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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.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Multigrid one shot methods for optimal control problems: Infinite dimensional control

The multigrid one shot method for optimal control problems, governed by elliptic systems, is introduced for the infinite dimensional control space. ln this case, the control variable is a function whose discrete representation involves_an increasing number of variables with grid refinement. The minimization algorithm uses Lagrange multipliers to calculate sensitivity gradients. A preconditioned gradient descent algorithm is accelerated by a set of coarse grids. It optimizes for different scales in the representation of the control variable on different discretization levels. An analysis which reduces the problem to the boundary is introduced. It is used to approximate the two level asymptotic convergence rate, to determine the amplitude of the minimization steps, and the choice of a high pass filter to be used when necessary. The effectiveness of the method is demonstrated on a series of test problems. The new method enables the solutions of optimal control problems at the same cost of solving the corresponding analysis problems just a few times.

Arian, Eyal↗
NASA NTRS2010

Development and Acceptance Testing of the Dual Wheel Mechanism for the Tunable Filter Imager Cryogenic Instrument on the JWST

The James Webb Space Telescope (JWST) will carry four scientific instruments, one of which is the Tunable Filter Imager (TFI), which is an instrument within the Fine Guidance Sensor. The Dual Wheel (DW) mechanism is being designed, built and tested by COM DEV Ltd. under contract from the Canadian Space Agency. The DW mechanism includes a pupil wheel (PW) holding seven coronagraphic masks and two calibration elements and a filter wheel (FW) holding nine blocking filters. The DW mechanism must operate at both room temperature and at 35K. Successful operation at 35K comprises positioning each optical element with the required repeatability, for several thousand occasions over the five year mission. The paper discusses the results of testing geared motors and bearings at the cryogenic temperature. In particular bearing retainer design and PGM-HT material, the effects of temperature gradients across bearings and the problems associated with cooling mechanisms down to cryogenic temperatures. The results of additional bearing tests are described that were employed to investigate an abnormally high initial torque experienced at cryogenic temperatures. The findings of these tests, was that the bearing retainer and the ball/race system could be adversely affected by the large temperature change from room temperature to cryogenic temperature and also the temperature gradient across the bearing. The DW mechanism is now performing successfully at both room temperature and at cryogenic temperature. The life testing of the mechanism is expected to be completed in the first quarter of 2010.

Leckie, Martin↗
NASA NTRS1991

Determination of shuttle orbiter center of gravity from flight measurements

Flight measurements of pitch, yaw, and roll rates and the resultant rotationally induced linear accelerations during three orbital maneuvers on Shuttle mission space transportation system (STS) 61-C were used to calculate the actual orbiter center-of-gravity location. The calculation technique reduces error due to lack of absolute calibration of the accelerometer measurements and compensates for accelerometer temperature bias and for the effects of gravity gradient. Accuracy of the technique was found to be limited by the nonrandom and asymmetrical distribution of orbiter structural vibration at the accelerometer mounting location. Fourier analysis of the vibration was performed to obtain the power spectral density profiles which show magnitudes in excess of 10(exp 4) ug (sup 2)/Hz for the actual vibration and over 500 ug (sup 2)/Hz for the filtered accelerometer measurements. The data from this analysis provide a characterization of the Shuttle acceleration environment which may be useful in future studies related to accelerometer system application and zero-g investigations or processes.

Hinson, E. W.↗
NASA NTRS1995

Performance analysis of a GPS Interferometric attitude determination system for a gravity gradient stabilized spacecraft

The performance of an unaided attitude determination system based on GPS interferometry is examined using linear covariance analysis. The modelled system includes four GPS antennae onboard a gravity gradient stabilized spacecraft, specifically the Air Force's RADCAL satellite. The principal error sources are identified and modelled. The optimal system's sensitivities to these error sources are examined through an error budget and by varying system parameters. The effects of two satellite selection algorithms, Geometric and Attitude Dilution of Precision (GDOP and ADOP, respectively) are examined. The attitude performance of two optimal-suboptimal filters is also presented. Based on this analysis, the limiting factors in attitude accuracy are the knowledge of the relative antenna locations, the electrical path lengths from the antennae to the receiver, and the multipath environment. The performance of the system is found to be fairly insensitive to torque errors, orbital inclination, and the two satellite geometry figures-of-merit tested.

