Total Mission Concept
Ground System Process Control
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AbstractEmbedded parallel processing provides unique advantages over sequential and symmetrical processing architectures. During the past decade, the architecture of ground control systems has evolved from utilizing sequential embedded processors to modular parallel, distributed, and/or symmetrical processing. The concept of utilizing embedded parallel processing exhibits key features such as modularity, flexibility, scalability, host independence, non-contention of host resources, and no requirement for an operating system. These key features provide the performance, reliability and efficiency while at the same time lowering costs. Proper utilization of embedded parallel processing on a host computer can provide fault tolerance and can greatly reduce the costs and the requirement of utilizing high-end workstations to perform the same level of real-time processing and computationally intensive tasks.
SponsorsInternational Foundation for Telemetering
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DSP BASED SIGNAL PROCESSING UNIT FOR REAL TIME PROCESSING OF VIBRATION AND ACOUSTIC SIGNALS OF SATELLITE LAUNCH VEHICLEST.N., Santhosh Kumar; A.K., Abdul Samad; K.M., Sarojini; Indian Space Research Organisation (International Foundation for Telemetering, 1995-11)Measurement of vibration and acoustic signals at various locations in the launch vehicle is important to establish the vibration and acoustic environment encountered by the launch vehicle during flight. The vibration and acoustic signals are wideband and require very large telemetry bandwidth if directly transmitted to ground. The DSP based Signal Processing Unit is designed to measure and analyse acoustic and vibration signals onboard the launch vehicle and transmit the computed spectrum to ground through centralised baseband telemetry system. The analysis techniques employed are power spectral density (PSD) computations using Fast Fourier Transform (FFT) and 1/3rd octave analysis using digital Infinite Impulse Response (IIR) filters. The programmability of all analysis parameters is achieved using EEPROM. This paper discusses the details of measurement and analysis techniques, design philosophy, tools used and implementation schemes. The paper also presents the performance results of flight models.
Towards understanding the processing of indirect speech acts: Reconsidering the standard pragmatic model of processingPolcar, Leah Elizabeth (The University of Arizona., 2003)This investigation tests whether a stage-type model of the processing of indirect speech acts is a fully explanatory model. A stage model, like the Standard Pragmatic Model (SPM), proposes that listeners understand the meaning of an indirect speech act by first determining direct meaning and then checking this meaning against context for sufficiency. It is only when direct meaning is found not to fully capture context that a listener proceeds to understand the meaning of an indirect speech act. This sort of model has been heavily criticized in the extant theoretical and empirical research, though this investigation shows much of this criticism to be faulty and/or irrelevant to indirect speech act processing. Here, minor revision of the SPM is proposed through the introduction of Cdirect and C indirect meanings that makes the modified SPM sensitive to issues of conventionality. Two experiments test this modified model (the MSPM). Results of the first experiment showed that the MSPM is the most explanatory model in explaining the processing of non-conventional indirect speech acts. The second experiment was designed to replicate an earlier experiment by Shapiro and Murphy (1993) and to investigate the influence of conventionality on the processing of indirect speech acts. The results of the conventionality analysis allow no clear conclusions about how conventional indirect speech acts are processed, but do call the results of the Shapiro and Murphy (1993) investigation into question. Additionally, some indirect proof is found that shows that conventionality influences the processing of indirect speech acts by making judgments of direct meaning difficult when conventional cues are present. Implications of these results are discussed and overall, the MSPM is found to be the best model for describing indirect speech act processing.
Processing High Purity Zirconium Diboride Ultra-High Temperature Ceramics: Small-to-Large Scale ProcessingPham, David (The University of Arizona., 2016)Next generation aerospace vehicles require thermal protection system (TPS) materials that are capable of withstanding the extreme aerothermal environment during hypersonic flight (>Mach 5 [>1700 m/s]). Ultra-high temperature ceramics (UHTC) such as zirconium diboride (ZrB₂) are candidate TPS materials due to their high-temperature thermal and mechanical properties and are often the basis for advanced composites for enhanced oxidation resistance. However, ZrB₂ matrix impurities in the form of boron trioxide (B₂O₃) and zirconium dioxide (ZrO₂) limit the high-temperature capabilities. Electric based sintering techniques, such as spark plasma sintering (SPS), that use joule heating have become the preferred densification method to process advanced ceramics due to its ability to produce high density parts with reduced densification times and limit grain growth. This study focuses on a combined experimental and thermodynamic assisted processing approach to enhance powder purity through a carbo- and borocarbo-thermal reduction of oxides using carbon (C) and boron carbide (B₄C). The amount of oxides on the powder surface are measured, the amount of additive required to remove oxides is calculated, and processing conditions (temperature, pressure, environment) are controlled to promote favorable thermodynamic reactions both during thermal processing in a tube furnace and SPS. Untreated ZrB₂ contains 0.18 wt%O after SPS. Additions of 0.75 wt%C is found to reduce powder surface oxides to 0.12 wt%O. A preliminary Zr-C-O computational thermodynamic model shows limited efficiency of carbon additions to completely remove oxygen due to the solubility of oxygen in zirconium carbide (ZrC) forming a zirconium oxycarbide (ZrCₓOᵧ). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with atomic scale elemental spectroscopy shows reduced oxygen content with amorphous Zr-B oxides and discreet ZrO₂ particle impurities in the microstructure. Processing ZrB₂ with minimal additions of B₄C (0.25 wt%) produces high purity parts after SPS with only 0.06 wt%O. STEM identifies unique “trash collector” oxides composed of manufacturer powder impurities of calcium, silver, and yttrium. A preliminary Zr-B-C-O thermodynamic model is used to show the potential reaction paths using B₄C that promotes oxide removal to produce high-purity ZrB₂ with fine grains (3.3 𝜇m) and superior mechanical properties (flexural strength of 660MPa) than the current state-of-the-art ZrB₂ ceramics. Due to the desirable properties produced using SPS, there is growing interest to advance processing techniques from lab-scale (20 mm discs) to large-scale (>100 mm). The advancement of SPS technologies has been stunted due to the limited power and load delivery of lab-scale furnaces. We use a large scale direct current sintering furnace (DCS) to address the challenges of producing industrially relevant sized parts. However, current-assisted sintering techniques, like SPS and DCS, are highly dependent on tooling resistances and the electrical conductivity of the sample, which influences the part uniformity through localized heating spots that are strongly dependent on the current flow path. We develop a coupled thermal-electrical finite element analysis model to investigate the development and effects of tooling and current density manipulation on an electrical conductor (ZrB₂) and an electrical insulator, silicon nitride (Si₃N₄), at the steady-state where material properties, temperature gradients and current/voltage input are constant. The model is built based on experimentally measured temperature gradients in the tooling for 20 mm discs and validated by producing 30 mm discs with similar temperature gradients and grain size uniformity across the part. The model aids in developing tooling to manipulate localize current density in specific regions to produce uniform 100 mm discs of ZrB₂ and Si₃N₄.