SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
There are no author-identified significant results in this report.
Ice/frost formation on the Space Shuttle cryogenic propellant tanks presents a different problem from that of past launch vehicles. Lift off weight addition has been the primary concern on past launch vehicles. The primary ice/frost concern on the Shuttle vehicle is damage to the Orbiter Thermal Protection System due to ice/frost impact. The approach used to arrive at a solution to this unique Shuttle problem is presented. The launch vehicle configuration selected and its limitations are described, along with contingency ground support equipment.
Explore the source record for details and available documents.
Goddard Space Flight Center has developed a large scale integrated circuit (type 623) which can perform pulse counting, storage, floating point compression, and serial transmission, using a single monolithic device. Counts of 27 or 19 bits can be converted to transmitted values of 12 or 8 bits respectively. Use of the 623 has resulted in substantial savaings in weight, volume, and dollar resources on at least 11 scientific instruments to be flown on 4 NASA spacecraft. The design, construction, and application of the 623 are described.
A critical review of maturity with respect to the abundance of implanted solar wind elements (SWE) in lunar soils indicates: (1) that the Rosiwal Principle has limited applicability in determining implantation of SWE in lunar soils, and (2) that despite a depletion of SWE in agglutinitic glass, agglutinates are enriched in SWE due to the presence of buried surfaces of numerous clasts within agglutinates. A statistical analysis of published data of several Apollo 17 soils indicates that the abundance of carbon and, by analogy, the abundance of other SWE are correlatable with the agglutinate content and the mean grain size of lunar soils. Microscopic examination of more than 5000 grains of agglutinates in polished thin sections reveals a wide range of variability in the mineralogy, grain size distribution, degree of recycling, etc., of the clast population in agglutinates. This indicates that the volume-correlated SWE content of agglutinates may vary and need not be constant.
The inhibition of translation which is observed after shifting Escherichia coli to low temperature was investigated. 70 S ribosomes were isolated from E. coli 8 hours after a shift to 5 C synthesized protein in the absence of added mRNA (i.e., endogenous protein synthesis by 70 S monosomes) at a rate which was three times greater than the rate of endogenous protein synthesis by 70 S ribosomes which were isolated at the time of the shift to 5 C. Calculations based on the rates of endogenous protein synthesis and polyphenylalanine synthesis indicate that 70 S monosomes comprise only 0.1% of the total E. coli 70 S ribosome population after 8 hours at 5 c. Experiments designed to test initiation complex formation on ApUpG or formaldehyde treated MS-2 viral RNA demonstrated that, although the rate of formation of 30 S initiation complexes was not inhibited, the rate of formation of active 70 S initiation complexes, able to react with puromycin, was inhibited to a great extent at 5 C. A model depicting the effects of low temperature on the E. coli translation system is proposed.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The tectonic framework causing seismicity on the San Andreas and North Anatolian faults can be understood in terms of plate tectonics. However, the mechanisms responsible for the distribution of seismicity in space and time on these faults are poorly understood. The upper part of the crust apparently behaves elastically in storing energy that is released during an earthquake. The relatively small distances from the fault in which stress is stored argue in favor of a plate with a thickness of 5-10 km. The interaction of this plate with a lower crust that is behaving as a fluid damps the seismic cycling in distances of the order of 10 km from the fault. Low measured heat flow also argues in favor of a thin plate with a low stress level on the fault. Future measurements of stress, strain, and heat flow should help to provide a better understanding of the basic mechanisms governing the behavior of strike-slip faults.
A computerized procedure was developed to model the response of a laminated composite plate subjected to low velocity impact. The methodology incorporated transient dynamics finite element analysis coupled with composite layer and interlaminar stress predictions. Damage was predicted using a stress based failure criteria and incorporated into the solution as stiffness modifications. The force-displacement relation between the impactor and plate was modelled with a nonlinear contact spring similar to Hertzian contact. Analyses performed predicted ply damage early in the impact event when the displacement fields were characteristic of high frequency flexurable response.
In the scenario of lunar origin in which the Moon is assumed to have accreted most of its mass while in orbit about the Earth, ismals on the accrea knowledge of the relative impact rates of heliocentric planetting Earth and Moon is essential for any attempt to establish dynamical constraints on lunar origin. Numerical integrations of the regularized equations of motion for four bodies (Sun, Earth, Moon, planetismal) were done. A planetismal impact trajectory was calculated by assuming that the planetismal has hit the surface of the Moon at an assumed location, traveling in an assumed direction, and with an assumed impact speed. Next, the equations of motion were numerically integrated backward in time in order to determine from where the planetismal has come. In this way those volumes in heliocentric orbital element space which contribute trajectories that directly impact the Moon.
