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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 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Secondary Electron Suppression with Carbonized Aerogels

The goal addressed by this project is reduced DC power for high data rate RF communications by increasing the efficiency of traveling Wave Tubes (TWT) for RF communication, which are used by most space missions for communication and radio science at microwave frequencies. The capability needed is a robust electron collector surface with a secondary electron emission lower than ordinary graphite, which is the state of the art. While it is known that replacing a smooth surface with a textured one will reduce secondary electron emission, no robust textured surface is known. Carbonized polyimide aerogels promise the necessary robustness along with reduced secondary electron emission, allowing further improvement of TWT efficiency, achieving a very good return on the low investment made. Aerogels are known to be robust materials, and carbon aerogels are expected to have low secondary electron emission because of their open surface structure. The objective of this proposal is to demonstrate the low secondary electron emission of carbon aerogels and their robustness.

Secondary electron sippression↗
NASA NTRS2026

Micromechanical Design of Carbon Nanotube Ribbon Reinforced Polymer Composite Materials

Lightweight materials are an important component of the design of aerospace structures. Carbon nanotube materials have been considered for this purpose due to the strength and stiffness of individual nanotubes, and the commercial availability of bulk formats such as fibers. These fibers can have a ribbon cross section which results in a different design space for their composites relative to traditional reinforcements which have a round cross section. This work applies brick-and-mortar micromechanical models and classical lamination theory with an inverse approach to investigate the design space of these composites. Using this approach, the influences of fiber geometry and axial and transverse mechanical properties are mapped. Finally, a sensitivity study is performed and the relative impacts of ±10% variations in the constituent material and geometric properties are ranked. Lamina axial moduli were found to range from a maximum of 3x to 1x minimum relative to a target quasi-isotropic laminate modulus depending on the anisotropy and shear modulus of the lamina. The fiber targets depended strongly on the fiber volume fraction in the lamina and the fiber axial modulus target was found to range from 4.8x to 3.2x the quasi-isotropic laminate target. The sensitivity analysis found that the largest driver of performance was the volume fraction, followed by the fiber axial modulus. While bio-based brick-and-mortar composites, such as nacre, can benefit from reinforcement aspect ratios above 10, for carbon nanotube ribbon (or carbon fiber)/polymer composites the sensitivity study indicated that the optimal cross-sectional aspect ratio was relatively smaller, potentially less than three.

Micromechanics↗
NASA NTRS2003

The Orbiting Carbon Observatory (OCO) Mission

This viewgraph presentation gives a general overview of The Orbiting Carbon Observatory (OCO) Mission. The contents include: 1) The Orbiting Carbon Observatory (OCO); 2) Why Measure CO2?; 3) An Uncertain Future; 4) Monitoring CO2 from Space; 5) Validation Program Ensures Accuracy and Minimizes Spatially Coherent Biases; 6) The OCO Instrument; 7) The OCO Spacecraft; 8) Mission Operations and Data Downlink; 9) OCO Data Products; 10) OCO Data Product Summary; 11) OCO in the A-Train; 12) Summary; and 13) Simulated Performance.

Pathfinder Program↗
NASA NTRS1972

Carbon dioxide concentrator

Passed exhaled air through electrochemical cell containing alkali metal carbonate aqueous solution, and utilizes platinized electrodes causing reaction of oxygen at cathode with water in electrolyte, producing hydroxyl ions which react with carbon dioxide to form carbonate ions.

Williams, C. F.↗
NASA NTRS1972

Carbon dioxide concentration indicator

Device will provide visual indication of concentration of carbon dioxide. It consists of small amounts of absorbent material contained in semipermeable membrane and device to detect color changes. Material will absorb quantity of carbon dioxide proportional to carbon dioxide concentration in atmosphere. Amount of absorption is indicated by color change.

King, P. H.↗
NASA NTRS1972

Flight test of carbon-phenolic on a spacecraft launched by the pacemaker vehicle system

Carbon-phenolic material consisting of 50 percent carbon fibers and 50 percent phenolic resin was flight tested on a recoverable spacecraft launched by the Pacemaker vehicle system. The heat shield of the spacecraft was fabricated so that the carbon fibers in the ablator material had different orientations over several areas of the spacecraft. The environment in which the spacecraft was tested produced heating rates on the hemispherical nose up to 13.6 MW/sq m (1200 Btu/sq ft/sec) and stagnation-point pressures up to 1.27 MN/sq m (12.5 atm). The experimental results are presented. Due to high heating rates and possible spallation and mechanical char removal the greatest mass loss occurred in the nose region. Essentially uniform surface recession and char thickness were observed on the conical section of the spacecraft. A comparison of measured heating rates with computed turbulent and laminar heating rates, as well as measurements of sound-pressure fluctuations in the boundary layer obtained with acoustic sensors, indicated that the boundary layer underwent transition. The acoustic sensor provides an interesting new data form for the general study of boundary-layer transition for free-flight investigations.

