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NASA NTRS1989

DSN 70-meter antenna X- and S-band calibration. Part 1: Gain measurements

Aperture efficiency measurements made during 1988 on the three 70-m stations (DSS-14, DSS-43, and DSS-63) at X-band (8420 MHz) and S-band (2295 MHz) have been analyzed and reduced to yield best estimates of antenna gain versus elevation. The analysis has been carried out by fitting the gain data to a theoretical expression based on the Ruze formula. Newly derived flux density and source-size correction factors for the natural radio calibration sources used in the measurements have been used in the reduction of the data. Peak gains measured at the three stations were 74.18 (plus or minus 0.10) dBi at X-band, and 63.34 (plus or minus 0.03) dBi at S-band, with corresponding peak aperture efficiencies of 0.687 (plus or minus 0.015) and 0.762 (plus or minus 0.006), respectively. The values quoted assume no atmosphere is present, and the estimated absolute accuracy of the gain measurements is approximately plus or minus 0.2 dB at X-band and plus or minus 0.1 dB at S-band (1-sigma values).

Richter, P. H.↗

NASA NTRS1989

On damping mechanisms in beams

A partial differential equation model of a cantilevered beam with a tip mass at its free end is used to study damping in a composite. Four separate damping mechanisms consisting of air damping, strain rate damping, spatial hysteresis and time hysteresis are considered experimentally. Dynamic tests were performed to produce time histories. The time history data is then used along with an approximate model to form a sequence of least squares problems. The solution of the least squares problem yields the estimated damping coefficients. The resulting experimentally determined analytical model is compared with the time histories via numerical simulation of the dynamic response. The procedure suggested here is compared with a standard modal damping ratio model commonly used in experimental modal analysis.

Banks, H. T.↗

NASA NTRS1990

In situ measurement of the cosmic microwave background temperature at a distance of 7.5 kiloparsecs

Absorption of orthoformaldehyde (H2CO) toward the giant H II region W51A (G49.5 - 0.4) has been used as a remote probe of the cosmic microwave background (CMB) at a distance of 7.5 kpc. VLA observations of the 6 cm and 2 cm wavelength transitions provided sufficient resolution and sensitivity to resolve condensations within the foregound clouds. Solutions to the equations of statistical equilibrium within each condensation in the context of a large velocity gradient model yielded an estimate for the CMB temperature at 2.1 mm wavelength of 3.2 + or - 0.9 K. The uncertainty is dominated by modeling of collisional pumping by neutral hydrogen molecules (H2).

Kogut, A.↗

NASA NTRS1990

The solar coronal density irregularity n squared bar/(n bar) squared derived from simultaneous measurements of the EUV and K-coronal brightness

Results are reported from a study of the low corona based on cospatial and cotemporal measurements of the K-coronal polarized brightness pB, and the intensity of the strong resonance line Mg x 625A as a function of height between 1.05 and 1.24 solar radius. Taken together, these measurements yield an estimate of the solar coronal density irregularity. This quantity, is found to be much greater than 1. On the basis of a simple two-component model, it is found that the well-studied resolved structures of the inner corona as presently understood are not capable of explaining the observed irregularity. It is conjectured that subresolution density fluctations associated with coronal dissipation and heating may be the source of the excess irregularity.

Orrall, F. Q.↗

NASA NTRS1991

Evaluation of panel code predictions with experimental results of inlet performance for a 17-inch ducted prop/fab simulator operating at Mach 0.2

An axisymmetric panel code was used to evaluate a series of ducted propeller inlets. The inlets were tested in the Lewis 9 by 15 Foot Low Speed Wind Tunnel. Three basic inlets having ratios of shroud length to propeller diameter of 0.2, 0.4, and 0.5 were tested with the Pratt and Whitney ducted prop/fan simulator. A fourth hybrid inlet consisting of the shroud from the shortest basic inlet coupled with the spinner from the largest basic inlet was also tested. This later configuration represented the shortest overall inlet. The simulator duct diameter at the propeller face was 17.25 inches. The short and long spinners provided hub-to-tip ratios of 0.44 at the propeller face. The four inlets were tested at a nominal free stream Mach number of 0.2 and at angles of attack from 0 degrees to 35 degrees. The panel code method incorporated a simple two-part separation model which yielded conservative estimates of inlet separation.

Boldman, D. R.↗

NASA NTRS1990

The production rate and spatial distribution of H2O for Comet P/Halley

Spectroscopic observations of the O I 1D lines for Comet P/Halley are used to derive water-production rates; 43 exposures during the period August 1985 to June 1986 are reduced. The reduction procedure involves sky subtraction, ratios with solar analog comparison stars, subtraction of contaminating NH2 emissions, and absolute flux calibration. The flux collected within the 2.5-arcsec-wide x 151-arcsec-long integration aperture is converted to a total comet O I 6300-A luminosity using a cometary gas outflow model. Water-production rates for 10 preperihelion dates and seven postperihelion dates are derived. An error budget yields an estimated uncertainty of + 30 percent in H2O production rates with a maximum error of + or - 50 percent. For the preperihelion period, a good fit of the water-production rate as a function of heliocentric distance can be obtained as Q(H2O) = 4.36 x 10 to the 29th x r exp -2.54. A postperihelion enhancement by about a factor of 1.8, which appears to dissipate by June 1986, is observed. Several values of enhanced water production agree well with the observed light curve of P/Halley. Comparison of H2O production rates with those deduced by other methods shows quite reasonable agreement.

