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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 109 records · Page 6
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NASA NTRS1977

Monte Carlo simulation of wave sensing with a short pulse radar

A Monte Carlo simulation is used to study the ocean wave sensing potential of a radar which scatters short pulses at small off-nadir angles. In the simulation, realizations of a random surface are created commensurate with an assigned probability density and power spectrum. Then the signal scattered back to the radar is computed for each realization using a physical optics analysis which takes wavefront curvature and finite radar-to-surface distance into account. In the case of a Pierson-Moskowitz spectrum and a normally distributed surface, reasonable assumptions for a fully developed sea, it has been found that the cumulative distribution of time intervals between peaks in the scattered power provides a measure of surface roughness. This observation is supported by experiments.

Levine, D. M.↗
NASA NTRS1978

Sizing-tube-fin space radiators

Temperature and size considerations of the tube fin space radiator were characterized by charts and equations. An approach of accurately assessing rejection capability commensurate with a phase A/B level output is reviewed. A computer program, based on Mackey's equations, is also presented which sizes the rejection area for a given thermal load. The program also handles the flow and thermal considerations of the film coefficient.

Peoples, J. A.↗
NASA NTRS1978

The analysis of high spatial resolution UV and X-ray images by computational modeling

Very high resolution stereoscopic images of high temperature loop structures observed at UV and X-ray wavelengths in the solar corona can be used to understand physical processes in the corona. An existing computational model is described and sample results are given to demonstrate that computational modeling of coronal structures can indeed take advantage of very high resolution images. The sample results include the run of temperature and number density along a typical loop and the variation of the differential emission measure with temperature. The integration of the differential emission measure with temperature along a column commensurate with an instrument's spatial resolution is the relevant parameter obtained from UV and X-ray observations. The effects of loop geometry and energy input are examined.

Vesecky, J. F.↗
NASA NTRS1978

Mercury - Magnetic field and interior

Present-day knowledge about the planetary magnetic field and interior of Mercury is reviewed. Radar observations are discussed which delineated the correct rotation rate of Mercury (58.646 days) and the planet's 3:2 spin-orbit resonance. The data obtained in Mariner 10 magnetic-field observations during the first and third encounters with Mercury are examined in detail, and theoretical studies of the planet's interior are summarized, including both steady-state models and those describing the thermal evolution of the planet. Two possible source mechanisms for the observed intrinsic planetary magnetic field are evaluated: an active dynamo and a passive paleomagnetic field frozen into the planet's outer layers at an earlier epoch. It is noted that neither the available magnetic-field data nor models of the planetary interior permit one to distinguish uniquely between the two mechanisms. The spin-orbit commensurability of Mercury is explained in the framework of the solar tides induced in the body of the planet, a nonaxisymmetric moment of inertia, and the highly eccentric orbit of the planet.

Ness, N. F.↗
NASA NTRS1978

The asteroids

The asteroids are small rocky bodies that orbit in modestly eccentric and inclined orbits, mainly between the orbits of Mars and Jupiter. With the comets, they are the only known population of residual planetesimals from the earliest epochs of solar system history. The observational characteristics of asteroids are discussed, taking into account aspects of photometry, rotations, masses and densities, spectrophotometry and surface compositions, surface textures and regoliths, size distribution, and erosion and fragmentation occurring as a result of interasteroidal collisions. Questions of dynamics and orbital evolution are investigated and ramifications for planetary evolution are explored. Attention is given to asteroids as planetesimals, aspects of early orbital evolution, the geochemical evolution of asteroids, commensurabilities and Kirkwood gaps, secular resonances, the material transport from the asteroid belt, Poisson's theorem, planetary masses, catalogs and selection effects, families, and Apollo, Amor, and Mars-crossing asteroids.

Chapman, C. R.↗
NASA NTRS1978

Dynamic model verification of large structural systems

The objective of the present methodology is two-fold: (1) to process test data obtained from either modal survey tests, or slow sine-sweep tests, to extract a set of orthogonal modes best matching the test data while being commensurate with the dynamic model, and (2) to modify submatrices of the dynamic model mass and stiffness matrices to adjust the model to best fit the test data. The method has been implemented using a linear statistical sequential estimator for computation on a CDC computer. Demonstration problems involving Space Shuttle quarter-scale vibration test data and dynamic models have been run. This paper will discuss the general methodology and experience to date.

