SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
This paper investigates a potential application of GPS signals for ocean altimetry. The altimetry information is derived from dual-frequency GPS signals reflected from the ocean surface and received at a low-altitude satellite.
Infrared (IR) spectra of the hydrocarbon ices C3H8 (propane), C3H6 (propylene, propene), and C3H4 (propyne, methylacetylene) are relevant to the study of the low-temperature chemistry and spectroscopy of objects within and beyond the Solar System, but IR band strengths and absorption coefficients are lacking for these compounds. Here we present new IR spectra of crystalline and non-crystalline forms of C3H8, C3H6, and C3H4. Measurements of ice density and refractive index also are reported, two quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, abundances of propane, propylene, and propyne in extraterrestrial environments and in laboratory experiments. Suggestions and interpretations are offered regarding the multiple crystalline forms of propane and propylene observed. Applications and extensions are described.
Infrared (IR) spectra of the hydrocarbon ices C3H8 (propane), C3H6 (propylene, propene), and C3H4 (propyne, methylacetylene) are relevant to the study of the low-temperature chemistry and spectroscopy of objects within and beyond the Solar System, but IR band strengths and absorption coefficients are lacking for these compounds. Here we present new IR spectra of crystalline and non-crystalline forms of C3H8, C3H6, and C3H4. Measurements of ice density and refractive index also are reported, two quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, abundances of propane, propylene, and propyne in extraterrestrial environments and in laboratory experiments. Suggestions and interpretations are offered regarding the multiple crystalline forms of propane and propylene observed. Applications and extensions are described.
Infrared (IR) spectra of the hydrocarbon ices C3H8 (propane), C3H6 (propylene, propene), and C3H4 (propyne, methylacetylene) are relevant to the study of the low-temperature chemistry and spectroscopy of objects within and beyond the Solar System, but IR band strengths and absorption coefficients are lacking for these compounds. Here we present new IR spectra of crystalline and non-crystalline forms of C3H8, C3H6, and C3H4. Measurements of ice density and refractive index also are reported, two quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, abundances of propane, propylene, and propyne in extrater-restrial environments and in laboratory experiments. Suggestions and interpretations are offered regarding the multiple crystalline forms of propane and propylene observed. Applications and extensions are described.
Infrared (IR) spectra of the hydrocarbon ices C3H8 (propane), C3H6 (propylene, propene), and C3H4 (propyne, methylacetylene) are relevant to the study of the low-temperature chemistry and spectroscopy of objects within and beyond the Solar System, but IR band strengths and absorption coefficients are lacking for these compounds. Here we present new IR spectra of crystalline and non-crystalline forms of C3H8, C3H6, and C3H4. Measurements of ice density and refractive index also are reported, two quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, abundances of propane, propylene, and propyne in extraterrestrial environments and in laboratory experiments. Suggestions and interpretations are offered regarding the multiple crystalline forms of propane and propylene observed. Applications and extensions are described.
Hot structures are multifunctional material systems that integrate the functions of thermal protection systems (TPS) and primary structure to increase mass efficiency in aerospace vehicles. The goal of this project was to improve our capabilities for developing lightweight, reusable, and reliable hot structures concepts to enable advanced space exploration missions. Specifically, current hot structure carbon/carbon (C/C) composite material systems have low interlaminar strength, which can lead to material failures at low load levels, and large material property variability in as-fabricated parts. Two parallel paths were followed to address these shortcomings. First, analysis models were developed to identify the conditions under which excessive interlaminar stresses occur and to evaluate the potential of stitching the C/C laminae to improve the interlaminar thermal-structural response. This effort included the development of high-fidelity, fracture-based thermal-structural finite element analysis models to evaluate critical features needed to produce efficient hot structure concepts. The second path focused on developing atomistic and mesoscale simulation tools to model the fabrication process in an effort to reduce the time and cost of production while improving the quality of the resulting parts. Aspects of the process currently being investigated include the infusion of the matrix precursor into the fiber preform, the cure of the precursor molecules into their polymeric form, and the carbonization and graphitization of the polymer to form the carbon matrix material. Results of the 6-month study are presented herein.
The feasibility of toughening the common types of matrix resins such as Narmco 5208 by utilizing a heterogeneous additive was examined. Some basic concepts and principles in the toughening of matrix resins for advanced composites were studied. The following conclusions were advanced: (1) the use of damage volume as a guide for measurement of impact resistance appears to be a valid determination; (2) short beam shear is a good test to determine the effect of toughening agents on mechanical properties; (3) rubber toughening results in improved laminate impact strength, but with substantial loss in high temperature dry and wet strength; (4) in the all-epoxy systems, the polycarbonate toughening agent seemed to be the most effective, although hot-wet strength is sacrificed; ABS was not as effective; and (5) in general, the toughened all-epoxy systems showed better damage tolerance, but less hot-wet strength; toughened bismaleimides had better hot-wet strength.