Fink, Uwe↗

NASA NTRS1991

Evaluation of panel code predictions with experimental results of inlet performance for a 17-inch ducted prop/fan simulator operating at Mach 0.2

An axisymmetric panel code was used to evaluate a series of ducted propeller inlets. The inlets were tested in the Lewis 9 by 15 Foot Low Speed Wind Tunnel. Three basic inlets having ratios of shroud length to propeller diameter of 0.2, 0.4, and 0.5 were tested with the Pratt and Whitney ducted prop/fan simulator. A fourth hybrid inlet consisting of the shroud from the shortest basic inlet coupled with the spinner from the largest basic inlet was also tested. This later configuration represented the shortest overall inlet. The simulator duct diameter at the propeller face was 17.25 inches. The short and long spinners provided hub-to-tip retios of 0.44 at the propeller face. The four inlets were tested at a nominal free stream Mach number of 0.2 and at angles of attack from 0 degrees to 35 degrees. The panel code method incorporated a simple two-part separation model which yielded conservative estimates of inlet separation.

Boldman, D. R.↗

NASA NTRS1991

Resonance structures in Saturn's rings probed by radio occultation. I - Methods and examples

Individual and comparative analyses are conducted for 29 of the wavelike features revealed by optical depth profiles of Saturn's rings; of these, 18 are in Ring A, one is in Ring B, and 10 are in Ring C. Only 20 of these were identifiable with known resonances, and all eight of the unexplained wave features are in Ring C. For 14 weak density waves in Ring A, a linear density wave theory modeling of the waveform near resonance yields independent estimates of the surface mass density together with reliable estimates of resonance location.

Rosen, Paul A.↗

NASA NTRS1991

Soot in the stratosphere - The impact of current and HSCT aircraft emissions

The emission of soot from existing and proposed aircraft and the contribution of this soot to concentrations observed in the troposphere and stratosphere are discussed. The implications of these emissions for issues in stratospheric physics and chemistry are examined. It is argued that, since soot concentrations in the stratosphere exceed those measured in the cleanest regions of the troposphere, it is possible that current aircraft emissions are the dominant source of stratospheric soot. A simple emission/dispersion model is presented that yields an estimate of aircraft contributions which is in agreement with the observations. The soot concentration is found to be too low to cause any detectable direct optical effects. It is estimated that emissions from the proposed fleet of high-speed civil transport stratospheric aircraft will lead to an increase in concentration of soot in the stratosphere by a factor of two or three.

Hansen, A. D. A.↗

NASA NTRS1991

On damping mechanisms in beams

Banks, H. T.↗

NASA NTRS1991

Physical properties of lava flows on the southwest flank of Tyrrhena Patera, Mars

Tyrrhena Patera (TP) (22 degrees S, 253.5 degrees W), a large, low-relief volcano located in the ancient southern highlands of Mars, is one of four highland paterae thought to be structurally associated with the Hellas basin. The highland paterae are Hesperian in age and among the oldest central vent volcanoes on Mars. The morphology and distribution of units in the eroded shield of TP are consistent with the emplacement of pyroclastic flows. A large flank unit extending from TP to the SW contains well-defined lava flow lobes and leveed channels. This flank unit is the first definitive evidence of effusive volcanic activity associated with the highland paterae and may include the best preserved lava flows observed in the Southern Hemisphere of Mars. Flank flow unit averages, channelized flow, flow thickness, and yield strength estimates are discussed. Analysis suggests the temporal evolution of Martian magmas.

Crown, David A.↗

NASA NTRS1991

Radar investigation of asteroids and planetary satellites

Radar reconnaissance of near-Earth asteroids, mainbelt asteroids, the Galilean satellites, the Martian satellites, and large Saturnian satellites, using the Arecibo 13-cm and the Goldstone 3.5-cm systems is discussed. Measurements of echo strength, polarization, delay/Doppler distribution of echo power provide information about dimensions, spin vector, large-scale topography, cm-to-m-scale morphology, and surface bulk density. The observations also yield refined estimates of target orbital elements.

Ostro, Steven J.↗

NASA NTRS1992

Viscous effects on a vortex wake in ground effect

Wake vortex trajectories and strengths are altered radically by interactions with the ground plane. Prediction of vortex strength and location is especially important in the vicinity of airports. Simple potential flow methods have been found to yield reasonable estimates of vortex descent rates in an otherwise quiescent ambient background, but those techniques cannot be adjusted for more realistic ambient conditions and they fail to provide satisfactory estimates of ground-coupled behavior. The authors have been involved in a systematic study concerned with including viscous effects in a wake-vortex system which is near the ground plane. The study has employed numerical solutions to the Navier-Stokes equations, as well as perturbation techniques to study ground coupling with a descending vortex pair. Results of a two-dimensional, unsteady numerical-theoretical study are presented in this paper. A time-based perturbation procedure has been developed which permits the use of analytical solutions to an inner and outer flow domain for the initial flow field. Predictions have been compared with previously reported laminar experimental results. In addition, the influence of stratification and turbulence on vortex behavior near the ground plane has been studied.

