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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A method of limit point calculation in finite element structural analysis

An approach is presented for the calculation of limit points for structures described by discrete coordinates, and whose governing equations derive from finite element concepts. The nonlinear load-displacement path of the imperfect structure is first traced by use of a direct iteration scheme and the determinant of the governing algebraic equations is calculated at each solution point. The limit point is then established by extrapolation and imposition of the condition of zero slope of the plot of load vs. determinant. Three problems are solved in illustration of the approach and in comparison with alternative procedures and test data.

Gallagher, R. H.↗
NASA NTRS1972

Investigation of the epoch state filter

A navigation filtering technique has been formulated using as state variables the initial or epoch position and velocity of the spacecraft. The estimate of this initial state is then improved by filtering new measurements. The current state may be obtained by a conic extrapolation of the epoch state. Results of a digital computer simulation of the epoch state filter show that this formulation of the navigational problem results in less computer run time and less computer storage space than conventional techniques. The errors produced by this technique have been demonstrated to be comparable to those obtained by conventional maximum-likelihood filtering.

Edwards, J. A.↗
NASA NTRS1971

Flow and criticality in the open cycle gas core.

A series of flowing gas experiments using air, argon, and freon has been conducted in Idaho. The purpose is to study methods of obtaining flow patterns which would create maximum possible system reactivity consistent with an acceptably low uranium to coolant-gas loss ratio. These have been conducted on both ?two-dimensional' and truly three-dimensional spherical configurations of diameters 18 to 42 inches. The larger diameter is that proposed for a minimum cost flowing gas critical experiment, and the size extremes make extrapolations to the large 6 and 8 foot diameter configurations more reliable. Results show that large enough inner gas (fuel) volume fractions can be achieved to attain criticality.

Kunze, J. F.↗
NASA NTRS1971

Kinetic limitations on the diffusional control theory of the ablation rate of carbon.

It is shown that the theoretical maximum oxidation rate is limited in many cases even at temperatures much higher than 1650 deg K, not by oxygen transport, but by the kinetics of the carbon-oxygen reaction itself. Mass-loss rates have been calculated at air pressures of 0.01 atm, 1 atm, and 100 atm. It is found that at high temperatures the rate of the oxidation reaction is much slower than has generally been assumed on the basis of a simple linear extrapolation of Scala's 'fast' and 'slow' rate expressions. Accordingly it cannot be assumed that a transport limitation inevitably must be reached at high temperatures.

Maahs, H. G.↗
NASA NTRS1972

Externally-blown-flap noise.

Noise data were obtained with a large externally blown flap model. A fan-jet engine exhaust was simulated by a 1/2-scale bypass nozzle supplied by pressurized air. The nozzle was pylon mounted on a wing section having a double-slotted flap for lift augmentation. Noise radiation patterns and spectra were obtained for nozzle exhaust velocities between 400 and 1150 ft/sec. The blown flap noise data are in good agreement with previous small model results extrapolated to test conditions by Strouhal scaling. The results indicate that blown flap noise must be suppressed to meet STOL aircraft noise goals.

Dorsch, R. G.↗
NASA NTRS1971

Computer simulation of the thermal environment of large-scale integrated circuits - Computer time-saving techniques.

This paper is concerned with the computer costs for both the steady-state and transient thermal responses of large-scale integrated circuits (LSI) when metal is present within the substrate. For the more cost-sensitive transient case, an extrapolation technique for computer time savings is compared with the accuracy loss in this study. This approach could be useful for design-cost planning.

Thompson, R. R.↗
NASA NTRS1972

Small-scale wind shear definition for aerospace vehicle design.

Rawinsonde wind profile data provide adequate wind shear information for vertical height intervals greater than 1 km. To specify wind shears for intervals below 1 km for space vehicle design, detailed wind-profile information like that provided by the FPS-16 Radar/Jimsphere system or an extrapolation procedure is required. This paper is concerned with the latter alternative. It is assumed that any realization from an ensemble of wind profiles can be represented in terms of a Fourier integral. This permits the calculation of the ensemble standard deviation and mean of the corresponding shear ensemble for any altitude and shear interval in terms of the power spectrum of the ensemble of wind profiles. The results of these calculations show that the mean and standard deviation of the wind shear ensemble, as well as the wind shear for any percentile, asymptotically behave like the vertical interval to the 0.7 power. This result is in excellent agreement with shear data from Cape Kennedy, Fla.

