Search NASA⌕ Search

SEARCH · Search NASA

Results for “COMB”

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.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Configuration development study of the X-24C hypersonic research airplane, phase 1

Four hypersonic research airplane configurations found to be the most cost effective were selected for further refinement. The selection was based on a systematic analysis and evaluation of realistic designs, involving nine different configurations, evolving from three different structural/thermal concepts, coupled with existing rocket and sustainer engines. All configurations were constrained by the mission profiles, research requirements, aerodynamic envelope and maximum launch weight established by NASA.

Combs, H. G.↗
NASA NTRS1977

Configuration development study of the X-24C hypersonic research airplane

Bottom line results were made of a three-phase study to determine the feasibility of designing, building, and operating, and maintaining an air-launched high performance aircraft capable of cruising at speeds up to Mach 8 for short durations. The results show that Lockalloy heat-sink structure affords the capability for a 'work-horse' vehicle which can serve as an excellent platform for this research. It was further concluded that the performance of a blended wing body configuration surpassed that of a lifting body design for typical X-24C missions. The cost of a two vehicle program, less engines, B-52 modification and contractor support after delivery, can be kept within $70M (in Jan. 1976 dollars).

Combs, H. G.↗
NASA NTRS1977

Configuration development study of the X-24C hypersonic research airplane, phase 2

The X-24C Hypersonic Research Vehicle, configured with a heat-sink structure, a launch mass limit of 31.75 Mg and powered by an LR-105 Rocket Engine plus 12 LR-101 Sustainer Engines, was found to be the more cost effective of the candidate configurations. In addition, the configuration provides the maximum off design growth potential capability and subsequently, was selected as the candidate configuration to be subjected to the design refinement study in the remaining segment of the study. Selection of this configuration was based on the analytical study conducted on the performance growth capabilities of the candidate configurations selected from the Phase 1 Study.

Combs, H. G.↗
NASA NTRS1977

Configuration development study of the X-24C hypersonic research airplane, phase 3

The conclusion evolved from the three phased study on the configuration development of the X-24C Hypersonic Research Airplane makes it evident that it is practical to design and build the high performance National Hypersonic Flight Research Facility airplane with today's state of the art within the cost and operational constraints established by NASA. The vehicle launched at 31.75 Mg from the B-52 can cruise for 40 seconds at Mach 6.78 on scramjets. Without scramjets it can approach Mach 8 with a 453.6 Kg payload or do 70 seconds of cruise at Mach 6 with a 2.27 Mg payload. Reduction in cost is possible with a vehicle scaled to a lesser mass and capability.

Combs, H. G.↗
NASA NTRS1981

Behavior of Titan's atmosphere during a total eclipse

During its emergence from the Saturnian shadow on June 28, 1980, Titan was observed simultaneously in the visible and IR ranges (6000-9000 A, and 11.8 and 20 microns). The eclipse observation indicates that thin-atmosphere models with a modest greenhouse effect are likely to be incorrect. A thin atmosphere of pure methane in equilibrium with an ice surface of methane is in marginal agreement with the present data, but improved VLA temperature measurements would be a crucial test of this model. Both the eclipse observation and VLA measurements agree with a nitrogen-dominant atmospheric model, as indicated by preliminary Voyager results.

Combes, M.↗
NASA NTRS1982

An estimate of the PH3, CH3D, and GeH4 abundances on Jupiter from the Voyager IRIS data at 4.5 microns

No evidence is found for large scale phosphine abundance variations over Jovian latitudes between -30 and +30 deg, in PH3, CH3D, and GeH4 abundances derived from the 2100-2250/cm region of the Voyager 1 IRIS spectra. The PH3/H2 value of (4.5 + or - 1.5) X 10 to the -7th derived from atmospheric regions corresponding to 170-200 K is 0.75 + or - 0.25 times the solar value, and suggests that the PH3/H2 ratio on Jupiter decreases with atmospheric pressure upon comparison with other PH3 determinations at 10 microns. In the 200-250 K region, CH3D/H2 and GeH4/H2 ratios of 2.0 X 10 to the -7th and 1.0 X 10 to the -9th, respectively, are derived within a factor of 2.0. Assuming a C/H value of 0.001, as derived from Voyager, the CH3D/H2 ratio obtained in this study implies a D/H ratio of 0.000018. This is in agreement with the interstellar medium value.

