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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Preliminary comparison of 3.5-cm and 12.6-cm wavelength continuous wave observations of Mars

Radar observations of Mars at Goldstone in 1990 were conducted by transmitting pure sinusoidal signals at 3.5-cm wavelengths and receiving the Doppler-spread echoes from Mars at Earth. Radar transmissions were circularly polarized and the echoes recorded in two senses: depolarized and polarized. Latitudes of the subradar points are between 3.5 deg and 11.1 deg S; longitude coverage is discontinuous. The observed depolarized and polarized echo total cross-sections and their ratios for two wavelengths were compared and discussed.

Moore, H. J.↗
NASA NTRS1993

GLRS-R 2-colour retroreflector target design and predicted performance

This paper reports on the retroreflector ground-target design for the GLRS-R spaceborne dual-wavelength laser ranging system. The described passive design flows down from the requirements of high station autonomy, high global FOV (up to 60 degrees zenith angle), little or no multiple pulse returns, and adequate optical cross section for most ranging geometries. The proposed solution makes use of 5 hollow cube-corner retroreflectors of which one points to the zenith and the remaining four are inclined from the vertical at uniform azimuthal spacings. The need for fairly large (is approximately 10 cm) retroreflectors is expected (within turbulence limitations) to generate quite narrow diffraction lobes, thus placing non-trivial requirements on the vectorial accuracy of velocity aberration corrections. A good compromise solution is found by appropriately spoiling just one of the retroreflector dihedral angles from 90 degrees, thus generating two symmetrically oriented diffraction lobes in the return beam. The required spoil angles are found to have little dependence on ground target latitude. Various link budget analyses are presented, showing the influence of such factors as point-ahead optimization, turbulence, ranging angle, atmospheric visibility and ground target thermal deformations.

Lund, Glenn↗
NASA NTRS1993

The modern rotor aerodynamic limits survey: A report and data survey

The first phase of the Modern Technology Rotor Program, the Modern Rotor Aerodynamic Limits Survey, was a flight test conducted by the United States Army Aviation Engineering Flight Activity for NASA Ames Research Center. The test was performed using a United States Army UH-60A Black Hawk aircraft and the United States Air Force HH-60A Night Hawk instrumented main-rotor blade. The primary purpose of this test was to gather high-speed, steady-state, and maneuvering data suitable for correlation purposes with analytical prediction tools. All aspects of the data base, flight-test instrumentation, and test procedures are presented and analyzed. Because of the high volume of data, only select data points are presented. However, access to the entire data set is available upon request.

Cross, J.↗
NASA NTRS1995

Large-Scale Structures in the Zone of Avoidance: The Galactic Anticenter Region

We have selected a sample of 876 galaxy candidates from the IRAS Point Source Catalog in the region of 2(exp h) < alpha < 10(exp h) and 0 deg < delta < 36 deg, which crosses the Galactic anticenter part of the Zone of Avoidance (ZOA) and includes most of the highly obscured Orion-Taurus complex region. We have identified galaxies among the candidate sources by attempting to detect the 21 cm H I line of those sources which were not known to be galaxies at the beginning of the survey. In this manner, we constructed a galaxy sample which is largely free from Galactic reddening. Of the 272 observed candidates, 89 were detected in the H I line up to a heliocentric velocity of v(sub h) approximately 16,000 km/s. The resulting galaxy sample of 717 galaxies is fairly complete (within about 10%) and uniform (within about 4%) in the part of the survey area 10 deg away from the Galactic plane and for velocities up to at least 9000 km/s. This provides, for the first time, a largely unbiased view on the large-scale structures in much of the survey area. Our main results are the following: (1) Several large voids are identified. In particular, a void between alpha approximately equals 3(sup h) and 4(sup h), up to v(sub h) approximately 6000 km/s, separates the Pisces-Perseus supercluster at alpha < 3(sup h) from structures at alpha > 4(sup h); and a "nearby void" occupies most of our survey area and reaches out to a redshift of nearly 3000 km/s. (2) We found no nearby galaxy concentration that could significantly contribute to the "Local Velocity Anomoly" (LVA), but a general excess of galaxies around v(sub h) approximately 5000 km/s in the survey area. (3) The contrast between the "Great Wall" at v(sub h) approximately 8500 km/s and the void in front of it appears to gradually diffuse out after it enters the Zone of Avoidance from the northern Galactic hemisphere. (4) Our data combined with other galaxy surveys in or near the Galactic anticenter part of the ZOA suggest that the main ridge of the Pisces-Perseus supercluster does not extend to Abell 569, a cluster in the northern Galactic hemisphere, and that the simple gravitational model consisting of the Local Void of Tully & Fisher, our nearby void, and Puppis and Fornax-Eridanus clusters would predict a LVA whose direction is probably too far away from that derived from observations.

