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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Internally heated mantle convection and the thermal and degassing history of the earth

An internally heated model of parameterized whole mantle convection with viscosity dependent on temperature and volatile content is examined. The model is run for 4l6 Gyr, and temperature, heat flow, degassing and regassing rates, stress, and viscosity are calculated. A nominal case is established which shows good agreement with accepted mantle values. The effects of changing various parameters are also tested. All cases show rapid cooling early in the planet's history and strong self-regulation of viscosity due to the temperature and volatile-content dependence. The effects of weakly stress-dependent viscosity are examined within the bounds of this model and are found to be small. Mantle water is typically outgassed rapidly to reach an equilibrium concentration on a time scale of less than 200 Myr for almost all models, the main exception being for models which start out with temperatures well below the melting temperature.

Williams, David R.↗
NASA NTRS1992

Zagami - Product of a two-stage magmatic history

Results of petrologic studies of new large samples of the Zagami shergottite are presented. Pyroxene crystals have homogeneous Mg-rich pigeonite and augite cores, overgrown by Fe-rich zoned pyroxene rims. Amphibole-bearing magmatic inclusions occur exclusively in the cores. It is concluded that Zagami experienced a two-stage crystallization history. The first stage occurred in a deep-seated, slowly cooling magma chamber. There, the homogeneous Mg-rich cores of the pyroxenes crystallized during relatively slow cooling. During the second stage, the Mg-rich pyroxenes were entrained into a magma that either intruded to the near-surface and cooled in a relatively thin dike or sill, or extruded to the surface and crystallized in a lava flow greater than 10 m thick, again without indications of crystal settling. The estimated depth of the magma chamber for Zagami of greater than 7.5 km and thickness of the putative lava flow of greater than 10 m are consistent with calculations and observations of volcanic constructs and flows in the Tharsis region of Mars.

Mccoy, Timothy J.↗
NASA NTRS1992

A history of the Lonar crater, India: An overview

The origin of the circular structure at Lonar, India, described variously as cauldron, pit, hollow, depression, and crater, has been a controversial subject since the early nineteenth century. A history of its origin and other aspects from 1823 to 1990 are overviewed. The structure in the Deccan Trap Basalt is nearly circular with a breach in the northeast, 1830 m in diameter, 150 m deep, with a saline lake in the crater floor. Over the years, the origin of the Lonar structure has risen from volcanism, subsidence, and cryptovolcanism to an authentic meteorite impact crater. Lonar is unique because it is probably the only terrestrial crater in basalt and is the closest analog with the Moon's craters. Some unresolved questions are suggested. The proposal is made that the young Lonar impact crater, which is less than 50,000 years old, should be considered as the best crater laboratory analogous to those of the Moon, be treated as a global monument, and preserved for scientists to comprehend more about the mysteries of nature and impact cratering, which is now emerging as a fundamental ubiquitous geological process in the evolution of the planets.

Nayak, V. K.↗
NASA NTRS1992

Toward a history of the space shuttle. An annotated bibliography

This selective, annotated bibliography discusses those works judged to be most essential for researchers writing scholarly studies on the Space Shuttle's history. A thematic arrangement of material concerning the Space Shuttle will hopefully bring clarity and simplicity to such a complex subject. Subjects include the precursors of the Space Shuttle, its design and development, testing and evaluation, and operations. Other topics revolve around the Challenger accident and its aftermath, promotion of the Space Shuttle, science on the Space Shuttle, commercial uses, the Space Shuttle's military implications, its astronaut crew, the Space Shuttle and international relations, the management of the Space Shuttle Program, and juvenile literature. Along with a summary of the contents of each item, judgments have been made on the quality, originality, or importance of some of these publications. An index concludes this work.

Launius, Roger D.↗
NASA NTRS1992

Erosional and depositional history of central Chryse Planitia

This map uses high resolution image data to assess the detailed depositional and erosional history of part of Chryse Planitia. This area is significant to the study of the global geology of Mars because it represents one of only two areas on the martian surface where planetary geologic mapping is assisted with 'ground truth.' In this case the ground truth was provided by Viking Lander 1. Additional questions addressed in this study are concerned with the following: the geologic context of the regional plains surface and the local surface of the Viking Lander 1 site; and the relative influence of volcanic, sedimentary, impact, aeolian, and tectonic processes at the regional and local scales.

