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NASA NTRS1974

Multidisciplinary research in space sciences and engineering with emphasis on theoretical chemistry

A broad program is reported of research in theoretical chemistry, particularly in molecular quantum and statistical mechanics, directed toward determination of the physical and chemical properties of materials, relation of these macroscopic properties to properties of individual molecules, and determination of the structure and properties of the individual molecules. Abstracts are presented for each research project conducted during the course of the program.

Hirschfelder, J. O.↗

NASA NTRS1974

The nature of the sunspot phenomenon. I - Solutions of the heat transport equation

It is pointed out that sunspots represent a disruption in the uniform flow of heat through the convective zone. The basic sunspot structure is, therefore, determined by the energy transport equation. The solutions of this equation for the case of stochastic heat transport are examined. It is concluded that a sunspot is basically a region of enhanced, rather than inhibited, energy transport and emissivity. The heat flow equations are discussed and attention is given to the shallow depth of the sunspot phenomenon. The sunspot is seen as a heat engine of high efficiency which converts most of the heat flux into hydromagnetic waves.

Parker, E. N.↗

NASA NTRS1974

Minimum-weight designs for hat-stiffened composite panels under uniaxial compression

Optimum hat-stiffened compression panel designs are determined by a structural synthesis technique. The effects of simplifying assumptions made in the buckling analysis for the optimization program are investigated by a linked plate element program. Optimization results for hat-stiffened graphite-epoxy panels show a 50-percent weight savings over optimized aluminum panels. Composite panels are shown to possess a variety of proportions at nearly constant weight.

Agarwal, B.↗

NASA NTRS1974

Is Jupiter's magnetosphere like a pulsar's or earth's?

The application of pulsar physics to determine the magnetic structure in the planet Jupiter outer magnetosphere is discussed. A variety of theoretical models are developed to illuminate broad areas of consistency and conflict between theory and experiment. Two possible models of Jupiter's magnetosphere, a pulsar-like radial outflow model and an earth-like convection model, are examined. A compilation of the simple order of magnitude estimates derivable from the various models is provided.

Kennel, C. F.↗

NASA NTRS1975

Scintillations during occultations by planets. 1. An approximate theory

Scintillations observed during occultations of both stars and spacecraft by planetary atmospheres are discussed theoretically. The effects of severe flattening of the Fresnel zone or source image by defocusing on occultations are presented, along with temporal power spectra. Other topics discussed include atmospheric turbulence, saturation of scintillation, effects of saturation on occultation curves, and some methods for a more accurate determination of atmospheric structure.

Young, A. T.↗

NASA NTRS1974

Radio occultation exploration of Mars

The present work summarizes the principal results of the radio occultation experiments carried out to date for Mars. The early measurements, made at the time of the Martian dust storm of 1971, showed greatly reduced temperature gradients in the daytime troposphere, indicating the heating effect of the dust. The temperature gradients that were measured later when the atmosphere was apparently free of dust, were still much lower than expected under conditions of radiative-convective balance, indicating that dynamics may play a large part in determining the temperature structure of the Martian troposphere. The surface atmospheric pressure was observed to vary widely with topography ranging from about 1 mb at the summit of the Middle Spot volcano (Pavonis Mons) to over 10 mb in the North circumpolar region. The radius of the planet was measured with accuracies ranging from about 0.25 to about 2.1 km over latitudes ranging from 86 to -80 deg. These measurements have shown that Mars has pronounced equatorial and north-south asymmetries, which make it difficult to represent its shape by a simple triaxial figure. The daytime ionosphere measurements indicated that the main ionization peak was similar in behavior to a terrestrial F1 layer and is probably produced by photoionization of carbon dioxide by solar extreme ultraviolet.

Kliore, A. J.↗

NASA NTRS1975

Monte Carlo treatment of Lyman-alpha. II - Radiation in a spherical atmosphere

Intensity and state of polarization of solar L-alpha photons as they diffuse through an inhomogeneous, spherically symmetric, isothermal geocorona are theoretically determined. The fine structure of L-alpha and Doppler redistribution of frequencies are taken into account. The calculation use the Monte Carlo technique involving Stokes vectors. Comparison of the results with OGO-4 and OSO-4 observed intensities at an altitude of 650 km shows good agreement. Calculations of the polarization versus solar zenith angle show a residual polarization at large zenith angles which is mainly due to multiply scattered photons.

