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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Characterization of the physico-chemical properties of polymeric materials for aerospace flight

Factors contributing to the final failure of Ni-Cd batteries are listed. A differential thermal analyzer was used to study several positive and negative battery electrodes. The negative plates show a very large peak (endotherm) between 245 C and 250C. The second endotherm occurs at 300C indicating the decomposition of Cd(OH)2. In positive plates, a first weak endotherm occurs at 100C, which indicates loss of H2O from Ni(OH)2(H2O)n molecules. A second large endotherm occurs in the range of 290C to 300C, indicating the decomposition of Ni(OH2) to NiO and H2O. Atomic absorption spectroscopy was used to determine nickel, cobalt, cadmium, and potassium content in battery electrolytes and electrodes. Results are presented in tables.

Rock, M.↗
NASA NTRS1981

The nature of the solar wind interaction with CO2/CO-dominated comets

The nature of the interaction of the solar wind with the ionospheres (field-free ion cavities) of comets with CO or CO2 as their dominant volatile species is considered and compared with the solar wind interaction with H2O-diominated comets. Calculations of the heliocentric variation of scale lengths defined as the nuclear distance at which the mean free path for ion-neutral collisions becomes equal to the nuclear distance, and the ion and neutral stand-off distances are presented for different modes of energy addition, nuclear radii and ionization time scales. Results indicate that whereas little activity can be expected from H2O-dominated comets at distances beyond 3 AU, COand CO2-dominated comets can be expected to be quite prolific at such distances. In contrast to H2O-dominated comets characterized by weak shocks, CO/CO2-dominated comet solar wind interactions are found to produce strong bow shocks within a specific heliocentric distance for the isothermal case of a CO-dominated comet, and a weak shock outside of this distance. In the general case, two types of cometary ionosphere transitions are found: a transition from strong to weak bow shock and from a compressible (soft) to an incompressible (hard) ionosphere, and a transition from a soft to a hard ionosphere with the bow shock remaining weak at a heliocentric distance dependant on atmospheric optical depth, bolometric albedo, nuclear radius, latent heat of sublimation of nuclear material, ionization time scale and type of heat addition. It is pointed out that the behavior of Comet Humason can be explained by solar wind interactions with a CO- or CO2-dominated comet.

Houpis, H. L. F.↗
NASA NTRS1983

High pressure cosmochemistry applied to major planetary interiors: Experimental studies

The infrared spectra of H2O ice VII and D2O ice VII were studied and techniques were developed for measuring adiabats of phases of NH3-H2O to 5 GPa. A mixing system for pressurized fluids was constructed in which liquid solutions of definite compositions can be prepared and loaded reliably into diamond cells in a project which seeks to determine the properties and boundaries of several high pressure phases of the H2-He-H2O-NH3-CH4 system. These data are needed to constrain theoretical models of the interiors of the major planets.

Nicol, M. F.↗
NASA NTRS1982

Heat transport in porous cometary nuclei

Heat transport in cometary nuclei is important because it leads to the formation of larger tails and comae after perihelia than before, to early outbursts caused by phase transitions, and to fragmentation. The role of gases in pores in icy (H2O and H2O + CO2) nuclei in the heat transport has been investigated in the viscous and Knudsen diffusion regions. It appears that in pure H2O-ices the heat flow is affected by the presence of pores but is affected only very close to the perihelion by water vapor contained in them. On the other hand, the presence of CO2 vapor in the pores significantly increases the heat flow in mixed nuclei at temperatures above 140 - 150 K. Thus for heliocentric distances between 3 and 5 AU, the above mentioned phenomena should be considerably enhanced in proportion to the admixture of CO2 ices. The overlap and channel formation by pores in nuclei with high porosities is discussed.

Smoluchowski, R.↗
NASA NTRS1983

The three micron 'ice' band in grain mantles

Attention is given to the influence of different mantle constituents on extinction and polarization due to H2O absorption in grain mantles, particularly the 3250/cm band. With respect to BN, the simultaneous reproduction of the extinction and polarization band shapes occurs by normal size particles containing mixtures of H2O with other molecules. As regards the 3-micron absorption in OH 231.8 plus 4.2, the data can be best fitted with pure amorphous H2O grains which have been heated to (or created at) about 80 K. The variation in grain mantle composition between young stellar objects and late-type stars loosing mass is attributed to a fundamental difference in grain formation and evolution.

