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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

EUV limb spectra of a surge observed from Skylab

The EUV spectra of a surge observed at plus 8 in. and plus 20 in. above the white light limb from Skylab are examined. The shape of the differential emission measure determined at 8 in. and 20 in. is nearly the same as for a quiet Sun spectrum at 8 in., but the emission measure of the surge at 8 in. is about an order of magnitude greater than for the quiet Sun. At 20 in. the emission measure of the surge is initially close to the quiet Sun distribution, but decreases by a factor of 4 within 6 min. The optically thin lines formed near 10 to the 5th power K show nonthermal broadening at 8 in., and electron densities near this temperature are derived from intersystem to resonance ratios. The volume of the emitting plasma at 8 in. above the limb was determined, concluding that a continuous energy input is required to explain the observations.

Doschek, G. A.↗
NASA NTRS1980

Solar Power Satellite Microwave Power Transmission System Description Executive Summary

The history of the concept of microwave power beaming to Earth is reviewed with emphasis on transmission frequency selection. Constraints on the system power level results from (1) required rejection of waste heat resulting from inefficiencies in the cover conversion of dc electric power to microwave power; (2) the rf power intensity in the ionosphere; and (3) the effect of sidelobe level on aperture illumination factors. Transmitter arrangement, the power distribution system, attitude control, subarrays, waveguides, and alignment are discussed.

Woodcock, G. R.↗
NASA NTRS1984

The Nimbus 7 ERB data set - A critical analysis

An analysis of the first year of the Nimbus 7 earth radiation budget data set reveals that there are systematic differences between wide and narrow field of view measurements. The larger differences appear in the albedo data and are due primarily to a bias introduced by the processing method. There are smaller differences, associated with the outgoing longwave radiation, which are probably due to errors in calibration. The bias in albedo originates in the factors used for converting the shortwave intensity measured at satellite altitude into a mean daily albedo at the top of the atmosphere. The factor that proves most troublesome is the one that converts measured intensity to the total instantaneous outgoing flux. That factor is determined by angular distribution models, which depend upon the type of scene within the target area. An alternative method of processing the data, which is model independent, is shown to have practically no bias and yields better over-all agreement with the wide field of view measurements.

Arking, A.↗
NASA NTRS1985

Ecophysiology of phototrophic sulfur bacteria in lakes: Vertical distribution of planktonic populations

The study of purple and green sulfur bacterial populations in nature is of interest for the following reasons: (1) high quantities of biomass, with low species diversity can be collected; (2) study of planktonic life permits one to understand the mechanisms, structural as well as physiological, used to maintain their vertical position without sinking; and (3) they are capable of sulfur oxidations and reductions that act as important intermediates in the global sulfur cycle. Purple and green photosynthetic bacteria, moreover, may be responsible for certain geological deposits. Planktonic phototrophic sulfur bacteria were analyzed in relation to their vertical distribution in the water column. Factors, including competition for light, that determine their sedimentation rates and the numerical changes in species and populations were assessed.

Guerrero, R.↗
NASA NTRS1986

Flight evaluation of a precision landing task for a powered-lift STOL aircraft

A flight research experiment was conducted with the NASA-Ames Research Center's Quiet Short-Haul Research Aircraft to determine the factors which influence the touchdown distribution for a powered-lift STOL aircraft. The pilots were given two tasks for each of a series of precision approaches flown using a microwave landing system (MLS) in simulated instrument meteorological conditions. They flew the aircraft, with forward vision obscured by a screen, to a 100-ft decision height using a flightpath-oriented, color electronic display and one of four levels of control augmentation. Approaches were flown along a nominal 6 deg glidepath, as well as to calibrated offsets at the decision height to establish a variety of initial conditions for the landing task. The screen was removed at the decision height and the pilot was briefed to land in a 200 foot touchdown zone of the STOLport with a sink rate less than 5 ft/sec. Statistical performance envelopes and pilot ratings are used to describe the results of this experiment. The data generated are expected to be useful for establishing STOL aircraft operating requirements and STOL MLS approach criteria.

