing. A final analysis is then presented of the opportunities for the transmission by packet radio (both terrestrial and satellite).

Optimal trajectory planning methods that implement convex optimization techniques are applied to the area of satellite rendezvous and proximity operations. This involves the development of linearized relative orbital motion dynamics and constraints for two satellites, where one maintains a near-circular reference orbit. The result is formulated as a convex optimization problem, where the objective is to minimize the amount of fuel required to transfer from a given initial condition to the desired final conditions. A traditional rendezvous and proximity operations scenario is analyzed, which includes examples of initial approach, inspection, final approach, and docking trajectories. This scenario may include trajectory constraints such as maximum allowable control acceleration levels, approach corridors, and spherical keep-out zones. A second scenario that ensures passive safety, in the event of control failures on the maneuvering satellite. The convex optimization problem is ultimately formulated as a second-order cone program. Algorithm CPU and memory requirements are analyzed. Several examples of resulting optimal trajectories are presented for both scenarios, and these trajectories are implemented in a nonlinear simulation.

The aim of this work is to find a method for removing haze from satellite imagery. This is done by taking two algorithms developed for images taken from the sur- face of the earth and adapting them for satellite images. The two algorithms are Single Image Haze Removal Using Dark Channel Prior by He et al. and Color Im- age Dehazing Using the Near-Infrared by Schaul et al. Both algorithms, altered to fit satellite images, plus the combination are applied on four sets of satellite images. The results are compared with each other and the unaltered images. The evaluation is both qualitative, i.e. looking at the images, and quantitative using three properties: colorfulness, contrast and saturated pixels. Both the qualitative and the quantitative evaluation determined that using only the altered version of Dark Channel Prior gives the result with the least amount of haze and whose colors look most like reality.

This thesis proposes a continuous low-thrust guidance and control strategy for satellite formation-flying. Stabilizing feedback based on mean relative orbit elements and Lyapunov theory is used. A novel feedback gain matrix inspired by the fuel-optimal impulsive solution is designed to achieve near-optimal fuel consumption. A reference governor is developed to autonomously guide the spacecraft through the relative state-space in order to allow for arbitrarily constrained satellite formations. Constraints include desired  thrust levels, time constraints, passive collision avoidance and locally constrained state-space areas. Keplerian dynamics are leveraged to further decrease fuel consumption. Simulations show fuel consumptions of only 4% higher delta-v than the fuel-optimal impulsive solution. The proposed control and guidance strategy is tested in a high-fidelity orbit propagation simulation using MATLAB/Simulink. Numerical simulations include orbit perturbations such as atmospheric drag, high-order geopotential, solar radiation pressure and third-body (Moon and Sun) effects. Test cases include reconfiguration scenarios with imposed wall, thrust and time constraints and a formation maintenance experiment as flown by TanDEM-X, the TanDEM-X Autonomous Formation-Flying (TAFF) experiment.