Modali, S. B.↗

NASA NTRS1975

Dynamic satellite geodesy

It is pointed out that during the time since the last quadrennial report dynamic satellite geodesy has been continually refined with several new and independent solutions for the gravity field and station coordination. The generalized geoid seems to be known to about 3 m. Satellite-to-satellite tracking has been investigated as a means of determining the fine structure of the gravity field. The earth tide continues to be studied with satellite perturbation analysis. Investigations of polar motion are also considered.

Gaposchkin, E. M.↗

NASA NTRS1975

Hot, cold, and annual reference atmospheres for Edwards Air Force Base, California (1975 version)

Reference atmospheres pertaining to summer (hot), winter (cold), and mean annual conditions for Edwards Air Force Base, California, are presented from surface to 90 km altitude (700 km for the annual model). Computed values of pressure, kinetic temperature, virtual temperature, and density and relative differences percentage departure from the Edwards reference atmospheres, 1975 (ERA-75) of the atmospheric parameters versus altitude are tabulated in 250 m increments. Hydrostatic and gas law equations were used in conjunction with radiosonde and rocketsonde thermodynamic data in determining the vertical structure of these atmospheric models. The thermodynamic parameters were all subjected to a fifth degree least-squares curve-fit procedure, and the resulting coefficients were incorporated into Univac 1108 computer subroutines so that any quantity may be recomputed at any desired altitude using these subroutines.

Johnson, D. L.↗

NASA NTRS1976

Gas phase chemistry in comets

The significance of gas phase reactions in determining the nuclear structure of comets is discussed. The sublimation of parent molecules such as H2O, CH4, CO2, and NH3 from the surface of the nucleus and their subsequent photodissociation and ionization in forming observed cometary molecular species are elaborated.

Oppenheimer, M.↗

NASA NTRS1976

Scintillations during occultations by planets. I - An approximate theory

Fluctuations are observed during occultations of both stars and spacecraft by planetary atmospheres. Existing treatments of spacecraft scintillations ignore a major effect unique to occultations: the severe flattening of the Fresnel zone or source image by defocusing. Other large effects, due to 'saturation' of the scintillation, have also been ignored. The deeper portions of atmospheric temperature and density profiles inferred from occultation data are seriously in error if other planets' atmospheres are as turbulent as our own. Thus, profiles obtained from entry probes (e.g., the Soviet Venera series) are probably more accurate than those from radio occultation (Mariner 5 and 10) data. Scintillation greatly reduces the information obtainable from occultation observations; much of the detail attributed to layering in published profiles is probably due to aliasing of turbulence. This paper gives an approximately correct theoretical treatment that is a substantial improvement over published theories, and shows how a more accurate theory could be constructed. Some methods for a more accurate determination of atmospheric structure are proposed.

Young, A. T.↗

NASA NTRS1976

High resolution radiometric measurements of convective storms during the GATE experiment

Using passive microwave data from the NASA CV-990 aircraft and radar data collected during the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE), an empirical model was developed relating brightness temperatures sensed at 19.35 GHz to surface rainfall rates. This model agreed well with theoretical computations of the relationship between microwave radiation and precipitation in the tropics. The GATE aircraft microwave data was then used to determine the detailed structure of convective systems. The high spatial resolution of the data permitted identification of individual cells which retained unique identities throughout their lifetimes in larger cloud masses and allowed analysis of the effects of cloud merger.

Fowler, G.↗

NASA NTRS1977

Venus - On the phase variation of CO2 line profiles

The shapes of Venus' CO2 profiles are found to vary with solar phase angle. High-resolution spectra of the P16 and P14 lines in the 8689- and 7820-A bands, respectively, are presented for phase angles ranging from 6 to 158 deg. The scattering mean free path at 80 mbar, approximately the effective pressure, is 1.7 km. Use of the van de Hulst (1974) similarity relations with simple parametric scattering models is inadequate to separate effects due to the scattering phase function from those due to inhomogeneities in depth when one attempts to determine the atmospheric structure by fitting a family of such models over a wide range of phase angles.

