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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Results of an International Space Crew Debrief

In order to identify potential multi-cultural and multinational problems for future International Space Station Freedom crew, a crew debrief questionnaire was developed for U.S. astronauts who flew on shuttle missions with one or more crew members from other countries. Methods: From 1981-90, a total of 20 U.S. astronauts flew on international space missions. Debriefs were mailed to all 20 with instructions not to identify themselves or their specific mission. The debrief focused primarily on preflight training and post flight incidents of misunderstanding, miscommunication, and interpersonal friction among crewmembers. Astronauts were also asked to rate the impact of the incident to the mission (low, medium, high). Results: Ten astronauts responded, but only nine responses were able to be scored, for a return rate of 45 percent. 42 incidents were reported, 9 in the preflight period, 26 inflight, and 7 in the postflight period. Most of the incidents were rated at a low or medium impact, but 5 of the inflight incidents were rated at a 'high' mission impact. A number of causes for the problems were listed, and are discussed. Conclusions: The debrief respondents provide useful and timely recommendations on preflight training which might help facilitate the integration of multinational crews and prevent multi-cultural or multinational factors from interfering with mission operations.

Santy, P. A.↗
NASA NTRS2003

Enhanced Raman Microprobe Imaging of Single-Wall Carbon Nanotubes

We explore Raman microprobe capabilities to visualize single wall carbon nanotubes (SWCNTs). Although this technique is limited to a micron scale, we demonstrate that images of individual SWCNTs, bundles or their agglomerates can be generated by mapping Raman active elementary excitations. We measured the Raman response from carbon vibrations in SWCNTs excited by confocal scanning of a focused laser beam. Carbon vibrations reveal key characteristics of SWCNTs as nanotube diameter distribution (radial breathing modes, RBM, 100-300 cm(exp -1)), presence of defects and functional groups (D-mode, 1300-1350 cm(exp -1)), strain and oxidation states of SWCNTs, as well as metallic or semiconducting character of the tubes encoded in the lineshape of the G-modes at 1520-1600 cm(exp - 1). In addition, SWCNTs are highly anisotropic scatterers. The Raman response from a SWCNT is maximal for incident light polarization parallel to the tube axis and vanishing for perpendicular directions. We show that the SWCNT bundle shape or direction can be determined, with some limitations, from a set of Raman images taken at two orthogonal directions of the incident light polarization.

Hadjiev, V. G.↗
NASA NTRS2015

A Symmetric Time-Varying Cluster Rate of Descent Model

A model of the time-varying rate of descent of the Orion vehicle was developed based on the observed correlation between canopy projected area and drag coefficient. This initial version of the model assumes cluster symmetry and only varies the vertical component of velocity. The cluster fly-out angle is modeled as a series of sine waves based on flight test data. The projected area of each canopy is synchronized with the primary fly-out angle mode. The sudden loss of projected area during canopy collisions is modeled at minimum fly-out angles, leading to brief increases in rate of descent. The cluster geometry is converted to drag coefficient using empirically derived constants. A more complete model is under development, which computes the aerodynamic response of each canopy to its local incidence angle.

Ray, Eric S.↗
NASA NTRS1977

Estimation of soil moisture with radar remote sensing

The radar response to soil moisture content was investigated using a truck-mounted 1-18 GHz (30-1.67 cm wavelength, respectively) active microwave spectrometer (MAS) system. The sensitivity to soil moisture content and the accuracy with which it could be estimated were evaluated for both bare and vegetation-covered fields. Bare field experiments were conducted to determine the optimum radar parameters (frequency, angle of incidence range, and polarization configuration) for minimizing the response to surface roughness while retaining strong sensitivity to moisture content. In the vegetation-covered case, the effects of crop type, crop height and row direction relative to the radar look direct were evaluated.

