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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Polynomial weights and code constructions.

Study of certain polynomials with the 'weight-retaining' property that any linear combination of these polynomials with coefficients in a general finite field has Hamming weight at least as great as that of the minimum-degree polynomial included. This fundamental property is used in applications to Reed-Muller codes, a new class of 'repeated-root' binary cyclic codes, two new classes of binary convolutional codes derived from binary cyclic codes, and two new classes of binary convolutional codes derived from Reed-Solomon codes.

Massey, J. L.↗
NASA NTRS1972

Some surface characteristics and gas interactions of Apollo 14 fines and rock fragments.

Comprehensive survey of the physical surface characteristics of Apollo 14 fines, two fragments of a breccia (14321), and a crystalline rock (14310). The survey was carried out with optical and both scanning and transmission electron microscopy and by studying the adsorption of a variety of gases including nitrogen, hydrogen, and water vapor. Our objective in the optical microscope study was to relate the visible geological and petrological features to the surface properties. Electron microscopy particularly helped relate surface roughness and particle fusion to gas adsorption and pore structure. The fine sample (14163,111) had a surface area of 0.210 sq m/g and a helium density of 2.9 g/cc. Similar values have been observed with breccia fragments. Other observations include physical adsorption of molecular hydrogen at low temperatures and of water vapor at ambient temperatures. It is concluded that these particular lunar materials, while capable of adsorbing water vapor, do not retain it for any significant time at low pressures, nor, under lunar conditions, is there any indication of absorption or penetration.

Cadenhead, D. A.↗
NASA NTRS1973

An improved separability approximation for line radiative transport in nonhomogeneous media.

A simple modification to the constant half-width approximation of Wilson and Greif, which is an extension of the well-known Curtis-Godson method to the treatment of temperature variations along the integration path, is introduced which permits a more accurate evaluation of line radiative transport in nonhomogeneous gases. To demonstrate the method's accuracy, comparisons are made with Wilson and Greif and numerical frequency integrated results for the line equivalent width and radiative flux in a planar slab with prescribed Planck function and line half-width spatial variations. These variations are chosen to represent typical shock layer conditions. It is found that the modified procedure reduces the inaccuracies inherent in Wilson and Greif's approximation by factors ranging from 5 to 10, while retaining the latter method's ease of application.

Boughner, R. E.↗
NASA NTRS1973

Differential transformation for satellite injection.

This paper provides an analytical method for computing the required orbital inclination change when the nominal orbital node rate is slightly modified to meet satellite mission requirements. A first-order theory retaining up to J sub 2 terms of the earth-oblateness perturbation has been found adequate to generate a four-decimal digit accuracy for required orbital changes. A numerical example of an actual ITOS series prelaunch analysis has been given to illustrate computational steps.

Sugai, I.↗
NASA NTRS1973

On the question of adequate hingeless rotor modeling in flight dynamics.

The somewhat controversial question of which elastic blade modes are essential in the flight mechanics of hingeless rotorcraft is studied on the basis of quasi-steady linear aerodynamics including reversed flow effects and uniform inflow. The modes are for the rotating blade, and intermode aerodynamic coupling terms are retained. The criteria for judging elastic mode effects include 19 hub moment and force derivatives, rotor trim data, rotor stability charts for lagged hub moment feedback, step gust and random gust responses. Fixed hub and constant chord blades with widely differing elasticity and inertia and with moderate twist are assumed.

Hohenemser, K. H.↗
NASA NTRS1973

Response of a rigid aircraft to nonstationary atmospheric turbulence.

The plunging response of an aircraft to a type of nonstationary turbulent excitation is considered. The latter consists of stationary Gaussian noise modulated by a well-defined envelope function. The intent of the investigation is to model the excitation experienced by an airplane flying through turbulence of varying intensity and to examine the influence of intensity variations on exceedance frequencies of the gust velocity and the airplane's plunging velocity and acceleration. One analytical advantage of the proposed model is that the Gaussian assumption for the gust excitation is retained. The analysis described herein is developed in terms of an envelope function of arbitrary form; however, numerical calculations are limited to the case of harmonic modulation.

Verdon, J. M.↗
NASA NTRS1973

Radiative property degradation of water impinging on thermally-controlled surfaces under space conditions.

Review of the results of an investigation aimed at determining experimentally the directional monochromatic reflectance changes caused under high-vacuum space conditions by a water spray impinging on thermally controlled surfaces consisting of three paint specimens (Z93, S13G, and 92-007) and an aluminum foil. The first two paints and the aluminum foil suffered considerable physical damage, but only small changes resulted in the reflectance of the paints while the reflectance of the aluminum foil decreased with increase in exposure time to the water jet. Only the 92-007 Dow Corning paint retained the same physical and reflective characteristics.

Maples, D.↗
NASA NTRS1973

A stochastic model of the galactic magnetic field.

Existing stochastic models of the galactic magnetic field are considered and found to suffer certain defects. A new model is proposed which overcomes faults of the previous theories while retaining their strenghts.

Kaiser, T. B.↗
NASA NTRS1973

An approach to the synthesis of separate surface automatic flight control systems.

