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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Interannual differences in the regressions of the polar caps of Mars

Analyses of the behavior of the Martian polar caps in the recent spacecraft and ground based observations seem to reveal the existence of year to year variations on their regressions. In order to investigate the interannual differences in the regressions of the polar caps, the earlier data by Fischbacher et al., were reexamined, which were based on the measurements of the large number of high quality photographic plates and films collected from 1905 to 1965 at the Lowell Observatory. The results are reported and discussed.

Iwasaki, K.↗
NASA NTRS1989

Calculation of steady and unsteady pressures at supersonic speeds with CAP-TSD

A finite difference technique is used to solve the transonic small disturbance flow equation making use of shock capturing to treat wave discontinuities. Thus the nonlinear effects of thickness and angle of attack are considered. Such an approach is made feasible by the development of a new code called CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance), and is based on a fully implicit approximate factorization (AF) finite difference method to solve the time dependent transonic small disturbance equation. The application of the CAP-TSD code to the calculation of low to moderate supersonic steady and unsteady flows is presented. In particular, comparisons with exact linear theory solutions are made for steady and unsteady cases to evaluate shock capturing and other features of the current method. In addition, steady solutions obtained from an Euler code are used to evaluate the small disturbance aspects of the code. Steady and unsteady pressure comparisons are made with measurements for an F-15 wing model and for the RAE tailplane model.

Bennett, Robert M.↗
NASA NTRS1989

Rocket measurements within a polar cap arc - Plasma, particle, and electric circuit parameters

Results are presented from the Polar Ionospheric Irregularities Experiment (PIIE), conducted from Sondrestrom, Greenland, on March 15, 1985, designed for an investigation of processes which lead to the generation of small-scale (less than 1 km) ionospheric irregularities within polar-cap F-layer auroras. An instrumented rocket was launched into a polar cap F layer aurora to measure energetic electron flux, plasma, and electric circuit parameters of a sun-aligned arc, coordinated with simultaneous measurements from the Sondrestrom incoherent scatter radar and the AFGL Airborne Ionospheric Observatory. Results indicated the existence of two different generation mechanisms on the dawnside and duskside of the arc. On the duskside, parameters are suggestive of an interchange process, while on the dawnside, fluctuation parameters are consistent with a velocity shear instability.

Weber, E. J.↗
NASA NTRS1990

Steel Foil Improves Performance Of Blasting Caps

Blasting caps, which commonly include deep-drawn aluminum cups, give significantly higher initiation performance by application of steel foils on output faces. Steel closures 0.005 in. (0.13 mm) thick more effective than aluminum. Caps with directly bonded steel foil produce fragment velocities of 9,300 ft/s (2.8 km/s) with large craters and unpredictable patterns to such degree that no attempts made to initiate explosions. Useful in military and aerospace applications and in specialized industries as mining and exploration for oil.

Bement, Laurence J.↗
NASA NTRS1990

Distribution of galaxies in the Southern Galactic Cap

Observations in the southern galactic hemisphere in the declination range between -17.5 and 2.5 degrees are combined with other available observation. The data set is used to study the spatial distribution of galaxies of a contiguous area of 3.13 sr of the Southern Galactic Cap. An approximately homogeneous magnitude-limited sample of galaxies in the Southern Galactic Cap is constructed from different catalogs. The resulting large scale structure is similar to that of previous surveys in which bright galaxies are distributed on surfaces which intersect at sharp corners and nearly surround voids that are almost empty of galaxies.

Pellegrini, P. S.↗
NASA NTRS1989

Application of the CAP-TSD unsteady transonic small disturbance program to wing flutter

The application and assessment of a computer program called CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) for flutter predictions are described. Flutter calculations are presented for two thin swept-and-tapered wing planforms with well-defined modal properties. One planform is a series of 45-degree swept wings and the other planform is a clipped delta wing. Comparisons are made between the results of CAP-TSD using the linear equation and no airfoil thickness and the results obtained from a subsonic kernel function analysis. The calculations cover a Mach number range from low subsonic to low supersonic values, including the transonic range, and are compared with subsonic linear theory and experimental data. It is noted that since both wings have very thin airfoil sections, the effects of thickness are minimal.