Crumpler, L. S.↗
NASA NTRS1993

Magnetic bearing turbomachinery case histories and applications for space related equipment

The concept of magnetic levitation is not a new one and can be easily traced back to the 1800's. It is only recently, however, that the congruous technologies of electronic control systems, power electronics, and magnetic materials have begun to merge to make the magnetic suspension device a viable product. A brief overview of an active magnetic bearing technology is provided. Case histories of various turbomachinery in North America presently operating on magnetic bearings are reviewed. Finally, projections are made as to the space related machinery that may be benefited by incorporating magnetic bearings into the equipment design.

Weise, David A.↗
NASA NTRS1992

On the origin of interplanetary dust within recorded history

The possibility of an abrupt origin of interplanetary dust as a result of a collision between asteroids or an extraordinary comet is considered. If all interplanetary dust were produced in one event within recorded history, it would have been visible from the Earth with the unaided eye. The rate, surface area, and brightness of asteroid collision remnants are derived. Ancient Chinese records are searched for extraordinary comets aand bright pointlike objects with small angular motion and concentration to the ecliptic.

Reach, William T.↗
NASA NTRS1992

Impact craters and Venus resurfacing history

The history of resurfacing by tectonism and volcanism on Venus is reconstructed by means of an analysis of Venusian impact crater size-frequency distributions, locations, and preservation states. An atmospheric transit model for meteoroids demonstrates that for craters larger than about 30 km, the size-frequency distribution is close to the atmosphere-free case. An age of cessation of rapid resurfacing of about 500 Ma is obtained. It is inferred that a range of surface ages are recorded by the impact crater population; e.g., the Aphrodite zone is relatively young. An end-member model is developed to quantify resurfacing scenarios. It is argued that Venus has been resurfacing at an average rate of about 1 sq km/yr. Numerical simulations of resurfacing showed that there are two solution branches that satisfy the completely spatially random location restraint for Venusian craters: a is less than 0.0003 (4 deg diameter circle) and a is greater than 0.1 (74 deg diameter circle).

Phillips, Roger J.↗
NASA NTRS1992

A dynamical history of the inner Neptunian satellites

The dynamical history of Neptune's satellite system is presently inferred on the basis of a Triton capture-origin scenario in which that moon's elongated postcapture orbit generated chaotic perturbations of the original satellites' eccentricities; this, in turn, led to mutual collisions among the inner satellites until a ring of debris was formed. Neptune's inner satellite system thereby reformed on equatorial orbits after the orbtal circularization of Triton. Attention is given to the 4.7-deg inclination of 1989N6, which may be due to a temporary inclination-resonance capture.

Banfield, Don↗
NASA NTRS1992

Mars - Epochal climate change and volatile history

The epochal climate change and volatile history of Mars are examined, with special attention given to evidence for and mechanisms of long-term climate change. Long-term climate change on Mars is indicated most directly by the presence, age, and distribution of the valley networks. They were almost certainly formed by running water, but it seems more likely that they were formed by groundwater sapping than by rainfall. It is argued to be physically plausible that a higher early intensity of surface insolation caused by a CO2 greenhouse effect could have overcompensated for an early weak sun and raised temperatures to the freezing point near the equator under favorable conditions of obliquity and eccentricity. This could account for the morphological changes.

Fanale, Fraser P.↗
NASA NTRS1993

Evolutionary history of the mesosiderite asteroid - A chronologic and petrologic synthesis

The evolutionary history of the mesosiderite parent body is composed of six principal epochs. (1) Accretion occurred about 4.56 Ga ago, and (2) initial melting occurred less than about 26 Ma after accretion. (3) Significant crustal remelting occurred more than 4.47 Ga ago, possibly during metal-silicate mixing caused by the accretion of a large metallic Fe-Ni core fragment with some overlying mantle to the MPB regolith. (4) Localized impact melting 4.5-3.9 Ga ago produced quench-textured clasts and caused mesosiderite metamorphism and the extensive melting of type-4 mesosiderites. (5) Collisional disruption and gravitational reassembly occurred about 3.9 Ga ago, causing extensive degassing of Ar and resetting the metallographic cooling rates to about 1 C/Ma. (6) Impact excavitation and ejection of deeply buried breccias occurred much less than 3.9 Ga.

Rubin, Alan E.↗
NASA NTRS1993

On the Bur Gheluai H5 chondrite and other meteorites with complex exposure histories

Isotopic concentrations and track densities measured in 13 samples of the Bur Gheluai meteorite fall are presented. Experimental methods are described and results are presented for isotopic ratios of noble gases and cosmogenic radionuclide contents. Evidence for complex irradiation is discussed and a model for two-stage exposure histories is presented. The duration of each irradiation stage and possible effects on isotope production rates are considered. Explanations are suggested for the discrepant Ne production rates.