Batlivala, P. P.↗
NASA NTRS2004

Calibration of the NEAR XRS Solar Monitor

The NEAR-Shoemaker X-ray spectrometer measured elemental abundance ratios for six elements (Mg, Al, Si, S, Ca, Fe) on the surface of 433 Eros by remote-sensing x-ray fluorescence spectroscopy (1,2). The fluorescent x-rays are excited by x-rays from the solar corona. Therefore, accurate knowledge of the incident solar spectrum was critically important to interpreting the fluorescence spectra received by the NEAR detectors in terms of elemental ratios on the asteroid's surface. NEAR, therefore, carried two additional X-ray spectrometers dedicated to monitoring the solar spectrum between 1 and 10 keV. One of these, a Si PIN photodiode, failed prior to orbit insertion. The second consisted of a gas-filled proportional counter similar to the asteroid-pointing detectors, but covered by a graded filter (3) intended to attenuate the incoming solar flux and increase the dynamic range of the detector. Unfortunately, the response of this filter as a function of solar incidence angle was not adequately determined in the laboratory prior to launch. The response function had to be calculated from the assumed properties of the graded filter.

Lim, L. F.↗
NASA NTRS1986

Hybrid X-ray telescope systems

It has been known for some time that glancing incidence X-ray optics have sharply peaked point response functions. The spatial resolution of Wolter X-ray telescope systems is frequently limited by the performance characteristics of the X-ray detector rather than by the optics, even when high resolution detectors such as photographic emulsions are used. This problem becomes even more severe when it is desirable to take advantage of the high sensitivity and broad wavelength response afforded by modern solid state detectors such as charge coupled devices or multi-anode microchannel arrays. Results of theoretical investigations of methods for increasing the telescope plate scale by the use of glancing incidence hyperboloid/ellipsoid X-ray microscope optics and normal incidence contoured layered synthetic microstructure optics for coupling the Wolter mirrors to the detector are reported. The relative merits of the different hybrid X-ray telescope systems which result will be discussed. Considerations will be made concerning applications of these systems to high resolution imagery and spectroscopy of astronomical X-ray/XUV sources.

Shealy, David L.↗
NASA NTRS1993

Probe shapes that measure time-averaged streamwise momentum and cross-stream turbulence intensity

A method and apparatus for directly measuring the time-averaged streamwise momentum in a turbulent stream use a probe which has total head response which varies as the cosine-squared of the angle of incidence. The probe has a nose with a slight indentation on its front face for providing the desired response. The method of making the probe incorporates unique design features. Another probe may be positioned in a side-by-side relationship to the first probe to provide a direct measurement of the total pressure. The difference between the two pressures yields the sum of the squares of the cross-stream components of the turbulence level.

Rossow, Vernon J.↗
NASA NTRS1981

Theory and tests of a thermal ion detector sensitive only at Near-normal incidence

Measurements of thermal ions are influenced by factors such as spacecraft potential, velocity, angle of attack, and sheath size. A theory is presented for the response of an instrument which accepts ions only within a small angle of incidence from normal. Although a more general theory is available and forms the basis of this one, the small angle restriction allows a simpler formulation which does not depend on sheath size. Furthermore, practical instruments are easily designed around this restriction. Laboratory tests verify that such instruments respond as expected and they illustrate how design details influence perturbations from the ideal response characteristics.

Robinson, J. W.↗
NASA NTRS1993

Colorimetric qualification of shear sensitive liquid crystal coatings

The work that has been done to date on the Shear Sensitive Liquid Crystal Project demonstrated that cholesteric liquid crystal coatings respond to both the direction and magnitude of a shearing force. The response of the coating is to selectively scatter incident white light into a spectrum of colors. Discernible color changes at a fixed angle of observation and illumination are the result of an applied shear stress. The intention was to be able to convert these observable color patterns from a flow visualization technique into a quantitative tool. One of the earlier intentions was to be able to use liquid crystals in dynamic flow fields. This was assumed possible because liquid crystals had made it possible to visualize transients in surface shear forces. Although the transients were visualized by color changes to an order one micro second, the time response of a coating to align to a shearing force is dependent on the magnitude of the change between its initial and final states. Unfortunately, the response is not instantaneous. It is for this reason any future attempt at quantifying the magnitude and directions of a shearing force are limited to surface shear stress vector fields in three dimensional steady state flows. This limitation does not significantly detract from the utility of liquid crystal coatings. The measurement of skin friction in the study of transition on wings, prediction of drag forces, performance assessment, and the investigation of boundary layer behavior is of great importance in aerodynamics. There exist numerous examples of techniques for the measurement of surface shear stress. Most techniques require arduous calibrations and necessitate extensive preparation of the receiving surfaces. However, the main draw back of instruments such as Preston tubes, hot films, buried wire gages, and floating element balances is that they only provide a point measurement. The advantages of capturing global shear data would be appreciable when compared with conventional point measurement sensors. It has yet to be determined if a repeatable correlation exists between the measured color of a liquid crystal coating and the magnitude/directional components of a shear vector imposed onto it.

