Showing papers by "Jet Propulsion Laboratory published in 1970"
TL;DR: In this paper, a statistical theory of material strength is proposed, where the strength of the elements is assumed to be a statistic a quantity, and as the material is loaded elements fracture randomly throughout the body causing localized stress concentrations.
Abstract: A Statistical theory of material strength is proposed. Materials are considered to be imperfect heterogeneous continua composed of discrete volume elements whose characteristics are related to material structure and imperfections. The strength of the elements is assumed to be a statistic a quantity, and as the material is loaded elements fracture randomly throughout the body causing localized stress concentrations. The accumulation of these breaks results in overall failure. By relating strength to material structure this theory attempts to bridge the gap between the microscopic and continuum approaches to fracture mechanics. The theory is applied to composite materials reinforced with whiskers and continuous fibers. Comparisons with experimental data show good agreement. Results for whisker-reinforced composites appear to provide a good prediction of strength and an explanation of the disparity between the strength of individual whiskers and the strength of the composites made from them.
288 citations
TL;DR: Turbulent boundary layer interaction with wavy wall in wind tunnel, discussing wall pressure drag and surface waves interaction as discussed by the authors, discussed wall pressure and surface wave interaction in the wind tunnel.
Abstract: Turbulent boundary layer interaction with wavy wall in wind tunnel, discussing wall pressure drag and surface waves interaction
167 citations
TL;DR: Observations will aid in the interpretation of a soil organic analysis experiment to be performed on the surface of Mars in 1975, which will include a combined pyrolysis-gas chromatography-mass spectrometry instrument as well as several "direct biology experiments" which are designed to search for extraterrestrial life.
Abstract: Pyrolysis-gas chromatography-mass spectrometric studies of two microorganisms, Micrococcus luteus and Bacillus subtilis var niger, indicate that the majority of thermal fragments originate from the principal classes of bio-organic matter found in living systems such as protein and carbohydrate Furthermore, there is a close qualitative similarity between the type of pyrolysis products found in microorganisms and the pyrolysates of other biological materials Conversely, there is very little correlation between microbial pyrolysates and comparable pyrolysis studies of meteoritic and fossil organic matter These observations will aid in the interpretation of a soil organic analysis experiment to be performed on the surface of Mars in 1975 The science payload of this landed mission will include a combined pyrolysis-gas chromatography-mass spectrometry instrument as well as several “direct biology experiments” which are designed to search for extraterrestrial life
118 citations
05 May 1970
TL;DR: A digital computer is said to be fault-tolerant when it can carry out its programs correctly in the presence of logic faults, which are defined as any deviations of the logic variables in a computer from the design values.
Abstract: The objective to attain fault-tolerant computing has been gaining an increasing amount of attention in the past several years. A digital computer is said to be fault-tolerant when it can carry out its programs correctly in the presence of logic faults, which are defined as any deviations of the logic variables in a computer from the design values. Faults can be either of transient or permanent duration. Their principal causes are: (1) component failures (either permanent or intermitent) in the circuits of the computer, and (2) external interference with the functioning of the computer, such as electric noise or transient variations in power supplies, electromagnetic interference, etc.
116 citations
TL;DR: Water vapor was found to reappear in the atmosphere of Mars during its southern hemisphere spring and summer season, with a maximum vertical column abundance of 45 to 50 microns of precipitable water averaged over the entire planet.
Abstract: Water vapor was found to reappear in the atmosphere of Mars during its southern hemisphere spring and summer season, with a maximum vertical column abundance of 45 to 50 microns of precipitable water averaged over the entire planet. Although the spring-summer seasons for each hemisphere are generally symmetrical with respect to the appearance of water vapor, the data suggest that water vapor may appear later in the season and in slightly larger amounts during the southern hemisphere spring-summer.
97 citations
TL;DR: Two cavity-type radiometers have been developed, based on first principles, having the capability of measuring an irradiance with an indicated error 0.3%, which indicates the degree of confidence that can be expected in measurements made with blackbody cavity radiometers.
