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NASA NTRS1972

The normalization of solar X-ray data from many experiments.

A conversion factor is used to convert Geiger (GM) tube count rates or ion chamber currents into units of the incident X-ray energy flux in a specified passband. A method is described which varies the passband to optimize these conversion factors such that they are relatively independent of the spectrum of the incident photons. This method was applied to GM tubes flown on Explorers 33 and 35 and Mariner 5 and to ion chambers flown on OSO 3 and OGO 4. Revised conversion factors and passbands are presented, and the resulting absolute solar X-ray fluxes based on these are shown to improve the agreement between the various experiments. Calculations have shown that, although the GM tubes on Explorer 33 viewed the Sun off-axis, the effective passband did not change appreciably, and the simple normalization of the count rates to the count rates of a similar GM tube on Explorer 35 was justified.

Wende, C. D.↗

NASA NTRS1974

Electrons and protons accelerated in Mercury's magnetic field

Fluxes of protons with energies of about 550 kev and electrons with energies of about 300 kev which exceed approximately 10,000 and 100,000 per sq cm per sec, respectively, have been discovered in the magnetosphere of Mercury. Electron fluxes greater than 1000 per sq cm per sec are also observed in the outbound pass of the Mariner 10 spacecraft through the magnetosheath. The intensity vs time profiles of the particle fluxes in the magnetosphere appear with sudden onsets beginning at interplanetary background levels and persisting for times equivalent to their being distributed spatially over regions having a scale size comparable to the planetary radius. It is shown that the radiation events observed in the magnetosphere and magnetosheath are transient and are not interpretable in terms of stable trapped particle populations.

Simpson, J. A.↗

NASA NTRS1976

Solar radiation pressure effects on the Helios spacecraft

A mathematical model of the solar radiation force and torques, developed for the Mariner 10 Venus/Mercury spacecraft mission, was used for a detailed analysis of the effects of solar light pressure on the Helios spacecraft. Due to the fact that the main body of the Helios spacecraft is a surface of enclosure, inside of which most of the reradiated thermal energy is lost, expressions for the portion of the solar radiation force, produced by the thermal reradiation, had to be given a different form. Hence the need for the derivation of a somewhat different theoretical model for the force acting on the main body of the spacecraft.

Georgevic, R. M.↗

NASA NTRS1981

Quasi-periodic climatic changes on Mars and earth

Evidence of climatic changes on Mars and the earth due to geologic and astronomical variations is discussed. Finely striped ice-free bands in the Martian polar caps have been taken to indicate that long term variations in the orbit and axial tilt of Mars have precipitated these features at the rate of a mm/yr. Photogrammetric and photometric methods have contributed to measurements of the composition and depth of the Martian caps (14-46 m), and observations of higher solar energy absorption in the northern ice cap implies greater dust deposition in that region than on the south cap; however, the transport mechanisms are not well understood. Comparisons of earth and Martian climatic variations data are made, noting a lack of information on the age intervals of marine and nonmarine sediments on the earth. The possibilities of using quantitative data other than layer thickness to constrain climate models are discussed, and the slope or albedo of layers, or the spacing of polar undulations are suggested.

Cutts, J. A.↗

NASA NTRS1983

The geology of the terrestrial planets

Knowledge regarding the geology of the terrestrial planets has increased considerably during the last four years. The present investigation provides a brief summary of work during these years on the geology of Mercury, Venus, moon, and Mars. Following the Mariner 10 encounter with Mercury in 1974, the geologic history of the planet was broadly outlined by Strom (1979). McCauley et al. (1981) recognized several facies of ejecta around Caloris. Hostetler and Drake (1980) showed that unless Mercury received more than 60-70 percent of its thermal energy from tidal interactions, it must have undergone early, almost global melting. Knowledge of the Venusian surface has increased substantially over the last few years both through improvement of earth-based observations and in connection with the Pioneer Venus mission. A topographic map of Venus is presented. Attention is also given to the composition and character of lunar highlands, the evolution of different maria, photographs obtained of almost the entire planet Mars, and Martian craters and volcanism.

