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.

State-of-the-art onboard spacecraft avionics use SpaceWire networks to interconnect payload data-handling sub-systems. This includes high data-rate sensors and instruments, processing units, and memory devices. SpaceWire is an interconnection network composed of nodes and routers connected by bi-directional, point-to-point, high-speed, serial-data communication links. SpaceWire is established as one of the main data-handling protocols and is being used on many ESA, NASA and JAXA spacecraft. SpaceWire is very successful for being fast, flexible and simple to use and implement. However it does not implement Quality of Service mechanisms, which aim to provide guarantees in terms of reliability and timely delivery to data generated by network clients. Quality of Service is increasingly being deployed in commercial ground technologies and its availability for space applications, which requires high reliability and performance, is of high interest for the space community. This thesis researches how Quality of Service can be provided to existing SpaceWire networks. Existing solutions for ground-based technologies cannot be directly used because of the constraints imposed by the limitations of space-qualified electronics. Due to these limitations SpaceWire uses wormhole routing which has many benefits but makes it more challenging to obtain timing guarantees and to achieve a deterministic behaviour. These challenges are addressed in this work with a careful analysis of existing Quality of Service techniques and the implementation of a novel set of protocols specifically designed for SpaceWire networks. These new protocols target specific use cases and utilise different mechanisms to achieve the required reliability, timely delivery and determinism. Traditional and novel techniques are deployed for first time in SpaceWire networks. In particular, segmentation, acknowledgements, retry, time-division multiplexing an cross-layer techniques are considered, analysed, implemented and evaluated with extensive prototyping efforts. SpaceWire provides high-rate data transfers but the next generation of payload instruments are going to require multi-gigabit capabilities. SpaceFibre is a new onboard networking technology under development which aims to satisfy these new requirements, keeping compatibility with SpaceWire user-applications. As a new standard, SpaceFibre offers the opportunity to implement Quality of Service techniques without the limitations imposed by the SpaceWire standard. The last part of this thesis focuses on the specification of the SpaceFibre standard in order to provide the Quality of Service required by next generation of space applications. This work includes analytical studies, software simulations, and hardware prototyping of new concepts which are the basis of the Quality of Service mechanisms defined in the new SpaceFibre standard. Therefore, a critical contribution is made to the definition and evaluation of a novel Quality of Service solution which provides high reliability, bandwidth reservation, priority and deterministic delivery to SpaceFibre links.

Research has been completed to determine the most effective thermal control architecture for modular satellites. This research investigated principles of modularity, modular spacecraft examples, thermal control methods, and advanced thermal control technologies. A modular spacecraft was designed as a case study to determine key influences and issues. A number of thermal control architectures were developed. Each was evaluated for compatibility with modularity principles, thermal control performance, and a realizable implementation. Thermal control performance was determined by simulating on-orbit conditions for a number of design reference missions, including traditional thermal control architecture used for comparison. An effective thermal control architecture was found that has all desired attributes. The methods of development, simulation, and evaluation are presented with results and key findings.

Traditional spacecraft guidance techniques have the objective of deterministically minimizing fuel consumption. These traditional approaches to guidance are developed independently of the navigation system, and without regard to stochastic effects. This work presents and demonstrates a new approach to guidance design. This new approach seeks to maximize the probability of mission success by minimizing the variance of trajectory dispersions subject to a fuel consumption constraint. The fuel consumption constraint is imposed by formulating the dynamics in terms of a steering command, and placing a constraint on the final time. Stochastic quadratic synthesis is then used to solve for the nominal control along with the estimator and feedback gains. This new approach to guidance is demonstrated by solving a simple Zermelo boat problem. This example shows that a significant reduction in terminal dispersions is possible with small increases to fuel budgeted for the maneuver.