Lu, Nanyao Y.↗
NASA NTRS2000

Kepler Mission: End-to-End System Demonstration

A test facility has been constructed to demonstrate the capability of differential ensemble photometry to detect transits of Earth-size planets orbiting solar-like stars. The main objective is to determine the effects of various noise sources on the capability of a CCD photometer to maintain a system relative precision of 1 x $10^(-5)$ for mv = 12 stars in the presence of system-induced noise sources. The facility includes a simulated star field, fast optics to simulate the telescope, a thinned back-illuminated CCD similar to those to be used on the spacecraft and computers to perform the onboard control, data processing and extraction. The test structure is thermally and mechanically isolated so that each source of noise can be introduced in a controlled fashion and evaluated for its contribution to the total noise budget. The effects of pointing errors or a changing thermal environment are imposed by piezo-electric devices. Transits are injected by heating small wires crossing apertures in the star plate. Signals as small as those from terrestrial-size transits of solar-like stars are introduced to demonstrate that such planets can be detected under realistic noise conditions. Examples of imposing several noise sources and the resulting detectabilities are presented. These show that a differential ensemble photometric approach CCD photometer can readily detect signals associated with Earth-size transits.

Borucki, William↗
NASA NTRS2003

ICESat Observations of Southern Alaska Glaciers

In late February and March, 2003, the Ice, Cloud, and land Elevation Satellite (ICESat) measured ice and land elevations along profiles across southern Alaska. During this initial data acquisition stage ICESat observations were made on 8-day repeat tracks to enable calibration and validation of the ICESat data products. Each profile consists of a series of single point values derived from centroid elevations of an $\approx$70 m diameter laser footprint. The points are s4pakated by $\approx$172 m along track. Data siets of 8-day observations (an ascending and descending ground track) crossed the Bering and Malaspina Glacier. Following its 1993--1995 surge; the Bering Glacier has undergone major terminus retreat as well as ike thinning in the abtation zone. During the later part of the 20th century, parts of the Malaspina thinned by about 1 m/yr. The multiple observation profiles across the Bering and Malaspina piedmont lobes obtained in February/March are being geolocated on Landsat images and the elevation profiles will be used for a number o scientific objectives. Based on our simulations of ICESat performance over the varied ice surface of the Jakobshavn Glacier of GReenland, 2003, we expect to measure annual, and possibly seasonal, ice elevation changes on the large Alaskan glaciers. Using elevation data obtained from a second laser, we plan to estimate ice elevation changes on the Bering Glacier between March and October 2003.

Sauber, Jeanne↗
NASA NTRS2008

Human Research Program Integrated Research Plan: December 20, 2007, Interim Baseline

The Human Research Program (HRP) delivers human health and performance countermeasures, knowledge, technologies, and tools to enable safe, reliable, and productive human space exploration. This Integrated Research Plan (IRP) describes the program s research activities that are intended to address the needs of human space exploration and serve HRP customers. The timescale of human space exploration is envisioned to take many decades. The IRP illustrates the program s research plan through the timescale of early lunar missions of extended duration. The document serves several purposes for the Human Research Program: The IRP provides a means to assure that the most significant risks to human space explorers are being adequately mitigated and/or addressed, The IRP shows the relationship of research activities to expected outcomes and need dates, The IRP shows the interrelationships among research activities that may interact to produce products that are integrative or cross defined research disciplines, The IRP illustrates the non-deterministic nature of research and technology activities by showing expected decision points and potential follow-on activities, The IRP shows the assignments of responsibility within the program organization and, as practical, the intended solicitation approach, The IRP shows the intended use of research platforms such as the International Space Station, NASA Space Radiation Laboratory, and various space flight analogs. The IRP does not show all budgeted activities of the Human research program, as some of these are enabling functions, such as management, facilities and infrastructure

