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NASA NTRS1972

The nature of the Herbig Ae- and Be-type stars associated with nebulosity.

A quantitative spectrophotometric study of the Herbig Ae and Be stars associated with nebulosity demonstrates that the majority have surface gravities appropriate to pre-main-sequence stars while the remainder have surface gravities characteristic of the zero-age main seee. This evidence, along with their gross spectroscopic and pc similarity to T Tauri-like stars and the fact that all these stars appear to be surrounded by circumstellar dust, places them among the youngest known stellar objects. The geometry of the circumstellar shells is discussed and the evidence seems to favor a nonspherical, possibly disklike shape. Finally, photographs taken with a 1-micron image-tube system reveal a large number of red stellar objects surrounding many of these stars. This suggests that the Herbig Ae and Be objects may be the brightest representatives of very recently formed stellar groups.-

Strom, S. E.↗

NASA NTRS1972

Effects of electrostatic rocket material deposited on solar cells.

If solar arrays on solar-electric spacecraft protrude into the exhaust hemisphere of the electric thrusters, they will receive fluxes (usually small) of both propellant and accelerator grid atoms. Unlike propellants, grid materials have low vapor pressures and will not reevaporate. An analysis is presented of degradation in the optical, thermal, and electrical performance of solar cells resulting from thin deposits of grid material (aluminum and molybdenum) on various array surfaces. The classical optical theory of thin films, heat balance equations, and a typical relationship for solar cell efficiency vs temperature are used to compute curves showing optical properties, temperature, and power output as functions of film thickness. The results compare favorably with available experimental data. It is shown that a few monolayers of metal deposition on the illuminated surface will seriously degrade cell performance. A means of estimating the arrival rate of these materials is provided.

Kemp, R. F.↗

NASA NTRS1972

U, Th, Pb and REE abundances and Pb 207/Pb 206 ages of individual minerals in returned lunar material by ion microprobe mass analysis.

Results of ion microprobe analyses of Apollo 11, 12 and 14 material, showing that U, Th, Pb and REE are concentrated in accessory minerals such as apatite, whitlockite, zircon, baddeleyite, zirkelite, and tranquillityite. Th/U ratios are found to vary by over a factor of 40 in these minerals. K, Ba, Rb and Sr have been localized in a K rich, U and Th poor glass phase that is commonly associated with the U and Th bearing accessory minerals. Li is observed to be fairly evenly distributed between the various accessory phases. The phosphates have been found to have REE abundance patterns (normalized to the chondrite abundances) that are fairly flat, while the Zr bearing minerals have patterns that rise steeply, by factors of ten or more, from La to Gd. All the accessory minerals have large negative Eu anomalies. Radiometric age dates (Pb 207/Pb 206) of the individual U and Th bearing minerals compare favorably with the Pb 207/Pb 206 age of the bulk rocks.

Andersen, C. A.↗

NASA NTRS1972

Oscillatory burning of solid propellants including gas phase time lag.

An analysis has been performed for oscillatory burning of solid propellants including gas phase time lag. The gaseous flame is assumed to be premixed and laminar with a one-step overall chemical reaction. The propellant is assumed to decompose according to the Arrenhius Law, with no condensed phase reaction. With this model, strong gas phase resonance has been found in certain cases at the characteristic gas-phase frequencies, but the peaking of the acoustic admittance is in the direction favoring the damping of pressure waves. At still higher frequencies, moderate wave-amplifying ability was found. The limit of low frequency response obtained previously by Denison and Baum was recovered, and the limitations of the quasi-steady theory were investigated.

T'Ien, J. S.↗

NASA NTRS1972

X-ray emission from white dwarfs.

It is suggested that both the 250-eV background radiation and the recently observed variations in the optical emission from certain white dwarfs may be due to thermal bremsstrahlung from hot coronae surrounding such stars. The X-ray flux from the variable white dwarfs is predicted and in the most favorable case, R548, is sufficiently large to allow an observational test of the model. The possibility that the variations observed in strong X-ray sources are due to pulsations in the coronae surrounding degenerate stars, rather than in stars themselves, is also discussed. For the white dwarfs, both pulsation and rotation of the central star are found to be adequate sources of coronal energy, with pulsation being subject to relatively easy observational test. The energy requirements for the strong X-ray sources are briefly discussed.