Zheng, Z.↗

NASA NTRS1992

Lidar Observations of the Pinatubo Volcanic Cloud over Hampton, Virginia

A series of eruptions of Mt. Pinatubo climaxed in a cataclysmic eruption on June 15-16, which greatly perturbed the stratospheric aerosol layer. These eruptions yielded an estimated 20 megatons of SO2, which is three times the amount produced by El Chichon. Lidar measurements taken by the 48-inch lidar system at Langley Research Center show the vertical distribution, intensity and spread of the Pinatubo aerosol layers over the middle latitude locations. A few observations have also been made using an airborne lidar system which measures scattering and depolarization. The magnitude and transport time of the volcanic aerosols following Pinatubo and El Chichon are compared. In addition, comparisons are made between the ground-based lidar measurements and near-coincident Stratospheric Aerosol and Gas Experiment (SAGE) 2 satellite observations of the Pinatubo aerosol layers.

Osborn, M. T.↗

NASA NTRS1991

Application of physical adsorption thermodynamics to heterogeneous chemistry on polar stratospheric clouds

Laboratory isotherms for the binding of several nonheterogeneously active atmospheric gases and for HCl to water ice are translated into adsorptive equilibrium constants and surface enthalpies. Extrapolation to polar conditions through the Clausius Clapeyron relation yields coverage estimates below the percent level for N2, Ar, CO2, and CO, suggesting that the crystal faces of type II stratospheric cloud particles may be regarded as clean with respect to these species. For HCl, and perhaps HF and HNO3, estimates rise to several percent, and the adsorbed layer may offer acid or proton sources alternate to the bulk solid for heterogeneous reactions with stratospheric nitrates. Measurements are lacking for many key atmospheric molecules on water ice, and almost entirely for nitric acid trihydrate as substrate. Adsorptive equilibria enter into gas to particle mass flux descriptions, and the binding energy determines rates for desorption of, and encounter between, potential surface reactants.

Elliott, Scott↗

NASA NTRS1992

Geochemistry of Precambrian carbonates. IV - Early Paleoproterozoic (2.25 +/- 0.25 Ga) seawater

The mineralogy, chemistry, and isotopic composition of the Malmani Dolomite, Duck Creek Dolomite, and Bruce 'Limestone' Member of the Espanola Formation are studied in an effort to restrict the first- and second-order variations in isotopic composition of Early Paleoproterozoic seawater. The diagenetic rank is found to increase in the order Duck Creek less than Bruce less than Malmani. The interpolation of alteration trends to 'best' value yields an estimate of 0.70550 for Sr-87/Sr-86. For delta C-13, the measured range of 0 +/- 1.5 percent PDB is similar to that observed for Phanerozoic marine carbonates, while the 'best' delta O-18 value for dolostones is -5 percent PDB, depleted in O-18 relative to Phanerozoic counterparts but comparable to estimates obtained for Archean facies. The isotope geochemistry and mineralogy of Bruce 'Limestone' Member is consistent with the proposition that the sequence was deposited in a lacustrine environment.

Veizer, Jan↗

NASA NTRS1992

Ginga observations of Centaurus X-3

Attention is given to a series of observations of Centaurus X-3 made with Ginga on March 22-24, 1989, over a complete orbital cycle. The data set includes a preeclipse dip, the eclipse ingress and egress, the eclipse itself, and a phase of high steady emission after egress. The mideclipse ephemeris obtained yields an estimate of the rate of change of the orbital period of -(1.738 +/- 0.004) x 10 exp 6/yr, confirming the rate of change reported by Kelley et al. (1983) and improving the precision by a factor of 20. The pulse profiles obtained with Ginga during the high postegress phase are double-peaked at low energies, and show a reversal of phase of 180 deg. No pulsations are detected during the eclipse and at low energies during the preeclipse dip, indicating that X-ray emission at these phases is due to scattering by extended matter. The energy of the iron emission line varies between 6.5 and 6.7 keV during the observation, while its equivalent width varies between 0.18 and 1.5 keV.

Nagase, F.↗

NASA NTRS1992

The shape of asteroid 1917 Cuyo

Lightcurves obtained for 1917 Cuyo at solar phase angles near 54 degrees have an amplitude delta m = 0.44 mag. However, convex-profile inversion of the lightcurves yields an estimate of the asteroid's mean cross section (C, a 2-D average of the 3-D shape) that is only slightly noncircular, with an elongation approximately 1.15. The estimate of C undoubtedly contains systematic errors, the most severe of which could arise from non-equatorial viewing/illumination geometry. However, Cuyo's radar echo shows very little variation in bandwidth vs. rotation phase, supporting the hypothesis that this asteroid's elongation is rather modest.

Ostro, Steven J.↗