Les technologies spatiales évoluent actuellement vers la fabrication de plusieurs microsatellites autonomes volant en formation plutôt que vers la construction de gros satellites. Cette stratégie est avantageuse. Par exemple, elle permet d'accroître la résolution des mesures en corrélant les signaux provenant des instruments scientifiques des microsatellites. Cette antenne synthétique de grande ouverture serait impossible à déployer avec un seul satellite. Pour profiter des avantages de cette stratégie, des lois de commande optimales (a au sens du temps et du coût en propergol) et autonome qui permettent de maintenir et de reconfigurer une formation doivent être développées. Ce travail de recherche s'intéresse à ce sujet. Plus précisément, il traite des aspects suivants: (1) Pour développer la loi de commande d'un système, il est nécessaire de savoir le modéliser. Ce document débute donc par une présentation des modèles dynamiques les plus utilisés pour décrire le mouvement relatif entre deux satellites volant en formation sur une orbite terrestre. (2) Plusieurs auteurs se sont intéressés à asservir une formation de satellites, les plus importantes de celles-ci sont présentées dans ce document. Par cette étude de la littérature, le candidat démontre que les lois de commande prédictives sont des solutions efficaces comportant plusieurs avantages. Par exemple, ces approches sont optimales et permettent de traiter des contraintes sur les entrées et les sorties du système asservi. (3) En lien avec ce qui précède, une étude détaillée de la théorie des lois de commande prédictives linéaires et non linéaires discrètes est présentée. (4) Par la suite, ces lois de commande prédictives sont appliquées sur un système simple, soit une grue à trois axes. Ces exemples ont été développés pour accroître l'expertise de l'auteur dans ce domaine ainsi que pour présenter les avantages et les performances des lois de commande prédictives. (5) Finalement, ce document présente le développement d'une loi de commande prédictive pour le vol en formation de satellites basée sur le modèle de Lawden et de GVE (Équations de Variation de Gauss) linéarisées.Les précédentes approches basées sur ce type de loi de commande reposaient sur l'optimisation de l'effort de commande soumis à des contraintes sur les entrées et les sorties du système en utilisant un algorithme complexe et non autonme pour maintenir et reconfigurer la formation. La technique proposée est plutôt de minimiser une fonction coût quadratique incluant directement les erreurs relatives futures, et ce, en considérant des contraintes sur les actionneurs (contraintes sur les entrées du système). La commande optimale est obtenue avec un algorithme analytique basé sur la projection de la fonction coût sur les contraintes permettant ainsi de réduire considérablement le temps de calcul.

The usage of 3D modelling is increasing fast, both for civilian and military areas, such as navigation, targeting and urban planning. When creating a 3D model from satellite images, clouds canbe problematic. Thus, automatic detection ofclouds inthe imagesis ofgreat use. This master thesis was carried out at Vricon, who produces 3D models of the earth from satellite images.This thesis aimed to investigate if Support Vector Machines could classify pixels into cloud or non-cloud, with a combination of texture and color as features. To solve the stated goal, the task was divided into several subproblems, where the first part was to extract features from the images. Then the images were preprocessed before fed to the classifier. After that, the classifier was trained, and finally evaluated.The two methods that gave the best results in this thesis had approximately 95 % correctly classified pixels. This result is better than the existing cloud segmentation method at Vricon, for the tested terrain and cloud types.

The most common approach to analysing satellite imagery is building or object segmentation,which expects an algorithm to find and segment objects with specific boundaries thatare present in the satellite imagery. The company Vricon takes satellite imagery analysisfurther with the goal of reproducing the entire world into a 3D mesh. This 3D reconstructionis performed by a set of complex algorithms excelling in different object reconstructionswhich need sufficient labeling in the original 2D satellite imagery to ensure validtransformations. Vricon believes that the labeling of areas can be used to improve the algorithmselection process further. Therefore, the company wants to investigate if multinomiallarge area classification can be performed successfully using the satellite image data availableat the company. To enable this type of classification, the company’s gold-standarddataset containing labeled objects such as individual buildings, single trees, roads amongothers, has been transformed into an large area gold-standard dataset in an unsupervisedmanner. This dataset was later used to evaluate large area classification using several stateof-the-art Deep Convolutional Neural Network (DCNN) semantic segmentation architectureson both RGB as well as RGB and Digital Surface Model (DSM) height data. Theresults yield close to 63% mIoU and close to 80% pixel accuracy on validation data withoutusing the DSM height data in the process. This thesis additionally contributes with a novelapproach for large area gold-standard creation from existing object labeled datasets.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.
Includes bibliographical references (p. 307-324).
The capability to routinely perform autonomous docking is a key enabling technology for future space exploration, as well as assembly and servicing missions for spacecraft and commercial satellites. Particularly, in more challenging situations where the target spacecraft or satellite is tumbling, algorithms and strategies must be implemented to ensure the safety of both docking entities in the event of anomalies. However, difficulties encountered in past docking missions conducted with expensive satellites on orbit have indicated a lack of maturity in the technologies required for such operations. Therefore, more experimentation must be performed to improve the current autonomous docking capabilities. The main objectives of the research presented in this thesis are to develop a guidance, navigation and control (GN&C) architecture that enables the safe and fuel-efficient docking with a free tumbling target in the presence of obstacles and anomalies, and to develop the software tools and verification processes necessary in order to successfully demonstrate the GN&C architecture in a relevant environment. The GN&C architecture was developed by integrating a spectrum of GN&C algorithms including estimation, control, path planning, and failure detection, isolation and recovery algorithms.
(cont.) The algorithms were implemented in GN&C software modules for real-time experimentation using the Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES) facility that was created by the MIT Space Systems Laboratory. Operated inside the International Space Station (ISS), SPHERES allow the incremental maturation of formation flight and autonomous docking algorithms in a risk-tolerant, microgravity environment. Multiple autonomous docking operations have been performed in the ISS to validate the GN&C architecture. These experiments led to the first autonomous docking with a tumbling target ever achieved in microgravity. Furthermore, the author also demonstrated successful docking in spite of the presence of measurement errors that were detected and rejected by an online fault detection algorithm. The results of these experiments will be discussed in this thesis. Finally, based on experiments in a laboratory environment, the author establishes two processes for the verification of GN&C software prior to on-orbit testing on the SPHERES testbed.
by Simon Nolet.
Sc.D.

