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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.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

A head-up display for mid-air drone recovery

During mid-air retrieval of parachute packages, the absence of a natural horizon creates serious difficulties for the pilot of the recovery helicopter. A head-up display (HUD) was tested in an attempt to solve this problem. Both a roll-stabilized HUD and a no-roll (pitch only) HUD were tested. The results show that fewer missed passes occurred with the roll-stabilized HUD when the horizon was obscured. The pilots also reported that the workload was greatly reduced. Roll-stabilization was required to prevent vertigo when flying in the absence of a natural horizon. Any HUD intended for mid-air retrieval should display pitch, roll, sideslip, airspeed, and vertical velocity.

Augustine, W. L.↗
NASA NTRS1978

Lunar dust transport by photoelectric charging at sunset

The motion of dust grains from a photoelectrically charged object at the moon's sunset terminator is studied with the aid of a simple model. It is shown that sunlit objects ranging in size from less than 0.01 cm to 5 cm in radius are responsible for the levitation of dust grains to heights of observed horizon glow. The transverse displacement of these grains is observed to be at least twice their maximum altitude, so that fitting the latter to horizon glow implies horizontal particle ranges typically 6 to 60 cm. Detachment of these grains from the sunlit areas takes place mainly along the contracting sunlight boundaries as the areas shrink during sunset. A high ratio of intergrain adhesion force to dust-grain weight is essential for the occurrence of horizon glow and significant dust transport from the subcentimeter sized sunlit areas.

Pelizzari, M. A.↗
NASA NTRS1980

Seasat. Volume 4: Attitude determination

The Seasat project was a feasibility demonstration of the use of orbital remote sensing for global ocean observation. The satellite was launched in June 1978 and was operated successfully until October 1978. A massive electrical failure occurred in the power system, terminating the mission prematurely. The actual implementation of the Seasat Attitude Determination system and the contents of the attitude data files generated by that system are documented. The deviations from plan caused by the anomalous Sun interference with horizon sensors, inflight calibration of Sun sensor head 2 alignment and horizon sensor biomass, estimation of yaw interpolation parameters, Sun and horizon sensor error sources, and yaw interpolation accuracy are included. Examples are given of flight attitude data from all modes of the Orbital Attitude Control System, of the ground processing effects on attitude data, and of cold cloud effects on pitch, and roll data.

Treder, A. J.↗
NASA NTRS1981

SAS 2 observations of the earth albedo gamma radiation above 35 MeV

The earth albedo gamma radiation above 35 MeV in the equatorial region is investigated using observations from the second Small Astronomy Satellite. The zenith angle distribution of the gamma radiation has a peak toward the horizon which is about an order of magnitude more intense than the radiation coming from the nadir, and nearly two orders of magnitude more intense than the gamma radiation from most parts of the sky. The gamma radiation originating from the western horizon is a factor of four more intense than the radiation from the eastern horizon and a factor of three more intense than that from the northern and southern directions. This reflects the geomagnetic effects on the incident cosmic rays whose interactions produce the albedo gamma rays. The variation of the upcoming gamma ray intensity with vertical cutoff rigidity is consistent with the empirical relationship found by Gur'yan et al. (1979).

Thompson, D. J.↗
NASA NTRS1982

A comparison of soil moisture characteristics predicted by the Arya-Paris model with laboratory-measured data

Soil moisture characteristics predicted by the Arya-Paris model were compared with the laboratory measured data for 181 New Jersey soil horizons. For a number of soil horizons, the predicted and the measured moisture characteristic curves are almost coincident; for a large number of other horizons, despite some disparity, their shapes are strikingly similar. Uncertainties in the model input and laboratory measurement of the moisture characteristic are indicated, and recommendations for additional experimentation and testing are made.

Arya, L. M.↗
NASA NTRS1984

Stimulus factors in motion perception and spatial orientation

The Malcolm horizon utilizes a large projected light stimulus Peripheral Vision Horizon Device (PVHD) as an attitude indicator in order to achieve a more compelling sense of roll than is obtained with smaller devices. The basic principle is that the larger stimulus is more similar to visibility of a real horizon during roll, and does not require fixation and attention to the degree that smaller displays do. Successful implementation of such a device requires adjustment of the parameters of the visual stimulus so that its effects on motion perception and spatial orientation are optimized. With this purpose in mind, the effects of relevant image variables on the perception of object motion, self motion and spatial orientation are reviewed.