Vogt, S. K.↗
NASA NTRS1993

The effects of history and predictive information on the ability of the transport aircraft pilot to predict an alert

The early detection of a developing aircraft-subsystem fault has the potential to lessen its ultimate severity. The lack of capability for such early detection is becoming critical in the aviation community. In the commercial sector, for example, twin-engine aircraft are being used for extended transport operations over water. One method to decrease the severity of a developing problem is to predict its behavior and to take appropriate corrective action. In order to investigate pilots' ability to predict events, an experiment was conducted where eighteen airline pilots predicted the time to an alert using three different displays of dials and three different time profile complexities. The three displays of dials were as follows: standard, resembling current aircraft dial presentations; history, indicating the value five seconds in the past; and predictive, indicating the value five seconds into the future. The time profiles describing the behavior of the parameter consisted of constant velocity profiles, decelerating profiles, and accelerating then decelerating profiles. Although pilots indicated that they preferred the predictive dial, the objective data did not support its use. The objective data did show that the time profiles had the most significant effect on performance in estimating the time to an alert.

Trujillo, Anna C.↗
NASA NTRS1950

Time histories of horizontal-tail loads, elevator loads, and deformations on a jet-powered bomber airplane during abrupt pitching maneuvers at approximately 20,000 feet

Time histories are presented of horizontal-tail loads, elevator loads, and deformations on a jet-powered bomber during abrupt pitching maneuvers at a pressure altitude of approximately 20,000 feet. The normal and pitching accelerations measured varied from -0.90b to 3.41g and from -0.73 to 0.80 radian per second per second (sic), respectively, with a Mach number variation of from 0.40 to o.75. The maximum horizontal-tail load measured was 17,250 pounds down. The maximum elevator load was 1900 pounds up. The stabilizer twisted a maximum of 0.76 degrees leading edge down at the tip. The greatest fuselage deflection at the tail was about 1.7 inches down.

Wiener, Bernard↗
NASA NTRS1994

Thermal History Of PMRs Via Pyrolysis-Gas Chromatography

Pyrolysis-gas chromatography (PY-GC) useful as analytical technique to determine extents of cure or postcure of PMR-15 polyimides and to lesser extent, cumulative thermal histories of PMR-15 polyimides exposed to high temperatures. Also applicable for same purposes to other PMR polyimides and to composite materials containing PMR polyimides. Valuable in reducing costs and promoting safety in aircraft industry by helping to identify improperly cured or postcured PMR-15 composite engine and airframe components and helping to identify composite parts nearing ends of their useful lives.

Gluyas, Richard E.↗
NASA NTRS1993

Geologic history of central Chryse Planitia and the Viking 1 landing site, Mars

A 1:500,000 scale geologic mapping was undertaken to synthesize the broad-scale geology of Chryse Planitia with the local geology of the Viking 1 landing site. The geology of Mars Transverse Mercators (MTM's) 20047 and 25047 has been presented previously. As part of the goals for the Mars Geologic Mapping program, the rational and scientific objectives for a return mission to Chryse Planitia and the Viking 1 Lander have also been presented. However, in mapping central Chryse Planitia our principle objective was to determine the depositional and erosional history of the Chryse Planitia basin. These results are presented.

Craddock, Robert A.↗
NASA NTRS1993

Volcanism in southern Guinevere Planitia, Venus: Regional volcanic history and morphology of volcanic domes

Guinevere Planitia is a low-lying region located between the highlands of Beta Regio and Eistla Regio. Analyses of Pioneer Venus, Goldstone, and Arecibo radar data suggested that the surface of Guinevere Planitia is dominated by volcanism, primarily in the form of bright, dark, and mottled plains units. Also identified in this region was the Beta-Eistla Deformation Zone, composed of ovoids and discontinuous segments of lineament belts that have been embayed by the surrounding plains. The resolution of Magellan SAR images allows detailed investigations of the volcanic deposits found in the area in order to determine the types of eruptive activity which have occurred and to constrain the regional volcanic history. Analyses of an area of southern Guinevere Planitia between 0-25 deg N and 300-330 deg indicate the presence of a wide variety of volcanic land forms, including large shield volcanoes, widespread plains, lava flow fields, and small domes, cones, and shields as well as coronae and other circular structures that have associated volcanic deposits.

Crown, David A.↗