Knowing where ships are located is a key factor to support safe maritime transports, harbor management as well as preventing accidents and illegal activities at sea. Present international solutions for geopositioning in the maritime domain exist such as the Automatic Identification System (AIS). However, AIS requires the ships to constantly transmit their location. Real time imaginary based on geostationary satellites has recently been proposed to complement the existing AIS system making locating and tracking more robust. This thesis investigated and compared two machine learning image analysis approaches – Faster R-CNN and SSD with FPN – for detection and tracking of ships in satellite images. Faster R-CNN is a two stage model which first proposes regions of interest followed by detection based on the proposals. SSD is a one stage model which directly detects objects with the additional FPN for better detection of objects covering few pixels. The MAritime SATellite Imagery dataset (MASATI) was used for training and evaluation of the candidate models with 5600 images taken from a wide variety of locations. The TensorFlow Object Detection API was used for the implementation of the two models. The results for detection show that Faster R-CNN achieved a 30.3% mean Average Precision (mAP) while SSD with FPN achieved only 0.0005% mAP on the unseen test part of the dataset. This study concluded that Faster R-CNN is a candidate for identifying and tracking ships in satellite images. SSD with FPN seems less suitable for this task. It is also concluded that the amount of training and choice of hyper-parameters impacted the results.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada
The UC Berkeley Extreme Ultraviolet Explorer (EUVE) Science Operations Center (ESOC) is developing and implementing knowledge-based software to automate the monitoring of satellite payload telemetry. Formerly, EUVE science payload data were received, archived, interpreted, and responded to during round-the-clock monitoring by human operators. Now, knowledge-based software will support, augment, and supplement human intervention. In response to and as a result of this re-engineering project, the creation, storage, revision, and communication of information (the information flow process) within the ESOC has been redesigned. We review the information flow process within the ESOC before, during, and after the re-engineering of telemetry monitoring. We identify six fundamental challenges we face in modifying the information flow process. (These modifications are necessary because of the shift from continuous human monitoring to a knowledge-based autonomous monitoring system with intermittent human response.) We describe the innovations we have implemented in the ESOC information systems, including innovations in each part of the information flow process for short-term or dynamic information (which changes or updates within a week) as well as for long-term or static information (which is valid for more than a week). We discuss our phased approach to these innovations, in which modifications were made in small increments and the lessons learned at each step were incorporated into subsequent modifications. We analyze some mistakes and present lessons learned from our experience.

