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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

An observational and theoretical study of Colorado lee cyclogenesis

A cyclogenesis event that occurred over Colorado in early March of 1981 is the focus of this study. Two features that seemed to play a role in storm initiation were a traveling upper troposphere disturbance associated with an undulation on the subtropical front and a warm-cored shallow surface trough that was guided along the eastern slope of the Rockies from Canada to Colorado. The arrival of the latter feature initiated a sudden shift of the surface flow from upslope to downslope on the eastern side of the continental divide. A time-dependent quasi-geostrophic model was used to study the interaction of the traveling short wave and a broad topographic surface ridge in the presence of a baroclinic mainly westerly background flow. Westerly and easterly background surface winds were used to determine whether the surface trough arrival had any influence on the vigor of lee cyclogenesis initiated by the upper troposphere short-wave trough. With surface westerlies rapid cyclogenesis occurred, while with surface easterlies little cyclogenesis was found to the east of the Rockies. Thus, the shallow surface trough's arrival seemed to be crucial to storm initiation. These findings were based on a linear model. It is shown, however, that the height of the Rockies necessitates the inclusion of finite amplitude effects associated with the lower boundary into the model.

Clark, John H. E.↗
NASA NTRS1992

Lunar radiator shade

An apparatus for rejecting waste heat from a system located on or near the lunar equator is presented. The system utilizes a reflective catenary shaped trough deployed about a vertical radiator to shade the radiator from heat emitted by the hot lunar surface. The catenary shaped trough is constructed from a film material and is aligned relative to the sun so that incoming solar energy is focused to a line just above the vertical radiator and can thereby isolate the radiator from the effects of direct sunlight. The film is in a collapsed position between side by side support rods, all of which are in a transport case. To deploy the film and support rods, a set of parallel tracks running perpendicular to length of the support rods are extended out from the transport case. After the support tracks are deployed, the support rods are positioned equidistant from each other along the length of the support tracks so that the flexible film shade between adjacent support rods is unfolded and hangs in a catenary shaped trough. A heat radiator is supported between each pair of support rods above each hanging reflective trough.

Ewert, Michael K.↗
NASA NTRS1993

Morphology and models for the evolution of eastern Hecate Chasma, Venus

Hecate Chasma is a deep trough characterized by a chain-like concentration of coronae and corona-like features trending approximately southwest-northeast between approximately 200 and 260 degrees east longitude (terminating at Beta Regio). The section of Hecate in which we have concentrated our study is centered at 15N, 249, where the trough is especially well-defined. Nearby, a smaller chain of eight coronae lies along a minor trough parallel to the general trend of the greater chain. The trough itself is unusual in this area because it has a highly asymmetric profile. Using Magellan radar and topography data, we have examined the morphology of this area in order to assess the tectonic and volcanic history of the area. After examining the most important types of features (linear, arcuate and circular) in eastern Hecate, we present two possible models of origin. A companion abstract presents an overview of the Hecate and Parga linear deformation zones.

Hamilton, Victoria E.↗
NASA NTRS1975

Influence of thermal plasma flow on the daytime F2 layer

Previous work on theoretical modeling of thermal plasma flow between the ionosphere and the plasmasphere on the night side of the earth, where photoionization is almost completely absent, is continued to cover ionosphere-magnetosphere coupling in the dayside ionosphere. Results indicate that the daytime plasmapause should be associated with the H(+) trough in the top-side ionosphere, but not with the trough in O(+) density or NmF2. At night the plasmapause can be identified with a trough in both H(+) and O(+) densities.

Park, C. G.↗
NASA NTRS1977

Geology of the Valles Marineris - First Analysis of Imaging from the Viking 1 Orbiter Primary Mission

The Valles Marineris on the planet Mars constitute an enormous group of steep-walled equatorial canyons extending over an area more than 4000 km long and up to 700 km wide. An overview of Valles Marineris is provided, taking into account canyon system subdivisions, imaging and topographic data, Noctis Labyrinthus, western troughs, central troughs, east central troughs, and eastern canyons. Aspects of canyon wall and canyon floor morphology are discussed, giving attention to erosional features, layered rocks in canyon walls, tectonic features, plains, landslide deposits, hilly terrain, fractured floor, and floor plateaus and ridges. Upland pits and closed depressions in the canyons are considered along with regional tectonics and regional erosional styles.

Blasius, K. R.↗
NASA NTRS1979

Supersonic burning in separated flow regions

Activities reported include: (1) the construction of a thermocouple with a protective coating or sheath for obtaining reliable temperature measurements of gases in the base region; (2) the construction of a multiposition back step plate for trough tests for step sizes 0.63 cm and 0.25 cm; and (3) flow pattern studies with the 6.35 cm trough to determine the complex flow resulting when a shear layer reattaches in a corner. Reliable ignition and stable burning were achieved at Mach = 2 for the 0.63 cm trough. Photographs of side wall oil streaks for M=2 flow, and some static and pitot pressure results at M = 3 are included.