Drossart, P.↗
NASA NTRS1983

Tentative confirmation of an aurora on Uranus

There have been three recent reports of the detection of Lyman-alpha radiation (due to atomic hydrogen, H, at wavelength 1,216 A) from Uranus by means of the International Ultraviolet Explorer (IUE) satellite. The interpretations of these results differ. Two reports conclude that there is a strong aurora on Uranus, but the third concludes that the source is resonance scattering of solar Lyman-alpha. This paper reports the detection of emission features due to molecular hydrogen, H2, near 1,600 A. This detection is near the limit of the IUE sensitivity. If it is real, the detection of H2 emission strongly supports the conclusion that Uranus has an aurora comparable in strength with those of the inner two giant planets, Jupiter and Saturn. The first published IUE spectra of the Saturn aurora are also presented.

Caldwell, J.↗
NASA NTRS1983

A determination of the composition of the Saturnian stratosphere using the IUE

Ultraviolet spectra of Saturn from the IUE satellite was reduced to produce a geometric albedo of the planet from 1500 to 3000 A. By matching computer models to the albedo a chemical composition consistent with the data was determined. This model includes C2H2 and C2H6 with mixing ratios and distributions of 9 + or - 3 x 10 to the -8th in the top 20 mbar of the atmosphere with none below for C2H2 and 6 + or 1 x 10 to the -6th also in the top 20 mbar with none below for C2H6. The C2H2 and C2H6 distributions and the C2H6 mixing ratio are taken directly from the Voyager IRIS model (R. Courtin et al., 1981). The Voyager IRIS model also includes PH3, which is not consistent with the UV albedo from 1800 to 2400 A. This model requires a previously unidentified absorber to explain the albedo near 1600 A. After considering several candidates, it is found that the best fit to the data is obtained with H2O, having a column density of 6 + or - 1 x 10 to the -3 cm-am.

Winkelstein, P.↗
NASA NTRS1984

Ultraviolet Observations of Uranus and Neptune Below 3000 Angstrom

From 2000 to 3000 A, both Uranus and Neptune have albedos that are about two times higher than Jupiter or Saturn's, implying that the outer giants have stratospheres that are relatively free of aerosol absorption. Uncertainties in the absolute calibration procedure allow discrepancies of order 15% between conservative models and the observations. A small amount of aerosol absorption is therefore possible. Below 2000 A the derived albedo is highly dependent on the solar spectrum source used in the data reduction. The most recent result for Uranus, first reported here, is consistent with a secular change in C2H2 mixing ratio from approximately three times ten to the minus eight in 1980 to less than or equal to ten to the minus ninth in 1983. These values are approximately 2 orders of magnitude less than the mixing ratios of this gas on Saturn, and comparable to the amount on Jupiter.

Caldwell, J.↗
NASA NTRS1984

Ultraviolet observations of Uranus and Neptune below 3000 A

From 2000 A to 3000 A, both Uranus and Neptune have albedos that are about two times higher than Jupiter or Saturn's, implying that the outer giants have stratospheres that are relatively free of aerosol absorption. Uncertainties in the absolute calibration procedure allow discrepancies of order 15% between conservative models and the observations. A small amount of aerosol absorption is therefore possible. Below 2000 A, the derived albedo is highly dependent on the solar spectrum source used in the data reduction. The most recent result for Uranus is consistent with a secular change in C2H2 mixing ratio from approximately 3 x (10 to the -8 power) in 1980 to or = 10 to the -9 power in 1983. These values are approximately 2 orders of magnitude less than the mixing ratios of this gas on Saturn, and comparable to the amount on Jupiter.

Caldwell, J.↗
NASA NTRS1985

Detection of interstellar CCD

The first detection of interstellar CCD has been obtained in the N = 3-2, J = 7/2-5/2 line at 216.3732 GHz towards the Kleinman-Low nebula. An abundance ratio CCD/CCH of 0.045 is found, indicating in this molecule a deuterium enhancement similar to that found for HNC, but an order of magnitude higher than for HCN. Negative results towards DR 21(OH), NGC 2264, L 134N, TM Cl, Rho OphB2, and IRC 10216 rule out a stronger D enhancement for CCD than for other deuterated molecules in these sources. Predictions of currently developed ion-molecule reaction schemes are consistent with the CCD line detected and the negative results.

