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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A Comparison of Quartz Crystal Microbalance Measurements with Mass Spectrometer Determinations

An experimental program was undertaken in which mass accretion rates, as determined by a liquid nitrogen cooled quartz crystal microbalance, were compared with the mass flux rates, as determined by both a cycloidal type and a quadrupole type residual gas analyzer for five simple materials. The data indicate a high degree of correlation between these instruments insofar as the shape of the curves. There are large variations however among the absolute values.

Kruger, R.↗
NASA NTRS1971

An Empirical Method for Determining the Lunar Gravity Field

A method has been devised to determine the spherical harmonic coefficients of the lunar gravity field. This method consists of a two-step data reduction and estimation process. In the first step, a weighted least-squares empirical orbit determination scheme is applied to Doppler tracking data from lunar orbits to estimate long-period Kepler elements and rates. Each of the Kepler elements is represented by an independent function of time. The long-period perturbing effects of the earth, sun, and solar radiation are explicitly modeled in this scheme. Kepler element variations estimated by this empirical processor are ascribed to the non-central lunar gravitation features. Doppler data are reduced in this manner for as many orbits as are available. In the second step, the Kepler element rates are used as input to a second least-squares processor that estimates lunar gravity coefficients using the long-period Lagrange perturbation equations.

Ferrari, A. J.↗
NASA NTRS1972

Flight-determined derivatives and dynamic characteristics of the CV-990 airplane

Flight-determined longitudinal and lateral-directional stability and control derivatives are presented for the CV-990 airplane for various combinations of Mach number, altitude, and flap setting throughout the flight envelope up to a Mach number of 0.87. Also presented are the dynamic characteristics of the aircraft calculated from the flight-obtained derivatives and the measured phugoid characteristics. The derivative characteristics were obtained from flight records of longitudinal and lateral-directional transient oscillation maneuvers by using a modified Newton-Raphson digital derivative determination technique. Generally the derivatives exhibited consistent variation with lift coefficient in the low-speed data and with Mach number and altitude in the high-speed data. Many also varied with flap deflection, notably spoiler effectiveness and directional stability.

Gilyard, G. B.↗
NASA NTRS1972

Development of a method for the determination of iodine in spacecraft potable water

A one-reagent indicator solution has been prepared for the analysis of iodine concentrations in the range of 0.5 to 12 mg/1 of I2 for use on the potable water proposed for the Skylab project. The indicator solution was formulated to contain the minimum concentrations of reagents for optimum analytical performance. Performance tests indicated that the reagent is stable for at least six months and is reliable for the determination of I2 under a variety of conditions of I(-) concentrations and sample temperatures. Visual estimations as low as 0.5 mg/1 were obtained without difficulty and the stability of the developed color allows visual determinations from 0.5 to 12 mg/1 of I2 with a relatively small error.

Whittle, G. P.↗
NASA NTRS1972

Heat transfer rate distribution on North American Rockwell delta wing orbiter determined by phase change paint technique at a Mach number of 8, volume 1

The results of a wind tunnel test program to determine aerodynamic heat transfer distributions on an orbiter configuration are presented. Heat-transfer rates were determined by the phase change paint technique on 0.013-scale Stycast models using Tempilaq as the surface temperature indicator. The nominal test conditions were; Mach 8, length Reynolds numbers of 6.0 x 1 million and 8.9 x 1 million, and angles of attack from 10 to 50 deg in 10-deg increments. At the higher Reynolds number, data were obtained with and without boundary layer trips. Model details, test conditions, and reduced heat-transfer data are presented. Data reduction of the phase-change paint photographs was performed by utilizing a new technique which is described in the data presentation section.

