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Brown, R. D.

Publications and source records attributed to Brown, R. D..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Ocean gravity and geoid determination

Gravity anomalies have been recovered in the North Atlantic and the Indian Ocean regions. Comparisons of 63 2 deg x 2 deg mean free air gravity anomalies recovered in the North Atlantic area and 24 5 deg x 5 deg mean free air gravity anomalies in the Indian Ocean area with surface gravimetric measurements have shown agreement to + or - 8 mGal for both solutions. Geoids derived from the altimeter solutions are consistent with altimetric sea surface height data to within the precision of the data, about + or - 2 m.

Kahn, W. D.↗
NASA NTRS1979

Exploratory investigation of two resin-matrix composites subjected to arc-tunnel heating

Flexture and short beam shear specimens of a graphite epoxy and a graphite polymimide composite material were tested in an arc tunnel environment. The materials were subjected to seven heating rates from 12.5 to 308 kW/sw m for test times from 5 to 1000 seconds. The temperature response of the specimens was measured and the strength degradation caused by the various heating environments was determined.

Pittman, C. M.↗
NASA NTRS1979

A search for interstellar glycine

A search has been made for the simplest amino acid - glycine - in Sgr B2, Ori A, and seven other molecular clouds. Six different lines were sought ranging from 83.4 GHz down to 22.7 GHz, and radio telescopes at Parkes, New South Wales, Kitt Peak, Arizona, and Onsala, Sweden, were used. On the assumption of reasonable values for excitation temperature and Boltzmann distributions over rotational energy states, upper limits of column densities for glycine of a few times 10 to the 12th per sq cm to a few times 10 to the 14th per sq cm were typically established in the sources surveyed. Glycine appears to be less abundant than ethanol or ethyl cyanide in molecular clouds such as Sgr B2 and Ori A.

Brown, R. D.↗
NASA NTRS1979

Mean sea level determination from satellite altimetry

The primary experiment on the Geodynamics Experimental Ocean Satellite-3 (GEOS-3) is the radar altimeter. This experiment's major objective is to demonstrate the utility of measuring the geometry of the ocean surface; i.e., the geoid. Results obtained from this experiment so far indicate that the planned objectives of measuring the topography of the ocean surface with an absolute accuracy of + or - 5 m can be met and perhaps exceeded. The GEOS-3 satellite altimeter measurements have an instrument precision in the range of + or - 25 cm to + or - 50 cm when the altimeter is operating in the 'short pulse' mode. After one year's operations of the altimeter, data from over 5000 altimeter passes have been collected. With the mathematical models developed and the altimeter data presently available, mapping of local areas of ocean topography has been realized to the planned accuracy levels and better. This paper presents the basic data processing methods employed and some interesting results achieved with the early data. Plots of mean sea surface heights as inferred by the altimeter measurements are compared with a detailed 1 by 1 deg gravimetric geoid.

Kahn, W. D.↗
NASA NTRS1977

Evaluation of a low-density polyimide foam in a dynamic, high temperature environment

A low density polyimide foam material was tested in an arc tunnel to determine its potential for heat shield application on aerospace vehicles. The results show that the material has some reuse potential at surface temperatures as high as 750 K. When a black refractory paint was applied to the surface of the material, the surface recession was negligible at 750 K. An analytical thermal conductivity was derived for this material which, combined with measured thermal property values, can be used to make preliminary design thickness calculations for heat shield applications.

Pittman, C. M.↗
NASA NTRS1977

Ocean gravity and geoid determination

Gravity anomalies have been recovered in the North Atlantic and the Indian Ocean regions. Comparisons of 63 2 deg x 2 deg mean free air gravity anomalies recovered in the North Atlantic area and 24 5 deg x 5 deg mean free air gravity anomalies in the Indian Ocean area with surface gravimetric measurements have shown agreement to + or - 8 mgals for both solutions. Geoids derived from the altimeter solutions are consistent with altimetric sea surface height data to within the precision of the data, about + or - 2 meters.

Kahn, W. D.↗
NASA NTRS1977

Detection of interstellar DNC - Difficulties of chemical equilibrium hypothesis for enrichment

The J = 1-0 transition of DNC at 76.3058 GHz has been observed in emission in NGC 2264. Comparison with previous observations of HN(C-13) indicates that deuterium is enriched in DNC similarly to the enrichment reported for DCO(+) in this source. The DNC/HNC ratio is estimated to be about 1/24. The results cannot readily be interpreted in terms of chemical equilibria relating to the formation of DNC. It is suggested that the explanation must be sought in isotope effects on rates of formation of interstellar molecules.

Godfrey, P. D.↗
NASA NTRS1977

Observation of J = 1-0 emission from H/N-15/C

Emission from the J = 1-0 transition of H(N-15)C has been detected in the direction of DR21(OH). The transition frequency of 88,865.69 MHz was measured in the laboratory by microwave absorption spectroscopy. The computed N-15/C-13 isotopic abundance ratio of 1.01 for DR21(OH) is larger than those calculated from isotopes of HCN in other interstellar clouds, perhaps implying a localized enrichment in N-15 in DR21(OH).

Brown, R. D.↗
NASA NTRS1977

Mean sea level determination from satellite altimetry

The primary experiment on the Geodynamics Experimental Ocean Satellite-3 (GEOS-3) is the radar altimeter. This experiment's major objective is to demonstrate the utility of measuring the geometry of the ocean surface, i.e. the geoid. Results obtained from this experiment so far indicate that the planned objectives of measuring the topography of the ocean surface with an absolute accuracy of + or - 5 meters can be met and perhaps exceeded. The GEOS-3 satellite altimeter measurements have an instrument precision in the range of + or - 25 cm to + or - 50 cm when the altimeter is operating in the short pulse mode.

