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NASA NTRS1989

Global backscatter assessment

The focus of this effort is the development of a global-scale model of aerosol backscatter for laser atmospheric wind sounder (LAWS) design and performance studies. Background parameters are derived from aerosol data sets with global-scale spatial and/or temporal coverage, using objective statistical decomposition and/or a priori stratification based on supplementary data. Backscatter coefficients at the LAWS design wavelength are derived from background aerosol physical, chemical, and optical data, or from direct backscatter measurements at other wavelengths, using background conversion factors. Direct measurements of aerosol backscatter at 10.6 microns from the Royal Signals and Radar Establishment (RSRE) and the Wave Propagation Laboratory (WPL) were selected. The RSRE backscatter data processing code were optimized under low backscatter conditions, performed detailed analyses of collocated intercomparisons between the two lidars, and assisted in the analysis of the long-term backscatter climatologies from the two lidars. Timely presentation of global backscattering experiment (GLOBE) research results to the global geophysical community is required.

Bowdle, David A.↗

NASA NTRS1990

On the use of IR lidar and K(sub a)-band radar for observing cirrus clouds

Advances in lidar and radar technology have potential for providing new and better information on climate significant parameters of cirrus. Consequently, the NOAA Wave Propagation Lab. is commencing CLARET (Cloud Lidar And Radar Exploratory Test) to evaluate the promise of these new capabilities. Parameters under study include cloud particle size distribution, height of cloud bases, tops, and multiple layers, and cloud dynamics revealed through measurement of vertical motions. The first phase of CLARET is planned for Sept. 1989. The CO2 coherent Doppler lidar and the sensitive K sub a band radar hold promise for providing valuable information on cirrus that is beyond the grasp of current visible lidars.

Eberhard, Wynn L.↗

NASA NTRS1990

Concave-outward slow shocks in coronal mass ejections

Formation of slow shocks in a simplified model corona consisting of closed magnetic field lines near the coronal base with overlying open magnetic field lines is analyzed. An increase in the magnetic field strength in the closed region is utilized to drive the corona outward, generating slow shocks for a suitable selection of parameters. The study demonstrates that concave-upward slow shocks can be formed in a magnetic environment, and provides evidence that nonlinear manifestations of all three wave modes (slow, intermediate, and fast) can occur as the corona adjusts from ambient conditions to those produced by the driver. The results show the existence of nonlinear disturbances due to all three wave modes in the coronal response to the expanding driver magnetic fields.

Steinolfson, R. S.↗

NASA NTRS1991

Advanced Solid-State Array Spectrometer (ASAS) data sets from the 1990 field season: A unique look at two forested ecosystems

The Advanced Solid-state Array Spectrometer (ASAS) is a pointable imaging spectrometer which uses a solid-state array to acquire imagery of terrestrial targets in 29 spectral bands from .4 to .8 microns. Performance and calibration of the instrument are described. The ASAS data sets obtained in 1990 provide a unique look at forest canopies from two different forest regions of the North America continent under varying temporal, spectral, and bidirectional conditions. These data sets will be used to study such parameters as the albedo of forest canopies, the dynamics of scene radiation due to factors such as canopy architecture, moisture stress, leaf chemistry, topography, and understory composition.

Walthall, Charles L.↗

NASA NTRS1991

Response of spacecraft window materials to hypervelocity projectile impact

This paper presents the results of an investigation of the response of window materials to hypervelocity projectile impact. Window impact damage is characterized according to the nature and extent of surface and internal damage. Analysis of the test data indicates that, for single-pane specimens, the extent of the damage to the test specimens can be written as functions of the impact parameters of the original projectile and the geometric and material properties of the projectile/ window system. These functions can be used to perform parameter-sensitivity studies and to evaluate hypothetical design applications and configurations.

Schonberg, William P.↗

NASA NTRS1990

High figure of merit thermoelectrics - Theoretical considerations

The thermoelectric figure of merit of a semiconductor, ZT, can be calculated from a small number of microscopic material parameters, the material composition, the doping level, and the temperature. The functional dependence of ZT on these parameters has been studied for a range of material parameters using a recently developed model which accurately and self-consistently describes the thermoelectric properties of n-type silicon-germanium alloys. ZT values several times larger than current state-of-the-art values of ZT of about 1 are shown to be entirely consistent with existing theory, even using material parameters already observed. A search for materials with much higher figure of merit values therefore remains of interest, in spite of several decades of relatively slow progress in this area.

Vining, Cronin B.↗

NASA NTRS1990

Steady-state analysis of a nonlinear rotor-housing system

The periodic steady state response of a high pressure oxygen turbopump (HBOTP) of a Space Shuttle main engine (SSME), involving a clearance between the bearing and housing carrier, is sought. A harmonic balance method utilizig Fast Fourier Transform (FFT) algorithm is developed for the analysis. An impedance method is used to reduce the number of degrees of freedom to the displacements at the bearing clearance. Harmonic and subharmonic responses to imbalance for various system parameters are studied. The results show that the computational technique developed in this study is an effective and flexible method for determining the stable and unstable periodic response of complex rotor-housing systems with clearance type nonlinearity.