Zumwalt, G. W.↗
NASA NTRS1979

Evolution of Martian polar landscapes - Interplay of long-term variations in perennial ice cover and dust storm intensity

The discovery of a new type of Martian polar terrain, called undulating plain, is reported and the evolution of the plains and other areas of the Martian polar region is discussed in terms of the trapping of dust by the perennial ice cover. High-resolution Viking Orbiter 2 observations of the north polar terrain reveal perennially ice-covered surfaces with low relief, wavelike, regularly spaced, parallel ridges and troughs (undulating plains) occupying areas of the polar terrain previously thought to be flat, and associated with troughs of considerable local relief which exhibit at least partial annual melting. It is proposed that the wavelike topography of the undulating plains originates from long-term periodic variations in cyclical dust precipitation at the margin of a growing or receding perennial polar cap in response to changes in insolation. The troughs are proposed to originate from areas of steep slope in the undulating terrain which have lost their perennial ice cover and have become incapable of trapping dust. The polar landscape thus appears to record the migrations, expansions and contractions of the Martian polar cap.

Cutts, J. A.↗
NASA NTRS1980

Conceptual design study of concentrator enhanced solar arrays for space applications. 2kW Si and GaAs systems at 1 AU

The effect of concentration level on the specific power for a deployable, thin, gallium arsenide cell array in geosynchronous orbit for 10 years in conjunction with a two dimensional flat plate trough concentrator (V trough) and also with a multiple flat plate concentrator was investigated as well as the effects for a conventional silicon cell array on a rigid substrate. For application to a thin GaAs array at 1 AU for 10 years, the V trough produces a 19% benefit in specific power and a dramatic reduction in array area, while the multiple flat plate collector design is not only of no benefit, but is a considerable detriment. The benefit it achieves by reducing array area is duplicated by the 2D design. For the silicon array on a rigid substrate, improvement in performance due to a concentrator with ordinary mirror coating is quite small: 9% increase in specific power, and 13% reduction in array area. When the concentrator mirrors are coated with an improved cold mirror coating, somewhat more significant results are obtained: 31% specific power improvement; and 27% area reduction. In both cases, a 10 year exposure reduces BOL output by 23%.

Source record↗
NASA NTRS1979

The evolution of dust deposits in the Martian north polar region

The origin and evolution of two major eolian deposits of the Martian north polar region, the layered deposits and the debris mantle, are examined. Both apparently result from deposition of dust along with the seasonal CO2 frost cap. Dust deposited onto the perennial ice is incorporated into the layered deposits, while dust deposited directly onto the surface becomes part of the debris mantle. Climatically induced fluctuation of the perennial ice margin has influenced the evolution of both units. Periodic exposure to the atmosphere has allowed erosion of curvilinear troughs in the surface of the layered deposits. Intervening periods of deposition may have resulted in gradual poleward migration of the trough forms, leaving behind sets of low-amplitude surface undulations in former trough locations. Advance and retreat of the perennial ice margin has also probably resulted in a fine interfingering of the layered deposits-debris mantle contract. Limited post-depositional stripping of the debris mantle has been accomplished by intense winds blowing outward from the pole.

Squyres, S. W.↗
NASA NTRS1981

Experiments on three-dimensional separating and reattaching flows

In studies of multijet rockets, failure to find solutions when using a reasonable mathematical model led to performing airflow tests of supersonic circular jets exhausting into noncircular channels of various sizes. Amomalous base pressure trends and puzzling wall pressure patterns resulted. A flow-into-the-corner test was then devised, using a 90 deg trough behind a back step. A vortex pair, generated by the unsymmetrical squeezing of the shear layer, was found to fill much of the corner and provided an explanation for the peculiar results of the previous tests. No previous reference could be found to this phenomenon. Further experiments of bodies with base fins defined the conditions for creating this trough vortex effect. The trough vortex was used successfully as an igniter/flameholder for combustion of hydrogen in a supersonic stream. Other applications are suggested for base drag reduction, base burning and for providing guidance to avoid errors in half-plane wind tunnel model testing.

Zumwalt, G. W.↗
NASA NTRS1984

Solar photochemical process engineering for production of fuels and chemicals

The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water were studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6% are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6%. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. The overall plant efficiency is the single most important factor in determining the cost of the fuel.

Biddle, J. R.↗
NASA NTRS1985

An investigation of the equatorial orographic-dynamic mechanism

A barotropic model over an equatorial beta-plane is used to investigate the response when a uniform zonal current crosses an isolated hypothetical mountain centered at the equator. The bounded derivative initialization method is applied to suppress gravity-inertia motions. A quasi-stationary trough is generated at the top of the orography. Its intensity is greater in the easterly case than in the westerly case of the initial zonal current. A diagnostic equation is derived to interpret this difference in the solution. The quasi-stationary orographic divergence field which is positive on the windward slope and negative on the leeward slope (for both easterly and westerly cases of the initial zonal current) is responsible for maintaining the trough. The difference in the intensity of the trough is due to the contribution of the beta-u effect, which changes sign with the direction of the initial zonal flow.

