This dissertation introduces novel techniques for exploiting the environmental aerodynamic forces to actively control the attitude of the spacecraft operating in the lower and middle thermosphere. It includes both simulations and real spacecraft attitude determination and control subsystem development, which provide a complete picture of the application of the aerodynamic forces to benefit space missions that are operating very close to Earth, as well as contribute to the knowledge of rarefied gas aerodynamics in the lower and middle part of the thermosphere. The research starts by reviewing the current progress of thermosphere science and rarefied gas aerodynamics to construct a high fidelity aerodynamic model for spacecraft operating in the rarefied gas (mainly atomic oxygen) environment in very low Earth orbits (below 450 km) and following by a brief system level analysis of the benefits and challenges for the spacecraft flying lower to Earth. A real spacecraft is also developed to validate of the application of the aerodynamic forces for attitude control. The aspect of the design included in this dissertation focuses mainly on the attitude determination and control system development of satellite. The CubeSat has a generic design with deployable solar panels that can be rotated to control the aerodynamic torques. Based on the common attitude control requirements of spacecraft operating in very low Earth orbits, and the hardware capability of the satellite three novel orbital aerodynamic attitude control strategies are proposed: Energy Optimized B-dot Detumbling into an Aerostable State; Active Orbital Aerodynamic Coarse Pitch/Yaw Control; a 3-axis Orbital Aerodynamic Torques Adaptive Sliding Mode Control. The control performance for each control algorithm is validated numerically in high-fidelity attitude propagators. Knowledge of the thermospheric winds is important as they influence the control performance and the dynamic response of the spacecraft, aerostable designs steering into the thermosphere wind vector. Two novel computational methods to measure the thermospheric wind from the dynamic response of the spacecraft due to aerodynamic forces are proposed. The in-situ measured wind vector benefits the attitude observation in the feedback control systems, which helps to improve the adapting performance and to increase the control accuracy. The proposed novel aerodynamic attitude control algorithms can be adapted for similar spacecraft operating in the very low Earth orbits with modifications to the deployable solar panels or adding movable aerodynamic control surfaces. In addition, this proposed orbital aerodynamic attitude control system works not only in the very low Earth orbits but can also be potentially implemented for spacecraft operating in the rarefied gas region of the atmospheres of other planets.

<p dir="ltr">Nutrients are essential to support fish production in aquatic systems but are detrimental in excess. To that end, the relationship between nutrient loading and fish biomass is hypothesized to be unimodal. In the mid-20^th century, numerous aquatic systems in North America and Europe were receiving excessive nutrients and were considered heavily degraded as a result. Since then, nutrient abatement programs have resulted in increased fish biomass in many systems throughout the two continents. However, few systems have complete records of fish biomass and nutrient loading to offer support for both sides of the unimodal fishery production curve. In Saginaw Bay, Lake Huron, total phosphorus estimates are available back to when nutrient abatement programs were first implemented in the system in the 1970s. In addition, a long-term fall bottom trawling dataset from an annual monitoring survey conducted by the Michigan Department of Natural Resources has indexed fish biomass and composition since 1970. In Chapter 2, we utilize these datasets to analyze trends in system-wide fish biomass as well as fish community trends since 1970 in response to continued nutrient abatement. We found increasing fish biomass from 1970 until the early 2000s concurrent with total phosphorus declines. However, more recently, we documented declines in system-wide fish biomass with reduced nutrient loads. We found planktivorous and benthivorous fish species displayed similar initial increases in biomass followed by more recent declines in biomass. However, we determined current total phosphorus loading was still sufficient to support piscivore biomass near peak levels.</p><p dir="ltr">While nutrients in Saginaw Bay are lower than at times in the past, the system is still highly productive. One consequence of productive systems is increased susceptibility to hypoxia, or low dissolved oxygen that can result from organic matter decomposition. Past studies have documented hypoxic conditions in Saginaw Bay in the summer and over-winter period. However, past studies have been limited in scale and have not estimated the extent or duration of hypoxia throughout the Saginaw Bay system. With climate change expected to increase the occurrence of hypoxia throughout the Laurentian Great Lakes, knowledge of dissolved oxygen dynamics in the system is becoming progressively more important. In Chapter 3, we used an array of high frequency data loggers deployed throughout inner Saginaw Bay over two summer and over-winter periods to document dissolved oxygen conditions. We also analyzed a time series dataset of bottom oxygen and environmental parameter measurements to determine the conditions that contribute to low dissolved oxygen in the bay. Further, through stable isotope analysis we investigated whether hypoxic conditions had an effect on the carbon and nitrogen (δ¹³C and δ¹⁵N) isotopic signatures of chironomid larvae, an important basal prey item in Saginaw Bay. We found instances of seasonal hypolimnetic hypoxia in the summers of 2021 and 2022 but normoxic conditions throughout the over-winter periods following each summer. We also determined bottom water and wind speed to be the most reliable predictors of low dissolved oxygen since 2011, indicating the temporary stratification that can occur during warm, calm summer periods likely precedes the development of hypoxic conditions in Saginaw Bay. Chironomid δ¹³C and δ¹⁵N values were highly variable, but some individuals displayed very low values, indicative of hypoxia exposure.</p>