Stoll, John C.↗
NASA NTRS1981

Lidar observation of the mesospheric sodium layer over Urbana, Illinois

Atmospheric sodium has been observed over Urbana (40 deg 10 min N, 88 deg 10 min W) using a monostatic lidar tuned to 589.0 nm. The photocount data are processed using ditital smoothing filters to obtain continuous estimates of the sodium density versus altitude. The filter cutoff frequency is related to the height resolution and accuracy of the estimated profile. Wavelike structures in the sodium layer have been observed with typical wavelengths of 3-15 km and phase velocities of 1-3 m/s. The layer is characterized by a sharp falloff on the bottomside and often an undulatory motion of the bottomside of the layer accompanies the wave motion. The topside gradient of the layer is frequently observed to decrease through the night.

Richter, E. S.↗
NASA NTRS1988

Automated seed manipulation and planting

The Mechanical Division fabricated three seed separators utilizing pressure gradients to move and separate wheat seeds. These separators are called minnow buckets and use air, water, or a combination of both to generate the pressure gradient. Electrostatic fields were employed in the seed separator constructed by the Electrical Division. This separator operates by forcing a temporary electric dipole on the wheat seeds and using charged electrodes to attract and move the seeds. Seed delivery to the hydroponic growth tray is accomplished by the seed cassette. The cassette is compatible with all the seed separators, and it consists of a plastic tube threaded with millipore filter paper. During planting operations, the seeds are placed in an empty cassette. The loaded cassette is then placed in the growth tray and nutrient solution provided. The solution wets the filter paper and capillary action draws the nutrients up to feed the seeds. These seeding systems were tested and showed encouraging results. Seeds were effectively separated and the cassette can support the growth of wheat plants. Problems remaining to be investigated include improving the success of delivering the seeds to the cassette and providing adequate spacing between seeds for the electric separator.

Garcia, Ray↗
NASA NTRS1984

Analysis of Doppler lidar wind measurements

New analysis methods were developed and refined for the synthesis of wind fields from multiple Doppler radar data. Considerable software was written and debugged for wind field synthesis. The analysis methods were applied to radar data collected during the CCOPE experiment in which lidar wind measurements were also made. The analysis method differs from existing methods in that interpolation (using filters with assigned weights) and advection of data, to account for time differential between data acquisition at different points, are not used. Instead, functional fits were used in space and time coordinates to transfer radial velocity data to a space-time grid. Subsequently the wind synthesis is performed. This method gives better space resolution in the synthesized winds, compared to other methods in common use, by better preserving the gradients of velocities. The wind fields show the cellular structure characteristic of boundary-layer convection. Also evident in the analysis are the sharp transitions and gradients in the wind field which were preserved by the synthesis.

Srivastava, R. C.↗
NASA NTRS1982

Orbital measurements of the Earth's radiation budget during the first decade of the space program

The instrumentation and data analysis methods applied to data from the Explorer 7, TIROS 2, 3, 4, and 7, and Nimbus 2 and 3 experimental satellites are summarized. Problems encountered in analyzing these data included: determining the value of the solar constant, inaccuracies introduced by degradation of the sensors in orbit, the need to infer the total reflected and emitted radiation from filtered measurements, the development of corrections for anisotropy in order to determine the outgoing flux densities at the moment of measurement, and the development of corrections to account for diurnal variability. The corrections for long- and shortwave anisotropy and historical determinations of the solar constant and albedo are treated in detail. These early measurements indicated that the planetary albedo was lower, the emitted radiation higher, and the equator-to-pole gradient of net radiation greater than previously supposed.

Bandeen, W. R.↗
NASA NTRS2010

Improving Global Mass Flux Solutions from Gravity Recovery and Climate Experiment (GRACE) Through Forward Modeling and Continuous Time Correlation