Hagen, W.↗
NASA NTRS1983

Ice in Comet Bowell

Results of observations of the reflected light in the 1-5 micron region of the spectrum from the Comet Bowell are presented as part of the attempt to directly detect the presence of frozen volatiles in the nucleus of a comet. A deep absorption at 3.25 microns is detected in Comet Bowell which is due to the presence of H2O ice. While other volatile ices have absorption features near 3 microns, it is shown that only H2O ice is a plausible identification at the heliocentric distance of Comet Bowell during the observations (3.4 AU) since only H2O grains are stable enough to have produced the observed absorption. The implications of these findings for models of cometary nuclei are examined.

Campins, H.↗
NASA NTRS1983

Loss of water from Venus. I - Hydrodynamic escape of hydrogen

A one-dimensional photochemical-dynamic model is used to study hydrodynamic loss of hydrogen from a primitive, water-rich atmosphere on Venus. The escape flux is calculated as a function of the H2O mixing ratio at the atmospheric cold trap. The cold trap mixing ratio is then related in an approximate fashion to the H2O concentration in the lower atmosphere. Hydrodynamic escape should have been the dominant loss process for hydroogen when the H2O mass mixing ratio in the lower atmosphere exceeded approximately 0.1. The escape rate would have depended upon the magnitude of the solar ultraviolet flux and the atmospheric EUV heating efficiency and, to a lesser extent, on the O2 content of the atmosphere. The time required for Venus to have lost the bulk of a terrestrial ocean of water is on the order of a billion years. Deuterium would have been swept away along with hydrogen if the escape rate was high enough, but some D/H enrichment should have occurred as the escape rate slowed down.

Kasting, J. F.↗
NASA NTRS1983

Remote sensing of tropospheric gases and aerosols with airborne DIAL system

The multipurpose airborne DIAL system developed at NASA Langley Research Center is characterized, and the published results of tropospheric O3, H2O, and aerosol-backscatter remote-sensing experiments performed in 1980 and 1981 are summarized. The system comprises two tunable dye lasers pumped by frequency-doubled Nd:YAG lasers, dielectric-coated steering optics, a 36-cm-diameter Cassegrain receiver telescope, gateable photomultiplier tubes, and a minicomputer data-processing unit for real-time calculation of gas concentrations and backscattering profiles. The transmitted energy of the 100-microsec-separated dye-laser pulses is 40, 80, or 50 mJ/pulse at around 300, 600, or 720-nm wavelength, respectively. Good agreement was found between DIAL-remote-sensed and in-situ H2O and O3 profiles of the lower troposphere and O3 profiles of the tropopause region, and the usefulness of DIAL backscattering measurements in the study of boundary-layer and tropospheric dynamics is demonstrated. The feasibility of DIAL sensing of power-plant or urban plume SO2, of urban-area (or rural-area column-content) NO2, and of temperature and H2O (simultaneously using a third laser) has been suggested by simulation studies.

Browell, E. V.↗
NASA NTRS1984

Shock vaporization and the accretion of the icy satellites of Jupiter and Saturn

The role of impact vaporization acting during the formation of the Jovian and Saturnian satellites is examined in an attempt to explain the observed density in terms of composition of these rock and ice objects. A hypothesis is examined which states that the smaller satellites of Saturn having mean densities in the 1.1 to 1.4 Mg/cu m range represent primordial accreted planetesimal condensates formed in the proto-Jovian and Saturnian accretionary planetary discs. These densities are in the range expected for water-ice/silicate mixtures constrained in the solar values of O/Si and O/Mg atomic ratios. It is demonstrated that if the large satellites accreted from the same group of planetesimals which formed the small Saturnian satellites impact vaporization of water upon accretion in a porous regolith, at low H2O partial pressure, can account for the increase in mean planetesimal density from 1.6 Mg/cu m (43% H2O + 57% silicate) to a mean planetary density of 1.9 Mg/cu m for Ganymedean-sized water silicate objects. If impact volatilization of initially porous planetesimals is assumed, it can be demonstrated starting with planetesimals composed of 54% H2O and 40% silicate partial devolatilization upon accretion will yield a Ganymede-sized planet, having a radius of 2600 km and a density of 1.85 kg/cu m, similar to that of Ganymede, Callisto, and Titan.