Combes, F.↗
NASA NTRS1986

A study of the upper atmosphere of Uranus using the IUE

IUE data on the 1600-2000 A spectral features for Uranus during 1980 are discussed in comparison with equivalent data for Saturn and Jupiter. Attention was focused on detecting possible temporal changes in the C2H2 abundance at 1700 A. The C2H2 abundance in 1980 is estimated to have been a column density of 3.4-10.2 x 10 to the 16th/sq cm. The presence of C2H2 was attributed to photochemical reactions in a layer below 100 km altitude, and was not controlled by saturation, which took place at lower altitudes. A K value of 100,000-1 million/sq cm per sec for Uranus was comparable to Jupiter's and 10-100 times lower than Saturn's.

Encrenaz, T.↗
NASA NTRS1987

Deuterated C3H2 as a clue to deuterium chemistry

The deuterated cyclopropenylidene ring molecule, C3HD, has been detected toward several sources in four rotational lines, at 19, 79, 104, and 107 GHz. The relative integrated intensities of the 2-sub-12 - 1-sub-01 lines of C3HD and C3H2 are found in the ratio 1:5, indicating a high deuterium fractionation ratio for cyclopropenylidene. The detection of the C-13 isotope of C3H2 at the same position allows a determination of the optical thickness (about 3) of the line. The detection of such a large enhancement in the deuterated form of C3H2 very strongly suggests that a molecular ion is the chemical precursor of the molecules. Consideration of the amount of the enhancement relative to that in other molecules suggests that the precursor ion is C3H3+.

Gerin, M.↗
NASA NTRS1987

Building validation tools for knowledge-based systems

The Expert Systems Validation Associate (EVA), a validation system under development at the Lockheed Artificial Intelligence Center for more than a year, provides a wide range of validation tools to check the correctness, consistency and completeness of a knowledge-based system. A declarative meta-language (higher-order language), is used to create a generic version of EVA to validate applications written in arbitrary expert system shells. The architecture and functionality of EVA are presented. The functionality includes Structure Check, Logic Check, Extended Structure Check (using semantic information), Extended Logic Check, Semantic Check, Omission Check, Rule Refinement, Control Check, Test Case Generation, Error Localization, and Behavior Verification.

Stachowitz, R. A.↗
NASA NTRS1988

Validation of expert systems

The validation of expert systems (ESs) has only recently become an active AI research topic. Current approaches have concentrated mainly on the validation of rule properties of such systems. The efforts presented improves on current methods by also exploiting the structural and semantic information of such systems. To increase programmer productivity, more and more companies have begun exploiting the advent of AI technology by developing applications using ES shells or other AI-based high level program generators. The architecture, functionality, and future goals of Expert Systems Validation are described along with the features that have been implemented for and in Automated Reasoning Tool, the ES shell presented.

Stachowitz, Rolf A.↗
NASA NTRS1987

The interstellar clouds toward 3C 154 and 3C 353

Molecular observations of the interstellar clouds toward the radio sources 3C 154 and 3C 353 were obtained in order to elucidate the physical conditions within the clouds. Maps of (C-12)O emission in the J = 1-0 and J = 2-1 lines were compared with observations of the (C-13)O, CH, and OH molecules. The peak emission in the (C-12)O transitions does not occur in the direction of the continuum sources, and thus, an incomplete picture arises when only one line of sight in the two clouds is analyzed. The cloud toward 3C 154 appears to have a low extinction, but a relatively high CO abundance, suggesting that it is similar to high-latitude clouds and CO-rich diffuse clouds. The cloud toward 3C 353 is considerably denser than that toward 3C 154 and may be more like a dark cloud.

Federman, S. R.↗
NASA NTRS1988

Detection of parent molecules in the IR spectrum of P/Halley with the IKS-Vega spectrometer

The two spectroscopic channels of the IKS experiment on board the Vega probes were designed for the detection of emission bands of parent molecules and/or cometary dust, in the 2.5 to 5 micrometer range and the 6 to 12 micron range respectively. On Vega 1, the experiment worked successfully, and cometary spectra were recorded at distances from the comet nucleus ranging from about 250,000 to 40,000 km. The field of view was 1 deg and the spectral resolving power was about 50. On Vega 2, no result could be obtained due to a failure of the cryogenic system. The emission spectra obtained are briefly analyzed.

Encrenaz, Therese↗