Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CaP”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Carbon dioxide-water clathrate as a reservoir of CO2 on Mars

It has been suggested that the residual polar caps of Mars contain a resorvoir of permanently frozen carbon dioxide which is controlling the atmospheric pressure. However, observational data and models of the polar heat balance suggest that the temperatures of the Martian poles are too high for solid CO2 to survive permanently. On the other hand, the icelike compound carbon dioxide-water clathrate could function as a CO2 reservoir instead of solid CO2, because it is stable at higher temperatures. This paper shows that the permanent polar caps may contain several millibars of CO2 in the form of clathrate, and discusses the implications of this permanent clathrate reservoir for the present and past atmospheric pressure on Mars.

Dobrovolskis, A.↗
NASA NTRS1976

A snapshot of the polar ionosphere

This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2) that passed over the region within a time interval of about 50 min on a magnetically quiet day. The horizontal distribution of electron densities at the peak of the F layer is found to be similar to synoptic results from the IGY. Energetic-particle and ionospheric-plasma data are also presented, and the F-layer data are discussed in terms of these measurements as well as in terms of electric-field and neutral N2 density measurements made by other satellites on other occasions. The major feature observed is a tongue of F-region ionization extending from the dayside across the polar cap, which is accounted for by antisunward drift due to magnetospheric convection. In the F layer and topside ionosphere, the main effect of auroral precipitation appears to be heating and expansion of the topside. A region of low F-layer density appears on the morning side of the polar cap, which may be due to convection and possibly also to enhanced N2 densities.

Whitteker, J. H.↗
NASA NTRS1975

Seasonal buffering of atmospheric pressure on Mars

An isothermal reservoir of carbon dioxide in gaseous contact with the Martian atmosphere would reduce the amplitude and advance the phase of global atmospheric pressure fluctuations caused by seasonal growth and decline of polar CO2 frost caps. Adsorbed carbon dioxide in the upper roughly 10 m of Martian regolith is sufficient to buffer the present atmosphere on a seasonal basis. Available observations and related polar cap models do not confirm or refute the operation of such a mechanism. Implications for the amplitude and phase of seasonal pressure fluctuations are subject to direct test by the upcoming Viking mission to Mars.

Dzurisin, D.↗
NASA NTRS1975

The sun's magnetic sector structure

The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at earth from 1959 to 1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south demarcation lines between regions of persistent magnetic-polarity imbalances. These regions extend up to about 35 deg in latitude on both sides of the equator. They generally do not extend into the polar caps. The polar-cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 by 10 to the 21st power Mx.

Svalgaard, L.↗
NASA NTRS1976

Martian glaciation and the flow of solid CO2

Results are discussed for a series of laboratory deformation experiments that were conducted to determine a flow law for solid CO2 so that a physical basis could be established for considering the possibility of CO2 glaciation in the Martian polar regions. The experimentally determined flow law indicates that (1) the concept of CO2 glacial flow at the Martian poles is not physically unrealistic, (2) the strength of CO2 near its sublimation point is considerably less than the strength of water ice near its melting point, and (3) CO2 is likely to flow over a broad range of temperatures below its melting point. A glacial model for the Martian polar caps is suggested in which CO2-rich layers deposited near the poles flowed outward laterally to relieve high internal shear stresses. It is shown that this model can explain the topography of the polar caps, the uniform layering of the layered deposits, and the general extent of the polar 'sediments'. Some problematic assumptions of the model are noted, including the large amounts of CO2 necessary to move the layered deposits and the need to increase vapor pressure and temperature with depth in the deposits.

Clark, B. R.↗
NASA NTRS1976

Pulsar extinction

The radiation properties of pulsars are reinvestigated in the context of the 'PCFB' model, according to which the radiation originates at the polar caps and the magnetic-field lines change from a closed to an open configuration at the 'force-balance' or 'corotation' radius. Major attention is given to the condition for electron-positron pair creation, which leads, in turn, to an extinction condition whereby any pulsar will cease to be a radio emitter after its period has increased beyond a certain value. This extinction condition is derived on the basis of a model where the magnetic field is the same as that of a point dipole located at the center of the star; effects of dipole distortion are also considered. A comparison of the results with observational data shows that most pulsars satisfy or nearly satisfy the pair-creation condition for undistorted dipoles and seem to satisfy the extinction condition. It is noted that pulsars which should be extinguished according to the undistorted-dipole model need not be if the magnetic field is sufficiently distorted at the polar caps.

Sturrock, P. A.↗
NASA NTRS1976

Effect of probe configuration on radiative heating during Jovian entry

The radiative heating to the probe's surface and the effects of the recession of the heat shield caused by this heating are analyzed for five initial probe configurations for a Jovian entry. The initial configurations are spherically capped, conical bodies and hyperboloids. The results show that severe blunting of the nose region occurs for all configurations due to ablation of the heat shield caused by the large radiative heating rates. Recession at the nose region can possibly cause a concavity at the stagnation point. Furthermore, the recession of the heat shield, especially for the spherically capped, conical bodies, will be underpredicted if the change in the probe's shape during the entry is neglected in an analysis.