Carr, M. H.↗

NASA NTRS1994

Roles of drizzle in a one-dimensional third-order turbulence closure model of the nocturnal stratus-topped marine boundary layer

This study focuses on the effects of drizzle in a one-dimensional third-order turbulence closure model of the nocturnal stratus-topped marine boundary layer. When the simulated drizzle rate is relatively small (maximum approximately equal to 0.6 mm/day), steady-state solutions are obtained. The boundary layer stabilizes essentially because drizzle causes evaporative cooling of the subcloud layer. This stabilization considerably reduces the buoyancy flux and turbulence kinetic energy below the stratus cloud. Thus, drizzle tends to decouple the cloud from the subcloud layer in the model, as suggested by many observational studies. In addition, the evaporation of drizzle in the subcloud layer creates small scattered clouds, which are likely to represent cumulus clouds, below the solid stratus cloud in the model. The sensitivity experiments show that these scattered clouds help maintain a coupled boundary layer. When the drizzle rate is relatively large (maximum approximately equal to 0.9 mm/day), the response of the model becomes transient with bursts in turbulent fluxes. This phenomenon is related to the formation of the scattered cloud layer below the solid stratus cloud. It appears that the model is inadequate to represent the heat and moisture transport by strong updrafts covering a small fractional area in cumulus convection.

Wang, Shouping↗

NASA NTRS2001

Toward a Unified Parameterization of the Boundary Layer and Moist Convection: Simulations of Clear and Cloudy Convection - Part 3

A model that employs a new form of mass-flux closure (described in Part I of this paper) is applied to a variety of clear and cloudy planetary boundary layers (PBLs) including dry convection from the Wangara Experiment, trade wind cumulus from the Barbados Oceanographic and Meteorological Experiment (BOMEX), and marine stratocumulus from the Atlantic Stratocumulus Experiment (ASTEX). For Wangara, the simulated variances and fluxes match that expected from similarity arguments, while the mean state is a little less mixed than the observations. In the BOMEX simulation. the shape and magnitude of the fluxes and the turbulence kinetic energy budget agree with LES results and observations. However, the liquid water mixing ratio is too large. This is attributed to an underprediction of the skewness. In agreement with observations from the ASTEX experiment, many of the model-simulated fields distinctly reflect a regime in transition between the trade wind cumulus and the classic stratocumulus-topped boundary layers. In general, the simulated entrainment rate tends to be a little underpredicted in regimes where there is little cloud-top radiative cooling (Wangara and BOMEX), while it is overpredicted in regimes where this process is more critical (e.g., ASTEX). Prior work suggests that this may be related to the manner in which the pressure terms are parameterized in the model. Overall, the model is able to capture some key physical features of these PBL regimes, and appears to have the potential to represent both cloud and boundary layer processes. Thus, this approach is a first step toward unifying these processes in large-scale models.

Lappen, Cara-Lyn↗

NASA NTRS1974

Mariner-9 based simulation of radiative convective temperature changes in the Martian dust-laden atmosphere-soil system

A numerical simulation of radiative, conductive, and convective heat transfer of the Martian dust-laden atmosphere-soil system is presented with particular emphasis given to heating/cooling in regions of sharp variation in temperature or absorption and its resultant impact on outgoing planetary spectral radiance, as measured by the Mariner 9 IRIS. Thermal coupling between the ground and atmospheric subsystems is modeled by the total heat flux balance at the interface. In the simulation procedure, local thermodynamic equilibrium (LTE) is assumed, and a combined strong-weak line transmission function permits short- and long-range exchanges of energy from the surface toward space. Direct absorption of insolation in the near-IR bands by both silicate dust and CO2 is incorporated.

Dannevik, W. P.↗

NASA NTRS1974

The ionospheres of Mars and Venus

Observations made by spacecraft in the Mariner and Venera series have provided considerable knowledge of the structure of the ionospheres and atmospheres of Mars and Venus. This paper begins with brief but complete discussions of these measurements and their interpretations. The principles for constructing models of ionospheres are presented from the standpoint of mass, momentum, and energy conservation. The relevant ion chemistry is presented, and the meaning and use of plasma scale heights are discussed. The models discussed are the model of Cloutier and co-workers; the models of Banks and Axford, of Whitten, and of Herman and co-workers; the model developed by McElroy and Strobel to account for the nighttime ionosphere of Venus; and the models developed by a number of investigators for the thermal structure of the Martian and Venusian ionospheres.