Recent findings concerning the budget and cycles of nitrous oxide on earth are summarized, and the sources and sinks for N2O on land, in the ocean, and in the atmosphere are examined in view of the N2O concentration increase of 0.2-0.4 percent per year, observed over the period of 1975-1982. Possible atmospheric and biospheric consequences of the N2O concentration increase are evaluated. N2O emission values are given for several major ecosystem types, such as forest, desert, cultivated land; values from different sources are compared and discussed. Analysis shows an excess of documented sources over sinks by 0-51 Tg N2O-N/yr.
The validity of the two-body approximation in calculating encounters between planetesimals has been evaluated as a function of the ratio of unperturbed planetesimal velocity (with respect to a circular orbit) to mutual escape velocity when their surfaces are in contact (V/V-sub-e). Impact rates as a function of this ratio are calculated to within about 20 percent by numerical integration of the equations of motion. It is found that when the ratio is greater than 0.4 the two-body approximation is a good one. Consequences of reducing the ratio to less than 0.02 are examined. Factors leading to an optimal size for growth of planetesimals from a swarm of given eccentricity and placing a limit on the extent of runaway accretion are derived.
Stressing and rupture of a locked zone adjacent to a creeping fault segment was studied with special reference to strength heterogeneity depthwise and along-strike. The resulting precursory temporal and spatial variations of surface strain rate profiles were compared to geodetic measurements on the San Andreas fault in central California. Crustal deformation in great California earthquake cycles was also studied with special reference to the temporal decay of strain rate observed since the 1957 and 1906 great earthquakes, and comtemporary surface strain rate and velocity profiles at several locations along the San Andreas. The effect of viscoelastic response in the deep aseismic shear zone on the surface deformation behavior was examined. Work was begun on a fundamental reformulation of the crustal deformation problem focusing on the crustal deformation process affected by deep aseismic slip as the slip zone progresses toward an instability and as deep seismic slip continues postseismically, the 3-D nature of the problem due to geometry and material heterogeneity, and the time-dependent source coming from the lithosphere/astenospheric coupling process.
The purpose of this paper is to review some of the latest understanding of the fatigue behavior of continuous fiber reinforced metal matrix composites. The emphasis is on the development of an understanding of different fatigue damage mechanisms and why and how they occur. The fatigue failure modes in continuous fiber reinforced metal matrix composites are controlled by the three constituents of the system: fiber, matrix, and fiber/matrix interface. The relative strains to fatigue failure of the fiber and matrix will determine the failure mode. Several examples of matrix, fiber, and self-similar damage growth dominated fatigue damage are given for several metal matrix composite systems. Composite analysis, failure modes, and damage modeling are discussed. Boron/aluminum, silicon-carbide/aluminum, FP/aluminum, and borsic/titanium metal matrix composites are discussed.
Explore the source record for details and available documents.
Assortment of documents describes simple, passive system that removes water formed from reaction of hydrogen and oxygen in proton-exchange-membrane fuel cell. Designed for use in zero gravity, system does not require any machinery or external source of power. Works by capillary action and differential pressure.
Geophysical evidence suggests a significant amount of north-south convergence occurs across the Santa Barbara Channel. Tectonic studies indicate a discrepancy between observed fault slip in California and the North American-Pacific plate motion. Newer plate motion models (NUVEL-1) yield a lower rate of convergence. Global Positioning System (GPS) data collected in the Santa Barbara Channel in 1987, when combined with 1971 trilateration measurements, should be sufficient to resolve the present-day convergence rate. In early 1987. from January 3 to 7, GPS data were collected at 14 sites in California and at 5 additional stations throughout North America. The data can be used to estimate the rate of crustal deformation (convergence) ocurring across the Santa Barbara Channel. The GPS baselines were computed with the Bernese 2nd generation software. A comparison was made between baseline lengths obtained with the Burnese and MIT softwares. Baseline changes from 1971 to January, 1987 (GPS-Bernese) across the Santa Barbara Channel were computed. A uniform strain model was calculated from the baseline changes. The present-day rate of convergence across the Santa Barbara Channel was determined to be 8 to 10 mm/yr. This conclusion is obtained from changes in the baseline length measured with a 1971 trilateration survey and a January, 1987, GPS survey. The rapid convergence rate, in addition to the history of large seismic events, suggests this region is a prime target for future geodetic and geophysical studies.