Watson, D. M.↗
NASA NTRS1990

Managing Information On Costs

Cost Management Model, CMM, software tool for planning, tracking, and reporting costs and information related to costs. Capable of estimating costs, comparing estimated to actual costs, performing "what-if" analyses on estimates of costs, and providing mechanism to maintain data on costs in format oriented to management. Number of supportive cost methods built in: escalation rates, production-learning curves, activity/event schedules, unit production schedules, set of spread distributions, tables of rates and factors defined by user, and full arithmetic capability. Import/export capability possible with 20/20 Spreadsheet available on Data General equipment. Program requires AOS/VS operating system available on Data General MV series computers. Written mainly in FORTRAN 77 but uses SGU (Screen Generation Utility).

Taulbee, Zoe A.↗
NASA NTRS1990

Bias correction for rainrate retrievals from satellite passive microwave sensors

Rainrates retrieved from past and present satellite-borne microwave sensors are affected by a fundamental remote sensing problem. Sensor fields-of-view are typically large enough to encompass substantial rainrate variability, whereas the retrieval algorithms, based on radiative transfer calculations, show a non-linear relationship between rainrate and microwave brightness temperature. Retrieved rainrates are systematically too low. A statistical model of the bias problem shows that bias correction factors depend on the probability distribution of instantaneous rainrate and on the average thickness of the rain layer.

Short, David A.↗
NASA NTRS1992

Latest COBE results, large-scale data, and predictions of inflation

One of the predictions of the inflationary scenario of cosmology is that the initial spectrum of primordial density fluctuations (PDFs) must have the Harrison-Zeldovich (HZ) form. Here, in order to test the inflationary scenario, predictions of the microwave background radiation (MBR) anisotropies measured by COBE are computed based on large-scale data for the universe and assuming Omega-1 and the HZ spectrum on large scales. It is found that the minimal scale where the spectrum can first enter the HZ regime is found, constraining the power spectrum of the mass distribution to within the bias factor b. This factor is determined and used to predict parameters of the MBR anisotropy field. For the spectrum of PDFs that reaches the HZ regime immediately after the scale accessible to the APM catalog, the numbers on MBR anisotropies are consistent with the COBE detections and thus the standard inflation can indeed be considered a viable theory for the origin of the large-scale structure in the universe.

Kashlinsky, A.↗
NASA NTRS1993

Isotopic fractionation of hydrogen in planetary exospheres due to ionosphere-exosphere coupling - Implications for Venus

The paper considers isotopic hydrogen fractionation processes in the Venusian exosphere due to ionosphere-exosphere coupling by addressing two deficiencies in the present theory of differential escape. First, a set of D/H isotopic fractionation curves is derived for the ion-neutral interactions of charge and collisional momentum transfer, and these are compared with the results of Gurwell and Yung (1993) for hot O collisional ejection. Then, the question of the relative importance of collisional ejection in atmospheric escape is reexamined using two simple exosphere models. It is shown that O-O collisions suppress the high energy component of the hot O distribution by more than a factor of 10. Moreover, the ballistic trajectories of fast O atoms that reach the nighttime reservoir of exospheric hydrogen favor downward scatter of D and H rather than their escape. It is concluded that, due to severe limits placed on the effectiveness of collisional ejection, the differential escape of D and H from Venus is determined by charge exchange interactions rather than the collisional ejection.

Hodges, R. R., Jr.↗
NASA NTRS1985

Global tropospheric methane: An indication of atmosphere-biosphere-climate interactions?

Methane is an important atmospheric gas with potentially critical roles in both photochemical and radiation transfer processes. A major natural source of atmospheric methane involves anaerobic fermentation of organic materials in wetland soils and sediments. A data base of field measurements of atmospheric methane was used in the development of a global methane emissions inventory. Calculations support the following hypotheses: (1) Human activities currently produce methane at a rate approximately equal to natural resources (these rapidly increasing anthropogenic sources can explain most of the recent increase observed in tropospheric methane); and (2) Prior to 200 B.P. (before the present), the influence of climate on wetland extent and distribution was probably a dominant factor controlling global biogenic methane emissions to the atmosphere.