Dans cette thèse, le problème du contrôle d’attitude de satellites agiles à l’aide de grappes d’actionneurs gyroscopiques (AGs) est considéré et plus particulièrement son application au contrôle de micro/nanosatellites (10-100 kg). Des outils d’analyse topologique sont tout d'abord développés. La comparaison de différentes configurations de grappes justifie le choix d'une géométrie pyramidale à six actionneurs gyroscopiques. Des analyses plus approfondies de cette grappe, avec et sans cas de panne, permettent de déduire des contraintes que la loi de pilotage doit vérifier pour être adaptée à ce système. Pour y répondre, après analyse de la littérature, une nouvelle structure de loi de pilotage ainsi qu’une formulation différente des équations cinématiques sont développées. Cette structure est basée sur l’algorithme du filtre de Kalman étendu. Elle a pour avantages de répondre aux exigences en termes de calcul temps réel au bord des satellites, de flexibilité sur la gestion des contraintes et de facilité d’adaptation en cas de pannes. En outre, une procédure de génération de boucle de commande, englobant la loi de pilotage et un contrôleur robuste du système, est proposée. La généralisation de cette boucle de commande est illustrée sur des bras manipulateurs à base fixe et spatiaux.En parallèle, l’étude du passage des singularités internes intraversables mène à une nouvelle stratégie d’évitement de ces singularités. Des simulations sur des modèles de satellites représentatifs illustrent les résultats. La grappe d’actionneurs et la boucle de commande développées seront testées dans le cadre d’une expérimentation en microgravité. / In this thesis, the attitude control problem for agile satellites with control moment gyro (CMG) clusters is studied. In particular, the problem applies to micro/nanosatellites (10-100kg). First, numerical tools are developed to analyse the compatibility of various cluster configurations with the nanosatellite constraints. The pyramidal six-CMG cluster is then selected. This cluster topology is analysed in depth, with and without actuator failures. Constraints on the development of a steering law adapted to our system are deduced. Among them, the singularity avoidance issue is emphasised. To meet the requirements, an analysis of the literature is carried out. Then, a new steering law structure and a different formulation of the kinematic equations are developed. This structure is based on the extended Kalman filter algorithm. It meets the requirements because it can be calculated in real-time onboard satellites, constraints imposed on the system are handled with flexibility and it is easily adaptable in case of actuator failures. In addition, a procedure to generate the control loop is proposed, containing a robust controller. The generalisation of this control loop is shown on space and fixed-base manipulator arms. Furthermore, the study of the internal elliptic singularities in CMG clusters leads to a new singularity avoidance strategy. Software simulations on highly representative simulators show the results of the steering law in various actuator failure cases. The CMG cluster and the control loop will be tested in a parabolic flight campaign, and the development of this experiment is detailed in this thesis.