Strittmatter, P. A.↗

NASA NTRS1972

Light-emission measurements of iron at simulated meteor conditions.

Ionization and spectral emission (3500-4200 A) cross-sections have been measured for FE + N2, O2 reactions between 350 and 2000 eV. Meteor luminous efficiencies from 3500 to 5400 A were calculated from these measurements. These results are thought to be accurate within plus or minus 40% for meteor velocities greater than 35 km/sec and at conditions where free molecular flow prevails. A general tendency is exhibited for a decrease in the luminous efficiency with increasing velocity. The present results compare favorably with previous meteor simulation experiments.

Boitnott, C. A.↗

NASA NTRS1972

The influence of laser ranging on selenodetic control.

In this paper, a mathematical model is presented which can be used to perform an adjustment using laser distances to improve coordinates of points of the earth and on the moon. The observation equations are given and the orientation of the earth and the moon is defined in terms of three Eulerian angles. Parameters related to the orientation of the two bodies are the six initial conditions in each case, for the numerical integration of the three angles and their time derivatives. Numerical experiments were performed for the purpose of investigating the expected accuracies of the various parameters in the adjustment model under differing conditions. The results of the experiments indicate that the statistics for both the coordinates of points on earth and on the moon, and for the orientation parameters of the two bodies, are favorable.

Mueller, I. I.↗

NASA NTRS1971

Coherent infrared receivers for laser communications and radar.

Review of infrared coherent detection processes. Three receivers are described which were built with the primary goal of exploiting quantum noise limited heterodyne detection in a spectral region where atmospheric transmission characteristics are favorable. The combination of high power, high efficiency carbon dioxide lasers, coherent heterodyne receivers with sensitivities approaching the quantum noise limit, and low-loss atmospheric transmission have presented new possibilities in infrared communications and radar. In particular, high sensitivity 10.6 micrometer heterodyne receivers with wide IF bandwidths have been developed.

Peyton, B.↗

NASA NTRS1972

Curved space cosmological bounds on the time variation of G.

Additional quantitative and revealing arguments are given in favor of author's previous suggestion (1971) that the introduction of pressure results in a decrease in the theoretical upper bound on the time variation of G, as predicted by the Brans-Dicke theory (1961) for Friedmann-type expanding cosmologies in flat space, and that this suggestion holds in curved spaces as well. Moreover, it is shown that the curvature contribution to G is of the same order of magnitude as the flat space contribution and adds to it or subtracts from it for positive or negative curvatures respectively.

Morganstern, R. E.↗

NASA NTRS1972

Experimental determination of three dimensional liquid rocket nozzle admittances.

The three dimensional nozzle admittance, an important parameter in combustion instability studies, was experimentally measured for several nozzle configurations. The admittance values were obtained using a modification of the classical impedance tube technique. The modified impedance tube method measures the admittance of a duct termination in the presence of one dimensional mean flow and three dimensional oscillations. Values of the nozzle admittance were obtained from pressure amplitude measurements taken at discrete points along the length of the tube. To determine the effects of nozzle geometry, nozzles were tested with half-angles of 15, 30, and 45 degrees and entrance Mach numbers of 0.08, 0.16, and 0.20. The admittance results are presented as functions of nondimensional frequency for mixed first tangential-longitudinal modes. These results are compared with available theoretical predictions and favorable agreement between theory and experiment is shown.

Zinn, B. T.↗

NASA NTRS1972

STOLports must be good neighbors.

Discussion of STOL aircraft and airport objectives, acceptance prerequisites, and realization requirements, and brief review of some STOL evaluation and feasibility studies performed by American Airlines. Ground, airport, and destination congestion and convenient STOLport location are examined as STOL-favoring factors, along with flight security and high-density routes. Approaches to neighborhood STOLport acceptance and the problem of STOL profit potential are given special attention.

Ransone, R. K.↗

NASA NTRS1972

Discrete-time demodulation of continuous-time signals.

