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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Water facilities in retrospect and prospect: An illuminating tool for vehicle design

Water facilities play a fundamental role in the design of air, ground, and marine vehicles by providing a qualitative, and sometimes quantitative, description of complex flow phenomena. Water tunnels, channels, and tow tanks used as flow-diagnostic tools have experienced a renaissance in recent years in response to the increased complexity of designs suitable for advanced technology vehicles. These vehicles are frequently characterized by large regions of steady and unsteady 3-D flow separation and ensuing vortical flows. The visualization and interpretation of the complicated fluid motions about isolated vehicle components and complete configurations in a time and cost effective manner in hydrodynamic test facilities is a key element in the development of flow control concepts, and, hence, improved vehicle designs. A historical perspective of the role of water facilities in the vehicle design process is presented. The application of water facilities to specific aerodynamic and hydrodynamic flow problems is discussed, and the strengths and limitations of these important experimental tools are emphasized.

Erickson, Gary E.↗
NASA NTRS1988

Voice stress analysis

In a study of the validity of eight candidate voice measures (fundamental frequency, amplitude, speech rate, frequency jitter, amplitude shimmer, Psychological Stress Evaluator scores, energy distribution, and the derived measure of the above measures) for determining psychological stress, 17 males age 21 to 35 were subjected to a tracking task on a microcomputer CRT while parameters of vocal production as well as heart rate were measured. Findings confirm those of earlier studies that increases in fundamental frequency, amplitude, and speech rate are found in speakers involved in extreme levels of stress. In addition, it was found that the same changes appear to occur in a regular fashion within a more subtle level of stress that may be characteristic, for example, of routine flying situations. None of the individual speech measures performed as robustly as did heart rate.

Brenner, Malcolm↗
NASA NTRS1987

Light aircraft sound transmission studies - Noise reduction model

Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.

Atwal, Mahabir S.↗
NASA NTRS1987

Cometary plasma - A review

Results of spacecraft probing of Comet Halley and Comet Giacobini-Zinner are used to investigate cometary plasma processes and large-scale structure. Examples of tail phenomena are discussed, with emphasis on the observed disconnection events (DEs). The sector boundary/magnetic reconnection model for DEs of Niedner and Brandt, (1978) is shown to be consistent with the times of known DEs in Comet Halley as well as the magnetic polarity data available from interplanetary and near-earth satellites, and from solar data. Results of the present review have application to understanding of the solar-wind/comet interaction during the 1985-1986 apparition of Comet Halley.

Brandt, John C.↗
NASA NTRS1987

Measurement of the absorption coefficient of acoustical materials using the sound intensity method

In this study the possibility of using the two-microphone sound intensity technique to measure the normal incidence and the random incidence sound absorption coefficient was investigated. The normal incidence absorption coefficient was determined by measuring the intensity incidence on the sample and the intensity reflected by the sample placed in an anechoic chamber. The random incidence absorption coefficient was determined by measuring the intensity incident on the sample and the intensity reflected by the sample placed in a reverberation chamber. Absorption coefficient results obtained by the sound intensity technique were compared with standard techniques, namely the reverberation chamber and the standing wave tube. The major advantages of using the sound intensity technique are that it permits 'in situ' measurements and the absorption coefficient for a large range of frequencies can be obtained from a single measurement.

Atwal, Mahabir S.↗
NASA NTRS1988

Antarctic chlorine chemistry - Possible global implications

Occurrence of heterogeneous reactions on the surface of polar stratospheric clouds (PSC) is a necessary component of the Cl-related chemical mechanisms proposed to explain the recently observed decrease of O3 during Antarctic spring. A one-dimensional model is used to assess the impact of these heterogeneous reactions on future global O3 trends if they were to occur on the global aerosol layer. The impact of these reactions on the concentration of Cl species in the present-day atmosphere is also calculated. The reaction (ClNO3 + HCl) could have a large impact on stratospheric O3. A fast rate for this reaction would greatly enhance the present concentration of ClO and reduce the abundance of HCl in the lower stratosphere. Because of the large differences between the Antarctic and global environments, the calculated global O3 trends are smaller than those calculated for Antarctica.

Rodriguez, Jose M.↗
NASA NTRS1988

Measurements of NO and total reactive odd-nitrogen, NOy, in the Antarctic stratosphere

Measurements of NO and total reactive N, NOy, were made as part of the Airborne Antarctic Ozone Experiment conducted in Punta Arenas, Chile during Aug. and Sept. 1987. The total reactive N reservoir includes the species NO, NO2, NO3, N2 O5, HNO3, and ClONO2. The instrument was located on board the NASA ER2 aircraft which conducted 12 flights over the Antarctic continent reaching altitudes of 18 km at 72 deg S latitude. The NOy technique utilized the conversion of component NOy species to NO on a gold catalyst and the subsequent detection of NO by the chemiluminescence reaction of NO with ozone. Since the inlet sample line is heated and the catalyst operates at 300 C, NOy incorporated in aerosols evaporates and is converted to NO. NO was measured on two separate flights by removing the catalyst from the sample inlet line.

