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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Elemental abundance analyses with coadded DAO spectrograms. VI - The mercury-manganese stars Nu Cancri, Iota Coronae Borealis and HR 8349

The elemental abundances of three mercury-manganese stars, Nu Cancri, Iota Coronae Borealis, and HR 8349, were found to be consistent with previous analyses of this series. As Iota CrB is a double-lined spectroscopic binary with a small velocity amplitude for most of its period, its study required determining whether the observed lines were produced in the primary or secondary or both. The derived abundances and effective termperatures were used along with those of mercury-manganese stars previously analyzed in order to extend the study of probable correlations between abundances, with the effective temperature and surface gravity in accordance with radiative diffusion explanations.

Adelman, Saul J.↗
NASA NTRS1990

A diffusion source for sodium and potassium in the atmospheres of Mercury and the moon

Deep grain-boundary diffusion and regolith diffusion through a fractured crust and regolith can account not only for the Na/K ratios observed in the Mercurian and lunar atmospheres, but the large Na abundance enhancement of Mercury over lunar levels. A hot component of Na and K at Mercury is noted to be smaller in proportion to the total abundances of these two constituents than at the moon; this hot component is consistent with a population of meteoritic substances similar to lunar ones, as well as with a surface composition which has undergone no greater K depletion than that of the moon.

Sprague, Ann L.↗
NASA NTRS1990

Energy coupling in the magnetospheres of earth and Mercury

The mechanisms involved in the dissipation of solar-wind energy during magnetospheric substorms are considered theoretically, comparing models for earth and Mercury. In the model for terrestrial substorms, IMF lines interconnect with terrestrial field lines near the front of the magnetosphere and are dragged back, carrying plasma and energy, to form tail lobes; a magnetic neutral region is then formed by reconnection of the open lines as the plasma sheet thins, and reconnective heating and acceleration of tail plasma lead to plasma inflow at the poles and formation of a plasmoid flowing down the tail at high velocity. Analogous phenomena on Mercury could produce precipitation of particles carrying 10-1000 GW of power into 'auroral zones' on the dark side of the planet. The feasibility of remote or in situ observations to detect such processes is discussed.

Baker, D. N.↗
NASA NTRS1991

Mercury Orbiter: Report of the Science Working Team

The results are presented of the Mercury Orbiter Science Working Team which held three workshops in 1988 to 1989 under the auspices of the Space Physics and Planetary Exploration Divisions of NASA Headquarters. Spacecraft engineering and mission design studies at the Jet Propulsion Lab were conducted in parallel with this effort and are detailed elsewhere. The findings of the engineering study, summarized herein, indicate that spin stabilized spacecraft carrying comprehensive particles and fields experiments and key planetology instruments in high elliptical orbits can survive and function in Mercury orbit without costly sun shields and active cooling systems.

Belcher, John W.↗
NASA NTRS1990

Orbit determination and gravitational field accuracy for a Mercury transponder satellite

Covariance studies were performed to investigate the orbit determination problem for a small transponder satellite in a nearly circular polar orbit with 4-hour period around Mercury. With X band and Ka band Doppler and range measurements, the analysis indicates that the gravitational field through degree and order 10 can be solved for from as few as 40 separate 8-hour arcs of tracking data. In addition, the earth-Mercury distance can be determined during each ranging period with about 6-cm accuracy. The expected geoid accuracy is 10 cm up through degree 5, and 1 m through degree 8. The main error sources were the geocentric range measurement error, the uncertainties in higher degree gravity field terms, which were not solved for, and the solar radiation pressure uncertainty.

Vincent, Mark A.↗
NASA NTRS1991

Radar and spacecraft ranging to Mercury between 1966 and 1988

Improved solutions have been obtained for the orbit and equatorial cross-section of Mercury using radar ranging data spanning 22 years. These data have yielded new results on the precession of Mercury's perihelion and better limits on a possible time variation in the gravitational constant G.

Anderson, John D.↗
NASA NTRS1949

Spark ignition of flowing gases I : energies to ignite propane-air mixtures in pressure range of 2 to 4 inches mercury absolute

Ignition studies of flowing gases were made to obtain information applicable to ignition problems in gas-turbine and ram-jet aircraft propulsion systems operating at altitude conditions.Spark energies required for ignition of a flowing propane-air mixture were determined for pressure of 2 to 4 inches mercury absolute, gas velocities of 5.0 to 54.2 feet per second, fuel-air ratios of 0.0607 to 0.1245, and spark durations of 1.5 to 24,400 microseconds. The results showed that at a pressure of 3 inches mercury absolute the minimum energy required for ignition occurred at fuel-air ratios of 0.08 to 0.095. The energy required for ignition increased almost linearly with increasing gas velocity. Shortening the spark duration from approximately 25,000 to 125 microseconds decreased the amount of energy required for ignition. A spark produced by the discharge of a condenser directly into the spark gap and having a duration of 1.5 microseconds required ignition energies larger than most of the long-duration sparks.