In 1999 Europe, through the European Commission and the European Space Agency, began detailed definition of a second generation Global Navigation Satellite System (GNSS). This GNSS development programme, known as “Galileo”, was intended to both complement and compete against the existing US Global Positioning System (GPS). Unlike GPS, Galileo is intended to be privately financed, following the initial development investment from the EC and ESA, which implies that Galileo should provide some revenue-earning services. From its earliest inception, the basis of these services has been assumed to be through the provision of Signal Integrity through an Integrity Flag broadcast through the Galileo system– a service which GPS cannot provide without some external system augmentation. This thesis undertakes a critical evaluation of the value of this integrity system in Galileo. This thesis has two parts. The first demonstrates that the conditions required to attract adequate private finance to the Galileo programme are incompatible with the system architecture derived from the early Galileo system studies and taken forward into the system early deployment phase, which includes an Integrity system within Galileo. The second part of this thesis aims to demonstrate that receivers which can combine the signals from GPS and Galileo may offer a free Integrity service which meet the needs of the majority of users, possibly up to the standards required for aviation precision approach. A novel Receiver Autonomous Integrity Monitoring (RAIM) technique is described, using an Errors in Variables/Total Least Squares approach to the detection of inconsistencies in an over-determined set of GNSS signal measurements. The mathematical basis for this technique is presented, along with results which compare the simulated performance of receivers using this algorithm against the expected performance of Galileo’s internal integrity determination system.

AIDA (Asteroid Impact and Deflection Assessment), is a joint NASA-ESA mission that will operate within 65803 Didymos binary system and whose main purpose is to experiment and investigate the kinetic impact technique for the deviation of the asteroid trajectories in space. HERA, the "mother" satellite designed by ESA, will aim to collect data about the chemical-physical composition of the binary system and about the characteristics of the impact between DART, the bullet-satellite realized and run by NASA, and the minor of the two celestial bodies that compose Didymos, which should occur around October 2022. HERA satellite will carry high-level technology onboard, including some CubeSats. This panorama also includes the DustCube mission, a project proposal for a CubeSat, whose main objective is to assist HERA in the acquisition of data. This thesis, as part of the DustCube project, aims at investigating the autonomous navigation of the CubeSat within the Didymos system, in particular through the development of a navigation filter based on optical observables. By making use of images gathered by a couple of infrared cameras, both LoS and range measurements are retrieved and fed to an Extended Kalman Filter. Results show that, even if implementing a reduced dynamical model within the filter, the expected position accuracy is below the requested 10 meters.