Source record↗
NASA NTRS2019

A TID and SEE Characterization of Multi-Terabit COTS 3D NAND Flash

Single-event effects and total ionizing dose testing are described for a 32-layer NAND flash memory, in both SLC and MLC configurations, with special considerations for unique three-dimensional test results. Extraction of three-dimensional heavy-ion test data presents a unique visualization of angular effects in NAND flash. Pattern dependence differences between SLC and MLC mode are noted, along with slightly non-uniform angular cross-section results due to the complex volume. Finally, TID data under different operating and bias conditions shows that the failure point remains the higher-voltage erasure circuitry.

Flash Memory↗
NASA NTRS1989

Doppler centroid estimation ambiguity for synthetic aperture radars

A technique for estimation of the Doppler centroid of an SAR in the presence of large uncertainty in antenna boresight pointing is described. Also investigated is the image degradation resulting from data processing that uses an ambiguous centroid. Two approaches for resolving ambiguities in Doppler centroid estimation (DCE) are presented: the range cross-correlation technique and the multiple-PRF (pulse repetition frequency) technique. Because other design factors control the PRF selection for SAR, a generalized algorithm is derived for PRFs not containing a common divisor. An example using the SIR-C parameters illustrates that this algorithm is capable of resolving the C-band DCE ambiguities for antenna pointing uncertainties of about 2-3 deg.

Chang, C. Y.↗
NASA NTRS1991

User's manual for tooth contact analysis of face-milled spiral bevel gears with given machine-tool settings

Research was performed to develop a computer program that will: (1) simulate the meshing and bearing contact for face milled spiral beval gears with given machine tool settings; and (2) to obtain the output, some of the data is required for hydrodynamic analysis. It is assumed that the machine tool settings and the blank data will be taken from the Gleason summaries. The theoretical aspects of the program are based on 'Local Synthesis and Tooth Contact Analysis of Face Mill Milled Spiral Bevel Gears'. The difference between the computer programs developed herein and the other one is as follows: (1) the mean contact point of tooth surfaces for gears with given machine tool settings must be determined iteratively, while parameters (H and V) are changed (H represents displacement along the pinion axis, V represents the gear displacement that is perpendicular to the plane drawn through the axes of the pinion and the gear of their initial positions), this means that when V differs from zero, the axis of the pionion and the gear are crossed but not intersected; (2) in addition to the regular output data (transmission errors and bearing contact), the new computer program provides information about the contacting force for each contact point and the sliding and the so-called rolling velocity. The following topics are covered: (1) instructions for the users as to how to insert the input data; (2) explanations regarding the output data; (3) numerical example; and (4) listing of the program.

Litvin, Faydor L.↗
NASA NTRS1989

The autocorrelation function of the North Pole dust

The angular scales on which local interstellar dust is distributed are so far rather unknown as are the geometrical shapes of the dust features. From the about 5000 color excesses resulting from a north polar survey with 4 to 5 stars per square degree the two-point autocorrelation function is derived for separations ranging from 10 min to 3 deg. For intercloud lines of sight, -0.020 is less than E(b - y) is less than -0.010 mag, the average cross products (E sub 1 x E sub 2)(sub theta) show no variation with separation theta(1,2) whereas products of cloud column densities, 0.030 is less than E(b - y) is less than 0.040 mag, seem to prefer discrete separations either less than 20 min, around 75 min, or finally at about 150 min. Surprisingly the two point autocorrelation function omega(sub E) = E(sub 1) x E(sub 2)/E squared - 1 equals 0 except for any separation except theta = 0. Omega(sub E)(theta)'s absence of variation is unexpected because omega(sub H)(theta) is known to vary exponentially above b = 40 deg for separations less than 3 deg. Atomic hydrogen and dust may thus not be entirely mixed or the moments (E sub 1 x E sub 2)(sub theta) may not characterize the dust distribution.