Bennett, Robert M.↗
NASA NTRS1991

Investigation of the aeroelastic stability of the AFW wind-tunnel model using CAP-TSD

The Computational Aeroelasticity Program - Transonic Small Disturbance (CAP-TSD) code, developed at the NASA Langley Research Center, is applied to the Active Flexible Wing (AFW) wind tunnel model for prediction of the model's transonic aeroelastic behavior. A semi-span computational model is used for evaluation of symmetric motions and a full span model is used for evaluation of antisymmetric motions. Static aeroelastic solutions using CAP-TSD are computed. Dynamic (flutter) analyses are then performed as perturbations about the static aeroelastic deformations and presented as flutter boundaries in terms of Mach number and dynamic pressure. Flutter boundaries that take into account modal refinements, vorticity and entropy corrections, antisymmetric motions and sensitivity to the modeling of the wing tip ballast stores are also presented and compared with experimental flutter results.

Silva, Walter A.↗
NASA NTRS1992

Investigation of the aeroelastic stability of the AFW wind-tunnel model using CAP-TSD

The Computational Aeroelasticity Program - Transonic Small Disturbance (CAP-TSD) code is applied to the Active Flexible Wing (AFW) wind tunnel model for prediction of the model's transonic aeroelastic behavior. A semi-span computational model is used for evaluation of symmetric motions and a full span model is used for evaluation of antisymmetric motions. Static aeroelastic solutions using CAP-TSD are computed. Dynamic flutter analyses are then performed as perturbations about the static aeroelastic deformations and presented as flutter boundaries in terms of Mach number and dynamic pressure. Flutter boundaries that take into account modal refinements, vorticity, and entropy corrections, antisymmetric motions and sensitivity to the modeling of the wing tip ballast stores are also presented and compared with experimental flutter results.

Silva, Walter A.↗
NASA NTRS1992

Mars secular obliquity change due to the seasonal polar caps

There is a weak positive feedback mechanism between the astronomy and meteorology of Mars. The mechanism is this: the seasonal waxing and waning polar caps cause small changes in Mars' dynamical flattening. Because the changes in flattening are out of phase with the sun, there is a net annual solar torque on the planet which increases the angle between the equatorial and orbital phanes. On the basis of Viking observations of the present climate and simple atmospheric models of past climates, these seasonal shifts of mass between the atmosphere and polar caps are capable of secularly increasing Mars' obliquity by about 1 or 2 deg since the origin of the solar system. Thus, the climate, driven largely by the axial tilt, reacts back on the planet and slightly enhances the seasons on Mars as time progresses. More sophisticated models will probably not change this result much; therefore this mechanism probably produced only minor changes in Mars' climate. It causes negligible changes in the axial tilt and climate of the earth.

Rubincam, David P.↗
NASA NTRS1990

A model of FTE footprints in the polar cap

The present investigation of the mapping of flux-transfer events (FTEs) onto the polar cap using the Toffoletto and Hill (1989) open version of Voigt's (1981) closed magnetic field model assumes that the magnetic flux associated with FTEs crosses the magnetopause through small regions of large normal components, whence these small flux tubes proceed to map to the polar cap ionosphere. It is found that while the footprint of a circular hole in the magnetopause of an otherwise closed magnetosphere becomes progressively distorted as the hole moves from the day to the night side, a similar region of enhanced open flux in an otherwise open magnetosphere retains an approximately circular footprint. Such regions, moving through the magnetosphere at a slower rate than the background, would generate the dipolar-electric field and current structures predicted by Southwood (1987).

Toffoletto, F. R.↗
NASA NTRS1992

The polar cap environment of outflowing O(+)

The properties of the core (0-50 eV) and 'energetic' (0-1 keV) ions, plasma waves, and auroral images obtained from Dynamics Explorer 1 (DE-1) and those of electrons, obtained from DE-2, are examined in the context of the polar cap environment. Results indicate the presence of two populations: high-speed (10-30 eV, or higher, streaming energies) polar beams and low-speed (generally less than 10-eV streaming energies) streams. The high-speed polar beams show an auroral connection (i.e., they are observed on or near the field lines threading auroral arcs), while the low-speed streams are on or near the field lines threading the dark polar cap and may be converted from the cleft ion fountain. Compared to the high-speed streams, the low-speed streams are significantly more stable with respect to energy and flux.

Horwitz, J. L.↗
NASA NTRS1993

Molecular-Weight-Controlled, End-Capped Polybenzimidazoles

Novel molecular-weight-controlled end-capped poly(arylene ether benzimidazole)s (PAEBI's) prepared by nucleophilic displacement reaction of di(hydroxyl)benzimidazole monomers with activated aromatic dihalides. Polymers prepared at various molecular weights by upsetting stoichiometry of monomers and end-capped with monohydroxybenzimidazole. Exhibit favorable physical and mechanical properties, improved solubility in polar aprotic solvents and better compression moldability. Potential applications as adhesives, coatings, films, fibers, membranes, moldings, and composite matrix resins.