Sutton, K.↗
NASA NTRS1976

The period-pulse-width distribution of pulsars and their division into three classes

The period-pulse-width (P-W) distribution of sample of 41 pulsars has been reanalyzed under two versions of a model where radiation is beamed from magnetic polar caps which are isotropically oriented with respect to the rotation axis of the neutron stars (IOPC models). It is found that neither IOPC model can explain the P-W distribution of the entire sample. Pulsars with simple unimodal (U) or complicated multimodal (M) pulse shapes show significantly different P-W distributions. Class M pulsars have a narrower P-W distribution than do class U pulsars and, taken separately, are compatible with either IOPC model. Class U pulsars divide into two subgroups, those with relatively narrower pulses (UN) and those with relatively wider pulses (UW), each of which is compatible with either IOPC model. One interpretation of these results is that the pulsars in classes UN, M, and UW have different intrinsic beam sizes, roughly in the ratios 1:2:4, respectively. The possible origins of the three classes are discussed in terms of the force-balance magnetosphere model (Roberts et al., 1972, 1973), where the differences may be attributed to different-mass neutron stars and the structure of the polar caps. An alternative interpretation is that the angle between the rotation and emission axes is not isotropically distributed, but can take only certain preferred values.

Roberts, D. H.↗
NASA NTRS1976

Ion convection velocity reversals in the dayside cleft

Nearly simultaneous measurements of energetic particle precipitation and vector ion velocity have been made for the first time on Atmosphere Explorer C. These data have revealed the existence of both shear and rotational reversals in the ion convection velocity within the region of dayside cleft particle precipitation. The ion velocity data have shown that substantial regions of the dayside polar cap boundary are nearly electric equipotentials at which cleft particle precipitation is also observed but which cannot be identified with a merging region producing open field lines. Asymmetries in the polar cap flow, first implied by Heppner, may be determined by the extent and location of the equipotential boundaries.

Heelis, R. A.↗
NASA NTRS1975

Methods for the computation of detailed geoids and their accuracy

Two methods for the computation of geoid undulations using potential coefficients and 1 deg x 1 deg terrestrial anomaly data are examined. It was found that both methods give the same final result but that one method allows a more simplified error analysis. Specific equations were considered for the effect of the mass of the atmosphere and a cap dependent zero-order undulation term was derived. Although a correction to a gravity anomaly for the effect of the atmosphere is only about -0.87 mgal, this correction causes a fairly large undulation correction that was not considered previously. The accuracy of a geoid undulation computed by these techniques was estimated considering anomaly data errors, potential coefficient errors, and truncation (only a finite set of potential coefficients being used) errors. It was found that an optimum cap size of 20 deg should be used. The geoid and its accuracy were computed in the Geos 3 calibration area using the GEM 6 potential coefficients and 1 deg x 1 deg terrestrial anomaly data. The accuracy of the computed geoid is on the order of plus or minus 2 m with respect to an unknown set of best earth parameter constants.

Rapp, R. H.↗
NASA NTRS1977

Heat-transfer test results for a .0275-scale space shuttle external tank with a 10 deg/40 deg double cone-ogive nose in the NASA/AMES 3.5-foot hypersonic wind tunnel (FH14), volume 2

A .0275 scale forebody model of the new baseline configuration of the space shuttle external tank vent cap configuration was tested to determine the flow field due to the double cone configuration. The tests were conducted in a 3.5 foot hypersonic wind tunnel at alpha = -5 deg, -4.59 deg, 0 deg, 5 deg, and 10 deg; beta = 0 deg, -3 deg, -5.51 deg, -6 deg, -9 deg, and +6 deg; nominal freestream Reynolds numbers per foot of 1.5 x 1 million, 3.0 x 1 million, and 5.0 x 1 million; and a nominal Mach number of 5. Separation and reattached flow from thermocouple data, shadowgraphs, and oil flows indicate that separation begins about 80% from the tip of the 10 deg cone, then reattaches on the vent cap and produces fully turbulent flow over most of the model forebody. The hardware disturbs the flow over a much larger area than present TPS application has assumed. A correction to the flow disturbance was experimentally suggested from the results of an additional test run.