We describe Earth's mass flux from April 2003 through November 2008 by deriving a time series of mas cons on a global 2deg x 2deg equal-area grid at 10 day intervals. We estimate the mass flux directly from K band range rate (KBRR) data provided by the Gravity Recovery and Climate Experiment (GRACE) mission. Using regularized least squares, we take into account the underlying process dynamics through continuous space and time-correlated constraints. In addition, we place the mascon approach in the context of other filtering techniques, showing its equivalence to anisotropic, nonsymmetric filtering, least squares collocation, and Kalman smoothing. We produce mascon time series from KBRR data that have and have not been corrected (forward modeled) for hydrological processes and fmd that the former produce superior results in oceanic areas by minimizing signal leakage from strong sources on land. By exploiting the structure of the spatiotemporal constraints, we are able to use a much more efficient (in storage and computation) inversion algorithm based upon the conjugate gradient method. This allows us to apply continuous rather than piecewise continuous time-correlated constraints, which we show via global maps and comparisons with ocean-bottom pressure gauges, to produce time series with reduced random variance and full systematic signal. Finally, we present a preferred global model, a hybrid whose oceanic portions are derived using forward modeling of hydrology but whose land portions are not, and thus represent a pure GRACE-derived signal.

Sabaka, T. J.↗
NASA NTRS2017

Assimilation of AERONET and MODIS AOT Observations Using Variational and Ensemble Data Assimilation Methods and Its Impact on Aerosol Forecasting Skill

Data assimilation of Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical thickness (AOT) for aerosol forecasting was tested within the Navy Aerosol Analysis Prediction System (NAAPS) framework, using variational and ensemble data assimilation methods. Navy aerosol forecasting currently makes use of a deterministic NAAPS simulation coupled to Navy Variational Data Assimilation System for aerosol optical depth, a two-dimensional variational data assimilation system, for MODIS AOT assimilation. An ensemble version of NAAPS (ENAAPS) coupled to an ensemble adjustment Kalman filter (EAKF) from the Data Assimilation Research Testbed was recently developed, allowing for a range of data assimilation and forecasting experiments to be run with deterministic NAAPS and ENAAPS. The main findings are that the EAKF, with its flow-dependent error covariances, makes better use of sparse observations such as AERONET AOT. Assimilating individual AERONET observations in the two-dimensional variational system can increase the analysis errors when observations are located in high AOT gradient regions. By including AERONET with MODIS AOT assimilation, the magnitudes of peak aerosol events (AOT> 1) were better captured with improved temporal variability, especially in India and Asia where aerosol prediction is a challenge. Assimilating AERONET AOT with MODIS had little impact on the 24 h forecast skill compared to MODIS assimilation only, but differences were found downwind of AERONET sites. The 24 h forecast skill was approximately the same for forecasts initialized with analyses from AERONET AOT assimilation alone compared to MODIS assimilation, particularly in regions where the AERONET network is dense; including the United States and Europe, indicating that AERONET could serve as a backup observation network for over-land synoptic-scale aerosol events.

Rubin, Juli I.↗
NASA NTRS2021

Large-Eddy Simulation of Variable Speed Power Turbine Cascade with Inflow Turbulence

Numerical results are presented from theNASAGlenn Research Center’sin-house turbomachinery code, Glenn-HT applied to the Variable Speed Power Turbine (VSPT) experiment at the NASA Transonic Turbine Blade Cascade Facility.The main goal of this paper is to implement a digital filtering method to generate turbulence upstream and a sub-grid model (Localized dynamic k-equation model (LDKM)) in the framework of LES in order to investigate the effect of inflow turbulence on the transition seen in the VSPT experimental data at the cruise condition (incidence angle of 40oand Tu = 0.5%, 5%,10%, and 15%). Although the boundary layer on thesuction side and pressure side of the blades is initially laminar due to favorable pressure gradient, the laminar flow can transition to turbulent flow past a separation zoneon the suction sideor by natural or by-pass transition. This process determinesthe total-pressure lossesin the wake. Therefore, it is desirable to develop a reliable prediction tool to accurately capture the transition mechanism in blade rows operated under the conditions of low Reynolds number andat a variety offree stream turbulence conditions. Our numerical studies reveal that the location of separationis rather insensitive to the level of Tu, however the effect ofincreasingTu seems to be in reducing the size and ultimately suppressing the separation bubble. In addition, we performedspectral analysis to identify the peak frequencies in the region where the separation bubble is formed, which provides valuable insights into the transition/separation mechanism.

