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At least 1,027 records · Page 57

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NASA NTRS1972

Thermal radiative properties: Coatings.

This volume consists, for the most part, of a presentation of numerical data compiled over the years in a most comprehensive manner on coatings for all applications, in particular, thermal control. After a moderately detailed discussion of the theoretical nature of the thermal radiative properties of coatings, together with an overview of predictive procedures and recognized experimental techniques, extensive numerical data on the thermal radiative properties of pigmented, contact, and conversion coatings are presented. These data cover metallic and nonmetallic pigmented coatings, enamels, metallic and nonmetallic contact coatings, antireflection coatings, resin coatings, metallic black coatings, and anodized and oxidized conversion coatings.

Touloukian, Y. S.↗

NASA NTRS1973

Non-linear flap-lag dynamics of hingeless helicopter blades in hover and in forward flight.

The aeroelastic instability of the coupled nonlinear flap-lag motion of a torsionally rigid helicopter blade is treated by using the perturbation method in multiple time scales. The nonlinearities present in the equations are those arising from the inclusion of moderately large deflections in the inertia and aerodynamic loading terms. The stability boundaries, amplitudes of nonlinear response, and conditions for existence of limit cycles are obtained analytically. Thus the different roles played by the forcing, parametric excitation, and nonlinear coupling in affecting the solution can be easily identified. Numerical results illustrating the behavior of the blade are presented.

Friedmann, P.↗

NASA NTRS1973

Effects of rehydration on +Gz tolerance after 14-days' bed rest.

Investigation of the magnitude of reduction in human tolerance to centrifugation following 2 weeks of bed rest with moderate daily exercise. The degree of hypovolemia associated with these exposures is assessed, and the possibility to improve or to return to control levels the tolerance to acceleration forces acting in the head-to-foot direction through rehydration prior to acceleration is explored.

Greenleaf, J. E.↗

NASA NTRS1973

Lunar bulk sample trace element contents and KREEP.

The geochemical coherence of KREEP-related labile (Cl) and refractory (F, K, P, and REE) elements in lunar soils is shown to provide some insights into the evolution of the lunar samples studied. Thus, this coherence may help define the physical conditions under which the samples evolved. These conditions range from high temperatures and relatively open systems for mare basalts to moderate temperatures and closed systems for KREEP-related material. The water leachable Cl may be the residuum of the Cl-containing phase with which mare and KREEP source material equilibrated.

Reed, G. W., Jr.↗

NASA NTRS1973

Mariner 9 ultraviolet spectrometer experiment - 1971 Mars' dust storm.

The brightness of a region on the south polar cap centered at approximately -87 deg S, 10 deg W was observed. Measurements taken at various incidence and emission angles show that the brightness increased with decreasing air mass. The observed intensity consists primarily of a component reflected from the cap and twice attenuated by the atmosphere and a component diffusely reflected from the atmosphere. The dust cloud over the polar cap was moderately thick between Nov. 26 and Dec. 2, 1971. At this time the optical thickness was near unity, and it decreased approximately linearly with time, reaching a value close to that of a Rayleigh atmosphere by mid-February. The optical thickness showed little dependence on the wavelength during the early orbital observations.

Pang, K.↗

NASA NTRS1973

Speed and thickness of the magnetopause.

We have used the finite gyroradius of protons with energies greater than 140 keV to determine the location of the magnetopause when the satellite is within the adjacent steep proton flux gradient. This steep gradient region is usually two to four 140-keV proton gyroradii, or about 1000 to 4000 km thick. The measurements described here were made within 45 deg of the earth-sun line on moderately disturbed days, when proton fluxes were unusually high. On these days, the magnetopause usually moves at a speed of less than 20 km/sec. The magnetopause velocity sometimes changes abruptly, while remaining below 20 km/sec. Very rapid (about 50 km/sec) radial motion appears to be associated with the propagation of single, isolated waves along the magnetopause. The thickness of the electric current sheet that produces the magnetic field rotation in the magnetopause is usually on the order of 10 times the gyroradius of a 1-keV proton, or about 1000 km.