Swett, Clyde C , Jr↗
NASA NTRS1994

Mercury: Mid-infrared (7.3 - 13.5 microns) spectroscopic observations showing features characteristic of plagioclase

Mid-infrared spectroscopic observations of the surface of Mercury are reported for the wavelength range 7.3 to 13.5 microns. The observed spectral radiance emanated from equatorial and low latitude regions between 110-130 deg Mercurian longitude. The area is primarily an intercrater plain. The spectra show distinct and recognizable features, the principal Christiansen emission peak being the most prominent. The Christiansen feature strongly suggests the presence of plagioclase (Ca,Na)(Al,Si)AlSi2O8, (in particular labradorite: Ab(50) - Ab(30)). In addition we have studied the effects of thermal gradients to gain insight into the effects of thermal conditions on the spectral radiance of rock samples. This simulates the thermophysical effects as the rotating surface of Mercury is alternately heated and cooled. The spectral features of the samples are retained; however, the relative and absolute amplitudes vary as illustrated by laboratory reflectance and emittance spectra from quartzite.

Kozlowski, R. W. H.↗
NASA NTRS1976

Mercury: Exploration of a Planet

The flight of the Mariner 10 spacecraft to Venus and Mercury is detailed in animation and photography. Views of Mercury are featured. Also included is animation on the origin of the solar system. Dr. Bruce C. Murray, director of the Jet Propulsion Laboratory, comments on the mission.

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NASA NTRS1960

Orbital Thermal Control of the Mercury Capsule

The approach to orbital thermal control of the Project Mercury capsule environment is relatively unsophisticated compared with that for many unmanned satellites. This is made possible by the relatively short orbital flight of about 4 1/2 hours and by the presence of the astronaut who is able to monitor the capsule systems and compensate for undesirable thermal conditions. The general external features of the Mercury configuration as it appears in the orbital phase of flight are shown. The conical afterbody is a double-wall structure. The inner wall serves as a pressure vessel for the manned compartment, and the outer wall, of shingle type construction, acts as a radiating shield during reentry. Surface treatment of the shingles calls for a stably oxidized surface to minimize reentry temperatures. The shingles are supported by insulated stringers attached to the inner skin. Areas between stringers are insulated by blankets of Thermoflex insulation. This insulation is especially effective at high altitude due to the reduction of its thermal conductivity with decreasing pressure. As a result of the design of the afterbody for the severe reentry conditions, the heat balance on the manned compartment indicates the necessity for moderate internal cooling to compensate for the heat generation due to human and electrical sources. This cooling is achieved by the controlled vaporization of water in the cabin and astronaut-suit heat exchangers.

Weston, Kenneth C.↗
NASA NTRS2001

A Minimal Radio and Plasma Wave Investigation For a Mercury Orbiter Mission

The primary thrust of the effort at The University of Iowa for the definition of an orbiter mission to Mercury is a minimum viable radio and plasma wave investigation. While it is simple to add sensors and capability to any payload, the challenge is to do reasonable science within limited resources; and viable missions to Mercury are especially limited in payload mass. For a wave investigation, this is a serious concern, as the sensor mass often makes up a significant fraction of the instrumentation mass.

Kurth, W. S.↗
NASA NTRS2001

Using Remotely Sensed Observations of Ancient Mare Deposits on the Moon as Possible Analogs to the Intercrater Plains on Mercury

Two commonly held models for the formation of the mercurian intercrater plains are: a global volcanic resurfacing event or basin-ejecta material. Although Mariner 10 images have provided morphologic and limited compositional information of the intercrater plains, the origin of these materials remains ambiguous. We examine whether Mariner 10 image at 355 (UV (ultraviolet)) and 575 nm (orange) can be used to distinguish between these models. Here we use Clementine image data (415 and 750 nm) for ancient lunar mare deposits to evaluate this suggestion. The inventorying of 'hidden' volcanic deposits is important to mercurian studies because they provide evidence of ancient volcanism, which yields clues to the thermal evolution of the planet. The greater abundance of intercrater plains on Mercury, relative to the intercrater plains observed within the lunar highlands, suggests that the resurfacing was comparably more intense. Mercury may represent an intermediate member of planet resurfacing; with the extremes being the Moon (approximately 17% resurfacing) and Venus (global resurfacing). Additional information is contained in the original extended abstract.

Gillis, J. J.↗
NASA NTRS2001

Radar Imaging of Mercury's North and South Poles at 3.5 cm Wavelength

The Goldstone Solar System Radar has been used to image the north and south poles of Mercury during the inferior conjunctions of February 2001 and June 2001. The sub-Earth latitude was -10.7 degrees in February during observations of the southern hemisphere, and +8.4 degrees in June during observations of the northern hemisphere. These excellent viewing angles provided an opportunity to resolve the radar bright material in polar craters at 6 km range resolution. Fine-scale (1.5 km) resolution images of the northern craters have previously been obtained at 13 cm wavelengths during the July 1999 inferior conjunction. However, due to geometric constraints, the Arecibo radar cannot observe the southern polar region of Mercury until 2004. Our new Goldstone 6 km data are a factor of two higher resolution than Arecibo data collected in March 1992 at 15 km range resolution, and will remain the most highly resolved images of the south polar region for the next few years. Additional information is contained in the original extended abstract.