Walton, T. E., Jr.↗
NASA NTRS1972

Development of a solid electrolyte carbon dioxide and water reduction system for oxygen recovery

A 1/4-man solid electrolyte oxygen regeneration system, consisting of an electrolyzer, a carbon deposition reactor, and palladium membranes for separating hydrogen, was operated continuously in a 180-day test. Oxygen recovery from the carbon dioxide-water feed was 95%. One percent of the oxygen was lost to vacuum with the hydrogen off-gas. In a space cabin, the remaining 4% would have been recycled to the cabin and recovered. None of the electrolysis cells used in the 180-day test failed. Electrolysis power rose 20% during the test; the average power was 283.5 watts/man. Crew time was limited to 18 min/day of which 12 min/day was used for removing carbon. The success achieved in operating the system can be attributed to an extensive component development program, which is described. Stability of operation, ease of control, and flexibility in feed composition were demonstrated by the life test.

Elikan, L.↗
NASA NTRS1972

Carbon isotopic studies of organic matter in Precambrian rocks.

A survey has been undertaken of the carbon composition of the total organic fraction of a suite of Precambrian sediments to detect isotopic trends possibly correlative with early evolutionary events. Early Precambrian cherts of the Fig Tree and upper and middle Onverwacht groups of South Africa were examined for this purpose. Reduced carbon in these cherts was found to be isotopically similar to photosynthetically produced organic matter of younger geological age. Reduced carbon in lower Onverwacht cherts was found to be anomalously heavy; it is suggested that this discontinuity may reflect a major event in biological evolution.

Oehler, D. Z.↗
NASA NTRS1972

Regeneration of oxygen from carbon dioxide and water.

In a closed ecological system it is necessary to reclaim most of the oxygen required for breathing from respired carbon dioxide and the remainder from waste water. One of the advanced physicochemical systems being developed for generating oxygen in manned spacecraft is the solid electrolyte-electrolysis system. The solid electrolyte system consists of two basic units, an electrolyzer and a carbon monoxide disproportionator. The electrolyzer can reclaim oxygen from both carbon dioxide and water. Electrolyzer preparation and assembly are discussed together with questions of reactor design and electrolyzer performance data.

Weissbart, J.↗
NASA NTRS1972

CMB-13 research on carbon and graphite

The research on graphite and carbon for this period is reported. Topics discussed include: effects of grinding on the Santa Marie graphites, properties and purities of coal-tar, resin-bonded graphite, carbonization of resin components, and glass-like carbon filler.

Smith, M. C.↗
NASA NTRS1973

Development of seal ring carbon-graphite materials (tasks 8, 9, and 10)

A screening study was conducted to develop improved carbon-graphite materials for use in self-acting seals at air temperatures to 1300 F (704 C). Property measurements on materials prepared during this study have shown that: (1) The mechanical properties of a carbon-graphite material were significantly improved by using a fine milled artificial graphite filler material and including intensive mixing, warm molding, and pitch impregnation in the processing; and (2) the oxidation resistance of a carbon-graphite material was improved by including fine milled boron carbide as an oxidation-inhibiting additive. These techniques were employed to develop a material that has 10 times more oxidation resistance than that of a widely used commercial grade and mechanical properties that approach those of the commercial grade.

Fechter, N. J.↗
NASA NTRS1972

Development of manufacturing process for large-diameter composite monofilaments by pyrolysis of resin-impregnated carbon-fiber bundles

Large diameter, carbon-carbon composite, monofilaments were produced from the pyrolysis of organic precursor resins reinforced with high-strenght carbon fibers. The mechanical properties were measured before and after pyrolysis and the results were correlated with the properties of the constituents. The composite resulting from the combination of Thornel 75 and GW-173 resin precursor produced the highest tensile strength. The importance of matching strain-to-failure of fibers and matrix to obtain all the potential reinforcement of fibers is discussed. Methods are described to reduce, within the carbonaceous matrix, pyrolysis flaws which tend to reduce the composite strength. Preliminary studies are described which demonstrated the feasibility of fiber-matrix copyrolysis to alleviate matrix cracking and provide an improved matrix-fiber interfacial bonding.

