Two unique spatial discretizations employing generalized indexing strategies suitable for use with space-marching algorithms are presented for the numerical solution of the equations of fluid dynamics. Both discretizations attempt to improve geometric flexibility as compared to structured indexing strategies and have been formulated while considering the current and future availability of unstructured grid generation techniques. The first discretization employs a generalized indexing strategy utilizing triangular elements in the two dimensions normal to the streamwise direction, while maintaining structure within the streamwise direction. The second discretization subdivides the domain into a collection of computational blocks. Each block has inflow and outflow boundaries suitable for space marching. A completely generalized indexing strategy utilizing tetrahedra is used within each computational block. The solution to the flow in each block is found independently in a fashion similar to the cross-flow planes of a structured discretization. Numerical algorithms have been developed for the solution of the governing equations on each of the two proposed discretizations. These spatial discretizations are obtained by applying a characteristic-based, upwind, finite volume scheme for the solution of the Euler equations. First-order and higher spatial accuracy is achieved with these implementations. A time dependent, space-marching algorithm is employed, with explicit time integration for convergence of individual computational blocks. Grid generation techniques suitable for the proposed discretizations are discussed. Applications of these discretization techniques include the high speed flow about a 5° cone, an analytic forebody, and a model SR71 aircraft. / Ph. D.

This thesis describes the architecture, verification, qualification, and packaging of a 16-channel silicon-germanium (SiGe) Remote Electronics Unit (REU) designed for use in extreme environment applications encountered on NASA's exploration roadmap. The SiGe REU was targeted for operation outside the protective electronic "vaults" in a lunar environment that exhibits cyclic temperature swings from -180ºC to 120ºC, a total ionizing dose (TID) radiation level of 100 krad, and heavy ion exposure (single event effects) over the mission lifetime. The REU leverages SiGe BiCMOS technological advantages and design methodologies, enabling exceptional extreme environment robustness. It utilizes a mixed-signal Remote Sensor Interface (RSI) ASIC and an HDL-based Remote Digital Control (RDC) architecture to read data from up to 16 sensors using three different analog channel types with customizable gain, current stimulus, calibration, and sample rate with 12-bit analog-to-digital conversion. The SiGe REU exhibits excellent channel sensitivity throughout the temperature range, hardness to at least 100 krad TID exposure, and single event latchup immunity, representing the cutting edge in cold-capable electronic systems. The SiGe REU is the first example within a potential paradigm shift in space-based electronics.

The Outer Space Treaty established the obligation to provide continuing supervision of its national space activities by the appropriate state. The implementation of this obligation remains a matter of state discretion. Since this Treaty came into force the world has evolved to become reliant on space based utilities to enable the global economy and state governance. Today, space faring states are increasingly dependent upon the supervision practices of other states to assure its space interests as the attribution of state responsibility becomes more difficult to ascribe. / Therefore, the absence of binding supervision standards may become an impediment to future space applications due to three identified trends. First, the trend towards space commercialization requires active state supervision. Second, the rise in environmental hazards requires minimal safety standards to decrease the harmful effects on space applications. Third, space security requires identification of intentional acts and prudent measures to safeguard vital space applications.

SiGe BiCMOS technology has many advantageous properties that, when leveraged, enable circuit design for extreme environments. This work will focus on designs targeted for space system avioinics platforms under the NASA ETDP program. The program specifications include operation under temperatures ranging from -180 C to +125 C and with radiation tolerance up to total ionizing dose of 100 krad with built-in single-event latch-up tolerance. To the author's knowledge, this work presents the first design and measurement of a wide temperature range enabled, radiation tolerant as built, RS-485 wireline transceiver in SiGe BiCMOS technology. This work also includes design and testing of a charge amplification channel front-end intended to act as the interface between a piezoelectric sensor and an ADC. An additional feature is the design and testing of a 50 Ohm output buffer utilized for testing of components in a lab setting.

Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Suivi de notre développement ou encore la compréhension de l’Univers. Deux technologies de capteurs d’image sont actuellement utilisées dans les missions d’imagerie de la Terre et de l’espace : les imageurs CCD (Charge Coupled Device) et CMOS. L’environnement radiatif spatial est constitué de particules énergétiques qui dégradent les performances des imageurs. Et il s’avère que les dégradations réelles observées en vol dépendent fortement des conditions orbitales et de fonctionnement et sont donc très difficiles à prédire. L’étude menée dans le cadre de cette thèse a pour objet la compréhension des dégradations subies par les capteurs CCD et CMOS lorsqu’ils sont soumis à l’environnement radiatif spatial et la proposition de méthodes d’évaluation mieux adaptées pour obtenir une meilleure prédiction de la dégradation réelle d’un imageur en orbite à partir de tests d’irradiation réalisés au sol. La démarche entreprise a tout d’abord consisté à identifier les paramètres d’essais au sol pouvant potentiellement être à l'origine des différences observées entre les résultats sol et vol. Un plan d’essai d’irradiation aux rayons y et aux protons a ainsi été défini afin d’évaluer la dégradation des imageurs CCD et CMOS dans des conditions de fonctionnement et d’irradiation proches de celles en vol. Nous avons étudié l’impact des conditions de mise en opération du composant durant l’irradiation (polarisation, rapport cyclique, etc.) mais aussi l’impact des conditions d’irradiation (débit de dose, énergies des protons, etc.). Le périmètre de cette thèse se limite à l’étude des effets sur le courant d’obscurité, sur la dispersion pixel-à-pixel du courant d’obscurité et sur l’apparition des pixels chauds, qui sont, au premier ordre, les principaux critères de performances dégradés d’un imageur par les radiations. L’étude de l’influence du débit de dose de l’irradiation a montré un phénomène ELDRS (Enhanced Low Dose Rate Sensitivity) pour la première fois sur un capteur CCD polarisé dynamiquement avec un rapport cyclique ON/OFF. Les conditions de polarisation dynamique évaluées sur les APS ont démontré que la dégradation est d’autant plus importante que la fréquence d’activation et le rapport cyclique sont grands. Les irradiations aux protons sur les imageurs CMOS ont aussi montré l’apparition et la guérison de pixels chauds après irradiation à température ambiante ainsi que l'apparition du bruit de signal aléatoire télégraphique (RTS). Ces deux modes de dégradation ont été analysés plus en détail afin d'évaluer leur comportement en guérison pour le premier et extraire les statistiques d'apparition sur l'autre, sur un grand nombre de pixels. En parallèle, un code de simulation de l’effet de dose dans les oxydes de structures élémentaires MOS, ACDC (Accumulation des Charges en Dose Cumulée), a été adapté et utilisé. Ce code a permis de mettre en évidence les constantes de temps impliquées dans la dégradation par effets ionisants dans ces structures. Ces constantes de temps sont utilisées pour l'interprétation des effets de la polarisation dynamique. Les résultats expérimentaux obtenus sur les capteurs d’image CCD et CMOS ont un impact sur l’assurance durcissement. Les irradiations aux protons des imageurs CMOS ont notamment montré un phénomène de guérison des pixels chauds plus marqué que sur les autres pixels, montrant l'intérêt d'une caractérisation de plusieurs semaines après irradiation. Pour les irradiations au Co60 des imageurs CMOS, il est recommandé de ne pas utiliser des temps de polarisation ON trop courts (périodes de cycle petites) car cela peut conduire à une sous-estimation de la dégradation (charge piégée et états d'interface). / Two imaging sensor technologies are presently used in Earth and space imagery missions: Charge Couple Devices (CCD) and CMOS detectors. The space radiation environment is composed of energetic particles that degrade imaging sensor’s performances. It has been shown that real in-orbit degradation of imaging sensors are strongly dependent of orbital and operating conditions and are, as a consequence, difficult to predict. The work performed in this thesis has for purpose an understanding of space radiation-induced degradations for both CCD and CMOS technologies and the proposal of better suited assessment methods for these specific devices in order to better prediction of real in-orbit detector’s degradation from on-ground irradiation tests. The first step of the work focused on the identification of on-ground test parameters that could possibly explain the differences observed between inorbit and on-ground data. Thus an irradiation test plan to y-rays and proton particles has been defined in order to assess the imaging sensor’s degradation for both CCD and CMOS technologies in operating and irradiation conditions close to in-orbit ones. The effects of detector’s operation conditions during irradiation (bias, duty cycle, etc.) but also the irradiation conditions (dose rate, proton energy, etc.) have been studied. The present work focuses on effects on dark current, on its pixel to pixel dispersion and on the presence of hot pixels, which are, at first order, the main performance parameters of an imaging sensor that is degraded by space radiations. The study of the irradiation dose rate influence has shown an Enhanced Low Dose Rate Sensitivity (ELDRS) phenomenon observed for the first time on a CCD imager under dynamic bias condition with a ON/OFF duty cycle. The tested bias conditions CMOS image sensors have demonstrated that the higher the activation frequency and duty cycle, the higher is the degradation. Besides, the proton irradiations performed on CMOS detectors have induced hot pixels that anneal just after irradiation at room temperature. A random telegraphic signal (RTS) behaviour of the dark current has also been shown on CMOS sensors. In parallel to the irradiation tests, a simulation code of ionizing dose effects on oxides of MOS elementary structures has been adapted and used. This program, called ACDC (Accumulation des Charges en Dose Cumulée), has allowed to assess the quantification time constants of physical mechanisms that induce ionizing dose degradation on these structures. These time constants are used for the interpretation of dynamic bias effects.