Semazzi, F. H. M.↗
NASA NTRS1985

Solar photochemical process engineering for production of fuels and chemicals

The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water were studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6 percent are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6 percent. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. The overall plant efficiency is the single most important factor in determining the cost of the fuel.

Biddle, J. R.↗
NASA NTRS1986

Airborne Lidar measurements of the atmospheric pressure profile with tunable Alexandrite lasers

The first remote measurements of the atmospheric pressure profile made from an airborne platform are described. The measurements utilize a differential absorption lidar and tunable solid state Alexandrite lasers. The pressure measurement technique uses a high resolution oxygen A band where the absorption is highly pressure sensitive due to collision broadening. Absorption troughs and regions of minimum absorption were used between pairs of stongly absorption lines for these measurements. The trough technique allows the measurement to be greatly desensitized to the effects of laser frequency instabilities. The lidar system was set up to measure pressure with the on-line laser tuned to the absorption trough at 13147.3/cm and with the reference laser tuned to a nonabsorbing frequency near 13170.0/cm. The lidar signal returns were sampled with a 200 range gate (30 vertical resoltion) and averaged over 100 shots.

Korb, C. L.↗
NASA NTRS1987

E and F region study of the evening sector auroral oval - A Chatanika/Dynamics Explorer 2/NOAA 6 comparison

Simultaneous data from the Chatanika radar and the DE 2 and NOAA 6 satellites are used to study the typical behavior of the winter evening-sector auroral plasma during moderate and steady magnetic activity. The equatorward edge of the auroral E layer, of the region 2 field-aligned currents, and of the region of intense convection are colocated. The auroral E layer extends several degrees south of the equatorward edge of the keV electron precipitation from the CPS. Although the main trough and ionization channel are embedded in a region of intense electric field where the plasma flows sunward at high speed, the flux tubes associated with these two features have different time histories. The midlatitude trough is located south of the region of electron precipitation, above a proton aurora. The ionization channel marks the poleward edge of the main trough and is colocated with the equatorward boundary of the electron precipitation from the central plasma sheet.

Senior, C.↗
NASA NTRS1988

The determination of the propagation constant for the traveling wave in an infinite ground plane

The propagation constant for the traveling wave in a trough in an infinite ground plane is examined. The null-field integral is used to determine the EM field in the trough structure, and pulse basis functions give the distribution of the aperture fields. From this, the propagation constant is solved for, using the Newton-Raphson iterative scheme. Various sizes of geometries are examined. The far-field patterns are calculated and compared with other solutions, thereby validating the integral formulation which subsequently provided the propagation constant. Measurements of two trough geometries are performed to validate the theoretical results.

Shamansky, Harry T.↗
NASA NTRS1989

Microscopic deformation in a heated unidirectional graphite-epoxy composite

Both in-plane and out-of-plane displacements were determined in patches of the toughened 1962-ERLX epoxy bounded by three closely packed high-modulus P75S graphite fibers. The P75S/1962-ERLX composite was unidirectional, with an average fiber volume of 60 percent. On heating to 44 C from room temperature, the epoxy confined between clusters of three fibers sank in a trough beneath the plane of the fiber ends by 50-120 nm. When the maximum temperature achieved in the prior thermal cycles exceeded 100 C the depth of the trough increased. However, when cycles exceeding 100 C were followed by thermal cycles of decreasing amplitude, chosen to reduce interfacial stress relaxation, the depth of the trough decreased. The results illustrate the feasibility of deducing quantitative data on local deformation from high-resolution strain measurements on cut surfaces.

Morris, W. L.↗
NASA NTRS1991

The ionospheric signatures of rapid subauroral ion drifts

Subauroral ion drifts (SAID) are latitudinally narrow regions of rapid westward ion drift located in the evening sector and centered on the equatorward edge of the diffuse aurora. Observations of SAID, as identified by the ion drift meters on the Atmosphere Explorer C and Dynamics Explorer B spacecraft, are utilized to determine their effect on the F region ion composition, their relationship to the midlatitude trough, and their temporal evolution. At altitudes near the F peak, a deep ionization trough is formed in regions of large ion drift where the O(+) concentration is considerably depleted and the NO(+) concentration is enhanced, while at higher altitudes the trough signature is considerably mitigated or even absent. SAID have been observed to last longer than 30 min but less than 3 hours, and their latitudinal width often becomes narrower as time progresses. The plasma flows westward equatorward of the SAID and becomes more westward as invariant latitude increases. Poleward of the SAID, the flow is, on average, westward throughout the auroral zone in the evening, while near midnight it becomes eastward.

Anderson, P. C.↗