Kahn, W. D.↗
NASA NTRS1976

Ablative performance of uncoated silicone-modified and shuttle baseline reinforced carbon composites

The relative ablative performance of uncoated silicone-modified reinforced carbon composite (RCC) and uncoated shuttle baseline RCC substrates was investigated. The test specimens were 13 plies (5.3 to 5.8 millimeters) thick and had a 25-millimeter-diameter test face. Prior to arc tunnel testing, all specimens were subjected to a heat treatment simulating the RCC coating process. During arc tunnel testing, the specimens were exposed to cold wall heating rates of 178 to 529 kilowatts/sq m and stagnation pressures ranging from 0.015 to 0.046 atmosphere at Mach 4.6 in air, with and without preheating in nitrogen. The results show that the ablative performance of uncoated silicone-modified RCC substrates is significantly superior to that of uncoated shuttle baseline RCC substrates over the range of heating conditions used. These results indicate that the silicone-modified RCC substrate would yield a substantially greater safety margin in the event of complete coating loss on the shuttle orbiter.

Dicus, D. L.↗
NASA NTRS1975

Surface recession characteristics of a cryogenic insulation subjected to arc-tunnel heating

Specimens of a cryogenic insulation, proposed for use on the space shuttle external tank, were tested in an arc tunnel over a range of heating rates, pressures, and enthalpies corresponding to the shuttle ascent environment. A regression analysis was used to correlate the test data. Correlation equations involving surface recession rate as a function of heating rate, pressure, and enthalpy were developed. These equations can be used to make total surface recession predictions for shuttle ascent flight environments.

Pittman, C. M.↗
NASA NTRS1975

Power spectra of geoid undulations

Data from spacecraft altimeters are expected to contribute to an improved determination of the marine geoid. To better define altimeter system design requirements for geoid recovery, amplitudes of geoid undulations at short wavelengths were examined. Models of detailed geoids in selected areas around the earth, developed from a combination of satellite derived spherical harmonics and 1 deg-by-1 deg area mean free-air gravity anomalies, were subjected to a spectral analysis. The resulting undulation power spectra were compared to existing estimates for the magnitude of geoid undulations at short wavelengths. The undulation spectra were found to be consistent with Kaula's rule of thumb, following an inverse third power relationship with spatial frequency for wavelengths at least as small as 300 km. The requirements imposed by this relationship on altimeter accuracy, data rate, and horizontal resolution to meet the goal of a detailed geoid description are discussed.

Brown, R. D.↗
NASA NTRS1975

Gravity fields of the solar system

The most frequently used formulations of the gravitational field are discussed and a standard set of models for the gravity fields of the earth, moon, sun, and other massive bodies in the solar system are defined. The formulas are presented in standard forms, some with instructions for conversion. A point-source or inverse-square model, which represents the external potential of a spherically symmetrical mass distribution by a mathematical point mass without physical dimensions, is considered. An oblate spheroid model is presented, accompanied by an introduction to zonal harmonics. This spheroid model is generalized and forms the basis for a number of the spherical harmonic models which were developed for the earth and moon. The triaxial ellipsoid model is also presented. These models and their application to space missions are discussed.

Zendell, A.↗
NASA NTRS1974

Heat-transfer and pressure distributions for laminar separated flows downstream of rearward-facing steps with and without mass suction

Heat-transfer and pressure distributions were measured for laminar separated flows downstream of rearward-facing steps with and without mass suction. The flow conditions were such that the boundary-layer thickness was comparable to or larger than the step height. For both suction and no-suction cases, an increase in the step height resulted in a sharp decrease in the initial heat-transfer rates behind the step. Downstream, however, the heat transfer gradually recovered back to less than or near attached-flow values. Mass suction from the step base area increased the local heat-transfer rates; however, this effect was relatively weak for the laminar flows considered. Even removal of the entire approaching boundary layer raised the post-step heat-transfer rates only about 10 percent above the flatplate values. Post-step pressure distributions were found to depend on the entrainment conditions at separation. In the case of the solid-faced step, a sharp pressure drop behind the step was followed by a very short plateau and relatively fast recompression. For the slotted-step connected to a large plenum but without suction, the pressure drop at the base was much smaller and the downstream recompression more gradual than that for solid-faced step.

Brown, R. D.↗
NASA NTRS1973

Thermoluminescent dosimetry for the Apollo 16 microbial response to space environment experiment (M191)

Lithium fluoride thermoluminescent chips were used to provide an integrated dose from the broad spectrum of ionizing radiation to the Microbial Response to Space Environment Experiment (M191). The chips were positioned in the flight hardware to provide data on ionizing radiation within specific volume segments. A uniform radiation dose of 4.8 x 0.001 plus or minus 2 x 0.0001 joule/kg resulted.

Brown, R. D.↗
NASA NTRS1972

Determination of the geoid from satellite altimeter data

The characteristics of the geoid surface are quantitatively described. A procedure for calculating the satellite altitude is developed. Error sources are described quantitatively, mathematically modeled, and evaluated in computer simulation. Procedures for maximum likelihood processing of altimeter data for recovery of orbit and geopotential information are presented for several geopotential models.

Brown, R. D.↗
NASA NTRS1966

Electric arc heater is self starting

Remote method initiates an electric arc over a large range of gaps between two water-cooled electrodes of an arc-heated wind tunnel without disassembling the arc unit. This type of starting system can be used on both three-phase ac arc heaters and dc arc heaters.

Brown, R. D.↗