Nonlinear stochastic estimation theory is applied to the problem of obtaining discrete-time demodulator structures for the common types of analog communication signals. A stochastic communication model is presented that can be treated with current results in estimation theory. Approximate algorithms are developed for the estimation problem that yield mathematically realizable receiver structures for the cases of AM, PC, and FM. The digital receivers yield performance characteristics that compare favorably with those of their analog counterparts.

Kelly, C. N.↗

NASA NTRS1972

Development of moldable carbonaceous materials for ablative rocket nozzles.

Description of a materials system developed for use as low-cost ablative nozzles for NASA's 260-in. solid rocket motor. Petroleum coke and carbon black fillers were employed; high density was achieved by controlling particle size distribution. An alumina catalyzed furfuryl ester resin which produced high carbon residues after pyrolysis was employed as the binder. Staple carbon fibers improved the strength and crack resistance of molded bodies. In static firing tests of two subscale nozzles, this material compared favorably in erosion rate with several other ablative systems.

Lockhart, R. J.↗

NASA NTRS1972

Parent-body models for the formation of iron meteorites.

The iron meteorites appear to have formed by both igneous and non-igneous processes in asteroid-sized parent bodies. Evidence regarding the IIIA-IIIB irons (the most common iron meteorite group) favors their having originated as a central core, which experienced fractional crystallization during solidification. A reevaluation of available data does not confirm earlier reports of variable cooling rates within group IIIA. Members of group IA-IB contain chondritic silicates, have short I-Xe formation intervals and do not show evidence of fractional crystallization. They appear to have formed nonigneously by inhomogeneous agglomeration and accretion of solar nebular condensates.

Wasson, J. T.↗

NASA NTRS1972

Attitude control of a spinning Skylab.

Active attitude control of a spinning Skylab is analyzed to determine a simple control law that will provide a satisfactory response, considering the dynamics of attached flexible appendages. A simplified model of the complex Skylab vehicle is selected to make it analytically tractable. The vehicle is modeled as a single rigid-core body with two attached flexible massless booms having masses on their tips. The equations of motion describing the attitude dynamics of the model are presented as a linear matrix-differential equation. The states of the vehicle are small perturbations about its steady-state spin. An analysis is performed to determine the domain of stability. Next, attitude dynamics are analyzed; both frequency domain (parameter plane) and time domain (an optimal linear quadratic loss program) techniques are compared. An analysis of the nonlinear effect of control torque saturation of Skylab's control moment gyroscopes is discussed. The results of the analysis compare favorably with a large-scale digital simulation of the Skylab.

Seltzer, S. M.↗

NASA NTRS1972

The octahedral shear strain theory and its relation to biaxial cumulative fatigue damage.

The octahedral shear strain range concept is used in analyzing multiaxial fatigue damage. Limited test data from a two-step loading sequence show that the loading effect is still pronounced in the multiaxial case and that the relation between damage and cycle ratio is nonlinear. Among uniaxial cumulative damage concepts, the modified multiaxial double linear damage rule seems to show the most favorable experimental results.

Zamrik, S. Y.↗

NASA NTRS1972

Correlation of liquid-film cooling mass transfer data.

An empirical correlation proposed by Gater and Ecuyer (1970) for liquid-film cooling mass transfer, accounting for film roughness and entrainment effects, is extended to include liquid films of arbitrary length. A favorable comparison between the predicted results and the experimental data of Kinney et al. (1952) and Emmons and Warner (1964) shows the utility of the mass transfer correlation for predictions over a wide range of experimental parameters.

Gater, R. A.↗

NASA NTRS1972

Visually directed pointing as a function of target distance, direction, and available cues.

In pointing at visual targets without sight of the hand, large errors occur. There is a tendency to overreach targets, and this tendency is much greater (about 25 cm) when convergence is the only cue to distance than when there are many cues (2 to 11 cm). Angular errors of up to 10 deg also occur. These tend to be to the side opposite the sighting eye, when the favored hand is used. The variance of the pointing response with convergence alone is reduced by approximately half with the introduction of several spatial cues. These results are interpreted as indicating that, for a target within the reach of the arm and with convergence alone as a cue, the depth signal produced by the visual system corresponds to a greater distance than that produced when many cues are available. The results are also consistent with the hypothesis that perceived direction tends to approximate direction from the sighting eye.

Foley, J. M.↗