Noah, S. T.↗

NASA NTRS1991

Theoretical spectroscopy of comets

Theoretical spectra were calculated of various emitting species in cometary comae both to study physical parameters that are measurable with cometary spectra and to provide fluorescence efficiencies for the derivation of abundances from fluxes.

Ahearn, Michael F.↗

NASA NTRS1992

Optimization of laminated stacking sequence for buckling load maximization by genetic algorithm

The use of a genetic algorithm to optimize the stacking sequence of a composite laminate for buckling load maximization is studied. Various genetic parameters including the population size, the probability of mutation, and the probability of crossover are optimized by numerical experiments. A new genetic operator - permutation - is proposed and shown to be effective in reducing the cost of the genetic search. Results are obtained for a graphite-epoxy plate, first when only the buckling load is considered, and then when constraints on ply contiguity and strain failure are added. The influence on the genetic search of the penalty parameter enforcing the contiguity constraint is studied. The advantage of the genetic algorithm in producing several near-optimal designs is discussed.

Le Riche, Rodolphe↗

NASA NTRS1992

High-energy gamma-ray emission from pion decay in a solar flare magnetic loop

The production of high-energy gamma rays resulting from pion decay in a solar flare magnetic loop is investigated. Magnetic mirroring, MHD pitch-angle scattering, and all of the relevant loss processes and photon production mechanisms are taken into account. The transport of both the primary ions and the secondary positrons resulting from the decay of the positive pions, as well as the transport of the produced gamma-ray emission are considered. The distributions of the gamma rays as a function of atmospheric depth, time, emission angle, and photon energy are calculated and the dependence of these distributions on the model parameters are studied. The obtained angular distributions are not sufficiently anisotropic to account for the observed limb brightening of the greater than 10 MeV flare emission, indicating that the bulk of this emission is bremsstrahlung from primary electrons.

Mandzhavidze, Natalie↗

NASA NTRS1992

A reconsideration of the effects of terminator ionopause height on the nightward ion transport at Venus

The ionopause altitude near the terminator is a crucial parameter for studies dealing with the maintenance of the nightside ionosphere of Venus. It is generally thought that, during high solar wind dynamic pressures (P(SW)) or during solar minimum conditions, the ionopause comes down to very low altitudes so that the dayside ionosphere is not able to supply sufficient plasma to maintain the observed nightside densities. However, there are a number of workable definitions of the ionopause. Near the terminator, the altitude of the ionopause differs considerably depending upon the definition. The ionopause deduced from the radio occultation experiment as well as the pressure ionopause can be significantly lower than the density ionopause deduced from the Langmuir probe at these locations. The latter refers to the altitude where the electron density falls to 100/cu cm. Using in situ data from the Pioneer Venus Orbiter, it is shown that the density ionopause remains fairly high even for high P(SW) conditions. Simple quantitative estimates indicate that significant flow of plasma is still possible under these conditions. Thus, nightward transport of plasma during high P(SW) conditions may be more efficient than has been assumed so far. Since such conditions are more prevalent during solar cycle minimum, it is argued that transport may be relevant in the maintenance of nightside ionosphere at that time also.

Kar, J.↗

NASA NTRS1992

Spacelab Life Sciences 1, development towards successive life sciences flights

A general review is presented of flight data and related hardware developments for Spacelab Life Sciences (SLS) 1 with an eye toward applying this knowledge to projected flight planning. Specific attention is given to the Research Animal Holding Facility (RAHF), the General Purpose Work Station (GPWS), the Small Mass Measuring Instrument (SMMI), and the Animal Enclosure Module (AEM). Preflight and in-flight testing methods are detailed including biocompatibility tests, parametric engineering sensitivity analyses, measurements of environmental parameters, and studies of operational interfaces. Particulate containment is demonstrated for some of the equipment, and successful use of the GPWS, RAHF, AEM, and SMMI are reported. The in-flight data are useful for developing more advanced hardware such as the AEM for SLS flight 2 and the modified RAHF for SLS flight 3.

Dalton, B. P.↗

NASA NTRS1993

ASRM Case Insulation development

The ASRM Case Insulation Program used design of experiments to develop a high performance case insulation. The program traded-off more than thirty properties in areas of ablation performance, material properties, processibility, bonding/aging. Kevlar pulp was found to be the most significant factor. The low-molecular weight ethylene propylene diene monomer, EPDM was the second most significant factor. The curative was the third most significant factor. The tackifier was the fourth most significant factor. The stripwinding process for applying the insulation onto the case inner surfaces was also studied. The parameters selected for experiment were extruder speed, upper roller temperature and extruder nozzle temperature. The extrudability results showed that non-Kevlar filled formulations displayed optimum edges but poor thickness continuity. High Kevlar filled formulations displayed optimum thickness continuity but poor strip edge ratings.