Kaufmann, R. L.↗

NASA NTRS1973

A new approach to long-life noncontacting electromechanical devices

Brushless dc motors are finding increasing application in space. Likewise, with the advent of the light emitting diode, noncontacting encoders are gradually replacing sliding contact types. The direct drive concept has proved its merit and is now the preferred approach for tape recorders and low to moderate torque instrument drives. The final step in this evolution is the magnetic bearing, which now appears feasible for several applications. Where it can be applied in a totally noncontacting system, life and reliability will be a function of the electronic controls, where redundancy, derating, and quality assurance approaches virtually assure the desired lifetime and failure rate.

Devine, E. J.↗

NASA NTRS1973

A systematic experimental investigation of significant parameters affecting model tire hydroplaning

The results of a comprehensive parametric study of model and small pneumatic tires operating on a wet surface are presented. Hydroplaning inception (spin down) and rolling restoration (spin up) are discussed. Conclusions indicate that hydroplaning inception occurs at a speed significantly higher than the rolling restoration speed. Hydroplaning speed increases considerably with tread depth, surface roughness and tire inflation pressure of footprint pressure, and only moderately with increased load. Water film thickness affects spin down speed only slightly. Spin down speed varies inversely as approximately the one-sixth power of film thickness. Empirical equations relating tire inflation pressure, normal load, tire diameter and water film thickness have been generated for various tire tread and surface configurations.

Wray, G. A.↗

NASA NTRS1973

Land use mapping and modelling for the Phoenix Quadrangle

The author has identified the following significant results. In comparing the land use changes from the overlay as detected from ERTS-1 and the high altitude change overlay, total areas of change were of the same magnitude. The greatest variations were a result of differences in dates and areas of coverage between ERTS-1 images and aerial photographs. Separation of citrus from other agricultural land has been moderately successful in the ERTS-1 1:100,000 scale Level 2 land use mapping around Phoenix, although accuracy estimates are not yet available. No feeding operations have been detected from ERTS-1 so far. Preliminary indications are that commercial and services, industrial, and institutional land are not separable from each other using present image interpretation techniques. Urban open areas such as parks and golf courses are readily detectable, particularly when local maps are consulted even though out-of-date. Strip and clustered settlements may be detected depending upon their size and contrast with the surrounding area on the ERTS-1 image.

Place, J. L.↗

NASA NTRS1973

Molding process for imidazopyrrolone polymers

A process is described for producing shaped articles of imidazopyrrolone polymers comprising molding imidazopyrrolone polymer molding power under pressure and at a temperature greater than 475 C. Moderate pressures may be employed. Preferably, prior to molding, a preform is prepared by isostatic compression. The preform may be molded at a relatively low initial pressure and temperature; as the temperature is increased to a value greater than 475 C., the pressure is also increased.

Johnson, C. L.↗

NASA NTRS1973

Double scattering corrections for the theory of the sun's aureole

Double scattering corrections for aureole radiances are calculated by adding the effects of two successive single scatterings. Atmospheric absorption, polarization, and variation of refractive index with altitude are ignored. Corrections due to spherical atmosphere were taken into account by the use of a generalized Chapman function. Realistic scattering phase functions based upon the Lorenz-Mie theory and model altitude-size distribution are used. The model distribution is assumed to be representable in terms of two separable particulate components. It was found that for a moderately clear day, tau (0) is approximately equal to 0.5, and for forward scattering angles, the radiance, B sub 2, due to double scattering is less than 6 percent of that due to single scattering.

Deepak, A.↗

NASA NTRS1973

Inherent redundacy electric heater

A cross-wound electrical heater comprising two resistance coils wound together with opposite pitches electrically connected at their crossing points, is reported. Each element is supplied by a separate power supply of the same magnitude, and each power supply is isolated from reverse currents by a diode. Failure of one of the windings results in only a moderate change in output power.

Kernodle, B. H.↗

NASA NTRS1974

Recognition of the geologic framework of porphyry deposits on ERTS-1 imagery

The author has identified the following significant results. Three major tectonic provinces have been mapped by geologic photointerpretation of ERTS-1 imagery over the Ok Tedi test site. These areas can be characterized as follows: (1) A broad area of low relief and mature topography suggesting a history of relative tectonic stability. (2) A narrow belt of moderate to high relief, broad open folds and prominent linear features. The Mount Fubilan-type porphyry copper deposits and recent volcanic effusive centers occur in this province. (3) A heterogeneous zone of high relief and high drainage density suggestive of relative structural complexity.