Harriss, Robert C.↗
NASA NTRS1992

Overview of feasibility study on conducting overflight measurements of shaped sonic boom signatures using RPV's

Before beginning this presentation, it is appropriate to acknowledge the sincere interest and financial support provided by the NASA LaRC under contract NAS9-17900. An outline of the material to be used in the present paper is given. It begins with a indication of the origin and objectives of the feasibility study. This is followed by a discussion of various simulation methods of establishing the persistence of shaped sonic boom signatures to large distances including the use of recoverable RPV/drones. The desirable features to be sought out in an RPV along with a rationale for the selection of a 'shaped' sonic boom signature will be addressed. Three candidate vehicles are examined as to their suitability with respect to a number of factors, in particular, modifiability. Area distributions and associated sonic boom signatures of the basic and modified Firebee vehicle will also be shown. An indication of the scope of the proposed wind tunnel and flight test programs will be presented including measurement technologies and predicted waveforms. Finally, some remarks will be made summarizing the study and highlighting the key findings.

Maglieri, Domenic J.↗
NASA NTRS1994

Advanced technologies in the ASI MLRO towards a new generation laser ranging system

Matera Laser Ranging Observatory (MLRO) is a high performance, highly automated optical and astronomical observatory currently under design and development by AlliedSignal for the Italian Space Agency (ASI). It is projected to become operational at the Centro Geodesia Spaziale in Matera, Italy, in 1997. MLRO, based on a 1.5-meter astronomical quality telescope, will perform ranging to spacecraft in earthbound orbits, lunar reflectors, and specially equipped deep space missions. The primary emphasis during design is to incorporate state-of-the-art technologies to produce an intelligent, automated, high accuracy ranging system that will mimic the characteristic features of a fifth generation laser ranging system. The telescope has multiple ports and foci to support future experiments in the areas of laser communications, lidar, astrometry, etc. The key features providing state-of-the-art ranging performance include: a diode-pumped picosecond (50 ps) laser, high speed (3-5 GHz) optoelectronic detection and signal processing, and a high accuracy (6 ps) high resolution (less than 2 ps) time measurement capability. The above combination of technologies is expected to yield millimeter laser ranging precision and accuracy on targets up to 300,000 km, surpassing the best operational instrument performance to date by a factor of five or more. Distributed processing and control using a state-of-the-art computing environment provides the framework for efficient operation, system optimization, and diagnostics. A computationally intelligent environment permits optimal planning, scheduling, tracking, and data processing. It also supports remote access, monitor, and control for joint experiments with other observatories.

Varghese, Thomas↗
NASA NTRS1995

Theoretical overview and modeling of the sodium and potassium atmospheres of mercury

A general theoretical overview for the sources, sinks, gas-surface interactions, and transport dynamics of sodium and potassium in the exospheric atmsophere of Mercury is given. Information for these four factors, which control the spatial distribution of these two alkali-group gases about the planet, is incorporated in numerical models. The spatial nature and relative importance of the initial source atom atmosphere and the ambient (ballistic hopping) atom atmosphere are then examined and are shown to be controlled and coupled to a great extent by the extremely large and variable solar radiation acceleration experienced by sodium and potassium as they resonantly scatter solar photons. The lateral (antisunward) transport rate of thermally accommodated sodium and potassium ambient atoms is shown to be driven by the solar radiation acceleration and, over a significant portion of Mercury's orbit about the Sun, is sufficiently rapid to be competitive with the short photoionization lifetimes for these atoms when they are located on the summit surface near or within about 30 deg of the terminator. The lateral transport rate is characterized by a migration time determined by model calculations for an ensemble of atoms initially starting at a point source on the surface (i.e., a numerical spacetime dependent Green's function). Four animations for the spacetime evolution of the sodium (or potassium) atmosphere produced by a point source on the surface are presented on a videotape format. For extended surface sources for sodium and potassium, the local column density is determined by competition between the photoionization lifetimes and the lateral transport times of atoms originating from different surface source locations. Sodium surface source fluxes (referenced to Mercury at perihelion) that are required on the sunlit hemisphere to reproduce the typically observed several megarayleighs of D2 emission-line brightness and the inferred column densities of 1-2 x 10(exp 11) atoms per sq cm range from approximately 2-5 x 10(exp 7) atoms/sq cm/sec. The sodium model is applied to study observational data that document an anticorrelation in the average sodium column density and solar radiation acceleration. Lateral transport driven by the solar radiation acceleration is shown to produce this behavior for combinations of different sources and surface accomodation coefficients. The best fit model fits to the observational data require a significant degree of thermal accommodation of the ambient sodium atoms to the surface and a source rate that decreases as an inverse power of 1.5 to 2 in heliocentric distance.