Connell, John W.↗
NASA NTRS1992

Condensation phase of the Martian south polar cap

One type of database that can be useful in limiting models of the Mars surface-atmosphere system is the time dependent boundary of CO2 frost for the polar caps. Data acquired by the thermal infrared sensors on spacecraft are not limited by the lighting problems that hamper visual observations. The surface temperature of solid CO2 is limited by Clapeyron's equation as a function of the local partial pressure of CO2 gas. The growth was studied of the Martian south polar cap using the Viking IRTM dataset. These data are available in five bands, four of which should correspond to surface radiation in clear conditions; the 20 micron data was examined in the first phase.

Capuano, J.↗
NASA NTRS1992

Evolution of the Martian atmosphere: The role of the polar caps

Lines of evidence indicate that early in Mars' history, it had a much thicker CO2 atmosphere than it does today. A model was constructed for the evolution of the Martian atmosphere that self consistently calculates the rates at which CO2 is stored in Mars' polar reservoirs. Given some initial abundance, which is assumed to be entirely in the atmosphere, the model calculates the annually averaged temperature of the equatorial region and the polar region, and the planetwide mean. Thus far, results obtained for the case where CO2 condensation in the atmosphere is not a limiting factor. Results fall into two categories: initial inventories above 1 bar and below 1 bar. For inventories above 1 bar, CO2 is partitioned between the atmosphere and regolith with the latter taking up almost 800 mbar of CO2. The rest remains in the atmosphere and is weathered out at a rate proportional to atmospheric pressure. For values less than 1 bar, the evolution scenario is different, polar caps form immediately since there is not enough greenhouse warming to prevent CO2 from going into the regolith and thereby reducing the atmospheric pressure to levels where caps can form. The results do not favor either scenario.

Haberle, R. M.↗
NASA NTRS1992

High resolution spectroscopy of the Martian atmosphere - Study of seasonal variations of CO, O3, H2O, and T on the north polar cap and a search for SO2, H2O2, and H2CO

An overview is presented of an observational campaign which will measure (1) the seasonal variations of the CO mixing ratio on the Martian polar cap due to accumulation and depletion of CO during the condensation and evaporation of CO2, as well as (2) the early spring ozone and water vapor of the Martian north polar cap, and (3) the presence of H2CO, H2O2, and SO2. The lines of these compounds will be measured by a combined 4-m telescope and Fourier-transform spectrometer 27097.

Krasnopolsky, V. A.↗
NASA NTRS1993

The hemispherical asymmetry in the Martian polar caps

An energy balance model is used to study the behavior of CO2 ice on Mars. The effect of the solar zenith angle dependence of albedo is to lengthen CO2 ice lifetimes at the poles. Hemispherical asymmetries in cloud and dust abundance could result in the survival of seasonal CO2 ice through summer in the south and not in the north, in agreement with observations. CO2 ice observed in the summertime polar cap in the south could be of recent origin, although a permanent CO2 polar cap cannot be ruled out.

Lindner, Bernhard L.↗
NASA NTRS1993

Parameterized study of the ionospheric modification associated with sun-aligned polar cap arcs

The local ionospheric modification that is due to a generalized steady state solar aligned (SA) arc structure is addressed. For a representative set of SA arc parameters which includes both convection and precipitation, emphasis is placed on the modification by SA polar cap arcs upon the F region electron density and the height integrated conductivity. At low fluxes and low characteristic energies, SA polar cap arcs have the most pronounced relative effect at F region altitudes in darkness for winter solar minimum conditions. The absolute enhancement in summer solar minimum and winter solar maximum is equivalent to that of winter solar minimum, but the higher ambient densities make the relative enhancement less. The TEC enhancement associated with an SA arc may be used to indicate the degree of plasma cross flow across the arc.

Crain, D. J.↗
NASA NTRS1993

On the microphysical state of the Martian seasonal caps

An analysis of the microphysical processes involved in pressureless sintering leads to the view that CO2 in the Martian seasonal polar caps can metamorphose into an annealed polycrystalline layer, if freshly condensed grains are smaller than 10 microns. Such large-area/low-porosity CO2 deposits may be associated with the mm-to-cm-scaled path lengths entailed by the explanation of several weak absorption features in the 1.5- and 2.3-micron spectral regions. Such an annealed layer would become transparent enough during the later stages of spring sublimation to establish a basis for the dichotomy between the north and south caps' albedos in the underlying substrate.

Eluszkiewicz, Janusz↗