Wilson, J. C.↗

NASA NTRS1973

Development of special lubricants for ball bearings operating in vacuum

A ball bearing life test program was performed to obtain data on the efficiencies of various lubricated and self-lubricating ball retainer systems for instrument bearings in a vacuum environment. The program utilized light to moderate radial loads at relatively low speeds on a NASA-GSFC designed and supplied test rig. Several systems were found which gave acceptable bearing life under the test conditions used, but the most consistent low running torques after testing resulted from oil lubrication.

Source record↗

NASA NTRS1974

Exploratory tests of two strut fuel injectors for supersonic combustion

Results of supersonic mixing and combustion tests performed with two simple strut injector configurations, one with parallel injectors and one with perpendicular injectors, are presented and analyzed. Good agreement is obtained between static pressure measured on the duct wall downstream of the strut injectors and distributions obtained from one-dimensional calculations. Measured duct heat load agrees with results of the one-dimensional calculations for moderate amounts of reaction, but is underestimated when large separated regions occur near the injection location. For the parallel injection strut, good agreement is obtained between the shape of the injected fuel distribution inferred from gas sample measurements at the duct exit and the distribution calculated with a multiple-jet mixing theory. The overall fraction of injected fuel reacted in the multiple-jet calculation closely matches the amount of fuel reaction necessary to match static pressure with the one-dimensional calculation. Gas sample measurements with the perpendicular injection strut also give results consistent with the amount of fuel reaction in the one-dimensional calculation.

Anderson, G. Y.↗

NASA NTRS1973

Experimental hingeless rotor characteristics at low advance ratio with thrust

An experimental investigation to determine the dynamic characteristics of a hingeless rotor operating at moderate to high lift was conducted on a small scale, 7.5-foot diameter, four-bladed hingeless rotor model in a 7 x 10-foot wind tunnel. The primary objective of this research program was the empirical determination of the rotor steady-state and frequency responses to swashplate and body excitations. Collective pitch was set from 0 to 20 degrees, with the setting at a particular advance ratio limited by the cyclic pitch available for hub moment trim. Advance ratio varied from 0.00 to 0.36 for blades with nondimensional first-flap frequencies at 1.15, 1.28 and 1.33 times the rotor rotation frequency. Several conditions were run with the rotor operating in the transition regime. Rotor response at high lift is shown to be generally nonlinear in this region. As a secondary objective an experimental investigation of the rotor response to 4/revolution swashplate excitations at advance ratios of 0.2 to 0.85 and at a nondimensional, first-flap modal frequency of 1.34 was also conducted, using the 7 x 10-foot wind tunnel. It is shown that 4/revolution swashplate inputs are a method for substantially reducing rotor-induced, shafttransmitted vibratory forces.

London, R. J.↗

NASA NTRS1973

Energy storage using high pressure electrolysis and methods for reconversion

Theoretical and experimental studies on high pressure electrolysis producing hydrogen and oxygen for energy storage and reconversion are reported. Moderate temperature, high pressure hydrogen/oxygen fuel cells with nickel electrodes are investigated for effects of pressure, temperature, and membrane porosity. Test results from an aphodid burner turbine generator combination obtained 40 percent kilowatt hours out of the fuel cell divided by kilowatt hours into the electrolyzer. It is concluded that high pressure hydrogenation of organic materials can be used to synthesize hydrozenes and methanes for making synthetic vehicular fuels.

Hughes, W. L.↗

NASA NTRS1974

Computer study of emergency shutdowns of a 60-kilowatt reactor Brayton space power system

A digital computer study of emergency shutdowns of a 60-kWe reactor Brayton power system was conducted. Malfunctions considered were (1) loss of reactor coolant flow, (2) loss of Brayton system gas flow, (3)turbine overspeed, and (4) a reactivity insertion error. Loss of reactor coolant flow was the most serious malfunction for the reactor. Methods for moderating the reactor transients due to this malfunction are considered.

Tew, R. C.↗