Ahrens, T. J.↗
NASA NTRS1984

Self-deactivation of water vapor - Role of the dimer

A phenomenological multiple-relaxation theory of the deactivation rate constant for the nu-2 (1 - 0) bending mode of water vapor is presented which incorporates the role not only of the excited monomer but also of the bound molecular complex, in particular the dimer. The deactivation takes place by means of three parallel processes: (1) collisional deexcitation of the excited monomer, (2) a two-step reaction involving association and spontaneous redissociation of an H2O collision complex, and (3) spontaneous dissociation of the stably bound H2O dimer. Oxygen, but not nitrogen or argon, serves as an effective chaperon for the formation of the activated complex. This observation explains the impurity dependence of the self-deactivation rate constant of water vapor. Analysis of an ultrasonic absorption peak based on the third process yields values for the standard entropy and enthalpy of dissociation of the stably bound H2O dimer.

Zuckerwar, A. J.↗
NASA NTRS1986

Development of a high-altitude airborne dial system: The Lidar Atmospheric Sensing Experiment (LASE)

The ability of a Differential Absorption Lidar (DIAL) system to measure vertical profiles of H2O in the lower atmosphere was demonstrated both in ground-based and airborne experiments. In these experiments, tunable lasers were used that required real-time experimenter control to locate and lock onto the atmospheric H2O absorption line for the DIAL measurements. The Lidar Atmospheric Sensing Experiment (LASE) is the first step in a long-range effort to develop and demonstrate an autonomous DIAL system for airborne and spaceborne flight experiments. The LASE instrument is being developed to measure H2O, aerosol, and cloud profiles from a high-altitude ER-2 (extended range U-2) aircraft. The science of the LASE program, the LASE system design, and the expected measurement capability of the system are discussed.

Browell, E. V.↗
NASA NTRS1986

An all-purpose computer program for lidar simulations and reduction of lidar data

A general computer program was written for the dual purpose of simulating lidar returm signals and extracting H2O vapor and temperature (T) profiles from actual lidar returns. This program will be used to retrieve H2O vapor and T profiles from data obtained with the University of Maryland ground-based lidar systems. The program is designed to simulate and to analyze lidar returns from a monostatic system for two cases: when the output laser pulse is monochromatic, and when the pulse has a known wavelength spectrum. The simulation part of the program has several model H2O vapor, T, and aerosol profiles which can be combined to form different model atmospheres. The simulation program also permits the testing of different methods of numerical filtering to suppress noise, and testing the accuracy of different methods of numerical integration.

Braun, C.↗
NASA NTRS1986

Ground-based observation of Comet Halley

Approximately five hundred Fabry-Perot scans of H2O+, H alpha, and (OI) emissions from comets Halley, Hartley-Good, and Thiele were obtained at Kitt Peak in November, December and January. The analysis of the data is in a very early stage, but preliminary results were obtained on the production rate Q(H) of hydrogen, Q(D) of metastable oxygen, and Q(H2O) of water. The rate Q(H) varied with heliocentric distance R as R to the power -3.5 + or - 0.5. The rate Q(D) varied as R to the power -4.8 + or - 0.1. The ratio of Q(H2O) to Q(D) was 15 + or - 5.

