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NASA NTRS1976

Temperature of the atmosphere of Jupiter from Pioneer 10/11 radio occultations

Radio-occultation data from the Pioneer 10 and 11 flybys are analyzed using an integral inversion technique combined with a model for Jupiter's shape based on gravity data in order to account for the oblateness of the planet's atmosphere. The inversion technique defines the center of refraction in terms of the radius of curvature and the normal to the equipotential surface at the closest approach point of the ray. An Abelian inversion of the data obtained during the Pioneer 10 entry, the Pioneer 10 exit, and the Pioneer 11 exit is performed by fixing the center of refraction at some average value for each occultation event. The results for all three measurements are found to be consistent and to show a temperature inversion between the 10-mb and the 100-mb levels, with temperatures of 130 to 170 K at 10 mb and 80 to 100 K at 100 mb. Major sources of error are discussed, and it is concluded that the range of reasonable temperature uncertainties at these levels does not exceed 40 K. It is noted that the temperature inversion was also inferred from Pioneer 10 IR radiometric data.

Kliore, A. J.↗

NASA NTRS1981

Glass shell manufacturing in space

Highly-uniform, hollow glass spheres (shells), which are used for inertial confinement fusion targets, were formed from metal-organic gel powder feedstock in a vertical furnace. As a result of the rapid pyrolysis caused by the furnace, the gel is transformed to a shell in five distinct stages: (a) surface closure of the porous gel; (b) generation of a closed-cell foam structure in the gel; (c) spheridization of the gel and further expansion of the foam; (d) coalescence of the closed-cell foam to a single-void shell; and (e) fining of the glass shell. The heat transfer from the furnace to the falling gel particle was modeled to determine the effective heating rate of the gel. The model predicts the temperature history for a particle as a function of mass, dimensions, specific heat, and absorptance as well as furnace temperature profile and thermal conductivity of the furnace gas. A model was developed that predicts the gravity-induced degradation of shell concentricity in falling molten shells as a function of shell characteristics and time.

Downs, R. L.↗

NASA NTRS1981

Structure, composition and thermal state of the crust in Brazil

Aeromagnetic survey data of the Minas Gerais areas were analyzed and compared with MAGSAT anomaly data. Initially the data set was used to determine the thickness of the magnetized crust. The value obtained is in agreement with crustal models derived from deep seismic sounding and gravity data, indicating that the bottom of the magnetized layer occurs close to the Moho transition. An analysis of the long wavelength pattern indicates that the anomalies form a series of lineations along the magnetic E-W. These are shown to be the result of attenuation. On the MAGSAT total intensity map localized anomalies are superimposed onto an anomaly background formed by alternating positive and negative patches. Implementation and testing of analysis software for MAGSAT data are also discussed.

Pacca, I. I. G.↗

NASA NTRS1982

Internal gravity waves in the solar atmosphere. II - Effects of radiative damping

In the solar photosphere, temperature fluctuations associated with acoustic-gravity waves may be rapidly smoothed by the transfer mechanism of radiation between hotter and cooler regions. The present investigation of the radiative effects on internal gravity waves takes into account the parameterization of the radiative energy, employing the Newtonian cooling approximation. A linear analysis of the propagation of internal gravity waves is carried out in a model of the solar atmosphere which is taken to be homogeneous in the horizontal coordinates. Linear wave properties both with and without radiative cooling are summarized, and the variation with height of energy fluxes and of nonlinearities in the waves is discussed. Attention is given to the significance of the obtained results in terms of energy balance in the chromosphere and in relation to spectral line observations.