Post, R. B.↗
NASA NTRS1984

NASA Ames-Dryden T-37 demonstration comments

A homemade peripheral vision horizon device (PVHD) made from an eight-ball attitude indicator, with a slit cut at the equator of the eight ball, and a light source at its center that was used on a I-37 for several years is discussed. The instrument produced a sharp white line about one-fourth of an inch that extended completely across the cockpit from about the left to the right quarterpanels. The line remained parallel to the real horizon during all maneuvers. Its brightness and vertical distance from the horizon were adjustable in flight, as was the lateral center-of-rotation in later flights. Flight demonstrations were done on visual flight rules (VFR) moonless nights and over terrain with few lights. Pilot responses were mostly favorable to enthusiastic, with no negative reactions. Problem areas noted were the upright-inverted ambiguity; one pilot recovered inverted following an unusual attitude exercise and a general deterioration in the naturalness of cuing at bank angles greater than 60 deg or pitch attitudes greater than 30 deg.

Source record↗
NASA NTRS1985

Empirical model for the Earth's cosmic ray shadow at 400 KM: Prohibited cosmic ray access

The possibility to construct a unit sphere of access that describes the cosmic radiation allowed to an Earth-orbiting spacecraft is discussed. It is found that it is possible to model the occluded portion of the cosmic ray sphere of access as a circular projection with a diameter bounded by the satellite-Earth horizon. Maintaining tangency at the eastern edge of the spacecraft-Earth horizon, this optically occluded area is projected downward by an angle beta which is a function of the magnetic field inclination and cosmic ray arrival direction. This projected plane, corresponding to the forbidden area of cosmic ray access, is bounded by the spacecraft-Earth horizon in easterly directions, and is rotated around the vertical axis by an angle alpha from the eastern direction, where the angle alpha is a function of the offset dipole latitude of the spacecraft.

Humble, J. E.↗
NASA NTRS1986

Ground plane interference elimination by passive element

The radiation pattern of a beam at elevation angles near the horizon is improved for phased array antennas by control of the radiation field intensity near the horizon to reduce multipath disturbances, and to improve the axial ratio of a circularly polarized phased array antenna. This is accomplished by placing a parasitic phase shifting element directly below the antenna beam axis. The waveguide section is designed to produce a phase shift in the portion of antenna radiation energy passing through it to cancel some of the radiation energy in the direction of the horizon. The spacing of the waveguide section in front of the antenna is determined empirically for optimum results, i.e., for reduction of beam power below about 20 deg. without affecting beam power at high elevation angles.

Bonebright, Mark E.↗
NASA NTRS1988

Geochemistry of K/T boundaries in India and contributions of Deccan volcanism

Three possible Cretaceous/Tertiary (K/T) boundary sections in the Indian subcontinent were studied for their geochemical and fossil characteristics. These include two marine sections of Meghalaya and Zanskar and one continental section of Nagpur. The Um Sohryngkew river section of Meghalaya shows a high iridium, osmium, iron, cobalt, nickel and chromium concentration in a 1.5 cm thick limonitic layer about 30 cm below the planktonic Cretaceous-Palaeocene boundary identified by the characteristic fossils. The Bottaccione and Contessa sections at Gubbio were also analyzed for these elements. The geochemical pattern at the boundary at the Um Sohryngkew river and Gubbio sections are similar but the peak concentrations and the enrichment factors are different. The biological boundary is not as sharp as the geochemical boundary and the extinction appears to be a prolonged process. The Zanskar section shows, in general, similar concentration of the siderophile, lithophile and rare earth elements but no evidence of enrichment of siderophiles has so far been observed. The Takli section is a shallow inter-trappean deposit within the Deccan province, sandwiched between flow 1 and flow 2. The geochemical stratigraphy of the inter-trappeans is presented. The various horizons of ash, clay and marl show concentration of Fe and Co, generally lower than the adjacent basalts. Two horizons of slight enrichment of iridium are found within the ash layers, one near the contact of flow 1 and other near the contact of flow 2, where iridium occurs at 170 and 260 pg/g. These levels are lower by a factor of 30 compared to Ir concentration in the K/T boundary in Meghalaya section. If the enhanced level of some elements in a few horizons of the ash layer are considered as volcanic contribution by some fractionation processes than the only elements for which it occurs are REE, Ir and possibly Cr.