Les informations contenues dans les cartes routières numériques revêtent une importance grandissante dans le domaine des véhicules intelligents. La prise en compte d’environnements de plus en plus complexes a augmenté le niveau de précision exigé des informations cartographiques. Les cartes routières numériques, considérées ici comme des bases de données géographiques, contiennent des informations contextuelles sur le réseau routier, facilitant la compréhension correcte de l’environnement. En les combinant avec les données provenant des capteurs embarqués, une représentation plus fine de l’environnement peut être obtenue, améliorant grandement la compréhension de contexte du véhicule et la prise de décision. La performance des différents capteurs peut varier grandement en fonction du lieu considéré, ceci étant principalement dû à des facteurs environnementaux. Au contraire, une carte peut fournir ses informations de manière fiable, sans être affectée par ces éléments extérieurs, mais pour cela, elle doit reposer sur un autre élément essentiel : une source de localisation. Le secteur automobile utilise les systèmes de localisation globale par satellite (GNSS) à des fins de localisation absolue, mais cette solution n’est pas parfaite, étant soumise à différentes sources d’erreur. Ces erreurs sont elles aussi dépendantes de l’environnent d’évolution du véhicule (par exemple, des multi-trajets causés par des bâtiments). Nous sommes donc en présence de deux systèmes centraux, dont les performances sont d´dépendantes du lieu considéré. Cette étude se focalise sur leur dénominateur commun : la carte routière numérique, et son utilisation en tant qu’outil d’évaluation de leur performance. L’idée développée durant cette thèse est d’utiliser la carte en tant que canevas d’apprentissage, pour stocker des informations géoréférencées sur la performance des diésèrent capteurs équipant le véhicule, au cours de trajets répétitifs. Pour cela, une localisation robuste, relative à la carte, est nécessaire au travers d’une méthode de map-matching. La problématique principale réside dans la différence de précision entre la carte et le positionnement GNSS, créant des situations ambigües. Durant cette thèse, un algorithme de map-matching a été conçu pour gérer ces ambigüités en fournissant des hypothèses multiples lorsque nécessaire. L’objectif est d’assurer l’intégrité de l’algorithme en retournant un ensemble d’hypothèses contenant l’hypothèse correcte avec une grande probabilité. Cet algorithme utilise les capteurs proprioceptifs dans une approche de navigation à l’estime aidée d’informations cartographiques. Une procédure d’évaluation de cohérence, utilisant le GNSS comme information redondante de positionnement est ensuite appliquée, visant à isoler une hypothèse cohérente unique qui pourra ainsi être utilisée avec confiance dans le processus d’écriture dans la carte. L’utilisation de la carte numérique en écriture/lecture a été évaluée et la procédure complète d’écriture a été testée sur des données réelles, enregistrées par des véhicules expérimentaux sur route ouverte
The information stored in digital road maps has become very important for intelligent vehicles. As intelligent vehicles address more complex environments, the accuracy requirements for this information have increased. Regarded as a geographic database, digital road maps contain contextual information about the road network, crucial for a good understanding of the environment. When combined with data acquired from on-board sensors, a better representation of the environment can be made, improving the vehicle’s situation understanding. Sensors performance can vary drastically depending on the location of the vehicle, mainly due to environmental factors. Comparatively, a map can provide prior information more reliably but to do so, it depends on another essential component: a localization system. Global Navigation Satellite Systems (GNSS) are commonly used in automotive to provide an absolute positioning of the vehicle, but its accuracy is not perfect: GNSS are prone to errors, also depending greatly on the environment (e.g., multipaths). Perception and localization systems are two important components of an intelligent vehicle whose performances vary in function of the vehicle location. This research focuses on their common denominator, the digital road map, and its use as a tool to assess their performance. The idea developed during this thesis is to use the map as a learning canvas, to store georeferenced information about the performance of the sensors during repetitive travels. This requires a robust localization with respect to the map to be available, through a process of map-matching. The main problematic is the discrepancy between the accuracy of the map and of the GNSS, creating ambiguous situations. This thesis develops a map-matching algorithm designed to cope with these ambiguities by providing multiple hypotheses when necessary. The objective is to ensure the integrity of the result by returning a hypothesis set containing the correct matching with high probability. The method relies on proprioceptive sensors via a dead-reckoning approach aided by the map. A coherence checking procedure using GNSS redundant information is then applied to isolate a single map-matching result that can be used to write learning data with confidence in the map. The possibility to handle the digital map in read/write operation has been assessed and the whole writing procedure has been tested on data recorded by test vehicles on open roads

Terrestrial target tracking using low Earth orbit satellites provides essential daily services and vital scientific data. In this thesis, the Attitude and Orbit Control System of such a terrestrial tracking satellite, Nanosatellite for Earth Monitoring and Observation Aerosol Monitor, is presented in detail. The satellite is a new generation Earth observation mission with the objective of detecting global atmospheric aerosol content through sub-degree pointing. The design is presented from initial hardware selection and budget development to operation definition and mission operation. The efficacy of performing precise autonomous Earth-pointing on a small satellite platform is validated through high fidelity simulations involving satellite and environmental dynamics, test-characterized hardware models and flight software-in-the-loop. The results provide practical target tracking methodologies which in the past have been publicly inaccessible to the author's best knowledge and which can be now be applied to a broad range of precise Earth-pointing satellites.