Fichtl, G. H.↗
NASA NTRS1972

Carbon-like spectra of Sc XVI, Ti XVII, and V XVIII in the range 16-22 A.

The spectra reported are important for the analysis of the spectra of CaXV and FeXXI. The extreme UV solar spectrum should contain some lines of these two ions. The spectroscopic source consisted of a low-inductance vacuum spark with electrodes made of the elements under investigation. Altogether 44 new lines in the region from 16 to 22 A were classified. Some previously unidentified lines of ClXII and ArXIII were also classified. The extrapolation of the ground-configuration energy levels is discussed.

Goldsmith, S.↗
NASA NTRS1971

Martian cratering. II - Asteroid impact history.

This paper considers the extent to which Martian craters can be explained by considering asteroidal impact. Sections I, II, and III of this paper derive the diameter distribution of hypothetical asteroidal craters on Mars from recent Palomar-Leiden asteroid statistics and show that the observed Martian craters correspond to a bombardment by roughly 100 times the present number of Mars-crossing asteroids. Section IV discusses the early bombardment history of Mars, based on the capture theory of Opik and probable orbital parameters of early planetesimals. These results show that the visible craters and surface of Mars should not be identified with the initial, accreted surface. A backward extrapolation of the impact rates based on surviving Mars-crossing asteroids can account for the majority of Mars craters over an interval of several aeons, indicating that we see back in time no further than part-way into a period of intense bombardment. An early period of erosion and deposition is thus suggested. Section V presents a comparison with results and terminology of other authors.

Hartmann, W. K.↗
NASA NTRS1972

Formulation of an effective safety design review for the Skylab Program.

The Skylab Program is presenting a unique set of requirements by extending the capabilities of both men and equipment to withstand extended periods of time in space. The progression of space programs which preceded Skylab have provided a set of building blocks of knowledge and experience coupled with an extensive ground test program which makes it possible to plan its flight program without earlier, unmanned test flights. This approach, however, makes it mandatory that to the maximum extent possible, we factor into the design review process all the 'lessons learned' which are applicable. It is this conscious review of the Skylab design, based on checklists prepared from design criteria, gleaned from a variety of sources and experiences, which is the subject of this paper. A brief description of the Skylab Program, its objectives, and the missions planned for it are presented briefly to better understand the degree of extrapolation of hardware development from previous programs.

Cohen, H.↗
NASA NTRS1971

The University of Virginia superconducting magnetic suspension and balance facility.

Description of a prototype facility comprising a superconducting magnetic suspension and balance and a supersonic wind tunnel. This facility was developed with the objectives of establishing the feasibility of applying the three-component magnetic balance concept to dynamic stability studies, and investigating design concepts and parameters that are critical for extrapolation to large-scale systems. Many important design and operational aspects, as well as safety considerations, are dictated by the cryogenic nature of this advanced-technology facility. Results of initial tests demonstrate that superconductors can be utilized safely and efficiently for wind-tunnel magnetic suspensions. At the present stage of development of this facility, controlled one-dimensional support of a spherical model has been achieved.

Zapata, R. N.↗
NASA NTRS1972

A calibration model for a stellar photometer using a SEC vidicon.

Description of a SEC vidicon response model that was used to calculate intensities of stars in the ultraviolet. The tube was used only as a stellar filter photometer. The model proposed is applicable for point sources. Experiments with both curve- or surface-fitting techniques and with extrapolation-interpolation procedures were conducted. The curve-fitting techniques were not successful, and the target gain was calculated with the aid of interpolation techniques.

Deutschman, W. A.↗
NASA NTRS1972

Grid-translation beam deflection systems for 5-cm and 30-cm diameter Kaufman thrusters.

A 5-cm grid translation mechanism has been developed capable of 10-deg beam deflection. A 2026-hour endurance test was run at a preset 10-deg deflection angle, and an extrapolated lifetime of better than 10,000 hours was obtained. Response time data for grid translation are presented. Preliminary results for a 30-cm diameter system are given, and results of a theoretical analysis of a dished grid system are discussed.