Mihalas, B. W.↗

NASA NTRS1984

Questions for the geologic exploration of Venus

Venus is the last terrestrial planet to be mapped in the Solar System. This is an indication not of its relative importance for comparative planetary studies but of the previous lack of demonstrated, affordable technology. Venus is, in fact, the most important planet to study for improving our understanding of global terrestrial processes such as plate tectonics. The next NASA mission to Venus, in 1988, will map the planet at a resolution comparable to that of the Mars Mariner 9 mission. The objective is 70 percent coverage at 1 km per line pair or better. This is the minimum resolution that will allow analysis of tectonic, volcanic, aeolian, meteorite impact and other features. An altimeter will provide a global map of topography that will considerably improve our data base and, together with gravity field measurements, provide better interior geophysical models.

Saunders, R. S.↗

NASA NTRS1985

A nonlinear steady model for moist hydrostatic mountain waves

The dynamics of hydrostatic gravity waves generated by the passage of a steady, stably stratified, moist flow over a two-dimensional topography is considered. Coriolis effects are neglected. The cloud region is determined by the dynamics, and within that region the Brunt-Vaisala frequency takes on a value smaller than the outside value. In both the dry and cloudy regions the Brunt-Vaisala frequency is constant with height. The moist layer is considered to be either next to the mountain or at midlevels and to be deep enough so that an entire cloud forms in that layer. The nonlinearity in the flow and lower boundary affects the dynamics of these waves and wave drag. The latter is found to depend upon: (1) the location of the moist layer with respect to the ground, (2) the amount of moisture, (3) the degree of nonlinearity and (4) the departure from symmetry in the bottom topography.

Barcilon, A.↗

NASA NTRS1986

Microwave emission and scattering from Earth surface and atmosphere

Nonlinear Electromagnetic (EM) wave interactions with the upper atmosphere were investigated during the period 15 December 1985 to 15 June 1986. Topics discussed include: the simultaneous excitation of ionospheric density irregularities and Earth's magnetic field fluctuations; the electron acceleration by Langmuir wave turbulence; and the occurrence of artificial spread F. The role of thermal effects in generating ionospheric irregularities by Whistler waves, intense Quasi-DC electric fields, atmospheric gravity waves, and electrojets was investigated. A model was developed to explain the discrete spectrum of the resonant ultralow frequency (ULF) waves that are commonly observed in the magnetosphere.

Kong, J. A.↗

NASA NTRS1986

Brans-Dicke-type models with nonmetricity

A scalar-tensor-nonmetric theory of gravity without matter fields is shown to be equivalent to the scalar-tensor-torsion theory proposed by German, the only difference being in the source of the Weyl vector or torsion vector (for equivalently the scalar field) which remains arbitrary in the theory. General extended conformal transformations, which leave the curvature tensor invariant, are presented and their implications for metric-affine theories and scalar-tensor theories are discussed.

Smalley, L. L.↗

NASA NTRS1987

Energetics and dynamics of the earth's thermosphere

An overview of current (1983-1986) research on the energetics and dynamics of the earth's thermosphere is presented. The global mean radiative and thermal balance in the thermosphere is examined, and the results of experimental investigations for the low-latitude, mid-latitude, and high-latitude upper thermosphere regions are discussed. Consideration is also given to research done in the lower thermosphere, including investigations of tidal and gravity wave processes. In addition, various thermospheric models are discussed together with the results obtained by the analysis of the thermosphere's energetics and dynamics.

Killeen, T. L.↗

NASA NTRS1988

Computer programs for calculation of sting pitch and roll angles required to obtain angles of attack and sideslip on wind tunnel models

Two programs have been developed to calculate the pitch and roll angles of a wind-tunnel sting drive system that will position a model at the desired angle of attack and and angle of sideslip in the wind tunnel. These programs account for the effects of sting offset angles, sting bending angles and wind-tunnel stream flow angles. In addition, the second program incorporates inputs from on-board accelerometers that measure model pitch and roll with respect to gravity. The programs are presented in the report and a description of the numerical operation of the programs with a definition of the variables used in the programs is given.