Spacecraft simulator platforms can simulate the microgravity environment of space on Earth, for the purposes of testing the Attitude and Orbit Control Subsystem of satellites. In order to do this, the satellite is mounted on a bench and the combined center of mass of this assembly is controlled by a series of moving masses. The objective is to bring this center or mass as close as possible to the center of rotation, since solids in microgravity always rotate around their own center of mass. The air-bearing platform located, designed and built at the NanoSat Laboratory of the Kiruna Space Campus of the Luleå University of Technology makes use of four balancing masses, which are displaced by that number of linear actuators. This document explains the process followed to design an algorithm for the estimation of the center of mass and the subsequent calculation of the required positions of the balancing masses to bring this center of mass back to the center of rotation. First, the equations of rotational motion of the bench were found through two formulations: quaternions and Euler-Lagrange. Secondly, these equations were used to obtain an estimation of the center of mass via Batch Least-Squares. Thirdly, the equations of the center of mass of a system of point masses were used to find the proper positions of the balancing masses. Finally, the complete algorithm was tested with Hardware-in-the-Loop simulations before testing it in the real hardware of the platform. The developed algorithm was not capable of estimating the center of mass with sufficient accuracy, which invalidated the obtained actuator positions, and thus was not able to compensate the offset of the center of mass. Recommended lines of development are provided to assist on the continuation of this work.

This thesis aims to design a reliable CubeSat platform, including the avionic subsystems that can sustain a high radiation environment for a mission having a lifetime of at least six months. The science instruments put stringent requirements on the platform to achieve and maintain the desired spin rate. The simulation background is set up in Systems Tool Kit (STK). A trade-off analysis for the Attitude and Orbit Control System (AOCS) of FORESAIL 2 was done, focusing on the actuators and their ability to offer the right amount of torque to fulfill the tether deployment. Mission design analyses were performed to conclude on the form factor of the CubeSat, its ability to generate power, its compliance with the Space Debris Mitigation (SDM) technical requirements, and the total radiation dose accumulated. It was found that a 6U form factor is preferred to allocate more space for each subsystem, alongside with generating enough power for the satellite to work in all modes wanted. The mission is compliant with European Cooperation for Space Standardization (ECSS) and International Organization for Standardization (ISO) standards if the CubeSat is to be launched in September 2022. To allow a threshold limit of 10 krads on the components of the satellite, a shielding wall of 7 mm should be implemented on the CubeSat’s structure. Major requirements for the designed mission were written to initialize the investigation on the sensors and actuators. The results showed that only a propulsion system provided the necessary angular momentum to deploy the tether. The lack of magnetic field makes magnetorquers almost unusable in the desired orbit, leaving reaction wheels as the only option remaining to assist the propulsion units. The different analyses and simulations led to a final AOCS configuration composed of five various sensors (Sun sensors, magnetometers, a GPS, an IMU, and housekeeping sensors) for the attitude determination. A propulsion system and reaction wheels will provide the necessary control over the satellite.

The subject of this thesis covers the process of online parameter estimation of agile satellites. Accurate knowledge of parameters such as moment of inertia and centre of mass play a crucial role in satellite attitude control and pointing performance. Typically, identification of parameters such as these is performed on-ground using post-processing algorithms. This thesis investigates the potential of performing the identification procedures in real-time on-board operating satellites, using only measurements available from typical satellite attitude sensors.    The thesis covers the areas of system identification and modelling of spacecraft attitude dynamics. An algorithm based on the Unscented Kalman Filter is developed for online parameter estimation of spacecraft moment of inertia parameters. The proposed method is successfully validated, both through simulation environments, and in practice using Airbus’ satellite hardware demonstrator INTREPID, a three-axis air-bearing table equipped with CMG actuators and typical attitude sensors.