Knude, Jens↗
NASA NTRS1983

X-ray imaging of extended objects using nonoverlapping redundant array

A common problem associated with X-ray imaging using coded apertures is the reconstruction of low-intensity extended objects. In the decoding of such objects, the overlapping images from the multiple pinholes give rise to noise cross talk and, in many cases, also to signal cross talk. In this paper, an alternate approach is proposed based on the principle used in an earlier (Yin et al., 1980) laboratory device for the real-time viewing of X-ray objects. It is shown that with this approach, the nonoverlapping redundant array, the sidelobes in the point spread function are not eliminated but merely displaced through a suitable choice of geometry. In this manner, the sidelobes no longer contribute to the background in the vicinity of a reconstructed image, and both signal and noise cross talks are completely eliminated. It may now be possible to reconstruct extended X-ray objects in 3-D by simple optical correlation and tomographically by a computer.

Yin, L.-I.↗
NASA NTRSDate not supplied

On-Orbit Performance of the NOAA-21 Advanced Technology Microwave Sounder (ATMS)

The Advanced Technology Microwave Sounder (ATMS) instrument provides sounding measurements of Earth’s atmosphere to collect temperature and water vapor data for NOAA’s Joint Polar Satellite System (JPSS) program. ATMS is a total-power passive microwave radiometer with 22 channels spanning a frequency range from 22 to 183 GHz. A general description of the ATMS instrument is detailed in [1]. Three ATMS units are currently on-orbit. The Suomi National Polar-orbiting Partnership (SNPP) unit was launched in 2011 and the NOAA-20 (previously JPSS-1) unit was launch in 2017. Both SNPP and NOAA-20 ATMS units are currently operational and the data is used for numerical weather prediction (NWP) models. The NOAA-21 (formerly JPSS-2) ATMS unit was launched on November 10, 2022 from Vandenberg Space Force Base in California [2]. The ATMS instrument began generating radiance data on November 21, 2022. At the time of this abstract NOAA-21 ATMS is currently completing on-orbit commissioning and checkout activities; it is expected that the commissioning activities will be complete by the IGARSS 2023 conference. This paper will focus on the on-orbit performance of the NOAA-21 ATMS instrument based on measurements and activities from the commissioning period. Comparisons will be made to specifications and to expected performance based on pre-launch test activities. Pre-launch JPSS-2 (NOAA-21) ATMS performance is detailed in [4]. Additionally, the NOAA-21 performance will be compared to the on-orbit performance of the SNPP and NOAA-21 ATMS units. The post-launch performance of SNPP ATMS is detailed in [1][5][6][7]. The post-launch performance of NOAA-20 ATMS is detailed in [5][7][8]. On-orbit performance is evaluated through data collects from nominal mission operations as well as specific post-launch tests and spacecraft maneuvers. Nominal mission operations can be used to evaluate parameters such as instrument thermal stability, Noise Equivalent Delta Temperature (NEDT)/radiometric sensitivity, geolocation, inter-channel noise correlation, striping, and radiometric bias and stability. Shortly after instrument activation, the instrument thermal stability as measured from onboard temperature sensors is evaluated to demonstrate stable and steady-state behavior. Methods for computing NEDT are described in [9][10][11]. Passive geolocation measurements are performed using the coastline inflection point (CIP) method, described in [8][12]. The striping index, used as a metric to quantify striping, is the ratio of along-track variance to cross-track variance of the observed brightness temperature [4][8][14]. Inter-channel noise correlation has been previously reported for SNPP and NOAA-20 [1][8]. Dedicated post-launch tests and spacecraft maneuvers are utilized during the commissioning phase for further evaluation of on-orbit instrument performance. These activities provide information on the optimal space view selection, noise power spectral density (PSD), gain stability, scan bias, interference from onboard transmitters, reflector emissivity, active geolocation, and radiometric bias and stability detection methods. The optimal space view selection is used to determine which of ATMS space view sectors is preferred for minimizing contamination of the space view [1]. Point and stare testing is used to generate noise PSD and gain stability information, as described in [1][8]. Spacecraft roll and pitch maneuvers allow the ATMS to view different zones, including deep space, and the data can be used to provide information on scan biases and antenna sidelobe contamination [1][8]. The pitch maneuver can also be used to assess interference from onboard Ka-band transmitters and reflector emissivity [8]. Active geolocation is evaluated as a method for geolocation, described in [15].