Solar transient eruptions are the main cause of interplanetary-magnetospheric disturbances leading to the phenomena known as geomagnetic storms. Eruptive solar events such as coronal mass ejections (CMEs) are currently considered the main cause of geomagnetic storms (GMS). GMS are strong perturbations of the Earth’s magnetic field that can affect space-borne and ground-based technological systems. The solar-terrestrial impact on modern technological systems is commonly known as Space Weather. Part of the research study described in this thesis was to investigate and establish a relationship between GMS (periods with Dst ≤ −50 nT) and their associated solar and interplanetary (IP) properties during solar cycle (SC) 23. Solar and IP geoeffective properties associated with or without CMEs were investigated and used to qualitatively characterise both intense and moderate storms. The results of this analysis specifically provide an estimate of the main sources of GMS during an average 11-year solar activity period. This study indicates that during SC 23, the majority of intense GMS (83%) were associated with CMEs, while the non-associated CME storms were dominant among moderate storms. GMS phenomena are the result of a complex and non-linear chaotic system involving the Sun, the IP medium, the magnetosphere and ionosphere, which make the prediction of these phenomena challenging. This thesis also explored the predictability of both the occurrence and strength of GMS. Due to their nonlinear driving mechanisms, the prediction of GMS was attempted by the use of neural network (NN) techniques, known for their non-linear modelling capabilities. To predict the occurrence of storms, a combination of solar and IP parameters were used as inputs in the NN model that proved to predict the occurrence of GMS with a probability of 87%. Using the solar wind (SW) and IP magnetic field (IMF) parameters, a separate NN-based model was developed to predict the storm-time strength as measured by the global Dst and ap geomagnetic indices, as well as by the locally measured K-index. The performance of the models was tested on data sets which were not part of the NN training process. The results obtained indicate that NN models provide a reliable alternative method for empirically predicting the occurrence and strength of GMS on the basis of solar and IP parameters. The demonstrated ability to predict the geoeffectiveness of solar and IP transient events is a key step in the goal towards improving space weather modelling and prediction.

Space weather and its effect on technological systems are important for scientific research. Developing an understanding of the behaviour, sources and effects of ionospheric events form a basis for improving space weather prediction. This thesis attempts to use co-located radars and instruments for the analysis of ionospheric events over South Africa. The HF Doppler radar, ionosonde, Global Positioning System (GPS) and GPS ionospheric scintillation monitor (GISTM) receivers are co-located in Hermanus (34.4°S, 19.2°E), one of the observatories for the space science directorate of the South African National Space Agency (SANSA). Data was obtained from these radars and instruments and analysed for ionospheric events. Only the Hermanus station was selected for this analysis, because it is currently the only South African station that hosts all the mentioned radars and instruments. Ionospheric events identified include wave-like structures, Doppler spread, sudden frequency deviations and ionospheric oscillations associated with geomagnetic pulsations. For the purpose of this work, ionospheric events are defined as any unusual structures observed on the received signal and inferred from observations made by the HF Doppler radar. They were identified by visual inspection of the Doppler shift spectrograms. The magnitude and nature of the events vary, depending on their source and were observed by all, some or one instrument. This study suggests that the inclusion of a wider data coverage and more stations in South Africa merit consideration, especially since plans are underway to host a co-located radar network similar to that in Hermanus at at least three additional observatory sites in South Africa. This study lays a foundation for multi-station co-located radar and instrument observation and analysis of ionospheric events which should enhance the accuracy of space weather and HF communication prediction.

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 1976 / Bibliography: p. 361-366. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Chemical Engineering

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