Lee, L. T.↗
NASA NTRS1978

FMR and magnetic studies of Luna 24 soils and greater than 1 mm soil particles

Six Luna 24 soils (24077, 24109, 24149, 24174, 24182, 24210), their grain-size separates, and twenty-five greater than 1 mm soil particles were analyzed by ferromagnetic resonance (FMR) and static magnetic techniques. The values of the FMR maturity index for the soils ranged from 19.0 to 39.0 units; soils 24077 and 24109 are submature and soils 24149, 24174, 24182, and 24210 are immature. The metallic iron contents of the soils ranged from 0.30 to 0.51 wt % and are commensurate with their maturities. The 'best estimate' value for the concentration of metallic iron of Luna 24 mare basalts is 0.038 wt %.

Morris, R. V.↗
NASA NTRS1980

Coherent substructure of turbulence near the stagnation zone of a bluff body

The evolution of freestream turbulence in crossflow about a circular cylinder was studied in order to identify the existence of a coherent substructure which is the outcome of the amplification of freesteam turbulence by the stretching mechanism in diverging flow about a bluff body. Visualization of the flow events revealed the selective stretching of cross-vortex tubes and the emergence of an organized turbulent flow pattern near the cylinder stagnation zone. Significant amplification of the total turbulent energy of the streamwise fluctuating velocity was consistently monitored. Realization of selective amplification at scales larger than the neutral scale of the stagnation flow was indicated by the variation of the discrete streamwise turbulent energy. A most amplified scale, characteristic of the energy containing eddies within the coherent substructure and commensurate with the boundary-layer thickness, was detected. Penetration of the amplified turbulence into the cylinder boundary layer led to the retardation of separation and to a concurrent decrease in the drag coefficient at subcritical cylinder-diameter Reynolds numbers.

Sadeh, W. Z.↗
NASA NTRS1980

Thermal management for high power space platform systems

With future spacecraft power requirements expected to be in the order of 100 to 250 kilowatts and orbital lifetimes in the order of five to ten years, new approaches and concepts will be required that can efficiently and cost effectively provide the required heat rejection and temperature control capabilities. A plan was established to develop the commensurate technologies necessary for the thermal management of a high power space platform representative of future requirements and to achieve technology readiness by 1987. The approach taken in developing the program was to view the thermal requirements of the spacecraft as a spacecraft system rather than each as an isolated thermal problem. The program plan proposes 45 technology tasks required to achieve technology readiness. Of this total, 24 tasks were subsequently identified as being pacing technology tasks and were recommended for initiation in FY 1980 and FY 1981.

Gualdoni, R. A.↗
NASA NTRS1980

Turbulence amplification in flow about an airfoil

An experimental investigation of the evolution of freestream turbulence in flow about an airfoil was conducted in order to ascertain its selective amplification induced by the stretching mechanism according to the vorticity-amplification theory. Significant amplification of the streamwise turbulent energy transpired even in the limiting flow situation studied of a symmetric airfoil at zero angle of attack where the stretching is the least. Substantiation of the stretching effect was provided by the almost 100 percent amplification of turbulence with respect to its background level in the absence of the airfoil. Realization of preferred amplification at scales larger than the neutral scale of the stagnation flow was clearly indicated by the variation of the discrete streamwise turbulent energy. Particularly important was the detection of a most amplified scale which is characteristic of the coherent substructure near the airfoil stagnation zone and, concurrently, commensurate with the boundary-layer thickness.

Sadeh, W. Z.↗
NASA NTRS1980

Research reports: The 1980 NASA/ASEE Summer Faculty Fellowship Program

The Summer Faculty Fellowship Research Program objectives are: to further the professional knowledge of qualified engineering and science faculty members; to stimulate an exchange of ideas between participants and NASA; to enrich and refresh the research and teaching activities of participants and institutions; and to contribute to the research objectives at the NASA centers. The Faculty Fellows engaged in research projects commensurate with their interests and background and worked in collaboration with a NASA/MSFC colleague.

Barfield, B. F.↗
NASA NTRS1980

Low level moisture from VAS

Previous research and current opinion are too pessimistic concerning the capability of defining moisture fields from satellite measurements. The TIROS-N sounder is a close analogue to what will fly on GEOS-D and can be used to investigate the probable capability of VAS. Basically, there are three frequencies applied to sensing moisture in the troposphere. The ability of these three measurements to define the moisture pattern is assessed. It is certainly true that one cannot achieve the detail available with a radiosonde hygristor. Sharp discontinuities cannot be sensed by a passive sounder, especially since the measurement tends to "saturate" with the first moisture layer encountered. However, the satellite measurements demonstrate a high degree of skill in defining the horizontal gradient. Moisture "tongues" and "dry lines" are readily delineated with some, perhaps two layers, of vertical definition. These attributes allow both the calculation of important advective quantities as well as (in concert with the temperature sounding) a gross definition of the vertical stability. The skill is demonstrably commensurate with subsynoptic forecast models and perhaps even to regional scale models.