Peterson, John B., Jr.↗

NASA NTRS1991

Effects of a giant impact on Uranus

The effects of a giant impact on Uranus with respect to the axis tilt of Uranus and its satellites are discussed. The simulations of possible giant impacts were carried out using Cray supercomputers. The technique used is called smooth particle hydrodynamics (SPH). In this technique, the material in the proto-Uranus planet and in the impactor is divided into a large number of particles which can overlap one another so that local averages over these particles determine density and pressure in the problem, and the particles themselves have their own temperatures and internal energies. During the course of the simulation, these particles move around under the influence of the forces acting on them: gravity and pressure gradients. The results of model simulations are presented.

Slattery, W. L.↗

NASA NTRS1991

Evolution to nonequilibrium in simple models of prominence filaments

The support of cold plasma against gravity by a line-tied magnetic field is considered. The normal component of the field at the boundaries, the mass/unit flux, and the magnetic shear are all specified. Fixing the first two of these quantities, and varying the third leads to evolutionary sequences. When the magnetic shear is less than a critical value, an infinite number of solutions exist. When the magnetic shear is sufficiently large, there are no solutions with the desired topology. These results support the idea that prominences erupt as a result of evolution to magnetic nonequilibrium.

Zweibel, Ellen G.↗

NASA NTRS1991

Computer programs for the calculation of dual sting pitch and roll angles required for an articulated sting to obtain angles of attack and sideslip on wind-tunnel models

Two programs were developed to calculate the pitch and roll position of the conventional sting drive and the pitch of a high angle articulated sting to position a wind tunnel model at the desired angle of attack and sideslip and position the model as near as possible to the centerline of the tunnel. These programs account for the effects of sting offset angles, sting bending angles, and wind-tunnel stream flow angles. In addition, the second program incorporates inputs form on-board accelerometers that measure model pitch and roll with respect to gravity. The programs are presented and a description of the numerical operation of the programs with a definition of the variables used in the programs is given.

Peterson, John B., Jr.↗

NASA NTRS1990

Cirrus cloud spectra and layers observed during the FIRE and GASP projects

A general characterization is developed for cirrus clouds in terms of their spectra, shapes, optical thicknesses, and radiative properties for use in numerical models. Data sets from the Global Atmospheric Sampling Project (GASP) of the upper troposphere and the First ISCCP Regional Experiment (FIRE) are combined and analyzed to study general traits of cirrus clouds. A definition is given for 2D turbulence, and the GASP and FIRE data sets are examined with respect to cirrus layers and entrainment and to dominant turbulent scales. The approach employs conditional sampling in cloudy and clear air, power-spectral analysis, and mixing-line-type diagrams. Evidence is given for a well mixed cloud deck and for the tendency of cirrus to be formed in multilayer structures. The results are of use in mesoscale and global circulation models which predict cirrus, in small-scale cirrus modeling, and in studying the role of gravity waves in the horizontal structure of upper tropospheric clouds.

Flatau, Piotr J.↗

NASA NTRS1996

Computational modeling of magnetically actuated propellant orientation

Unlike terrestrial applications where gravity positions liquid at the 'bottom' of the tank, the location of liquid propellant in spacecraft tanks is uncertain unless specific actions are taken or special features are built into the tank. Some mission events require knowledge of liquid position prior to a particular action: liquid must be positioned over the tank outlet prior to starting the main engines and must be moved away from the tank vent before vapor can be released overboard to reduce pressure. It may also be desirable to positively position liquid to improve propulsion system performance: moving liquid away from the tank walls will dramatically decrease the rate of heat transfer to the propellant, suppressing the boil-off rate, thereby reducing overall mission propellant requirements. The process of moving propellant to a desired position is referred to as propellant orientation or reorientation. Several techniques have been developed to positively position propellant in spacecraft tanks and each technique imposes additional requirements on vehicle design. Propulsive reorientation relies on small auxiliary thrusters to accelerate the tank. The inertia of the liquid causes it to collect in the aft-end of the tank if the acceleration is forward. This technique requires that additional thrusters be added to the vehicle, that additional propellant be carried in the vehicle, and that an additional operational maneuver be executed. Another technique uses Liquid Acquisition Devices (LAD's) to positively position propellants. These devices rely on surface tension to hold the liquid within special geometries (i.e. vanes, wire-mesh channels, start-baskets). While avoiding some of the penalties of propulsive orientation, this technique requires the addition of complicated hardware inside the propellant tank and performance for long duration missions is uncertain. The subject of the present research is an alternate technique for positively positioning liquid within spacecraft propellant tanks: magnetic fields.