CFD↗
NASA NTRS2011

The Role of African Easterly Wave on Dust Transport and the Interaction Between Saharan Dust Layer and Atlantic ITCZ During Boreal Summer

Saharan dust outbreaks not only transport large amount of dust to the northern Atlantic Ocean, but also alter African easterly jet and wave activities along the jet by changing north-south temperature gradient. Recent modeling and observational studies show that during periods of enhance outbreaks, rainfall on the northern part of ITCZ increases in conjunction with a northward shift of ITCZ toward the dust layer. In this paper, we study the radiative forcing of Saharan dust and its interactions with the Atlantic Inter-tropical Convergence Zone (ITCZ), through African easterly waves (AEW), African easterly jet (AEJ), using the Terra/Aqua observations as well as MERRA data. Using band pass filtered EOF analysis, we find that African easterly waves propagating westward along two principal tracks, centered at 15-25N and 5-10N respectively. The easterly waves in the northern track are slower, with propagation speed of 9 ms-1, and highly correlated with major dust outbreak over North Africa. On the other hand, easterly waves along the southern track are faster with propagating speed of 10 ms-1, and are closely tied to rainfall/cloud variations along the Atlantic ITCZ. Dust transport along the southern track leads rainfall/cloud anomalies in the same region by one or two days, suggesting the southern tracks of dust outbreak are regions of strong interaction between Saharan dust layer and Atlantic ITCZ. Possible linkage between two tracks of easterly waves, as well as the long-term change of easterly wave activities and dust outbreaks, are also discussed.

Kim, Kyu-Myong↗
NASA NTRS2002

Production of Ultra-Light Normal Incidence Mirrors

Mirrors fabrication for large aperture telescopes is an important aspect in space exploration programs. One of the cost effective techniques to obtain such mirrors is electroplating of Ni-Co alloys from sulfamate solution. The Center for Irradiation of Materials at Alabama A&M University - Research Institute has been involved in a NASA-MSFC project for producing ultra-light Ni-Co alloy mirrors since the summer of year 2000. The goal of this project is to obtain ultra-light, high strength electroformed large aperture normal incidence replicated mirrors, (weighting less than 5 kg/m2), free of stress, with a good figure and reproducible thickness variation. In order to simplify the control of parameters such as temperature gradient, concentration gradient, distribution of the electric field lines and flow control, the proposed geometry involves a cylindrical main tank contained in another cylindrical tank, which plays the role of a weir. Designs were created to accommodate the new horizontal position of the mandrel and the pipes fitting through the outer tank's lid. The inner tank contains the working electrodes and a series of sensors for monitoring temperature, flow, stress and pH. The outer tank holds the electric heaters, the filters and a part of the piping system. Another two tanks complete the setup and serve for rinsing/preheating and equilibrating the electroplating bath. This paper will describe advantages of the new experimental setup and the parameters achieved in the electroplating bath for the proposed geometry.

Jones, Ruth↗
NASA NTRS1991

The pulse-pair algorithm as a robust estimator of turbulent weather spectral parameters using airborne pulse Doppler radar

The pulse pair method for spectrum parameter estimation is commonly used in pulse Doppler weather radar signal processing since it is economical to implement and can be shown to be a maximum likelihood estimator. With the use of airborne weather radar for windshear detection, the turbulent weather and strong ground clutter return spectrum differs from that assumed in its derivation, so the performance robustness of the pulse pair technique must be understood. Here, the effect of radar system pulse to pulse phase jitter and signal spectrum skew on the pulse pair algorithm performance is discussed. Phase jitter effect may be significant when the weather return signal to clutter ratio is very low and clutter rejection filtering is attempted. The analysis can be used to develop design specifications for airborne radar system phase stability. It is also shown that the weather return spectrum skew can cause a significant bias in the pulse pair mean windspeed estimates, and that the poly pulse pair algorithm can reduce this bias. It is suggested that use of a spectrum mode estimator may be more appropriate in characterizing the windspeed within a radar range resolution cell for detection of hazardous windspeed gradients.

Baxa, Ernest G., Jr.↗
NASA NTRS2005

Hydrothermal Vent Sampler: Does Life Exist in High Temperature Environments?