Lathem, W. C.↗
NASA NTRS1972

Dynamic response analysis of geometrically non-linear structures subjected to high impact.

Description of an efficient digital computer method for the determination of the propagation of elastic stresses and deformations in certain geometrically nonlinear structures subjected to high impact loading. The finite-element matrix displacement approach utilizing curved quadrilateral shell elements in conjunction with a nodewise predictor-corrector method employing Runge-Kutta extrapolation techniques has been adopted for the present solution. The related computer program written in FORTRAN V for the UNIVAC 1108 computer has proved to be effective for the solution of a range of practical problems including rectangular and cylindrical panels. Numerical results are presented for a relevant structure, the cell container, and the negative electrode of an impact-resistant battery subjected to high impact, simulating its free landing on a planetary surface.

Gupta, K. K.↗
NASA NTRS1972

EEG monitoring of a free-swimming diver at a working depth of 15 meters.

Feasibility has been shown for underwater transmission of physiological signals, using frequency modulation of carriers transmitted by return-current-density methods, as part of a personal biotelemetry system. In the prototype system, a standard IRIG subcarrier frequency (2300 Hz) was used. Power requirements, antenna design, and signal attenuation are compatible with free-ranging diving activity at distances up to 15 meters from the receiver. Extrapolation from this study and further developments are expected to substantially increase the range. Advantages of this system include subcarrier compatibility with standard IRIG demodulators using channels 1 through 10, the absence of highly specialized antenna requirements, and reasonable attenuation characteristics for transmission through the turbidity of typical seawater. Moreover, the system would not appear to be depth limited, and to be compatible with use of high-powered transponders of the same type for long-distance transmission, with or without further encoding.

Zweizig, J. R.↗
NASA NTRS1971

Calibration of solar cells using high-altitude aircraft.

A high altitude airplane has been used to obtain the outer space short circuit current of solar cells. The solar cells are mounted in a collimating tube and are measured at approximately 5000 foot intervals between 12,000 and 47,000 feet. The air mass is calculated for each altitude using the standard formula and the resulting curve is extrapolated to air mass zero. The effects on the solar cell output of a haze layer located at the tropopause has been observed. It is necessary to fly above this layer to ensure accurate results. Airplane calibrations of several primary standard cells calibrated on high altitude balloons show agreement within 0.5 per cent. Prediction of the output of satellite power supplies using airplane calibrated cells shows an accuracy of better than 1 per cent.

Brandhorst, H. W., Jr.↗
NASA NTRS1972

Abrasion and catastrophic rupture of lunar rocks - Some implications to the micrometeoroid flux at 1 AU.

Results from laboratory studies of hypervelocity impact against crystalline rocks, combined with estimates of the micrometeoroid flux at the lunar surface, provide a basis for calculating abrasion rates and survival times before catastrophic rupture of rocks on the lunar surface. The surface residence times observed for lunar rocks of the order of 10 m.y. (derived from the track densities of iron group nuclei) restrict the mass range of impacting particles of interest to masses less than about 1.01 gram. Extrapolation downward to smaller masses following flux distributions suggested by early satellite data and photographic meteor observations leads to absurd rates of abrasion. Consistent with the observed crater populations on the lunar rocks and with the Pegasus, Explorer, and Pioneer satellite data, the slope of the mass-flux distribution must decrease markedly for masses below 1 to .1 microgram.

Gault, D. E.↗
NASA NTRS1972

High resolution spectra of Venus.

The existing high resolution spectra of Venus show considerable variations in the abundance of CO2. As this is the major constituent of the atmosphere, these day-to-day variations indicate the effective reflecting cloud layer is undergoing substantial vertical displacements over a relatively short time scale. The published observations indicate that CO is uniformly mixed with the CO2, but that the lines of HF may be formed deeper in the atmosphere and HCl lines considerably deeper. These conclusions are based on extrapolations of laboratory measurements and could be considerably altered by new laboratory measurements made under conditions similar to those near the tropopause in Venus.

Young, L. D. G.↗