Muratore, Joseph J., Jr.↗
NASA NTRS1991

A novel technique for response function determination of shear sensitive cholesteric liquid crystals for boundary layer investigations

A description of the design and setup of an experimental technique for measurement of the response function in shear sensitive liquid crystals has been reported. Utilizing the selective reflection characteristics of cholesteric liquid crystals, the method is capable of measuring the delay, rise, and relaxation times in response to a given dynamic shear stress as a function of the wavelength of the incident light. Application of a step input shear stress results in a liquid crystal time response that can be described as consisting of an initial delay, a shear induced helix deformation, and a relaxation to the initial state through diffusion processes. The method has been used for quantitative calibration of a shear sensitive liquid crystal by observing the peak in reflected light intensity, at a given wavelength, as a function of the shear stress.

Parmar, D. S.↗
NASA NTRS2018

Characterizing Aerodynamic Damping of a Supersonic Missile with CFD

Time accurate solutions of the Euler and Navier{Stokes equations are used as an approach to elucidate aerodynamic coefficients that include rigid body motion effects. The Army-Navy Finner geometry is used for work flow development due to its simple shape, inexpensive grid generation, and available literature that include aerodynamic damping derivatives obtained from ight test, wind tunnel tests, and computational fluid dynamics. Supersonic conditions for pitch and roll damping include angles of attack up to 90 deg. Aerodynamic responses due to rigid body maneuvers with prescribed wind incidence angles and body rates are computed using the DoD CREATE Kestrel and NASA FUN3D flow solvers. First, reference numerical and experimental results provide validation of aero- dynamic damping terms computed by traditional periodic motion in roll and pitch. Next, individual, impulse motion inputs provide the canonical responses for general input-output modeling based on classical superposition and convolution concepts. Finally, simultaneous impulse excitation of all inputs provides an efficient system identification training scenario for accurate aerodynamic model construction in state space via the NASA Sys- tem/Observer/Controller Identification Toolbox.

Shelton, Andrew↗
NASA NTRS1974

Soft X-ray bremsstrahlung and fluorescent line production in the atmosphere by low energy electrons

The effect of low energy quasi-trapped or precipitating electrons which impact on the counter windows of soft X-ray detectors are discussed. The errors caused by X-rays produced in the residual atmosphere above a rocket-borne detector because of the resemblance to X-rays of cosmic origin are examined. The design and development of counter windows which make it possible to identify the atmospherically produced X-rays are described. Curves are presented to show the following: (1) preliminary low energy electron data from Atmospheric Explorer C, (2) X-ray flux in electron-excited nitrogen and oxygen, (3) typical proportional counter response to low energy cosmic rays, and (4) proportional counter response to X-radiation produced by electrons incident upon a gas of oxygen to nitrogen number of 0.4.

Kraushaar, W. L.↗
NASA NTRS1976

Multilayered models for electromagnetic reflection amplitudes

The remote sensing of snowpack characteristics with surface installations or with an airborne system could have important applications in water resource management and flood prediction. To derive some insight into such applications, the electromagnetic response of multilayer snow models is analyzed. Normally incident plane waves are assumed at frequencies ranging from 10 to the 6th power to 10 to the 10th power Hz, and amplitude reflection coefficients are calculated for models having various snow-layer combinations, including ice sheets. Layers are defined by a thickness, permittivity, and conductivity; the electrical parameters are constant or prescribed functions of frequency. To illustrate the effect of various layering combinations, results are given in the form of curves of amplitude reflection coefficients, versus frequency for a variety of models. Under simplifying assumptions, the snow thickness and effective dielectric constant can be estimated from the reflection coefficient variations as a function of frequency.