The main purpose of this research is to search for the existence of biomass under extreme temperature and pressure conditions to determine the upper bounds of environments on which life can exist. Vents are, simply put, underwater volcano openings located at the bottom of the sea. The conditions at these locations are considerably extreme with pressures of up to 10,000 psi, and enormous temperature gradients. The temperature of the water near these vents is around 400 C, while that of the surrounding water is about 3 C. The extremity of these conditions makes it hard to estimate the existence of life in those environments. I n order to find whether such existence happens, we need to search for biomass inside these vents. The vent sampler is a device that has the purpose of safely and accurately collecting this biomass for examination. This sampler is constituted of a Series of filters of the order of 100-0.2 microns in size. Since this is a 3-year project, it has not concluded yet; however, during the time I contributed to this project, I worked with the mechanical design of this sampler device including the selection, assembly, and testing of the various subsystems and the design and construction of the electronics enclosure.

Rivadeneyra, Cesar R.↗
NASA NTRS1989

A Simple Algebraic Grid Adaptation Scheme with Applications to Two- and Three-dimensional Flow Problems

An algebraic adaptive grid scheme based on the concept of arc equidistribution is presented. The scheme locally adjusts the grid density based on gradients of selected flow variables from either finite difference or finite volume calculations. A user-prescribed grid stretching can be specified such that control of the grid spacing can be maintained in areas of known flowfield behavior. For example, the grid can be clustered near a wall for boundary layer resolution and made coarse near the outer boundary of an external flow. A grid smoothing technique is incorporated into the adaptive grid routine, which is found to be more robust and efficient than the weight function filtering technique employed by other researchers. Since the present algebraic scheme requires no iteration or solution of differential equations, the computer time needed for grid adaptation is trivial, making the scheme useful for three-dimensional flow problems. Applications to two- and three-dimensional flow problems show that a considerable improvement in flowfield resolution can be achieved by using the proposed adaptive grid scheme. Although the scheme was developed with steady flow in mind, it is a good candidate for unsteady flow computations because of its efficiency.

Hsu, Andrew T.↗
NASA NTRS2010

Boundary Layers, Transitions and Separation

Effects of roughness in boundary layers have to be addressed. Until adverse pressure gradient effects are understood, roughness will not significantly drive design. Mechanisms responsible for separation not understood. Effects on Zero Pressure Gradient boundary layers (shear stress). Effects on separation in pressure gradient (prediction of separation). Effect on scalar transport (heat transfer) not understood. Model for skin friction needed in simulations - first grid point likely to be in buffer layer. Definition of roughness important for useful experiments. A lot of validation experiments will be needed. How to get to ks for roughness of engineering interest? - depends on wavelength height, etc. for engineering interest? Re-discovering the wheel should be avoided: existing knowledge (theoretical and experimental) should find its way into the engineering models. It is a task of the industry to filter out the existing information in the literature for results relevant to its application, being external or internal.

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NASA NTRS2005

NASA Tech Briefs, August 2005

Topics include: Hidden Identification on Parts: Magnetic Machine-Readable Matrix Symbols; System for Processing Coded OFDM Under Doppler and Fading; Multipurpose Hyperspectral Imaging System; Magnetic-Flux-Compensated Voltage Divider; High-Performance Satellite/Terrestrial-Network Gateway; Internet-Based System for Voice Communication With the ISS; Stripline/Microstrip Transition in Multilayer Circuit Board; Dual-Band Feed for a Microwave Reflector Antenna; Quadratic Programming for Allocating Control Effort; Range Process Simulation Tool; Simulator of Space Communication Networks; Computing Q-D Relationships for Storage of Rocket Fuels; Contour Error Map Algorithm; Portfolio Analysis Tool; Glass Frit Filters for Collecting Metal Oxide Nanoparticles; Anhydrous Proton-Conducting Membranes for Fuel Cells; Portable Electron-Beam Free-Form Fabrication System; Miniature Laboratory for Detecting Sparse Biomolecules; Multicompartment Liquid-Cooling/Warming Protective Garments; Laser Metrology for an Optical-Path-Length Modulator; PCM Passive Cooling System Containing Active Subsystems; Automated Electrostatics Environmental Chamber; Estimating Aeroheating of a 3D Body Using a 2D Flow Solver; Artificial Immune System for Recognizing Patterns; Computing the Thermodynamic State of a Cryogenic Fluid; Safety and Mission Assurance Performance Metric; Magnetic Control of Concentration Gradient in Microgravity; Avionics for a Small Robotic Inspection Spacecraft; and Simulation of Dynamics of a Flexible Miniature Airplane.

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