Tam, W. F. S.↗

NASA NTRS1993

Sedimentation, volcanism, and ancestral lakes in the Valles Marineris: Clues from topography

Compilation of a simplified geologic/geomorphic map onto a digital terrain model of Valles Marineris has permitted quantitative evaluations of topographic parameters. The study showed that, if their interior layered deposits are lacustrine, the ancestral Valles Marineris must have consisted of isolated basins. If, on the other hand, the troughs were interconnected as they are today, the deposits are most likely to volcanic origin, and the mesas in the peripheral troughs may be table mountains. The material eroded from the trough walls was probably not sufficient to form all of the interior layered deposits, but it may have contributed significantly to their formation.

Lucchitta, B. K.↗

NASA NTRS1993

Simulation reduction using the Taguchi method

A large amount of engineering effort is consumed in conducting experiments to obtain information needed for making design decisions. Efficiency in generating such information is the key to meeting market windows, keeping development and manufacturing costs low, and having high-quality products. The principal focus of this project is to develop and implement applications of Taguchi's quality engineering techniques. In particular, we show how these techniques are applied to reduce the number of experiments for trajectory simulation of the LifeSat space vehicle. Orthogonal arrays are used to study many parameters simultaneously with a minimum of time and resources. Taguchi's signal to noise ratio is being employed to measure quality. A compromise Decision Support Problem and Robust Design are applied to demonstrate how quality is designed into a product in the early stages of designing.

Mistree, Farrokh↗

NASA NTRS1994

Comparative performance of a modified Space Shuttle Reentry Anti-G Suit (REAGS) with and without pressure socks

In a prior study, the Armstrong Laboratory (AL) demonstrated that +G(sub z) protection during simulated shuttle reentry could be improved with an extended coverage anti-G suit with pressure socks but no abdominal bladder (REAGS). In a subsequent study conducted at the NASA Johnson Space Center it was shown that REAGS had a down side which included restricted mobility (during simulated shuttle egress) and a larger boot size needed for the pressure socks. The present study was conducted using a modified REAGS to increase mobility during egress. The size of the crotch opening was increased, and the fabric covering the buttocks was replaced with more elastic material. Six healthy male members of the AL centrifuge panel served as subjects for the study. As in the earlier study, subjects received 20 to 35 mg of IV Lasix approximately 6 hours before being exposed to a simulated space shuttle reentry +G(sub z) profile on the AL centrifuge, which induced a mean weight loss of 2.8 percent, range 2.1 percent to 3.7 percent. The REAGS was inflated to 1.0 psig 10 minutes prior to G onset. The G-profile was identical to that used in the previous REAGS study. Physiologic parameters monitored were also the same, i.e., eye-level systolic blood pressure (ELBP) using the Finapres digital cuff technique and heart rate and rhythm. Subjective comments were obtained from questionnaires administered after the increased G exposure. Systolic ELBP was maintained at 60 mm Hg or above by pressurizing the anti-G suit in 0.5 psig increments up to a maximum pressure of 2.5 psig. There were no significant differences in mean G-suit pressure required to maintain systolic ELBP at 60 mm Hg or above between the REAGS worn with and without pressure socks. Maximum mean G-levels achieved during the GOR were also the same under both experimental conditions, i.e., 4.7 G with socks and 4.6 G without socks. These G-levels were essentially the same as recorded earlier with the unmodified REAGS. There were no significant differences in comfort rating during the G exposure assigned by subjects when they wore the modified REAGS with or without the pressure socks.

Krutz, R. W., Jr.↗

NASA NTRS1995

Polarimetric signatures of sea ice. 2: Experimental observations

Experimental observations of polarimetric signatures are presented for sea ice in the Beaufort Sea under cold winter conditions and interpreted with the composite model developed in Part 1. Polarimetric data were acquired in March 1988 with the Jet Propulsion Laboratory multifrequency airborne synthetic aperture radar (SAR) during the Beaufort Sea Flight Campaign. The experimental area was located near 75 N latitude and spanned 140 deg-145 deg W longitude. Selected sea ice scenes contain various ice types, including multiyear, thick first-year, and thin lead ice. Additionally, the C band SAR on the first European Remote Sensing Satellite provides supplementary backscattering data of winter Beaufort Sea ice for small incident angles (20 deg-26 deg) at vertical polarization. Sea ice characterization and environment data used in the model were collected at the Applied Physics Laboratory drifting ice station to the northeast of Prudhoe Bay; additional data from field and laboratory experiments are also utilized in this analysis. The model related sea ice polarimetric backscattering signatures to physical, structural, and electromagnetic properties of sea ice. Scattering mechanisms contributing to sea ice signatures are explained, and sensitivies of polarimetric signatures to sea ice characterization parameters are studied.

Nghiem, S. V.↗

NASA NTRS1995

The extent of far-IR emission in luminous galaxies

The size of far-infrared emission in luminous IR galaxies is an important parameter in studies of its source. The KAO is the largest aperture that can be brought to bear on the continuum emission of these galaxies at their far-infrared spectral peak. It therefore offers the best opportunity for probing the extent of this emission on the smallest possible scales. In this paper, I give a retrospective on efforts at the University of Texas, over the last decade, to use the KAO to understand the distribution of far-infrared continuum emission in luminous IR galaxies.

Lester, Dan F.↗