Bhandari, N.↗
NASA NTRS1989

The formation of topological defects in phase transitions

It was argued, and fought through numerical work that the results of non-dynamical Monte Carlo computer simulations cannot be applied to describe the formation of topological defects when the correlation length at the Ginzburg temperature is significantly smaller than the horizon size. To test the current hypothesis that infinite strings at formation are essentially described by Brownian walks of size the correlation length at the Ginzburg temperature, fields at the Ginzburg temperature were equilibrated. Infinite structure do not exist in equilibrium for reasonable definitions of the Ginzburg temperature, and horizons must be included in a proper treatment. A phase transition, from small-scale to large-scale string or domain wall structure, is found to occur very close to the Ginzburg temperature, in agreement with recent work. The formation process of domain walls and global strings were investigated through the breaking of initially ordered states. To mimic conditions in the early Universe, cooling times are chosen so that horizons exist in the sample volume when topological structure formation occurs. The classical fields are evolved in real-time by the numerical solution of Langevin equations of motion on a three dimensional spatial lattice. The results indicate that it is possible for most of the string energy to be in small loops, rather than in long strings, at formation.

Hodges, Hardy M.↗
NASA NTRS1990

On the continuous dependence with respect to sampling of the linear quadratic regulator problem for distributed parameter systems

The convergence of solutions to the discrete or sampled time linear quadratic regulator problem and associated Riccati equation for infinite dimensional systems to the solutions to the corresponding continuous time problem and equation, as the length of the sampling interval (the sampling rate) tends toward zero (infinity) is established. Both the finite and infinite time horizon problems are studied. In the finite time horizon case, strong continuity of the operators which define the control system and performance index together with a stability and consistency condition on the sampling scheme are required. For the infinite time horizon problem, in addition, the sampled systems must be stabilizable and detectable, uniformly with respect to the sampling rate. Classes of systems for which this condition can be verified are discussed. Results of numerical studies involving the control of a heat/diffusion equation, a hereditary of delay system, and a flexible beam are presented and discussed.

Rosen, I. G.↗
NASA NTRS1991

A global data set of soil particle size properties

A standardized global data set of soil horizon thicknesses and textures (particle size distributions) was compiled. This data set will be used by the improved ground hydrology parameterization designed for the Goddard Institute for Space Studies General Circulation Model (GISS GCM) Model 3. The data set specifies the top and bottom depths and the percent abundance of sand, silt, and clay of individual soil horizons in each of the 106 soil types cataloged for nine continental divisions. When combined with the World Soil Data File, the result is a global data set of variations in physical properties throughout the soil profile. These properties are important in the determination of water storage in individual soil horizons and exchange of water with the lower atmosphere. The incorporation of this data set into the GISS GCM should improve model performance by including more realistic variability in land-surface properties.

Webb, Robert S.↗
NASA NTRS1991

New evidence for a dramatic rise in atmosphere oxygen ca. 1,900 m.y. ago

Several lines of geologic evidence have pointed to a significant increase in P sub O2 about 2,000 m.y. ago, but the magnitude of P sub O2 before and after that time has been quite uncertain. The data that we have recently accumulated suggest that P sub O2 was approximately less than 2 x 10 (exp -3) atm more than 2,000 m.y. ago, and approximately greater than 0.03 atm more recently than ca. 1,900 m.y. ago. These estimates are based on the behavior of iron in Precambrian weathering horizons. More than ca. 2,000 m.y. ago, Fe(+2), released during the weathering of basalts was not oxidized to Fe(+3), and was removed in ground water from the upper layers of soil horizons. More recently than ca. 1,850 m.y. ago, Fe(+2) was oxidized to Fe(+3) and precipitated as iron oxides and hydroxides in such soil horizons and in the weathering products of a carbonate facies banded iron formation in Griqualand West, South Africa. The O2 content of the atmosphere must have increased dramatically about 1,900 m.y. ago to explain these observations. The reasons for the increase are still obscure, but are probably related to changes in the biologic productivity of the oceans. Eukaryotes appear to have developed shortly after the increase in P sub O2, perhaps in response to the subsequent increase in the supply of nitrate from the atmosphere to the oceans.