Hayden, C. M.↗
NASA NTRS1980

Visual evaluation of nystagmus intensity in points to diagnose vestibular dysfunction

The amplitude of nystagmus multiplied by its frequency gives a value commensurate to the velocity of slow phase. If the amplitude and the frequency during the visual observation are expressed in relative units (e.g., in points ranging from 1 to 3) the results of multiplication are used for a relative evaluation of nystagmus intensity. The relative evaluation of nystagmus intensity is used to compare the responses and, in particular, to calculate the coefficients of labyrinth asymmetry and of directional preponderance. A suggestion is made to analyze the formal results of caloric tests using a simple graphic model reflecting the left-right interactions by which the obtained coefficients are conditioned.

Levashov, M. M.↗
NASA NTRS1980

A 5.57 hr modulation in the optical counterpart of 2S 1822-371

A periodic 5.57 hr modulation has been observed in the optical counterpart of the X-ray source 2S 1822-371. Two alternative periods are consistent with the data: P = 0.232114d and P = 0.232191d, with statistical uncertainties of 0.000015d in each case. Minimum light occurred at JD 2,444,105.668 + or - 0.005. The amplitude of the modulation is about 1 mag, independent of UBV color, and no variability exceeding the 2% level other than the 5.57 hr effect is found on time scales down to a few seconds. The light curve of the star can be understood in terms of a highly inclined close binary system which contains a relatively large, luminous accretion disk that is periodically occulted by a companion star and an associated gas stream. On the assumption that the companion is a main-sequence star, the distance of the system is found to be more than 600 pc, based on the absence of color variations commensurate with the 5.57 hr intensity cycle.

Mason, K. O.↗
NASA NTRS1980

Seasat orbit refinement for altimetry application

This paper describes the use of stochastic differential correction models in refining the Seasat orbit based on post-flight analysis of tracking data. The objective is to obtain orbital-height precision that is commensurate with the inherent Seasat altimetry data precision level of 10 cms. Local corrections to a mean ballistic arc, perturbed principally by atmospheric drag variations and local gravitational anomalies, are obtained by the introduction of stochastic dynamical models in conjunction with optimal estimation/smoothing techniques. Assessment of the resulting orbit with 'ground truth' provided by Seasat altimetry data shows that the orbital height precision is improved by 32% when compared to a conventional least-squares solution using the same data set. The orbital height precision realized by employing stochastic differential correction models is in the range of 73 cms to 208 cms rms.

Mohan, S. N.↗
NASA NTRS1980

Dynamic properties of the thermosphere inferred from Pioneer Venus mass spectrometer measurements

The data obtained by the Pioneer Venus spectrometer experiments indicate that the day-night temperature contrast on Venus is associated with wind velocities of about 200 m/s which transport oxygen, helium, and hydrogen toward the night side. A mass exchange with the mesosphere commensurate with an eddy diffusion coefficient of 3 x 10 to the 7th is required to buffer the horizontal advection so as to reproduce the observed day time bulge in oxygen and the small diurnal variations in helium. The observed time response and magnitude of the day-night density variations require transport processes to be effective over time periods between five and ten days, implying a superrotation rate or prevailing winds in excess of 50 m/s at the equator. Nonlinear mass transport results in wave steepening and contributes to the amplification of the density extrema in hydrogen and helium.

Mayr, H. G.↗
NASA NTRS1981

Spherical earth gravity and magnetic anomaly analysis by equivalent point source inversion

To facilitate geologic interpretation of satellite elevation potential field data, analysis techniques are developed and verified in the spherical domain that are commensurate with conventional flat earth methods of potential field interpretation. A powerful approach to the spherical earth problem relates potential field anomalies to a distribution of equivalent point sources by least squares matrix inversion. Linear transformations of the equivalent source field lead to corresponding geoidal anomalies, pseudo-anomalies, vector anomaly components, spatial derivatives, continuations, and differential magnetic pole reductions. A number of examples using 1 deg-averaged surface free-air gravity anomalies of POGO satellite magnetometer data for the United States, Mexico, and Central America illustrate the capabilities of the method.

Von Frese, R. R. B.↗
NASA NTRS1980

Sweeping of the Jovian resonances and the evolution of the asteroids

During the formation of the solar system the variation of the gravitational field produced by removal of a nebula with its moderately massive accretion disk led to sweeping of the Jovian commensurability resonances through the asteroid zone. This process produced increased eccentricities and random velocities of the early planetesimals which resulted in collisional comminution rather than accretion. The existence of the asteroids, their low mass density, and their high relative velocities are interpreted as due to disruption of the accretion processes of the terrestrial planets by the influences of Jupiter.

Torbett, M.↗