Abstract: Two cavity-type radiometers have been developed, based on first principles, having the capability of measuring an irradiance with an indicated error 0.3%. The prerequisites for this accuracy are a measured aperture area, a measurement of electric voltages, and an effective absorptance of its blackbody cavity from 0.998 to 0.999 throughout the uv, visible, and ir spectral ranges. The first cavity-type radiometer is designed to operate only in a vacuum of <10−5 Torr and to measure intensities from 10 mW cm−1 to 300 mW cm−2. By using this radiometer in an evacuated cold chamber, an experimental determination of the Stefan-Boltzmann constant is obtained at a value that differs from the theoretical value by 0.3%, which indicates the degree of confidence that can be expected in measurements made with blackbody cavity radiometers. The second type of radiometer is designed to operate in either air or vacuum. Although its aperture opening is windowless, it is unaffected by wind. The range of intensities accurately measurable is from about 10 mW cm−2 to 800 mW cm−2; the indicated accuracy is also 0.3%.
80 citations
01 Apr 1970
TL;DR: A digital transition tracking synchronizer which operates with less than 0.03-dB degradation at ST/N_{0} = -3 dB and at rates of 5.6 bit/s to 250 kbit/s is described.
Abstract: In coded telemetry systems symbol synchronization must be performed at low symbol signal-to-noise ratios ( ST/N_{0} ) with negligible degradation from the perfect synchronization case. A digital transition tracking synchronizer which operates with less than 0.03-dB degradation at ST/N_{0} = -3 dB and at rates of 5.6 bit/s to 250 kbit/s is described.
45 citations
TL;DR: Heat transfer from turbulent boundary layer interacting with shock and expansion waves in supersonic flow was studied in this article. But the results were limited to the case of a single wave.
Abstract: Heat transfer from turbulent boundary layer interacting with shock and expansion waves in supersonic flow
43 citations
TL;DR: In this article, a three-stage process for the design of attitude control systems for flexible vehicles is described: preliminary design is based on root locus plots for single-axis response of linearized systems with sharply truncated modal coordinate matrices; modifications are imposed as required by eigenvalue analyses of coupled linear systems; and design confirmation is established by complex, nonlinear differential equation simulation using digital computer numerical integration.
Abstract: Explicit analyses are presented in sufficient detail to establish the utility in flexible space vehicle control system design of a hybrid coordinate formulation, employing a combination of discrete and distributed (modal) coordinates. A three-stage process for the design of attitude control systems for flexible vehicles is described: 1) preliminary design is based on root locus plots for single-axis response of linearized systems with sharply truncated modal coordinate matrices; 2) modifications are imposed as required by eigenvalue analyses of coupled linear systems; and 3) design confirmation is established by complex, nonlinear differential equation simulation using digital computer numerical integration. These procedures are illustrated by application to two vehicle models. A very simple model is used to demonstrate the potentially destabilizing influence of vehicle flexibility, and corresponding results are shown for a realistically complex model of the Thermoelectric Outer Planet Spacecraft (TOPS).
43 citations
TL;DR: The analytical results provide direct evidence for chemical differentiation in the moon and indicate a lunar crust of appreciably lower density than the whole moon and with lower density and higher albedo than lunar mare material.
Abstract: More precise and comprehensive analytical results for lunar surface material in a terra region have been derived from the data of the alpha-scattering experiment on Surveyor 7. The silicon content and the low sodium abundance are close to that of mare material. The abundances of titanium and iron are at least a factor of 2 lower, whereas the abundances of aluminum and calcium are significantly higher. The analytical results provide direct evidence for chemical differentiation in the moon and indicate a lunar crust of appreciably lower density than the whole moon and with lower density and higher albedo than lunar mare material.
43 citations
TL;DR: In this paper, a statistical theory of material strength is proposed, where the strength of the elements is assumed to be a statistic a quantity, and as the material is loaded elements fracture randomly throughout the body causing localized stress concentrations.
TL;DR: Several types of positive propellant expulsion systems have been developed for orbital spacecraft, each with advantages and problems, as summarized in Table 1. as mentioned in this paper, and the reliability concern of the mission planner increases when very long missions are considered because there are no established accelerated life testing techniques.
Abstract: T task of a propellant expulsion system is to supply gas-free propellant on demand to spacecraft thrusters for the duration of the mission. For orbital spacecraft, which may experience periods of adverse or near zero-gf accelerations, the expulsion system must assure that all or portions of the propellants are in contact with the tank outlet; that gas is prevented from entering the tank outlet during thruster startup; that pressurization gas entrained in the settling propellant bulk does not enter the tank outlet; and that propellant vortexing, gas pull-through, and propellant slosh do not significantly reduce the system expulsion efficiency. Many types of positive propellant expulsion systems have been developed for orbital spacecraft, each with advantages and problems, as summarized in Table 1. Development of these devices usually centers on. mechanical testing in simulated prototype environments. Although performance of these devices has been good, the reliability concern of the mission planner increases when very long missions are considered because there are no established accelerated life testing techniques. Recent experience with capillary systems has shown that they satisfy expulsion system requirements as well as the desire for passive simplicity. Indeed, the question of long-
TL;DR: In this article, the authors investigated Ford's method for generating a de Bruijn cycle of degree n and showed that the feedback function which generates the cycle has the minimum possible number of positions equal to 1 and gave an algorithm which finds those positions for all n.