Matthews, R. K.↗
NASA NTRS1972

Heat transfer rate distributions on McDonnell-Douglas booster determined by phase change technique for nominal Mach number of 8

The results of a wind tunnel test program to determine aerodynamic heat transfer distributions on the McDonnell Douglas Booster configuration are presented. Heat-transfer rates were determined by the phase-change paint technique on 0.009-scale Stycast models using Tempilaq as the surface temperature indicator. The nominal test conditions were; Mach 8, length Reynolds numbers 5 million and 7.3 million, and angles of attack of 40, 50, and 60 deg. At the higher Reynolds number, data were obtained with and without boundary layer trips. Model details, test conditions, and reduced heat-transfer data are presented. Data reduction of the phase-change paint photographs was performed by utilizing a new technique which is described.

Matthews, R. K.↗
NASA NTRS1972

A shielding application of perturbation theory to determine changes in neutron and gamma doses due to changes in shield layers

The perturbation theory for fixed sources was applied to radiation shielding problems to determine changes in neutron and gamma ray doses due to changes in various shield layers. For a given source and detector position the perturbation method enables dose derivatives due to all layer changes to be determined from one forward and one inhomogeneous adjoint calculation. The direct approach requires two forward calculations for the derivative due to a single layer change. Hence, the perturbation method for obtaining dose derivatives permits an appreciable savings in computation for a multilayered shield. For an illustrative problem, a comparison was made of the fractional change in the dose per unit change in the thickness of each shield layer as calculated by perturbation theory and by successive direct calculations; excellent agreement was obtained between the two methods.

Fieno, D.↗
NASA NTRS1972

Nonlinear least squares - An aid to thermal property determination

Nonlinear least squares techniques can be used to determine effective thermal conductivity values from experimental data. Comparisons between measured and predicted conductivity values indicate that the analytically determined values can be used with confidence in performing thermal protection system analyses. A study was performed to compare the relative efficiencies of different minimizing techniques; techniques; the method of Peckham was the most efficient.

Curry, D. M.↗
NASA NTRS1972

An approach to attitude determination for a spin-stabilized spacecraft (IMP 1)

The analysis and the FORTRAN program are presented for the determination of attitude of a spin-stabilized spacecraft. The use of telemetry data that provide information about two reference vectors and their relation to the spin is outlined. A technique for the determination of the spin-axis orientation that employs only simple calculations is described.

Fang, A. C.↗
NASA NTRS1972

Nonlinear estimation theory applied to orbit determination

The development of an approximate nonlinear filter using the Martingale theory and appropriate smoothing properties is considered. Both the first order and the second order moments were estimated. The filter developed can be classified as a modified Gaussian second order filter. Its performance was evaluated in a simulated study of the problem of estimating the state of an interplanetary space vehicle during both a simulated Jupiter flyby and a simulated Jupiter orbiter mission. In addition to the modified Gaussian second order filter, the modified truncated second order filter was also evaluated in the simulated study. Results obtained with each of these filters were compared with numerical results obtained with the extended Kalman filter and the performance of each filter is determined by comparison with the actual estimation errors. The simulations were designed to determine the effects of the second order terms in the dynamic state relations, the observation state relations, and the Kalman gain compensation term. It is shown that the Kalman gain-compensated filter which includes only the Kalman gain compensation term is superior to all of the other filters.

Choe, C. Y.↗
NASA NTRS1972

A multispectral method of determining sea surface temperatures

A multispectral method for determining sea surface temperatures is discussed. The specifications of the equipment and the atmospheric conditions required for successful multispectral data acquisition are described. Examples of data obtained in the North Atlantic Ocean are presented. The differences between the actual sea surface temperatures and the equivalent blackbody temperatures as determined by a radiometer are plotted.

Shenk, W. E.↗
NASA NTRS1971

Precise laboratory determination of rotational transition frequencies in cyanoacetylene.

The results are discussed of a high-precision laboratory determination of the rotational constants and transition frequencies in the ground vibrational state of the linear molecule cyanoacetylene, discovered in the direction of the galactic center by Turner (1971). The values obtained make it possible to determine more precisely the interstellar cyanoacetylene velocities and to simplify the identification of additional interstellar rotational transitions.