Harcke, L. J.↗
NASA NTRS2001

The Distant Sodium Tail of Mercury

Models of the sodium atmosphere of Mercury predict the possible existence of a cornet-like sodium tail. Detection and mapping of the predicted sodium tail would provide quantitative data on the energy of the process that produces sodium atoms from the planetary surface. Previous efforts to detect the sodium tail by means of observations done during daylight hours have been only partially successful because scattered sunlight obscured the weak sodium emissions in the tail. However, at greatest eastern elongation around the March equinox in the northern hemisphere, Mercury can be seen as an evening star in astronomical twilight. At this time, the intensity of scattered sunlight is low enough that sodium emissions as low as 500 Rayleighs can be detected. Additional information is contained in the original extended abstract.

Potter, A. E.↗
NASA NTRS2002

Space Weathering Processes on Mercury

Like the Moon, Mercury has no atmosphere to protect it from the harsh space environment and therefore it is expected that it will incur the effects of space weathering. These weathering processes are capable of both creating regolith and altering its optical properties. However, there are many important differences between the environments of Mercury and the Moon. These environmental differences will almost certainly affect the weathering processes as well as the products of those processes. It should be possible to observe the effects of these differences in Vis/NIR spectra of the type expected to be returned by MESSENGER. More importantly, understanding these weathering processes and their consequences is essential for evaluating the spectral data returned from MESSENGER and other missions in order to determine the mineralogy and the iron content of the Mercurian surface. Theoretical and experimental work has been undertaken in order to better understand these consequences.

Noble, S. K.↗
NASA NTRS2003

Multi-Wavelength Observations of the Mercury Transit of November 1999

The Mercury transit of the Sun, 15 November 1999, was observed at the Prairie View Solar Observatory (PVSO) and with three channels of the TRACE satellite. These CCD observations enabled an objective study of the historic Black Drop under different conditions and with different filters. The Black Drop phenomenon has a much subtler counterpart referred to as the 'Gray Drop phenomenon', of which the former is a more prominent component of the latter. The optical causes of both effects are very similar and appear to require a sharp, uniform boundary of sufficient contrast (e.g. the solar limb against a sky at least as dark as the center of Mercury's disk), coupled with a blurring agent. Without all these conditions in place, the visibility of the Black Drop is greatly reduced or eliminated. Such was the case of the transit as observed with Ha at line center, the TRACE UV (1600A) channel, and the EUV (171A) channel. This suppression of visibility in these cases was due to the contrast-lowering background of the chromosphere or corona.

Cudnik, B. M.↗
NASA NTRS2003

New Ground-based Spectral Observations of Mercury and Comparison with the Moon

Spectroscopic observations (400-670 nm) of Mercury were made at La Palma with the Nordic Optical Telescope (NOT) in June and July of 2002. Extensive observations of solar analog standard stars and validation spectra of 7 Iris and a variety of locations on the Moon were also collected. The 2002 Mercury data were also combined with previous observations (520-970 nm) from the Swedish Solar Vacuum Telescope (SVST). A spectrum (400-970 nm) calibrated to standard bidirectional geometry (alpha=i=30deg, e=0deg) was constructed based on the spectral slopes from 2002. The combined spectrum permits analysis with the Lucey lunar abundance relations for FeO and TiO2.

Blewett, D. T.↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Moon and Mercury

The session" Moon and Mercury" included the following reports:Helium Production of Prompt Neutrinos on the Moon; Vapor Deposition and Solar Wind Implantation on Lunar Soil-Grain Surfaces as Comparable Processes; A New Lunar Geologic Mapping Program; Physical Backgrounds to Measure Instantaneous Spin Components of Terrestrial Planets from Earth with Arcsecond Accuracy; Preliminary Findings of a Study of the Lunar Global Megaregolith; Maps Characterizing the Lunar Regolith Maturity; Probable Model of Anomalies in the Polar Regions of Mercury; Parameters of the Maximum of Positive Polarization of the Moon; Database Structure Development for Space Surveying Results by Moon -Zond Program; CM2-type Micrometeoritic Lunar Winds During the Late Heavy Bombardment; A Comparison of Textural and Chemical Features of Spinel Within Lunar Mare Basalts; The Reiner Gamma Formation as Characterized by Earth-based Photometry at Large Phase Angles; The Significance of the Geometries of Linear Graben for the Widths of Shallow Dike Intrusions on the Moon; Lunar Prospector Data, Surface Roughness and IR Thermal Emission of the Moon; The Influence of a Magma Ocean on the Lunar Global Stress Field Due to Tidal Interaction Between the Earth and Moon; Variations of the Mercurian Photometric Relief; A Model of Positive Polarization of Regolith; Ground Truth and Lunar Global Thorium Map Calibration: Are We There Yet?;and Space Weathering of Apollo 16 Sample 62255: Lunar Rocks as Witness Plates for Deciphering Regolith Formation Processes.

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