Whitten, R. C.↗

NASA NTRS1979

Prediction of the occurrence and intensity of magnetospheric substorms

The solar wind and IMF data obtained by the Venus probe Mariner 5 (at a distance of 460 earth radii) and by the earthbound Explorer 34 satellite, on June 24, 25, and 26, 1967 were examined. It is demonstrated that the occurrence and intensity of magnetospheric substorms can be predicted about 1-3 hours prior to their onsets by monitoring the energy coupling function at a distance of a few hundred earth radii upstream of the solar wind. It appears that the 'epsilon signal' propagates with different speeds, perhaps depending on the propagation time of disturbances which increase epsilon.

Akasofu, S.-I.↗

NASA NTRS1984

Electromagnetic bias of 10-GHz radar altimeter measurements of MSL

Electromagnetic bias, the small difference that exists between the radar measured mean sea level and the geometric mean sea level is an important issue in high precision satellite altimetry. Present day satellite altimetry has achieved, with SEASAT-1, a precision of 5 cm rms in the range measurement. Future altimeter designs are expected to improve the range measurement precision to cm rms. In order to exploit the capability of these precise radar altimeters are marine geodesy and oceanography, it is necessary to understand and account for all of the known biases in the range measurement. The electromagnetic bias or the EM bias, which has been attributed to the observed fact that ocean wave troughs tend to be better reflectors of nadir viewing microwave radar energy than ocean wave crests, can be observed with high resolution airborne radar. This report presents the results of the EM bias measurements made by NRL using an airborne radar altimeter operating at 10 GHz with a 1 ns range resolution. Data were taken for various sea states and wind conditions. The experimental results are compared with current theories.

Choy, L. W.↗

NASA NTRS1988

Provenance of the K/T boundary layers

An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively.

Hildebrand, A. R.↗

NASA NTRS1993

Oxidation state of the Earth's upper mantle during the last 3800 million years: Implications for the origin of life

A popular, as well as scientifically rigorous, scenario for the origin of life on Earth involves the production of organic molecules by interaction of lightning (or other forms of energy) with a chemically reducing atmosphere in the early history of Earth. Experiments since the 1950's have convincingly demonstrated that the yield of organic molecules is high when the atmosphere contains molecular hydrogen, methane, ammonia, and water vapor. Additional work has also shown that such a highly reducing atmosphere might not, however, have been sufficiently long-lived in the presence of intense solar ultraviolet radiation for life to have formed from it. One way of maintaining such an atmosphere would be to have a continual replenishment of the reduced gases by prolonged volcanic outgassing from a reducing of Earth's interior. The length of time that this replenishment might need to continue is in part constrained by the flux of asteroids onto the Earth's surface containing sufficient energy to destroy most, if not all, life that had developed up to that point in time. If a reducing atmosphere is a key ingredient for the origin of life on Earth, the time of the last environmental sterilization due to large impacts would be an important constraint. In a deep marine setting (e.g., hydrothermal vent), the last global sterilization might have occurred at 4200-4000 Ma. On the Earth's surface, the last global sterilization event might have occurred at 4000-3700 Ma. If these are meaningful constraints, how likely is it that a reducing atmosphere could have survived on the Earth until about 3800 Ma ago? Due to the importance of replenishing this atmosphere with reducing components by volcanic outgassing from the mantle, geochemical information on the history of the mantle's oxidation state would be useful for addressing this question. Geochemical and experimental data discussed in this abstract suggest that extrusive mafic volcanics derived from the upper mantle have had oxidation states near the fayalite-magnetite quartz buffer throughout the last 3800 Ma. At magmatic temperatures, the gases released from volcanoes having this oxidation state would have been, as they are today, composed dominantly of carbon dioxide and water vapor, and would not contain the ingredients for maintaining a reducing atmosphere. Consequently, geochemical data do not favor the survival of a reducing atmosphere until about 3800 Ma. Alternative venues and pathways for the origin of life need to be investigated (e.g., hydrothermal vents along oceanic ridges).