Carroll, H. R.↗
NASA NTRS1976

Spectrophotometry of the X-ray binary HZ Herculis

An extensive set of absolute spectrophotometric observations of HZ Her over the wavelength range from 3300 to 10,000 A is presented and analyzed to determine to what extent the observations can be interpreted in terms of a model for the system. The specific model to be tested consists of a large star (HZ Her) with a hot cap beneath the X-ray source, an accretion disk around the X-ray source, and a gas stream flowing between the primary star and the disk. It is found that the model is compatible to a large extent with the detailed observations and that the physical characteristics of the various components can be derived. The mass, luminosity, and radius of the primary star, the mass of the X-ray object, and the orbital dimensions are obtained by analyzing the energy distribution at minimum light and X-ray eclipse data. The angle and effective temperature of the hot cap on the primary are also determined along with the energy distribution, diameter, and thickness of the accretion disk. It is concluded that HZ Her fills its Roche lobe and is an A7 V star, that the logarithm of its surface gravity is about 3.6, and that the mass of the X-ray object is 1.95 solar masses.

Oke, J. B.↗
NASA NTRS1976

Substorm effects observed in the auroral plasma

The effects of substorm temporal development on high-latitude particle precipitation and ionospheric convection patterns near midnight were studied with the aid of data from Atmosphere Explorer C. During quiet periods generally Maxwellian electron precipitation is observed from the central plasma sheet, which is completely contained within the sunward flow region. As substorms grow and begin to recover, a strong sunward flow appears within the high latitude ionospheric electron trough, equatorward of the central plasma sheet electron precipitation. Intense inverted-V electron structures consistent with strong electrostatic acceleration appear near the Harang discontinuity and extend poleward to the polar cap boundary. Then the trough flow weakens, the Harang discontinuity becomes a gradual reversal, and the electron inverted-V precipitation becomes localized at the polar cap boundary.

Burch, J. L.↗
NASA NTRS1977

Coronal holes and high-speed wind streams

Coronal holes, regions of unusually low density and low temperature in the solar corona, are identified as Bartel's M regions, i.e., sources of high-speed wind streams that produce recurrent geomagnetic variations. Throughout the Skylab period the polar caps of the sun were coronal holes, and at lower latitudes the most persistent and recurrent holes were equatorial extensions of the polar caps. The holes rotated 'rigidly' at the equatorial synodic rate. They formed in regions of unipolar photospheric magnetic field, and their internal magnetic fields diverged rapidly with increasing distance from the sun. The geometry of the magnetic field in the inner corona seems to control both the physical properties of the holes and the global distribution of high-speed wind streams in the heliosphere. Phenomenological models for the birth and decay of coronal holes have been proposed.

Zirker, J. B.↗
NASA NTRS1978

Automated space fabrication of structural elements

A description is presented of an automated space fabrication technique for basic structural elements, taking into account as representative the design loads and requirements of the solar power satellite structure. Roll forming for continuous cap and brace members is applicable for all proposed metallic materials. Spot-welding, electron beam welding, ultrasonic welding, laser welding, cold welding, and various mechanical fastening techniques are applicable for the automated fabrication process. Termination of the formed cap and brace members can be accomplished by sawing, shearing, punching, and laser cutting. The most cost effective materials were found to be the aluminum alloys. Selected for further study were AL20224T3 and AL2219-T62. In the area of fiber composites, thermoplastic matrix materials with graphite fibers were selected for future studies.

Engler, E. E.↗
NASA NTRS1980

Isolator/retainer for connectors

Double-ended cap holds mating plugs and receptacle, preventing electrical contact between them when not in use. Cap maintains continuous electrical ground between plug and receptacle protecting against electromagnetic-interference pickup. Device is also useful for isolation of sensitive circuits from each other during storage, transit, or testing.

Alpenia, J. L.↗
NASA NTRS1978

Early climate on earth-reduced gas models and early climate on Mars-reduced gas and obliquity models

At high obliquity, Martian polar ground temperatures could exceed the melting point of ice for considerable periods of time (approximately 90 Earth days). Under special conditions ice itself might melt. Carbon dioxide adsorbed on the Martian regolith is not expected to buffer the seasonal pressure wave except in the unlikely event that the soil pore size is very large (50 micron). For a basaltic soil composition the maximum CO2 that could be desorbed over obliquity time scales due to thermal forces is a few millibars. At low obliquities the atmospheric pressures may drop, desorbing the soil. The only means to achieve higher CO2 pressures is to have much higher planet-wide temperatures due to some greenhouse effect, or to be at an epoch before the regolith or carbonates formed. The water ice budget between north and south polar caps was considered and summer sublimation rates imply that the ice could be exchanged between the poles during obliquity cycles. A critical factor in the polar cap water budget is the interaction of water and dust. The origin of the Martian polar laminae is probably due to variations in this interaction.

Toon, O. B.↗
NASA NTRS1979

Calorimeter probes for measuring high thermal flux

Expendable, slug-type calorimeter probes were developed for measuring high heat-flux levels of 10-30 kW/sq cm in electric-arc jet facilities. The probes were constructed with thin tungsten caps mounted on Teflon bodies. The temperature of the back surface of the tungsten cap is measured, and its time rate of change gives the steady-state absorbed heat flux as the calorimeter probe heats to destruction when inserted into the arc jet. Design, construction, test, and performance data are presented.

Russell, L. D.↗