Linlor, W. I.↗
NASA NTRS1979

A simplified method of evaluating the stress wave environment of internal equipment

A simplified method called the transfer function technique (TFT) was devised for evaluating the stress wave environment in a structure containing internal equipment. The TFT consists of following the initial in-plane stress wave that propagates through a structure subjected to a dynamic load and characterizing how the wave is altered as it is transmitted through intersections of structural members. As a basis for evaluating the TFT, impact experiments and detailed stress wave analyses were performed for structures with two or three, or more members. Transfer functions that relate the wave transmitted through an intersection to the incident wave were deduced from the predicted wave response. By sequentially applying these transfer functions to a structure with several intersections, it was found that the environment produced by the initial stress wave propagating through the structure can be approximated well. The TFT can be used as a design tool or as an analytical tool to determine whether a more detailed wave analysis is warranted.

Colton, J. D.↗
NASA NTRS1986

Microwave backscatter coefficients of artificially grown first-year sea ice

The radar backscattering coefficient of simulated first year sea ice was measured at 5.2, 9.6, 13.6, and 16.6 GHz, using a dual-antenna FM-CW scatterometer. The measurements were corrected for antenna separation and beamwidth, to obtain true values of scattering coefficient. Above 15 deg, snow-covered and rough gray ice have similar angular responses, while the decrease in scattering coefficient with incidence angle is more rapid for smoother surfaces. True scattering coefficients and surface roughness data estimated with an antenna-beamwidth correction based on a physical-optics model give values close to those measured.

Xue, D.↗
NASA NTRS1994

Phytoplankton production in the Sargasso Sea as determined using optical mooring data

Optical measurements from an untended mooring provide high-frequency observations of in-water optical properties and permit the estimation of important biological parameters continuously as a function of time. A 9-month time series, composed of three separate deployments, of optical data from the BIOWATT 1987 deep-sea mooring located in the oligotrophic waters of the Sargasso Sea at 34 deg N, 70 deg W are presented. These data have been tested using several bio-optical models for the purpose of providing a continuous estimate of phytoplankton productivity. The data are discussed in the context of contemporaneous shipboard observations and for future ocean color satellite observations. We present a continuous estimation of phytoplankton productivity for the 9-month time series. Results from the first 70-day deployment are emphasized to demonstrate the utility of optical observations as proxy measures of biological parameters, to present preliminary analysis, and to compare our bio-optical observations with concurrent physical observations. The bio-optical features show variation in response to physical forcings including diel variations of incident solar irradiance, episodic changes corresponding to wind forcing, variability caused by advective mesoscale eddy events in the vicinity of the mooring, and seasonal variability corresponding to changes in solar radiation, shoaling of the mixed layer depth, and succession of phytoplankton populations.

Waters, K. J.↗
NASA NTRS1997

Utility of BRDF Models for Estimating Optimal View Angles in Classification of Remotely Sensed Images

Statistical classification of remotely sensed images attempts to discriminate between surface cover types on the basis of the spectral response recorded by a sensor. It is well known that surfaces reflect incident radiation as a function of wavelength producing a spectral signature specific to the material under investigation. Multispectral and hyperspectral sensors sample the spectral response over tens and even hundreds of wavelength bands to capture the variation of spectral response with wavelength. Classification algorithms then exploit these differences in spectral response to distinguish between materials of interest. Sensors of this type, however, collect detailed spectral information from one direction (usually nadir); consequently, do not consider the directional nature of reflectance potentially detectable at different sensor view angles. Improvements in sensor technology have resulted in remote sensing platforms capable of detecting reflected energy across wavelengths (spectral signatures) and from multiple view angles (angular signatures) in the fore and aft directions. Sensors of this type include: the moderate resolution imaging spectroradiometer (MODIS), the multiangle imaging spectroradiometer (MISR), and the airborne solid-state array spectroradiometer (ASAS). A goal of this paper, then, is to explore the utility of Bidirectional Reflectance Distribution Function (BRDF) models in the selection of optimal view angles for the classification of remotely sensed images by employing a strategy of searching for the maximum difference between surface BRDFs. After a brief discussion of directional reflect ante in Section 2, attention is directed to the Beard-Maxwell BRDF model and its use in predicting the bidirectional reflectance of a surface. The selection of optimal viewing angles is addressed in Section 3, followed by conclusions and future work in Section 4.

Valdez, P. F.↗