A method is presented for the analysis of separate surface automatic flight control systems. The feasibility of such systems is demonstrated by the analysis of an example system, a separate surface wing-leveler for a Cessna 172. This example system employs a separate surface aileron with 15% of the basic airplane roll control power. A 90% reduction in bank-angle gust response can be obtained when compared with the basic airplane. The system does not feed back to the pilot's wheel. When failed (even hardover) the pilot retains more than adequate control of the airplane.

Roskam, J.↗
NASA NTRS1972

Studies of the performance of W-Re type thermocouples.

The effect of exposure of bare-wire and BeO-insulated commercial W-Re thermocouple materials to high temperatures in gaseous environments was investigated. The temperature range of interest was primarily 2000 to 2400 K, and the investigations were confined to thermocouple wires of 0.25 mm diameter. Thermoelements were examined for metallurgical structural changes and chemical changes by conventional methods. In the temperature range of interest, grain growth was inhibited in the chemically doped W-3% Re alloy, and excellent room-temperature ductility was retained subsequent to the exposure. The compatibility of high purity (in excess of 99.8%), sintered BeO insulators with the thermoelements differed, depending upon whether the BeO-insulated thermoelement assemblies were self-heated electrically or heated in a furnace; in tests in argon environments, highly reliable performance occurred when the assemblies were heated in a furnace. BeO-insulated W-3% Re vs W-25% Re thermocouples, constructed with degassed and aged materials, exhibited drifts equivalent to about 3 mK/hr during 1000 hours of exposure at 2073 K in argon while in the presence of tantalum.

Burns, G. W.↗
NASA NTRS1973

Remote measurement of salinity in an estuarine environment.

The microwave emission of sea water is dependent upon salinity in the low microwave spectrum, and it appears possible to measure remotely surface salinity at 21-cm wavelength with an accuracy up to one part salt per thousand parts water (.1%) for a .5 to 3.5% salinity range. The dielectric constant of sea water can be represented by that of NaCl, except that the sea water conductivity is retained. The effects of the atmosphere, cosmic noise, sea surface roughness, and constant radiometer errors can be corrected by using surface calibration measurements. In experiments performed in Mississippi and Louisiana coastal waters salinity accuracies of .3 to .5 were obtained. It is believed that the accuracy was limited by the radiometer used.

Thomann, G. C.↗
NASA NTRS1973

Higher order Compton-Getting anisotropies.

The Compton-Getting effect relates the distribution function of a particle population in a given frame of reference to that in another frame, moving at constant velocity V relative to the first. A study is made of the effects that arise when, contrary to previous assumptions, second-order terms in (V/v), where v is the particle velocity, are retained, and when the given distribution function is not isotropic. The importance of the extra terms is then examined in the specific case of low-energy solar protons in interplanetary space.

Balogh, A.↗
NASA NTRS1974

Propellant acquisition device for use with a spinning toroidal tank

System consists of four radially disposed communication channels attached to propellant-retaining ring situated at bottom of toroidal tank. Ring-and-channel acquisition system design provides uniform propellant distribution within spinning tank during all mission phases.

Anderson, J. E.↗
NASA NTRS1973

A computer program to calculate zeroes, extrema, and interval integrals for the associated Legendre functions

A computer program is described for the calculation of the zeroes of the associated Legendre functions, Pnm, and their derivatives, for the calculation of the extrema of Pnm and also the integral between pairs of successive zeroes. The program has been run for all n,m from (0,0) to (20,20) and selected cases beyond that for n up to 40. Up to (20,20), the program (written in double precision) retains nearly full accuracy, and indications are that up to (40,40) there is still sufficient precision (4-5 decimal digits for a 54-bit mantissa) for estimation of various bounds and errors involved in geopotential modelling, the purpose for which the program was written.

Payne, M. H.↗
NASA NTRS1973

Intermediate energy proton-deuteron elastic scattering

A fully symmetrized multiple scattering series is considered for the description of proton-deuteron elastic scattering. An off-shell continuation of the experimentally known twobody amplitudes that retains the exchange symmeteries required for the calculation is presented. The one boson exchange terms of the two body amplitudes are evaluated exactly in this off-shell prescription. The first two terms of the multiple scattering series are calculated explicitly whereas multiple scattering effects are obtained as minimum variance estimates from the 146-MeV data of Postma and Wilson. The multiple scattering corrections indeed consist of low order partial waves as suggested by Sloan based on model studies with separable interactions. The Hamada-Johnston wave function is shown consistent with the data for internucleon distances greater than about 0.84 fm.

Wilson, J. W.↗
NASA NTRS1973

Energy distribution in parallel plate plasma accelerators

A parallel plate accelerator operated in the quasi-steady regime of argon mass flow discharges permits, on account of its geometry, the appraisal of the initial ratio of energy disposition into the kinetic and thermal modes of the plasma while retaining the essential features of coaxial high power self-field MPD accelerators. The energy disposition ratio, calculated as the ratio of kinetic energy to enthalpy in the exhaust flow, shows reasonable agreement with the ratio of the induced emf in the accelerator to resistive voltage drop. Both these ratios indicate that the discharge imparts more energy to the flow by resistive heating than by direct body force acceleration. This is turn suggests that other acceleration mechanisms must be responsible for the high performance of conventional MPD arcs.

Dicapua, M. S.↗
NASA NTRS1972

The origin and chemical composition of the earth's core

The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.

Murthy, V. R.↗