Edward Kim↗
NASA NTRS1992

Theoretical characterization of the potential energy surface for NH + NO

The potential energy surface (PES) for NH + NO was characterized using complete active space self-consistent field (CASSCF) gradient calculations to determine the stationary point geometries and frequencies followed by CASSCF/internally contracted configuration interaction (CCI) calculations to refine the energetics. The present results are in qualitative accord with the BAC-MP4 calculations, but there are differences as large as 8 kcal/mol in the detailed energetics. Addition of NH to NO on a (2)A' surface, which correlated with N2 + OH or H + N2O products, involves barriers of 3.2 kcal/mol (trans) and 6.3 kcal/mol (cis). Experimental evidence for these barriers is found in earlier works. The (2)A' surface has no barrier to addition, but does not correlate with products. Surface crossings between the barrierless (2)A' surface and the (2)A' surface may be important. Production of N2 + OH products is predicted to occur via a planar saddle point of (2)A' symmetry. This is in accord with the preferential formation of II(A') lambda doublet levels of OH in earlier experiments. Addition of NH (1)delta to NO is found to occur on an excited state surface and is predicted to lead to N2O product as observed in earlier works.

Walch, Stephen P.↗
NASA NTRS1972

Cross-spectral functions based on von Karman's spectral equation

Cross-spectral functions for the vertical and longitudinal components of turbulence of a two-dimensional gust field are derived from the point correlation function for turbulence due to von Karman. Closed form solutions in terms of Bessel functions of order 5/6 and 11/6 are found. An asymptotic expression for large values of the frequency argument, and series results for small values of frequency, are also given. These results now form the base for studying the effect of spanwise variations in turbulence for a turbulence environment which is characterized by the von Karman isotropic spectral relations. Previous studies were based mainly on the Dryden-type spectral representation.

Houbolt, J. C.↗
NASA NTRS1973

Ultrasonic measurement of elastic moduli in slender specimens using extensional and torsional wave pulses.

The pulse-echo method using extensional and torsional waves is described relative to determining elastic properties and other characteristics of specimens which are slender acoustically. Several applications are reviewed, including: glass fibers of diameter 16 to 42 microns; glass rods of diameter about 1 mm, tested to 700 C; iron-base alloys of diameter 3.2 mm, tested from nearly -200 up to +200 C; titanium specimens of rectangular cross section, 1.5 by 3 mm; and tantalum-base alloys of diameter 6.4 mm, tested up to 1400 C. Limitations are pointed out regarding dispersive materials and geometry.

Lynnworth, L. C.↗
NASA NTRS1975

Environmental effects on the torsion and flexure fatigue properties of graphite-epoxy composites

Effects of torsional and flexural fatigue on the long-time integrity of advanced graphite-epoxy structural composites have been investigated. Reversed (R = - 1) and unidirectional (R = 0) torsional fatigue tests were made on unidirectional, cross-plied and woven graphite fiber materials in air and water at room temperature and at 74 C. Flexural fatigue tests (4-point bending) with R = - 1 were run in air and water at room temperature, and at R = 0 in air. Results show that in torsional cycling, both water environment and higher test temperature contribute to significant degradation of torsional stiffness. The degradation of stiffness from torsional stress cycling was observed to be much greater with R = - 1 than with simple R = 0 cycling. The effect of environment is also greater in the fully reversed cycling.

Sumsion, H. T.↗
NASA NTRS1976

Optimum vibrating beams with stress and deflection constraints

The fundamental frequency of vibration of an Euler-Bernoulli or a Timoshenko beam of a specified constant volume is maximized subject to the constraint that under a prescribed loading the maximum stress or maximum deflection at any point along the beam axis will not exceed a specified value. In contrast with the inequality constraint which controls the minimum cross-section, the present inequality constraints lead to more meaningful designs. The inequality constraint on stresses is as easily implemented as the minimum cross-section constraint but the inequality constraint on deflection uses a treatment which is an extension of the matrix partitioning technique of prescribing displacements in finite element analysis.

Kamat, M. P.↗