Smyth, William H.↗
NASA NTRS1995

Theoretical overview and modeling of the sodium and potassium atmospheres of the moon

A general theoretical overview for the sources, sinks, gas-surface interactions, and transport dynamics of sodium and potassium in the exospheric atmosphere of the Moon is given. These four factors, which control the spatial distribution of these two alkali-group gases about the Moon, are incorporated in numerical models. The spatial nature and relative importance of the initial source atoms atmosphere (which must be nonthermal to explain observational data) and the ambient (ballistic hopping) atom atmosphere are examined. The transport dynamics, atmospheric structure, and lunar escape of the nonthermal source atoms are time variable with season of the year and lunar phase because of their dependence on the radiation acceleration experienced by sodium and potassium atoms as they resonantly scatter solar photons. The dynamic transport time of fully thermally accomodated ambient atoms along the surface because of solar radiation acceleration (only several percent of surface gravity) is larger than the photoionization lifetimes and hence unimportant in determining the local density, although for potassium the situation is borderline. The sodium model was applied to analyze sodium observations of the sunward brightness profiles acquired near last quarter by Potter & Morgan (1988b) extending from the surface to an altitude of 1200 km, and near first quarter by Mendillo, Baumgardner, & Flynn (1991), extending in altitude from approximately 1430 to approximately 7000 km. The observations at larger altitudes could be fitted only for source atoms having a velocity distribution with a tail that is mildly nonthermal (like an approximately 1000 K Maxwell-Boltzmann distribution). Solar wind sputtering appears to a be a viable source atom mechanism for the sodium observations with photon-simulated desorption also possible but highly uncertain, although micrometeoroid impact vaporization appears to have a source that is too small and too hot, with likely an incorrect angular distribution about the Moon.

Smyth, William H.↗
NASA NTRS1994

Effect of 1partial thickness actuation on stress concentration reduction near a hole

Recently, there has been much interest in adaptive structures that can respond to a varying environment by changing their properties. Piezoelectric materials and shape memory alloys (SMA) are often used as partial thickness actuators to create such adaptivity by applied energy, usually electric curent. These actuators can be used to inducce strains in a structure and reduce stresses in regions of high stress concentration. Two of the present authors show that axisymmetric actuation strains applied troughout the thickness of a plate with a hole can reduce the stress concentration factor (SCF) in an isotropic plate from 3 to 2. However, in most cases actuators are expected to be bonded to or embedded in the plate, so that the actuation strains are applied in the actuators and not directly in the plate. The objective of this note is to show that such partial-thickness actuation cannot be used to reduce the stress concentration factor with axisymmetric actuations strain distribution.

Sensharma, P. K.↗
NASA NTRS1995

Polarimetric signatures of sea ice. 1: Theoretical model

Physical, structral, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarmetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies to interpretation of sea ice polarimetric signatures.

Nghiem, S. V.↗
NASA NTRS1995

Polarimetric Signatures of Sea Ice: Theoretical Model - Part 1

Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures.

Nghiem, S. V.↗
NASA NTRS1965

Airplane Spinning

A summary on spinning is presented to point out the state of the art and the most important parameters', and to show the effects of these parameters on the spin and spin-recovery characteristics. The discussion presented applies to the fully developed spin, but does not apply to the spin entry, or incipient spin. The principal factors in spinning are mass distribution, which is by far the most important single parameter, and tail design, which is particularly important for conditions of zero or near-zero loading. By knowing the mass distribution and tail design, it is possible in many cases to predict whether an airplane has satisfactory spin-recovery characteristics. In other cases, however, it is necessary to make spin tests to assure satisfactory recovery.

Bowman, James S.↗