TL;DR: In this article, line strengths have been computed for the transition arrays 5 p 5 6 s -5 p 5 six s -6 p 5 7 p and 5 p 6 s −5 p 7 p.
Abstract: Line strengths have been computed for the transition arrays 5 p 5 6 s -5 p 5 6 p and 5 p 5 6 s -5 p 5 7 p .
TL;DR: In this article, the saturation of stellar scintillation at large zenith angles cannot be explained by dispersion, but can be accounted for by a combination of dispersion and seeing-disk filtering.
Abstract: Simple dimensional analysis shows that many scintillation phenomena can be interpreted in terms of aperture filtering. The saturation of stellar scintillation at large zenith angles cannot be accounted for by dispersion, but can be accounted for by a combination of dispersion and seeing-disk filtering.
TL;DR: The magnitude of this effect, as estimated from stellar scintillation data, agrees well with the minimum resolution predicted by Fried and by Hulett as discussed by the authors, and is correlated as expected with the strength of scintillations in the zenith.
Abstract: Recent observations of stellar scintillation provide new evidence that atmospheric dispersion alone is not sufficient to cause the saturation observed at large zenith angles. Saturation is produced by lateral spreading of the (initially collimated) light in traversing the turbulent atmosphere—a phenomenon called seeing by astronomers, or multiple scattering by optical physicists. The magnitude of this effect, as estimated from stellar scintillation data, agrees well with the minimum resolution predicted by Fried and by Hulett, and is correlated as expected with the strength of scintillation in the zenith.
TL;DR: The lack of such a deposit at two other lunar sites suggests lower local concentrations of uranium there and the presence of polonium-210 in amounts that are close to equilibrium indicates a continuous turnover rate of lunar material at this site of less than 0.1 micrometer per year.
Abstract: Evidence has been obtained for a radioactive deposit on the lunar surface at Mare Tranquillitatis with a total intensity of 0.09 ± 0.03 alpha disintegration per second per square centimeter. The presence of polonium-210 in amounts that are close to equilibrium indicates a continuous turnover rate of lunar material at this site of less than 0.1 micrometer per year. The lack of such a deposit at two other lunar sites suggests lower local concentrations of uranium there.
TL;DR: Upper and lower bounds on error probability for systematic convolutional codes are obtained and show that the probability of error for a systematic Convolutional code is larger than the probabilities for a nonsystematic convolutionAL code of the same encoder-shift-register length.
Abstract: Upper and lower bounds on error probability for systematic convolutional codes are obtained. These bounds show that the probability of error for a systematic convolutional code is larger than the probability of error for a nonsystematic convolutional code of the same encoder-shift-register length. Two different interpretations of these results are given.
TL;DR: The Doppler residuals from the Apollo 12 lunar module radio tracking data indicate large negative accelerations over the craters Ptolemaeus and Albategnius.
Abstract: The Doppler residuals from the Apollo 12 lunar module radio tracking data indicate large negative accelerations over the craters Ptolemaeus and Albategnius. The mass deficienicies required to produce these accelerations are approximately equivalent to the removal of the surface material to a depth of 1 kilometer over the entire area of these craters. Several other features of the gravity fine structure can also be correlated with topography.
TL;DR: In this article, the 15 best spectra were combined with spectra obtained several years earlier to derive the rotational temperatures of the 10 362-A band of carbon dioxide in the spectrum of Venus.
TL;DR: Ferroelectric ceramics are piezoelectric and optically birefringent, and their coefficients of piezelectricity and birefitting are electrically variable as mentioned in this paper.
Abstract: Ferroelectric ceramics are piezoelectric and optically birefringent. Moreover, their coefficients of piezoelectricity and birefringence are electrically variable. Consequently, these ceramics are applicable to a variety of devices: electrically tuned oscillators and transformers; miniaturized high-Q, high-frequency filters; FM discriminators; optical memories; electrically Controlled light shutters and valves; and electrically activated multicolor displays. This article deals with some possibilities for devices that exploit the electrically controllable optical effects. A later article will consider piezoelectric applications.