Scherb, F.↗
NASA NTRS1986

Calculations of electric currents in Europa

Electrical currents should flow in the Galilean satellite, Europa, because it is located in Jupiter's corotating magnetosphere. The possible magnitudes of these currents are calculated by assuming that Europa is a differentiated body consisting of an outer H2O layer and a silicate core. Two types of models are considered here: one in which the water is completely frozen and a second in which there is an intermediate liquid layer. For the transverse electric mode (eddy currents), the calculated current density in a liquid layer is approximately 10 to the -5/Am. For the transverse magnetic mode (unipolar generator), the calculated current density in the liquid is severely constrained by the ice layer to a range of only 10 to the -10 to -11th power/ Am, for a total H2O thickness of 100 km, provided that neither layer is less than 4 km thick. The current density is less for a completely frozen H2O layer. If transient cracks were to appear in the ice layer, thereby exposing liquid, the calculated current density could rise to a range of 10 to the -6 to 10 to the -5/Am, depending on layer thicknesses, which would require an exposed area of 10 to the -9 to 10 to the -8 of the Europa surface. The corresponding total current of 2.3x10 to the 5th power A could in 1 yr. electrolyze 7x10 to the 5th power kg of water (and more if the cells were in series), and thereby store up to 10 the 8th power J of energy, but it is not clear how electrolysis can take place in the absence of suitable electrodes. Electrical heating would be significant only if the ice-layer thickness were on the order of 1 m, such as might occur if an exposed liquid surface were to freeze over; the heating under this condition could hinder the thickening of the ice layer.

Colburn, D. S.↗
NASA NTRS1987

Lidar measurements from space for tropospheric chemistry investigations: Summary of workshop overview presentation

Over the past decade, NASA has played a lead role in defining the scientific objectives and technology requirements for spaceborne lidar investigations of the atmosphere. An assessment of the potential for conducting lidar measurements from space for investigations that pertain specifically to tropospheric chemistry is presented. A description of potential lidar measurement techniques is given, and the scientific requirements for tropospheric chemistry are reviewed. The current status of airborne lidar measurements of aerosols, O3, and H2O is discussed, and a brief description of the evolution of lidar technology to space is given. Also, the measurement of tropospheric gases with a spaceborne lidar system is evaluated for a wide range of gas species. From this general assessment, it appears feasible to measure aerosols, H2O, O3, NH3, CO, CH4, NO2, atmospheric pressure and temperature, and wind with a lidar from space provided that the appropriate laser and receiver technology is available. For the mid-1990's, it is expected that lidar technology will be available for the measurement of aerosols, H2O, and O3 from a space platform.

Browell, Edward V.↗
NASA NTRS1986

Velocity-resolved observations of water in comet Halley

High-resolution observations of H2O in comet Halley are presented. The positions and widths of the H2O emission line profiles are indicative of the coma's velocity field characteristics. Spectral line shape changes are used to infer temporal variations in the kinematic properties of the outflow. The results suggest that H2O is released into the coma by way of multiple jets.

Larson, Harold P.↗
NASA NTRS1986

The water vapour budget of the stratosphere studied using LIMS and SAMS satellite data

Monthly zonal mean observations of H2O and CH4 made by the limb infrared monitor of the stratosphere and the stratospheric and mesospheric sounder instruments on Nimbus 7 have been used to investigate whether the H2O mixing ratios in the stratosphere are consistent with a source via the oxidation of CH4. While both sets of data show considerable seasonally varying structure, total hydrogen (neglecting molecular hydrogen) is relatively featureless with a mean value over the stratosphere of 6.0 + or - 0.35 ppmm(1sigma) for the five-month period studied. The uniformity of the total hydrogen fields points to the validity of the CH4 oxidation hypothesis. The derived fields of total hydrogen are used to deduce a mean H2O mixing ratio for air as it enters the stratosphere of 2.7 + or - 0.35 ppmv (1sigma) from which a desiccation temperature may be deduced.

Jones, R. L.↗
NASA NTRS1986

Infrared heating of Comet Halleys atmosphere

The warm circumnuclear dust in the inner cometary coma reradiates in the IR in the wavelength range of the ground state rotational band of the dominant atmospheric molecule H2O. However, the interaction of this radiation with H2O has hitherto not been taken into account in cometary atmospheric models. Here, an earlier two-phase, multifluid model of the dusty atmosphere is extended by including this effect. Although this IR radiation initially pumps the rotational levels of H2O, frequent intermolecular collisions in the inner coma transfer this energy from rotational modes to translational modes. As a result the temperature in the innermost coma no longer decreases to about 10 K, as predicted by the earlier models, but reaches a minimum of only about 120 K.

Marconi, M. L.↗