The current Solid Rocket Booster (SRB) launch vehicle has several metal based components that require a Thermal Protective System (TPS) be applied to the exterior surface to ensure its structural integrity and to protect the interior hardware from aerodynamic heating. TPS materials have distinct disadvantages associated with their use. One disadvantage to the application of TPS is that it can act as a debris source to the Space Shuttle Orbiter during flight and it also adds weight to the system without directly contributing any structural strength. One of the specific areas examined under this program was to replace a metal/TPS system with polymer based composites. A polymer matrix based sandwich composite was developed which had both structural and insulative properties to meet the high aerodynamic structural and heating load survival requirements. The SRB Nose Cap was selected as a candidate for this application. The sandwich system being qualified for this application is a carbon/epoxy outer and inner skin with a high strength-low thermal conductivity syntactic foam core.
The electrification of aircraft propulsion systems has opened the design space for engineers by allowing for unique and highly specialized propulsion system and vehicle designs. NASA developed the Electrical Power System – Sizing and Analysis Tool (EPS-SAT) to conduct high-level trade studies and sensitivity studies on the various propulsion system designs that can be implemented in electrified aircraft. The results of these studies would be used to better direct investment dollars and determine strengths and weaknesses of propulsion system designs. In this paper, the results of the EPS-SAT tool were validated with hardware data extracted from the NASA Revolutionary Vertical Lift Technology (RVLT) Advanced Reconfigurable Electric Aircraft Lab (AREAL). Updated performance maps were added to the EPS-SAT library so that high-fidelity results could be calculated.
Friction-stir-welding (FSW) is a solid-state joining process where joint properties are dependent on welding process parameters. In the current study three critical process parameters including spindle speed (𝑁), plunge force (𝐹𝑧), and welding speed (𝑉) are considered key factors in the determination of ultimate tensile strength (UTS) of welded aluminum alloy joints. A total of 73 weld schedules were welded and tensile properties were subsequently obtained experimentally. It is observed that all three process parameters have direct influence on UTS of the welded joints. Utilizing experimental data, an optimized adaptive neuro-fuzzy inference system (ANFIS) model has been developed to predict UTS of FSW joints. A total of 1200 models were developed by varying the number of membership functions (MFs), type of MFs, and combination of four input variables (𝑁,𝑉,𝐹𝑧,𝐸𝐹𝐼) utilizing a MATLAB platform. Note EFI denotes an empirical force index derived from the three process parameters. For comparison, optimized artificial neural network (ANN) models were also developed to predict UTS from FSW process parameters. By comparing ANFIS and ANN predicted results, it was found that optimized ANFIS models provide better results than ANN. This newly developed best ANFIS model could be utilized for prediction of UTS of FSW joints.
Calibrated signal-strength data obtained at 10 sites in the Rockies and NASA telemetry data regarding the signal levels in the ATS 6 spacecraft are presented along with methodology to use the data to compute the carrier-to-noise rations and signal-to-noise rations at each of the calibrated sites. The data and methodology are also used to estimate the median values of these quantities for sites in the Rockies, Alaska, and Appalachia. Results are discussed.
Measurements of the relative strength of ocean surface wave spectral components have been made from an aircraft using the two-frequency microwave resonance technique. A coherent Ku-band radar was used to study the Bragg type resonance matching (at the difference frequency Delta-f) to the surface wave components. The spatial spectrum of the surface reflectivity modulation was then computed as the value of Delta-f was varied over a matching range of approximately 15 150 m in surface wavelength. This paper contains experimental results from flights conducted during the 1979 MARSEN project and the 1980 ARSLOE project, and the objective here is to present the radar results in terms of the variety of surface illumination geometries encountered. It will be shown that the MARSEN results, with the narrow footprint, are consistent with a one-dimensional theoretical approach and that the ARSLOE results, with a symmetric beam pattern, agree well with the existing two-dimensional theory.
