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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 577 records · Page 32

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NASA NTRS1973

Instabilities in fissioning plasmas as applied to the gas-core nuclear rocket-engine

The compressional wave spectrum excited in a fissioning uranium plasma confined in a cavity such as a gas cored nuclear reactor, is studied. Computer results are presented that solve the fluid equations for this problem including the effects of spatial gradients, nonlinearities, and neutron density gradients in the reactor. Typically the asymptotic fluctuation level for the plasma pressure is of order 1 percent.

Source record↗

NASA NTRS1972

Optimal speed sharing characteristics of a series-hybrid bearing.

A series-hybrid bearing assembly consisting of a conical hydrostatic fluid-film bearing and a ball bearing is described. Computer studies are used to predict friction torque and life characteristics of a 150-mm ball bearing. A conical hydrostatic fluid-film bearing is designed for minimum friction and maximum speed reduction of the ball-bearing component of the series-hybrid bearing. At a thrust load of 4000 lb and speeds corresponding to DN (bearing bore in millimeters times shaft speed in rpm) values of 3 and 4 million, ball-bearing speed may be reduced to 30%. This speed reduction corresponds to ball-bearing fatigue life improvement factors of 3.4 at 3 million DN and 5.9 at 4 million DN. An oil flow rate at 18.2 lb/min is required to maintain a fluid-film thickness of 0.001 in. in the hydrostatic bearing.

Nypan, L. J.↗

NASA NTRS1973

Nonlinear analysis of phased-locked loops with rapidly varying phase

The performance of command and telemetry systems, useful in deep-space communications, is frequently affected by the radio-frequency phase error which is introduced at the point of reception by means of the carrier tracking loop. In low data rate communications, this phase error may vary rapidly over the duration of the signaling interval. In this paper such phase variation is characterized by a sinusoidal input phase, K sin (omega sub o t+, pi/6), which models a typical phase variation in communication over turbulent media. Conditions for synchronization stability and the acquisition behavior are examined by detailed computer study of the phase-plane trajectories for the second and third-order loops with perfect integrator. It is demonstrated that for the phase variation considered the third-order loop has no real advantage over the second-order loop. Finally, it is shown that nonzero initial conditions may result in large steady-state phase error.

Chen, C.↗

NASA NTRS1973

A study of morphology, provenance, and movement of desert sand seas in Africa, Asia, and Australia

The author has identified the following significant results. Recent acquisition of generally high quality color prints for most of the test sites has enabled the project to make significant advances in preparing mosaics of sand desert areas under study. Computer enhancement of imagery of selected sites, where details of complex dune forms need to be determined, has been achieved with arrival of computer-compatible ERTS-1 tapes. Further, a comparator, recently received, gives precise visual measurements of width, length, and spacing of sand bodies and so improves comparison of patterns in various test sites. Considerable additional meteorological data recently received on sand-moving winds in China, Pakistan, Libya and other areas enabled much progress to be made in developing overlays for the dune mosaics. These data show direction, speed, and frequency of winds. Other new data for use in preparing overlays used with ERTS-1 image mosaics include ground truth on moisture control, geologic settings, and plant distribution. With the addition of visual observation data and prints from hand-held photography now being obtained by the Skylab mission, much progress in interpreting the patterns of sand seas for 17 desert sites is anticipated.

Mckee, E. D.↗

NASA NTRS1973

Delta modulation

The overshoot suppression algorithm has been more extensively studied. Computer generated test-pictures show a radical improvement due to the overshoot suppression algorithm. Considering the delta modulator link as a nonlinear digital filter, a formula that relates the minimum rise time that can be handled for given filter parameters and voltage swings has been developed. The settling time has been calculated for the case of overshoot suppression as well as when no suppression is employed. The results indicate a significant decrease in settling time when overshoot suppression is used. An algorithm for correcting channel errors has been developed. It is shown that pulse stuffing PCM words in the DM bit stream results in a significant reduction in error length.