Insulators used in the construction of spacecraft are irradiated with high-energy electrons in the space environment and this sometimes causes the insulators to charge to very high voltages. Such charged insulators can generate spontaneous electric partial-discharge pulses of the order of mA to tens of A. These pulses sometimes last enough time to destroy the expensive micro-circuitry present in the spacecraft. In evaluating the threat to the spacecraft due to these discharges, calculation of the resistivity becomes a critical parameter since it determines how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. So far, resistivity values for the insulators for spacecraft applications have been simply imported from tabulated results measured using standard American Society for Testing and Materials (ASTM) and International Electro-technical Commission (IEC) methods. This thesis work provides the details of the charge storage method which has been found to be more appropriate in calculating the resistivity of spacecraft insulators by emulating the space environment better. This method is based on the concept that the resistivity is better measured as the decay of the charge deposited on the surface of an insulator, rather than by the flow of current across two electrodes around the sample which is the case with the classical method of measurements. From the results obtained from the charge storage method, it has been found that the ASTM resistivity values for thin film insulating spacecraft materials have been found to under-predict charge transport values applicable to many spacecraft charging problems, by 10 to 104 times. The charge storage method has only one side of the insulator in vacuum exposed to charged particles, light and plasma, with a metal electrode attached to the other side of the insulator. The chamber for measuring the charge storage decay has been designed with the capability to measure 32 samples simultaneously. The details of the apparatus, instrumentation, test methods, data acquisition methods, and data analysis for measuring resistivity of the spacecraft insulators are given here. Details about the vacuum environment, sample mounting, isolation of the samples, charging of the samples, measurement of the surface charge, rotary motion of the sample carousel, etc., are also given. The report also includes differences between the classical methods and the charge storage method both in terms instrumentation and methodology. The results obtained from both methods are tabulated showing the superiority of the charge storage method. Recommendations for future work are also included.

Conformal antennas have widespread applications in communication systems for vehicular bodies, aircrafts, and spacecrafts etc. They are non-protruding and can arbitrarily take any shape on the surface where they are etched. This thesis is a summary of two main projects. The first project employs a conformal array of four S-band and four GPS-band antennas for sub-payload of a sounding rocket. The sub-payload is a small cylinder and therefore the eight conformal antennas are based on curved patch geometry. The second project employs a conformal antenna for a CubeSat. The antenna is based on a cavitybacked slot and therefore can be conveniently integrated around the surface-mount solar cells of the CubeSat. Such an integration has enormous merits for CubeSat because there is no competition between the antennas and solar cells for the limited surface real estate. The antenna design operates UHF band with circular polarization, making it the first UHF nondeployed antenna for CubeSats. For both projects, problems such as isolation, impedance bandwidth, axial ratio bandwidth, and EMI shielding have been analyzed and resolved. This thesis work yields a prototype-ready design for the first project, and a final prototype and measurements for the second project.

This thesis presents a comparison of controller designs and a system software design for a general Guidance, Navigation and Control (GNC) system. The first part of the thesis investigates four control algorithms based on Lyapunov Direct Method in conjunction with sliding mode and adaptive control. These algorithms address three practical issues in controller design: maximum actuation limitation, external disturbances, and imperfect dynamic models. Each of the algorithms is proven to be globally asymptotically stable within its constraints. A simulation is then used to model a cube-satellite attitude maneuver using each of the controllers to evaluate its performance. The second part of this thesis discusses the development of a high-level flight software architecture capable of handling common tasks, including ground station communication and attitude maneuvers, as well as power or device failures. / text