Macy, W., Jr.↗

NASA NTRS1977

A mission design for the Halley comet rendezvous using Ion Drive

The Ion Drive propulsion system, a derivative of the old Solar Electric Propulsion (SEP) technology is considered adequate to perform all mission objectives of a proposed Halley's comet rendezvous (scheduled for launch in 1982) except one: control of thermal energy from the concentrating solar arrays. This problem can be solved, however, by adding a separable tail probe to the baseline system. The system consists of an Ion Propulsion Module (IPM) and a Mission Module (MM). Scientific objectives include a determination of the structure of the comet nucleus, an evaluation of nucleus evolution, an assay of the comet's atmosphere and ionosphere, and a study of the interaction between the comet and the interplanetary medium. Attention is given to the navigation parameters necessary for heliocentric transfer and post-rendezvous circumnavigation of the comet.

Boain, R. J.↗

NASA NTRS1979

Mesospheric heating due to intense tropospheric convection

A series of rocket measurements made twice daily at Wallops Island, Va., revealed a rapid heating of the mesosphere on the order of 10 K on days when thunderstorms or squall lines were in the area. This heating is explained as the result of frictional dissipation of vertically propagating internal gravity waves generated by intense tropospheric convection. Ray-tracing theory is used to determine the spectrum of gravity wave groups that actually reach mesospheric heights. This knowledge is used in an equation describing the spectral energy density of a penetrative convective element to calculate the fraction of the total energy initially available to excite those waves that do reach the level of heating. This value, converted into a vertical velocity, is used as the lower boundary condition for a multilayer model used to determine the detailed structure of the vertically propagating waves. The amount of frictional dissipation produced by the waves is calculated from the solutions of the frictionless model by use of a vertically varying eddy viscosity coefficient. The heating produced by the dissipation is then calculated from the thermodynamic equation.

Taylor, L. L.↗

NASA NTRS1979

Estimation of the ocean geoid near the Blake Escarpment using GEOS-3 satellite altimetry

The accuracy with which the local ocean geoid structure could be determined using satellite altimetry data was investigated. The undulation and along-track component of the vertical deflection for selected passes of GEOS-3 near the Blake Escarpment were estimated and compared with independent analogous estimates based on U. S. Navy surface gravimetric survey data. The results of these comparisons show agreement in the geoid undulation values generally to within one or two meters. The nature of the discrepancy in the undulation values was primarily that of a bias error believed to be due essentially to radial orbit uncertainties. The agreement between the vertical deflection estimates was not significantly affected by orbit uncertainties over the track lengths considered in this study (100 - 1500 km), and the comparisons show typical rms differences of between one and two arc secs. In addition, the capability of the altimeter to resolve short wavelength features of the geoid was determined. This analysis involved spectrum and cross spectrum analysis of sets of closely spaced parallel subtracks to determine statistically significant short wavelength geoid resolution capability. The results of this analysis show that resolution can be achieved down to wavelengths as short as 30 km - 80 km depending on regional geoid variations.

Brammer, R. F.↗

NASA NTRS1981

Improved methods for fan sound field determination

Several methods for determining acoustic mode structure in aircraft turbofan engines using wall microphone data were studied. A method for reducing data was devised and implemented which makes the definition of discrete coherent sound fields measured in the presence of engine speed fluctuation more accurate. For the analytical methods, algorithms were developed to define the dominant circumferential modes from full and partial circumferential arrays of microphones. Axial arrays were explored to define mode structure as a function of cutoff ratio, and the use of data taken at several constant speeds was also evaluated in an attempt to reduce instrumentation requirements. Sensitivities of the various methods to microphone density, array size and measurement error were evaluated and results of these studies showed these new methods to be impractical. The data reduction method used to reduce the effects of engine speed variation consisted of an electronic circuit which windowed the data so that signal enhancement could occur only when the speed was within a narrow range.

Cicon, D. E.↗

NASA NTRS1981

Optimum damper locations for a free-free beam

Algorithms to optimally locate and design dampers for large space structures were developed. The requirements for distributed sensing and actuation in control of structural systems were determined. Mathematical programming was used to solve for optimum damping rate and location. Actuator dynamics were considered to solve for optimum actuator mass.

Horner, G. C.↗