Schilling, D. L.↗

NASA NTRS1974

Experimental low-speed and calculated high-speed aerodynamic characteristics of a hypersonic research airplane concept having a 65 deg swept delta wing

An experimental wind-tunnel investigation has been carried out to determine the static longitudinal, lateral, and directional stability and control characteristics of a model of a large-body, delta-wing hypersonic research airplane concept at low speed. This investigation was conducted at a dynamic pressure of 239.4 Pa (5 psf) and a Reynolds number, based on fuselage length, of 2 million. The configuration variables included vertical fins, engine modules, canards, and a canopy. The aerodynamic results of a computer study at Mach numbers of 3 to 12 are presented.

Penland, J. A.↗

NASA NTRS1974

Simulation of random wind fluctuations

A technique was developed for the simulation of random wind fluctuations for use in computer studies of the space shuttle ascent control. The simulated wind fluctuations were generated using the techniques of control theory that have statistical characteristics similar to the characteristics obtained from wind data at Kennedy Space Center.

Perlmutter, M.↗

NASA NTRS1974

Major uncertainties influencing entry probe heat shield design

Factors influencing the design of an outer planet probe heat shield are discussed. Major factors included are: uncertainties in composition and scale height of the planet atmospheres; the augmentation/attenuation of entry heating by ablation products requires more computer study and testing; carbon heat shields, especially carbon phenolic, possessing improved resistance to spallation need developing; and white silica reflecting heat shields with improved resistance to bulk vitrification need further developing.

Congdon, W.↗

NASA NTRS1974

Planetary entry aerothermodynamics. I - Technology requirements and experimental facilities

Consideration has been given to the entry of vehicles into the atmospheres of all planets with the exception of Pluto and to missions for returning samples to Earth from all the planets (excepting Pluto), the satellites of Mars, Jupiter, and Saturn, the Moon, the asteroids, and certain comets. The efficient planning of the space missions including the appropriate design of the spacecraft requires that operational and environmental parameter values for the large range of mission options included be adequately known. The need to obtain the data required as a basis for the computational studies involved makes it necessary to conduct a comprehensive experimental research program. Details concerning the experimental facilities employed in this program are discussed, giving attention to shock tubes, the planetary-entry radiation facility, ballistic ranges, an expansion tube, a hypersonic tetrafluoromethane tunnel, and arcjet facilities.

Olstad, W. B.↗

NASA NTRS1975

A corrugated horn antenna using V-shape corrugations

Corrugated horns use corrugations on the E-plane walls that are operating in the cutoff condition. In this paper, attention is focused on replacing the rectangular shaped corrugation with a V-shaped corrugation. The properties of the V corrugations are obtained using an integral equation solution; the results of the computational studies indicate that for operation of the V corrugations in the forbidden zone the depth of the corrugations lie between 0.3125 to 0.625 times the wavelength in contrast to the rectangular corrugations where the corresponding depth is 0.25 to 0.5 times the wavelength. The radiation patterns and impedance of two identical rectangular horns with corrugated E-plane walls using either V or rectangular corrugations are directly compared.

Mentzer, C. A.↗

NASA NTRS1978

Prediction of aircraft sideline noise attenuation

A computational study is made using the recommended ground effect theory by Pao, Wenzel, and Oncley. It is shown that this theory adequately predicts the measured ground attenuation data by Parkin and Scholes, which is the only available large data set. It is also shown, however, that the ground effect theory does not predict the measured lateral attenuations from actual aircraft flyovers. There remain one or more important lateral effects on aircraft noise, such as sideline shielding of sources, which must be incorporated in the prediction methods. Experiments at low elevation angles (0 deg to 10 deg) and low-to-intermediate frequencies are recommended to further validate the ground effect theory.

Zorumski, W. E.↗

NASA NTRS1977

On the factorization and fitting of molecular scattering information

The reported analysis is based on the factored IOS T-matrix. It is shown that line shape measurements may be used over a range of temperatures to evaluate inelastic scattering cross sections. Basic factorization or parameterization relations are derived by considering the wavefunction equations. The parameterization of cross sections is considered, taking into account the differential scattering amplitude and cross section, integral cross sections, phenomenological cross sections for general relaxation processes, and viscosity and diffusion cross sections. Thermal averages and rates are discussed, giving attention to integral cross sections and rates, and general phenomenological cross sections. The results of computational studies are also presented.