Fahey, D. W.↗
NASA NTRS1988

Photochemical modeling of the Antarctic stratosphere: Observational constraints from the airborne Antarctic ozone experiment and implications for ozone behavior

The rapid decrease in O3 column densities observed during Antarctic spring has been attributed to several chemical mechanisms involving nitrogen, bromine, or chlorine species, to dynamical mechanisms, or to a combination of the above. Chlorine-related theories, in particular, predict greatly elevated concentrations of ClO and OClO and suppressed abundances of NO2 below 22 km. The heterogeneous reactions and phase transitions proposed by these theories could also impact the concentrations of HCl, ClNO3 and HNO3 in this region. Observations of the above species have been carried out from the ground by the National Ozone Expedition (NOZE-I, 1986, and NOZE-II, 1987), and from aircrafts by the Airborne Antarctic Ozone Experiment (AAOE) during the austral spring of 1987. Observations of aerosol concentrations, size distribution and backscattering ratio from AAOE, and of aerosol extinction coefficients from the SAM-II satellite can also be used to deduce the altitude and temporal behavior of surfaces which catalyze heterogeneous mechanisms. All these observations provide important constraints on the photochemical processes suggested for the spring Antarctic stratosphere. Results are presented for the concentrations and time development of key trace gases in the Antarctic stratosphere, utilizing the AER photochemical model. This model includes complete gas-phase photochemistry, as well as heterogeneous reactions. Heterogeneous chemistry is parameterized in terms of surface concentrations of aerosols, collision frequencies between gas molecules and aerosol surfaces, concentrations of HCl/H2O in the frozen particles, and probability of reaction per collision (gamma). Values of gamma are taken from the latest laboratory measurements. The heterogeneous chemistry and phase transitions are assumed to occur between 12 and 22 km. The behavior of trace species at higher altitudes is calculated by the AER 2-D model without heterogeneous chemistry. Calculations are performed for solar illumination conditions typical of 60, 70, and 80 S, from July 15 to October 31.

Rodriguez, Jose M.↗
NASA NTRS1988

Antarctic ozone decrease: Possible impact on the seasonal and latitudinal distribution of total ozone as simulated by a 2-D model

Satellite borne instruments, the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet spectrometer (SBUV), show that total column ozone has decreased by more than 5 percent in the neighborhood of 60 S at all seasons since 1979. This is considerably larger than the decrease calculated by 2-D models which take into account solar flux variation and increases of trace gas concentrations over the same period. The meteorological conditions (warmer temperature and the apparent lack of polar stratospheric clouds) at these latitudes do not seem to favor heterogeneous chemistry as the direct cause for the observed ozone reduction. A mechanism involving the seasonal transport of ozone-poor air mass from within the polar vortex to lower latitudes (the so-called dilution effect) is proposed as a possible explanation for the observed year-round ozone reduction in regions away from the vortex.

Ko, Malcolm K. W.↗
NASA NTRS1988

Imaging studies of comets

Schmidt camera plates of comet Bradfield were secured on several nights in October 1987. The images of October 20 show the development of a huge bend in the plasma tail travelling several hundred kilometers per second down the tail; the likely solar-wind origin of this event is being explored. A charged coupled device (CCD) detector has been obtained. Calibration of the CCD is still underway, but high-quality, filtered cometary images shoud be possible in the near future.

Niedner, Malcolm B., Jr.↗
NASA NTRS1988

Extravehicular activities limitations study. Volume 1: Physiological limitations to extravehicular activity in space

This report contains the results of a comprehensive literature search on physiological aspects of EVA. Specifically, the topics covered are: (1) Oxygen levels; (2) Optimum EVA work; (3) Food and Water; (4) Carbon dioxide levels; (5) Repetitive decompressions; (6) Thermal, and (7) Urine collection. The literature was assessed on each of these topics, followed by statements on conclusions and recommended future research needs.