TL;DR: Spectral reflectance and albedo measurements of fresh rock powders before and after both laboratory proton irradiation and fusion indicate that vitrification may be an important mechanism of lunar darkening.
Abstract: Luminescence measurements of Tranquillity samples indicate that energy efficiencies for excitation by protons and ultraviolet are in the range 10 -6 or below; natural and induced thermoluminescence is even weaker. If these samples are typical, lunar surface luminescence cannot occur at reported levels. Comparison of proton luminescence spectra from the exterior and interior of rocks and fine fragments provides evidence of solar wind impingement on the moon9s surface. Spectral reflectance and albedo measurements of fresh rock powders before and after both laboratory proton irradiation and fusion indicate that vitrification may be an important mechanism of lunar darkening.
TL;DR: In this paper, the ultraviolet atomic lines were computed by adding the individual line absorption coefficients to the continuum at 1 2 A intervals, thus accounting for reabsorption due to line-line overlap.
Abstract: Radiative intensity calculations have been performed for plasmas of 100% CO2 and 90% CO2-10% N2 for temperatures of from 10 000 to 20 000°K, densities from 0.0001 to 0.1 earth standard density, and path lengths from 1.0 to 30.0 cm. The actual spectral detail of the continuum absorption coefficient was computed from 240 to 30 000 A. The ultraviolet atomic lines were computed by adding the individual line absorption coefficients to the continuum at 1 2 A intervals, thus accounting for reabsorption due to line-line overlap. The visible and infrared lines are individually integrated and added to the total intensity. The total radiation is found to consist primarily of ultraviolet radiation, the lines being generally more important than the continuum. The addition of small amounts of N2 to CO2 seems to have only a small effect on the total radiant intensity.
TL;DR: In this paper, a new method for the reduction of radiation and particle background in X-ray proportional counters has been developed and tested and a pulse shape discriminator which compares the amplitude of the current pulse with the total charge collected in the counter is described.
TL;DR: Optimum penetration and separation mixing of unlike doublet injector element with hypergolic hydrazine and nitrogen tetroxide propellants was studied in this paper, where the doublet element was used to inject a doublet with hyper golic hydrasine and hydroxide.
Abstract: Optimum penetration and separation mixing of unlike doublet injector element with hypergolic hydrazine and nitrogen tetroxide propellants
TL;DR: The functional aspects of the instrument performance and the details related to the optical design and performance are described and the objectives and constraints guiding and affecting the instrument development are described.
Abstract: A television instrument was developed to observe the features of Mars at resolutions and accuracies greater than those obtainable from earth-based telescopes and from photographs obtained by Mariner IV. The television instruments developed for Mariners VI and VII are of a two-camera configuration, exposed alternately during the planetary encounter and providing both analog and digital data to two tape recorders on each spacecraft. Video data from the tape recorders are transmitted in digital form to earth-based tracking stations. This paper describes the functional aspects of the instrument performance and the details related to the optical design and performance. In addition, the objectives and constraints guiding and affecting the instrument development are described.
TL;DR: Orifice length-to-diameter ratio effect on spray mixture uniformity from unlike impinging jets was studied in this paper, where the authors showed that the effect of the length to diameter ratio on the uniformity of spray mixture was negligible.
Abstract: Orifice length-to-diameter ratio effect on spray mixture uniformity from unlike impinging jets
TL;DR: In this paper, the optimal presquaring filter is derived under the assumptions that the modulating spectrum is narrow with respect to the carrier frequency and that the phase-locked loop bandwidth is much narrower than the modulation spectrum.
Abstract: Squaring loops are often discussed as a means of establishing a coherent carrier reference for bi-phase PSK modulation. The optimal presquaring filter is derived under the assumptions that the modulating spectrum as narrow with respect to the carrier frequency and that the phase-locked loop bandwidth is much narrower than the modulating spectrum.
01 Jan 1970
TL;DR: A two-loop lithium-boiling potassium facility was constructed and tested at the Jet Propulsion Laboratory to simulate the major elements and working fluids of a nuclear, turbo-plant concept of interest for spacecraft propulsion as discussed by the authors.
Abstract: A two-loop lithium-boiling potassium facility was constructed and tested at the Jet Propulsion Laboratory to simulate the major elements and working fluids of a two-loop, nuclear, turbo-plant concept of interest for spacecraft propulsion.
TL;DR: Digital image processing techniques have been developed at the Jet Propulsion Laboratory which enable us to characterize these various distortions using calibration data, and to remove them from images returned by the two Mariner spacecraft.