Goldflam, R.↗

NASA NTRS1979

Computer predictions of photochemical oxidant levels for initial precursor concentrations characteristic of southeastern Virginia

A computer study was performed with a photochemical box model, using a contemporary chemical mechanism and procedure, and a range of initial input pollutant concentrations thought to encompass those characteristic of the Southeastern Virginia region before a photochemical oxidant episode. The model predictions are consistent with the expectation of high summer afternoon ozone levels when initial nonmethane hydrocarbon (NMHC) levels are in the range 0.30-0.40 ppmC and NOx levels are in the range 0.02-0.05 ppm. Calculations made with a Lagrangian model, for one of the previously calculated cases, which had produced intermediate afternoon ozone levels, suggest that urban source additions of NMHC and NOx exacerbate the photochemical oxidant condition.

Wakelyn, N. T.↗

NASA NTRS1979

A sensitivity analysis of volcanic aerosol dispersion in the stratosphere

A computer sensitivity analysis was performed to determine the uncertainties involved in the calculation of volcanic aerosol dispersion in the stratosphere using a 2 dimensional model. The Fuego volcanic event of 1974 was used. Aerosol dispersion processes that were included are: transport, sedimentation, gas phase sulfur chemistry, and aerosol growth. Calculated uncertainties are established from variations in the stratospheric aerosol layer decay times at 37 latitude for each dispersion process. Model profiles are also compared with lidar measurements. Results of the computer study are quite sensitive (factor of 2) to the assumed volcanic aerosol source function and the large variations in the parameterized transport between 15 and 20 km at subtropical latitudes. Sedimentation effects are uncertain by up to a factor of 1.5 because of the lack of aerosol size distribution data. The aerosol chemistry and growth, assuming that the stated mechanisms are correct, are essentially complete in several months after the eruption and cannot explain the differences between measured and modeled results.

Butler, C. F.↗

NASA NTRS1980

Configuration effects on satellite charging response

The paper presents a computer study of the response of various spacecraft configurations to a charging environment in sunlight using the NASCAP code. Configuration features considered include geometry, type of stabilization, and overall size. The most striking configuration effect observed is that type of stabilization. A spinning spacecraft is expected to exhibit slower charging of its structure but to develop larger electric field stresses across shaded insulation than is an identical spacecraft which is three-axis stabilized. Data from the ATS-5 and ATS-6 spacecraft are presented and discussed.

Purvis, C. K.↗

NASA NTRS1980

A new semiclassical decoupling scheme for electronic transitions in molecular collisions - Application to vibrational-to-electronic energy transfer

A new semiclassical decoupling scheme (the trajectory-based decoupling scheme) is introduced in a computational study of vibrational-to-electronic energy transfer for a simple model system that simulates collinear atom-diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic-energy separation (lambda), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate-based decoupling scheme) failed. Interference effects are not exhibited in P vs lambda results.

Lee, H.-W.↗

NASA NTRS1983

Shuttle Communications Blackout Study

Space Shuttle Orbiter Entry Communications Blackout Study computer program models, investigates, and predicts communication blackout envelopes based on mission entry trajectory and associated data from tracking stations. Of interest to those designing and using communications systems susceptible to blackout. Program is readily adapted to predict entry communications blackout for any nonablative entry vehicle.

Haben, R. L.↗

NASA NTRS1981

A mathematical model of LANDSAT-D attitude dynamics with internal motion

An algorithm to model the effects of internal motion by the solar array and the high gain antenna on the attitude of the LANDSAT-D spacecraft is presented. The relative torque and angular momenta arising from the internal motions are assumed to be attitude independent but are considered to be a source of attitude perturbations. The equation of motion for the three body problem is derived and then compared with the one body case. The effect of the internal motion on the control of the spacecraft is shown in a computer study of the problem.

Oh, S. D.↗