Hochstein, John I.↗

NASA NTRS1996

Gravitational Effects on Closed-Cellular-Foam Microstructure

Polyurethane foam has been produced in low gravity for the first time. The cause and distribution of different void or pore sizes are elucidated from direct comparison of unit-gravity and low-gravity samples. Low gravity is found to increase the pore roundness by 17% and reduce the void size by 50%. The standard deviation for pores becomes narrower (a more homogeneous foam is produced) in low gravity. Both a Gaussian and a Weibull model fail to describe the statistical distribution of void areas, and hence the governing dynamics do not combine small voids in either a uniform or a dependent fashion to make larger voids. Instead, the void areas follow an exponential law, which effectively randomizes the production of void sizes in a nondependent fashion consistent more with single nucleation than with multiple or combining events.

Noever, David A.↗

NASA NTRS2002

Recent Results from CHAMP Tracking and Accelerometer Data Analysis

The CHAMP mission's unique combination of sensors and orbit configuration will enable unprecedented improvements in modeling and understanding the Earth's static gravity field and its temporal variations. CHAMP is the first of two missions (GRACE to be launched in the early part of 02') that combine a new generation of Global Positioning System (GPS) receivers, a high precision three-axis accelerometer, and star cameras for the precision attitude determination. In order to isolate the gravity signal for science investigations, it is necessary to perform a detailed reduction and analysis of the GPS and Satellite Laser Ranging (SLR) tracking data in conjunction with the accelerometer and attitude data. Precision orbit determination based on the GPS and SLR tracking data will isolate the orbit perturbations, while the accelerometer data will be used to distinguish the non-gravitational forces from those due to the geopotential (static, and time varying). In preparation for the CHAMP and GRACE missions, extensive modifications have been made to NASA/GSFC's GEODYN orbit determination software to enable the simultaneous reduction of spacecraft tracking (e.g. GPS and SLR), three-axis accelerometer and precise attitude data. Several weeks of CHAMP tracking and accelerometer data have been analyzed and the results will be presented. Precision orbit determination analysis based on tracking data alone in addition to results based on the simultaneous reduction of tracking and accelerometer data will be discussed. Results from a calibration of the accelerometer will be presented along with the results from various orbit determination strategies.

Luthcke, S. B.↗

NASA NTRS2005

Perturbed Equations of Motion for Formation Flight Near the Sun-Earth L2 Point

This Memorandum Report consists of a compilation of three individual reports, of increasing complexity, describing investigations of formation flight of spacecraft in the vicinity of the L2 Sun-Earth 1ibration point. The individual reports form the following parts of this compilation: - Introduction to the relative motion of spacecraft about the Sun-Earth L2 Point - Linear and quadratic modelling and solution of the relative motion - Modelling the Perturbations - Elliptical Earth Orbit, Lunar Gravity, Solar Radiation Pressure, Thrusters. The three parts are self-contained, with somewhat, varying notation and terminology. After fair1y significant literature searches: this new work (of Parts 2 and 3) is deemed to be unique because it describes the primary perturbations to the description of relative motion between nearby spacecraft. The effect of the elliptical motion of the Earth about the Sun was verified to be the dominant perturbation to the circular restricted three body problem. Contributions due to lunar gravity and solar radiation pressure are seen to have much smaller effect.

Segerman, Alan M.↗