Delano, J. W.↗

NASA NTRS2003

Solidification Using a Baffle in Sealed Ampoules (SUBSA)

Solidification Using a Baffle in Sealed Ampoules (SUBSA) will be the first materials science experiment conducted in the Microgravity Science Glovebox (MSG) Facility at the International Space Station (ISS) Alpha. The launch is schedule for May 31, 2002. Using the specially developed furnace, 10 Te and Zn-doped single crystals of InSb will be directionally solidified in microgravity. A key goal of the SUBSA investigation is to (i) clarify the origin of the melt motion in space laboratories and (ii) to reduce the magnitude of the melt motion to the point that it does not interfere with the transport phenomena. These goals will be accomplished through a special ampoule and furnace design. A disk-shaped baffle, positioned close to the freezing front, is used to reduce melt motion. Furthermore, the solidification will be visualized by using a transparent furnace, with a video camera, continuously sending images to the earth. This allows detection of bubbles and melt de-wetting that could cause surface tension driven convection. In preparation for the space experiments, 30 ground-based experiments were conducted. The results of ground based tests and numerical modeling will be presented. Based on numerical modeling, 12 mm 1D silica ampoules were selected. The small diameter ampoule favors closer placement of the baffle to the interface, without excessive radial segregation caused by forced convection while providing more damping of natural convection. The parts in the silica ampoule include 2 carbon springs made by Energy Science Laboratories, Inc., a pyrocarbon-coated graphite cylinder, pyrocarbon-coated graphite a baffle with the shaft and the InSb charge with the seed crystal grown by W.A. Bonner of Crystallod Inc.

Marin, C.↗

NASA NTRS1974

Preliminary report of results from the plasma science experiment on Mariner 10

Preliminary measurements of electron number density and temperature near Venus and Mercury and some results on flow speeds are presented. It is concluded that the interaction of the solar wind with Venus probably results in a bow shock characterized by H/r = 0.01 (ratio of the ionospheric scale height to the planetocentric distance of the nose of the ionopause); an extended exosphere appears unlikely. This direct interaction is indicated by the behavior of electrons with energies of 100-500 eV. Some unusual downstream effects suggest a comet-like tail several hundred scale lengths long. Near Mercury, a fully developed bow shock and magnetosheath were observed. Inside the magnetosheath there is a region analogous to the magnetosphere of the earth and populated by electrons of lower density and temperature than those found in the solar wind. The solar wind ram pressure corresponds to a stagnation pressure equivalent to a 170 gamma magnetic field. The strong solar wind interaction with Mercury is definitely magnetic, but not ionospheric or atmospheric. Spectra and particle flux varied widely while the spaceship was within the magnetosphere itself; temporal events like substorms may be responsible.

Bridge, H. S.↗

NASA NTRS1975

Current cosmic-ray programs in the United States

Approved NASA cosmic ray programs for the next five years are reviewed. In deep space, four new missions are planned. The first two, Helios A and B, will go inwards to approximately 0.3 AU, and the second two, Mariner Jupiter-Saturn, will go outwards to Saturn at 9.5 AU. Two missions in the earth orbital program promise to provide major new information on cosmic ray isotopes and on very heavy cosmic rays. These are the C mission of the International Sun-Earth Explorer, and the C mission of the High Energy Astronomy Observatory. The balloon research program is also mentioned.

Opp, A. G.↗

NASA NTRS1976

Comparison of remotely sensed continental-shelf wave spectra with spectra computed by using a wave refraction computer model

An initial attempt was made to verify the Langley Research Center and Virginia Institute of Marine Science mid-Atlantic continental-shelf wave refraction model. The model was used to simulate refraction occurring during a continental-shelf remote sensing experiment conducted on August 17, 1973. Simulated wave spectra compared favorably, in a qualitative sense, with the experimental spectra. However, it was observed that most of the wave energy resided at frequencies higher than those for which refraction and shoaling effects were predicted, In addition, variations among the experimental spectra were so small that they were not considered statistically significant. In order to verify the refraction model, simulation must be performed in conjunction with a set of significantly varying spectra in which a considerable portion of the total energy resides at frequencies for which refraction and shoaling effects are likely.

Poole, L. R.↗

NASA NTRS1978

Performance comparison of earth and space storable bipropellant systems in interplanetary missions

The paper evaluates and compares the performance of earth-storable and space-storable liquid bipropellant propulsion systems in high-energy planetary mission applications, including specifically Saturn and Mercury orbiters, as well as asteroid and comet rendezvous missions. The discussion covers a brief review of the status of space-storable propulsion technology, along with an illustrative propulsion module design for a three-axis stabilized outer planet and cometary mission spacecraft of the Mariner class. The results take revised Shuttle/Upper Stage performance projections into account. It is shown that in some of the missions the performance improvement achievable in the ballistic transfer mode with space-storable spacecraft propulsion can provide a possible alternative to the use of solar-electric propulsion.

Meissinger, H. F.↗