De Zafra, R. L.↗
NASA NTRS1971

Astrodynamics. Volume 1 - Orbit determination, space navigation, celestial mechanics.

Essential navigational, physical, and mathematical problems of space exploration are covered. The introductory chapters dealing with conic sections, orientation, and the integration of the two-body problem are followed by an introduction to orbit determination and design. Systems of units and constants, as well as ephemerides, representations, reference systems, and data are then dealt with. A detailed attention is given to rendezvous problems and to differential processes in observational orbit correction, and in rendezvous or guidance correction. Finally, the Laplacian methods for determining preliminary orbits, and the orbit methods of Lagrange, Gauss, and Gibbs are reviewed.

Herrick, S.↗
NASA NTRS1972

Technique for rapid determination of relative ages of lunar areas from orbital photography.

Development of a technique for determining relative ages of regions of the lunar surface from orbital photography using a model of small-impact erosion. The erosion model relates the shape of a crater to the integrated flux of debris that has impacted the surface since that crater was fresh. The shape of the most modified crater of a particular diameter is thereby related to the relative age of the surface. Application of this analysis to orbital photography reveals that the major mare units vary in the accumulation of impacts by more than a factor of 3. Comparison of these data with crystallization ages determined from samples collected during the Apollo 11 and 12 missions indicates that the impact fluxes were decreasing during the stages of mare formation. An exponentially decaying flux for the last 3.5 b.y. with a half-life of 0.6 to 1.4 b.y. is compatible with the data.

Soderblom, L. A.↗
NASA NTRS1972

Determination of Van der Waals broadening at temperatures of astrophysical interest.

Discussion of the results of experiments analyzing the widths of shock-excited emission lines at temperatures of about 5000 K. The width of two neutral silicon lines (4102 and 5948 A) were measured as broadened by argon, and the shift of one of these lines (4102 A) was determined. Likewise, the width one of the lines of cesium (4593 A) was measured as broadened by argon and neon. These data are compared with other experimental data to determine the temperature dependence of the broadening. Significant disagreements with simple theory are found, the experimental values of the widths being larger than the theoretical values by factors of 1.5-2.

Evans, J. M., Jr.↗
NASA NTRS1972

A multispectral technique to determine sea surface temperature using Nimbus 2 data.

Three channels of the Nimbus 2 five-channel Medium Resolution Infrared Radiometer have been employed in the development of a technique to determine sea surface temperature. Two of the channels in the 0.2-4.0 and 6.4-6.9 micron spectral regions are used to indicate a cloud-free line of sight and the third, a high signal-to-noise window channel (10-11 microns), measures the equivalent blackbody temperature (Tbb) which is a function of the thermal emission from the sea surface and the intervening atmosphere. Equivalent blackbody temperatures and normalized reflectance thresholds were established using frequency distributions from the 6.4-6.9 and 0.2-4.0 micron channels, respectively, to determine the existence of cloud-free conditions. The window Tbb's were compared with ship ocean temperature measurements for a one-month period over the western North Atlantic. This comparison revealed a plus or minus 1.5 K dispersion about the mean difference between the ship temperatures and window Tbb's between 31-34 N.

Shenk, W. E.↗
NASA NTRS1972

The role of time-frequency in satellite position determination systems.

Tests were conducted by NASA on radio navigation satellite systems that employ the use of time-frequency determination. The satellites used for this purpose were the ATS 1 and 3, and the Nimbus 3 and 4. Several systems were tested in order to examine the feasibility of three satellite navigation concepts: (1) multiple satellite range measurements, (2) satellite range rate, or range and range rate measurements and (3) satellite angle measurements. Test results indicate that locations of ships and aircraft can be determined to within 3-5 km, one sigma, by these satellite methods, and that location accuracy is both a function of the RF employed and of the extent of knowledge of the satellite orbit.

Ehrlich, E.↗