Holland, H. D.↗
NASA NTRS1991

Black holes in magnetic monopoles

We study magnetically charged classical solutions of a spontaneously broken gauge theory interacting with gravity. We show that nonsingular monopole solutions exist only if the Higgs field vacuum expectation value v is less than or equal to a critical value v sub cr, which is of the order of the Planck mass. In the limiting case, the monopole becomes a black hole, with the region outside the horizon described by the critical Reissner-Nordstrom solution. For v less than v sub cr, we find additional solutions which are singular at f = 0, but which have this singularity hidden within a horizon. These have nontrivial matter fields outside the horizon, and may be interpreted as small black holes lying within a magnetic monopole. The nature of these solutions as a function of v and of the total mass M and their relation to the Reissner-Nordstrom solutions is discussed.

Lee, Kimyeong↗
NASA NTRS1991

Future missions studies: Combining Schatten's solar activity prediction model with a chaotic prediction model

K. Schatten (1991) recently developed a method for combining his prediction model with our chaotic model. The philosophy behind this combined model and his method of combination is explained. Because the Schatten solar prediction model (KS) uses a dynamo to mimic solar dynamics, accurate prediction is limited to long-term solar behavior (10 to 20 years). The Chaotic prediction model (SA) uses the recently developed techniques of nonlinear dynamics to predict solar activity. It can be used to predict activity only up to the horizon. In theory, the chaotic prediction should be several orders of magnitude better than statistical predictions up to that horizon; beyond the horizon, chaotic predictions would theoretically be just as good as statistical predictions. Therefore, chaos theory puts a fundamental limit on predictability.

Ashrafi, S.↗
NASA NTRS1992

On the continuous dependence with respect to sampling of the linear quadratic regulator problem for distributed parameter system

The convergence of solutions to the discrete- or sampled-time linear quadratic regulator problem and associated Riccati equation for infinite-dimensional systems to the solutions to the corresponding continuous time problem and equation, as the length of the sampling interval (the sampling rate) tends toward zero(infinity) is established. Both the finite-and infinite-time horizon problems are studied. In the finite-time horizon case, strong continuity of the operators that define the control system and performance index, together with a stability and consistency condition on the sampling scheme are required. For the infinite-time horizon problem, in addition, the sampled systems must be stabilizable and detectable, uniformly with respect to the sampling rate. Classes of systems for which this condition can be verified are discussed. Results of numerical studies involving the control of a heat/diffusion equation, a hereditary or delay system, and a flexible beam are presented and discussed.

Rosen, I. G.↗
NASA NTRS1992

Geological evidence for a 2.6-Ga strewn field of impact spherules in the Hamersley Basin of Western Australia

Sand-sized spherules up to 1.7 mm across with spherulitic, vesicular, and other crystalline textures that consist mainly of K-feldspar help define a unique horizon in the well-preserved 2.6-Ga Wittenoom Formation in the Hamersley Basin of Western Australia. This layer is informally known as the spherule marker bed. In the northeastern part of the Hamersley Basin, similar spherules again occur at only one horizon, but here they are a minor constituent of a dolomitic debris-flow deposit known as the dolomixtite layer. The dolomixtite layer occurs in the Carawine Dolomite, which is stratigraphically equivalent to the Wittenoom Formation. Moreover, paleocurrent data from closely associated carbonate and volcaniclastic turbidites indicate the spherule marker bed was deposited in deeper-water paleoenvironments than the dolomixtite layer. Therefore, the dolomixtite layer is believed to be a proximal equivalent of the spherule marker bed. The layers that host the spherules are interpreted to be the deposits of a major sediment gravity flow that exhumed and redeposited most of the spherules after shallow burial, although the flow is not believed to have been a direct result of the proposed impact. The most likely site for the proposed impact would have been in the early Precambrian ocean close to the northeastern edge of the Pilbara Craton. Another thin horizon in the overlying Brockman Iron Formation contains spherules that again consist largely of K-feldspar and have internal textures strikingly similar to those of the Wittenoom Formation and Carawine Dolomite. The close resemblance of these spherules to those of the Wittenoom Formation and Carawine Dolomite suggests they also originated as impact melt droplets, even though they are admixed with volcaniclastic detritus. The stratigraphic separation between the two suggests that a second major impact occurred near the Hamersley Basin after a time interval of about 75 m.y. elapsed. This suggests the record of impacts in early Precambrian strata is richer than is generally appreciated.

Simonson, Bruce M.↗