The University of Texas at Austin (UT-Austin) Satellite Design Lab (SDL) is currently designing two 3U CubeSat spacecraft – Bevo-2 and ARMADILLO – which serve as the foundation for the design reusability and cost analysis of this thesis. The thesis explores the reasons why a small satellite would want to incorporate a reusable design and the processes needed in order for this reusable design to be implemented for future projects. Design and process reusability reduces the total cost of the spacecraft, as future projects need only alter the components or documents necessary in order to create a new mission. The thesis also details a grassroots approach to determining the total cost of a 3U CubeSat satellite development project and highlights the costs which may be considered non-recurring and recurring in order to show the financial benefit of reusability. The thesis then compares these results to typical models used for cost analysis in industry applications. The cost analysis determines that there is a crucial gap in the cost estimating of nanosatellites which may be seen by comparing two widely-used cost models, the Small Satellite Cost Model (SSCM <100 kg) and the NASA/Air Force Cost Model (NAFCOM), as they apply to a 3U CubeSat project. While each of these models provides a basic understanding of the elements which go into cost estimating, the Cost Estimating Relationships (CERs) do not have enough historical data of picosatellites and nanosatellites (<50 kg) to accurately reflect mission costs. Thus, the thesis documents a discrepancy between widely used industry spacecraft cost models and the needs of the picosatellite and nanosatellite community, specifically universities, to accurately predict their mission costs. It is recommended to develop a nanosatellite/CubeSat cost model with which university and industry developers alike can determine their mission costs during the designing, building and operational stages. Because cost models require the use of many missions to form a database, it is important to start this process now at the beginning of the nanosatellite/CubeSat boom. / text

Within the first decade of the 21st century, the aerospace community has seen many more opportunities to launch small spacecraft in the 10 to 100 kg mass class. Coupled with this has been consistent interest from the government in developing small-spacecraft platforms to expand civil and military mission possibilities. Small spacecraft have also given small organizations such as universities an increased access to space. Because small satellites are limited in size, power, and mass, new and often nontraditional capabilities must be explored and developed to make them viable and attractive when compared with larger and more proven spacecraft. Moreover, small organizations that wish to contribute technically are often limited by the small size of their teams and available resources, and need creative solutions for meeting mission requirements. A key need is in space-to-ground communications. Complex missions typically require large amounts of data transfer to the ground and in a timely fashion. Available options trade hardware cost, available ground stations or networks, available operating-frequency range, data-rate performance, and ease of use. A system for small spacecraft will be presented based upon Radio Frequency Integrated Circuits (RFIC) that minimizes development effort and maximizes interface control to meet typical small-spacecraft communications requirements. RFICs are low-cost components that feature pre-built radio hardware on a chip that can be expanded easily by developers with little or no radio experience. These devices are widespread in domestic applications for short-range connectivity. A preliminary design and prototype is presented that meets basic spaceflight requirements, offers data rates in the 55 to 85 kbps range, and has completed basic proof-of-concept testing. While there are higher-data-rate alternatives in existence, the solution presented here strikes a useful balance among data rate, parts cost, and ease of use for non experts, and gives the user operational control necessary to make air-to-ground communications time effective.

The term Gossamer is used to describe ultra-lightweight spacecraft structures that solve the aerospace challenge of obtaining maximum performance while reducing the launch costs of the spacecraft. Gossamer structures are extremely compliant, which complicates control design and ground testing in full scale. One approach is to design and construct smaller test articles and verify their computational models experimentally, so that similar computational models can be used to predict the dynamic performance of full-scale structures. Though measurement of both in-plane and out-of-plane displacements is required to characterize the dynamic response of the surface of these structures, this thesis lays the groundwork for dynamic measurement of the in-plane component. The measurement of thin films must be performed using non-contacting sensors because any contacting sensor would change the dynamics of the structure. Moreover, the thin films dealt with in this work are coated with either gold or aluminum for special applications making the film optically smooth and therefore requiring a surface pattern. A Krypton Fluoride excimer laser system was selected to fabricate patterns on thin-film mirror test articles. Parameters required for pattern fabrication were investigated. Effects of the pattern on the thin-film dynamics were studied using finite element analysis. Photogrammetry was used to study the static in-plane displacement of the thin-film mirror. This was performed to determine the feasibility of the photogrammetric approach for future dynamic tests. It was concluded that photogrammetry could be used efficiently to quantify dynamic in-plane displacement with high-resolution cameras and sub-pixel target marking.