Furr, Paul A.↗
NASA NTRS1989

MSAT signalling and network management architectures

Spar Aerospace has been active in the design and definition of Mobile Satellite Systems since the mid 1970's. In work sponsored by the Canadian Department of Communications, various payload configurations have evolved. In addressing the payload configuration, the requirements of the mobile user, the service provider and the satellite operator have always been the most important consideration. The current Spar 11 beam satellite design is reviewed, and its capabilities to provide flexibility and potential for network growth within the WARC87 allocations are explored. To enable the full capabilities of the payload to be realized, a large amount of ground based Switching and Network Management infrastructure will be required, when space segment becomes available. Early indications were that a single custom designed Demand Assignment Multiple Access (DAMA) switch should be implemented to provide efficient use of the space segment. As MSAT has evolved into a multiple service concept, supporting many service providers, this architecture should be reviewed. Some possible signalling and Network Management solutions are explored.

Garland, Peter↗
NASA NTRS1989

Analysis and interpretation of observations of airglow at 297 nm in the Venus thermosphere

Data obtained by the Pioneer Venus Orbiter's UV spectrometer for the limb profiles near periapsis, with the instrument's grating set to a bandpass-center wavelength of 297 nm, are analyzed to identify the sources giving rise to the observed signals, which are forbidden O I 2972 A and C I 2967 A. Structure in the forbidden O I 2972 A emission profile in the lower thermosphere is explained in terms of large temperature excursions altering the quenching rate of O(1S) by CO2.

Lecompte, Malcolm A.↗
NASA NTRS1988

Spacecraft alignment estimation

A numerically well-behaved factorized methodology is developed for estimating spacecraft sensor alignments from prelaunch and inflight data without the need to compute the spacecraft attitude or angular velocity. Such a methodology permits the estimation of sensor alignments (or other biases) in a framework free of unknown dynamical variables. In actual mission implementation such an algorithm is usually better behaved than one that must compute sensor alignments simultaneously with the spacecraft attitude, for example by means of a Kalman filter. In particular, such a methodology is less sensitive to data dropouts of long duration, and the derived measurement used in the attitude-independent algorithm usually makes data checking and editing of outliers much simpler than would be the case in the filter.

Shuster, Malcolm D.↗
NASA NTRS1988

Sulfur speciation in hydrous experimental glasses of varying oxidation state - Results from measured wavelength shifts of sulfur X-rays

The focusing geometry of an electron microprobe has been used to measure the wavelength shifts of sulfur X-rays from hydrous experimental melts synthesized at oxygen fugacities that range from near the iron-wustite buffer to the magnetite-hermatite buffer. It is found that the proportion of dissolved sulfur which is present as sulfate increases with increasing oxygen fugacity. It is noted that in natural melts that have equilibrated at or below fayalite-magnetite-quartz values of +1, sulfur is probably present mainly as S(2-).

Carroll, Michael R.↗
NASA NTRS1986

Judgments of eye level in light and in darkness

Subjects judged eye level in the light and in the dark by raising and lowering themselves in a dental chair until a stationary target appeared to be at the level of their eyes. This method reduced the possibility of subjects' using visible landmarks as reference points for setting eye level during lighted trials, which may have contributed to artificially low estimates of the variability of this judgment in previous studies. Chair settings were 2.5 deg higher in the dark than in the light, and variability was approximately 66 percent greater in the dark than in the light. These results are discussed in terms of possible interactions of two separate systems, one sensitive to the orientations of visible surfaces and the other sensitive to bodily and gravitational information.

Stoper, Arnold E.↗
NASA NTRS1989

Ageostrophic effects on the stratospheric residual circulation and tracer distributions

The behaviors of idealized geostrophic and ageostrophic circulations forced by differential heating and parameterized eddy mixing in the absence of boundary drag are examined for a range of mixing values and boundary conditions, using a nonlinear version of Holton's (1986) channel model. It was found that geostrophic and ageostrophic flows can have fundamentally different behaviors. This may have important implications for the circulation and trace gas distributions in the stratosphere. It is shown that, as eddy forcing vanishes, an ageostrophic system is not constrained to approach radiative equilibrium and may tend to the limit of an inviscid diabatic circulation under a range of boundary conditions.

Hou, Arthur Y.↗
NASA NTRS1989

An evaluation of the role of eddy diffusion in stratospheric interactive two-dimensional models

An interactive two-dimensional model of the stratosphere, consisting of a primitive equation dynamics module, a simplified HO(x) ozone model, and a full radiative transfer scheme, is used to study the effect of eddy diffusion in the model. Consideration is given to the effects of nonlocal forcing from dissipation in the model troposphere and frictional drag at mesospheric levels, mechanical damping in the stratosphere itself, and potential vorticity flux due to large scale waves. It is found that the ozone distributions generated with the model are very sensitive to the choice of values for the friction and the eddy diffusion coefficients. It is shown that reasonable latitudinal gradients of ozone may be obtained by using small values for the mechanical damping for the mid- and high-latitude stratopsphere.

Schneider, Hans R.↗