Receiver timing synchronization of an optical Pulse-Position Modulation (PPM) communication system can be achieved using a phased-locked loop (PLL), provided the photodetector output is suitably processed. The magnitude of the PLL phase error is a good indicator of the timing error at the receiver decoder. The statistics of the phase error are investigated while varying several key system parameters such as PPM order, signal and background strengths, and PPL bandwidth. A practical optical communication system utilizing a laser diode transmitter and an avalanche photodiode in the receiver is described, and the sampled phase error data are presented. A linear regression analysis is applied to the data to obtain estimates of the relational constants involving the phase error variance and incident signal power.
This paper describes the development of methodology that provides for quantification of uncertainties in lifetime strength of aerospace materials subjected to a number of diverse effects. A probabilistic material degradation model, in the form of a randomized multifactor interaction equation, has been postulated for lifetime strength degradation of structural components of aerospace propulsion systems. The model includes effects that typically reduce lifetime strength and may include temperature, mechanical fatigue, creep and others. The paper also includes the analysis of experimental data from the open literature for Inconel 718. These data are used to provide an initial check for model validity, as well as for calibration of the model's empirical material constants. The model validity check and calibration is carried out for three effects, namely, high temperature, mechanical fatigue and creep.
For the next generation of reusable launch vehicles, NASA is investigating introducing ceramic matrix composites (CMCs) in place of current superalloys for structural propulsion applications (e.g., nozzles, vanes, combustors, and heat exchangers). The higher use temperatures of CMCs will reduce vehicle weight by eliminating and/or reducing cooling system requirements. The increased strength-to-weight ratio of CMCs relative to superalloys further enhances their weight savings potential. However, in order to provide safe designs for components made of these new materials, a comprehensive life prediction methodology for CMC structures needs to be developed. A robust methodology for lifing composite structures has yet to be adopted by the engineering community. Current industry design practice continues to utilize deterministic empirically based models borrowed from metals design for predicting material life capabilities. The deterministic nature of these models inadequately addresses the stochastic character of brittle composites, and their empirical reliance makes predictions beyond the experimental test conditions a risky extrapolation. A team of engineers at the NASA Glenn Research Center has been developing a new life prediction engineering model. The Probabilistic Residual Strength (PRS) model uses the residual strength of the composite as its damage metric. Expected life and material strength are both considered probabilistically to account for the observed stochastic material response. Extensive experimental testing has been carried out on C/SiC (a candidate aerospace CMC material system) in a controlled 1000 ppm O2/argon environment at elevated temperatures of 800 and 1200 C. The test matrix was established to allow observation of the material behavior, characterization of the model, and validation of the model's predictive capabilities. Sample results of the validation study are illustrated in the graphs.
The Virtual Habitat (V-HAB) is a dynamic Life Support System (LSS) simulation, created for investigation of future human spaceflight missions. It provides the capability to optimize LSS during early design phases. The focal point of the paper is the correlation and validation of V-HAB against ground test and flight data. In order to utilize V-HAB to design an Environmental Control and Life Support System (ECLSS) it is important to know the accuracy of simulations, strengths and weaknesses. Therefore, simulations of real systems are essential. The modeling of the International Space Station (ISS) ECLSS in terms of single technologies as well as an integrated system and correlation against ground and flight test data is described. The results of the simulations make it possible to prove the approach taken by V-HAB.
TDA documents determine the personnel strengths for each Army installation. They reflect the number of people required to accomplish a certain mission by various characteristics. U.S. Army Training and Doctrine Command (TRADOC) analysts continuously scrutinize these documents to ensure that they comply with provided guidance. Part of this guidance has been used to develop a set of manual rules. Analysts apply these rules to the TDA to eliminate positions, downgrade positions, or reduce position strength. However, this process is very time consuming. ln addition, human involvement introduces inconsistencies and errors that are difficult to detect later. This paper explains how I represented these rules using the 'C' Language Production System (CLIPS) to develop an expert system that is applied consistently and comprehensively for all TRADOC installations. The TDA System Analyzer reduces the review process from about five days to just twenty minutes; giving the user more time to analyze the results and thereby make better decisions. Furthermore, the user is assured that the rules are applied uniformly to every TDA document. This paper also explains the integration of the TDA System Analyzer into TRADOC's On-Line TDA System. Providing the analyst an extra utility module that can be accessed from a familiar environment.
The influence of a constant magnetic field with a strength of 2500 oersteds on the coagulatory system of the blood in rabbits was studied; the animals were subjected to this field for one and five hours. The magnetic field acts on the coagulatory system of the blood after only one hour exposure. Repeated 5-hour exposures cause activation of the anticoagulatory system in the blood and causes distinctive effects on the subsequent changes in the coagulatory system of the blood. It is quite likely that in this instance the adaptational properties of the organism make themselves felt.