Bradshaw, W. G.↗
NASA NTRS1973

Development of a breadboard model correlation interferometer for the carbon monoxide pollution experiment

The breadboard model of the correlation interferometer for the Carbon Monoxide Pollution Experiment has been designed, fabricated, and tested. Laboratory, long-path, and atmospheric tests which were performed show the technique to be a feasible method for obtaining a global carbon monoxide map and a vertical carbon monoxide profile and similar information is readily obtainable for methane as well. In addition, the technique is readily applicable to other trace gases by minor instrumental changes. As shown by the results and the conclusions, it has been determined that CO and CH4 data can be obtained with an accuracy of 10% using this technique on the spectral region around 2.3 microns.

Bortner, M. H.↗
NASA NTRS1974

Silver oxide sorbent for carbon dioxide

Material can be regenerated at least 20 times by heating at 250 C. Sorbent is compatible with environment of high humidity; up to 20% by weight of carbon dioxide can be absorbed. Material is prepared from silver carbonate, potassium hydroxide or carbonate, and sodium silicate.

Colombo, G. V.↗
NASA NTRS1973

A high-pressure carbon dioxide gasdynamic laser

A carbon dioxide gasdynamic laser was operated over a range of reservoir pressure and temperature, test-gas mixture, and nozzle geometry. A significant result is the dominant influence of nozzle geometry on laser power at high pressure. High reservoir pressure can be effectively utilized to increase laser power if nozzle geometry is chosen to efficiently freeze the test gas. Maximum power density increased from 3.3 W/cu cm of optical cavity volume for an inefficient nozzle to 83.4 W/cu cm at 115 atm for a more efficient nozzle. Variation in the composition of the test gas also caused large changes in laser power output. Most notable is the influence of the catalyst (helium or water vapor) that was used to depopulate the lower vibrational state of the carbon dioxide. Water caused an extreme deterioration of laser power at high pressure (100 atm), whereas, at low pressure the laser for the two catalysts approached similar values. It appears that at high pressure the depopulation of the upper laser level of the carbon dioxide by the water predominates over the lower state depopulation, thus destroying the inversion.

Kuehn, D. M.↗
NASA NTRS1974

Additional development of large diameter carbon monofilament

The chemical vapor process for preparing a large diameter carbon-base monofilament from a BCl3, Ch4 and H2 gas mixture with a carbon substrate fiber was studied. The effect of reactor geometry, total gas flows and deposition temperature on the tensile strength of the monofilament were investigated. It was noted that consistent results could only be obtained when the carbon substrate fiber was cleaned. The strength of the monofilament was found to depend on the highest temperature and the temperature profile of the monofilament in the reactor. The strength of monofilament produced in the dc and RF reactors were found to be similar and similar alloy compositions in the monofilament were attained when the same gas ratios were used. The tensile strength of the monofilament at 500 C was found to be 60 to 70% of the room temperature tensile strength. No degradation was noted after exposure to molten aluminum.

Jacob, B. A.↗
NASA NTRS1974

Carbon dioxide in the atmosphere

Research projects for the period ending September 15, 1973 are reported as follows: (1) the abundances of carbon dioxide in the atmosphere, and the processes by which it is released from carbonate deposits in the earth and then transferred to organic material by photosynthesis; the pathways for movement of carbon and oxygen through the atmosphere; (2) space science computation assistance by PDP computer; the performance characteristics and user instances; (3) OGO-6 data analysis studies of the variations of nighttime ion temperature in the upper atmosphere.

Johnson, F. S.↗
NASA NTRS1974

Free energies of formation of WC and WzC and the thermodynamic properties of carbon in solid tungsten

The activity of carbon in the two-phase regions - W + WC and W + W2C was obtained from the carbon content of iron rods equilibrated with mixtures of metal plus carbide powders. From this activity data the standard free energies of formation of WC and W2C were calculated. The temperature of the invariant reaction W2C = W + WC was fixed at 1570 + or - 5K. Using available solubility data for C in solid W, the partial molar free energy of C in the dilute solid solution was also calculated. The heat of solution of C in W, and the excess entropy for the interstitial solid solution, were computed, assuming that the carbon atoms reside in the octahedral interstices of bcc W.

Gupta, D. K.↗