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102 records · Page 6

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NASA NTRS2016

Seasonal and static Gravity Field of Mars from MGS, Mars Odyssey and MRO Radio Science

We present a spherical harmonic solution of the static gravity field of Mars to degree and order 120, GMM-3, that has been calculated using the Deep Space Network tracking data of the NASA Mars missions, Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). We have also jointly determined spherical harmonic solutions for the static and time-variable gravity field of Mars, and the Mars k(sub 2) Love numbers, exclusive of the gravity contribution of the atmosphere. Consequently, the retrieved time-varying gravity coefficients and the Love number k(sub 2) solely yield seasonal variations in the mass of the polar caps and the solid tides of Mars, respectively. We obtain a Mars Love number k(sub 2) of 0.1697 +/- 0.0027 (3- sigma). The inclusion of MRO tracking data results in improved seasonal gravity field coefficients C(sub 30) and, for the first time, C 50. Refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic C(sub 30) for approximately 1.5 solar cycles (16 years). This gravity model shows improved correlations with MOLA topography up to 15% larger at higher harmonics ( l = 60-80) than previous solutions.

Genova, Antonio↗

NASA NTRS1999

Dust Optical Properties derived from Sun/Sky Measurements and Satellite Data

We derive the optical properties of dust originating from the Sahara and nearby regions using a combination of ground based and satellite measurements. The AErosol ROBotic NETwork (AERONET) sun/sky radiances from Cap Verde and Sede Boker are used together with Landsat TM data over Senegal and the Atlantic Ocean. The data introduce a cascade of increasing complexity of dust optical properties: The sky aureole radiance is sensitive mainly to the dust size distribution; the TM data over the ocean at 150 deg scattering angle are also sensitive to the spectral refractive index from 470 to 2,210 nm. The TM data over the land measure the balance between the dust scattering and absorption of light reflected by the bright surface, thus very sensitive to dust spectral absorption. Sky radiance at scattering angle of 120 deg, add sensitivity to the dust nonsphericity. Preliminary results, indicative of the ambient dust in the entire atmospheric column, show that dust is less absorbing and with smaller nonspherical properties than anticipated from in situ measurements. Dust is dominated by particles with effective radius of 2 to 2.5 micron, refractive index for wavelengths less then 1 micron of 1.53-0.001i and nonsphericity that increases the phase function at 120 deg above that of spheres by 1.8 and 1.7 at 673 nm down to 1.2 and 1.3 for 1020 nm for Cap Verde and Sede Boker respectively. No significant nonsphericity effect is noticed for scattering angle of 150 deg. This agrees with a mixture of 30% and 45% respectively of Mishchenko et al (JGR, 102, 1997: plate 5 on page 16,841) "polydisperse equiprobable shape mixture of prolate and oblate spheroids with aspect ratios ranging from 1.4 to 2.21, with the rest being spherical particles.

Kaufman, Yoram J.↗

NASA NTRS2013

Light emitting, photovoltaic or other electronic apparatus and system

The present invention provides an electronic apparatus, such as a lighting device comprised of light emitting diodes (LEDs) or a power generating apparatus comprising photovoltaic diodes, which may be created through a printing process, using a semiconductor or other substrate particle ink or suspension and using a lens particle ink or suspension. An exemplary apparatus comprises a base; at least one first conductor; a plurality of substantially spherical or optically resonant diodes coupled to the at least one first conductor; at least one second conductor coupled to the plurality of diodes; and a plurality of substantially spherical lenses suspended in a polymer attached or deposited over the diodes. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes have a ratio of mean diameters or lengths between about 10:1 and 2:1. The diodes may be LEDs or photovoltaic diodes, and in some embodiments, have a junction formed at least partially as a hemispherical shell or cap.

Ray, William Johnstone↗

NASA NTRS2016

Light Emitting, Photovoltaic or Other Electronic Apparatus and System

Ray, William Johnstone↗

NASA NTRS1979

The Martian polar vortex - Theory of seasonal variation and observations of eolian features

Observations of eolian features in the south polar region of Mars show strikingly axisymmetric patterns. The paper presents an explanation for the patterns in terms of the simplest dynamical model possible. Piraglia's (1975) model is simplified by neglecting compressibility and by assuming a cylindrical rather than spherical geometry, but this model is extended by including the nonlinear transport terms (of order Rossby number) and the seasonal mass transfer terms. The proposed model is therefore focused on determining the surface stress in polar regions rather than the atmospheric structure. The model is described, the parameter values are discussed, and the solutions are compared with observations. It is shown that the model predicts seasonal behavior which can be divided into four periods: formation of the south polar cap, its maximum extent, sublimation, and absence.

French, R. G.↗

NASA NTRS1972

Atmospheric and surface properties of Mars obtained by infrared spectroscopy on Mariner 9

During the eleven month operational lifetime of Mariner 9, the infrared spectroscopy experiment obtained data over a large portion of Mars. Recently obtained spectra indicate that strong seasonal variations in the water vapor distribution over both polar regions occurred. The wettest atmospheric conditions observed so far contain 20 to 30 precipitable microns of water over the north polar cap during northern spring. A low resolution pressure map is presented which covers that portion of the planet between latitudes -60 deg and +25 deg. A more detailed study of the Coprates canyon indicates that at its lowest point the canyon floor must be at least 5 km below the rim. Applications of tidal theory to temperature fields derived from the spectra indicate diurnal surface pressure fluctuations of as much as 12 percent during the great dust storm of 1971-72. Qualitative arguments based on radiative transfer calculations for model dust clouds composed of spherical quartz particles suggest that particle radii during the storm were of the order of a few microns.

Conrath, B.↗

NASA NTRS1977

Injun 5 observations of vehicle potential fluctuations at 2500 km

The AFGL spherical electrostatic analyzers aboard the polar orbiting Injun 5 satellite were designed to measure the temperature and density of the plasma as well as the vehicle potential. Significant vehicle potential fluctuations were observed at altitudes near 2500 km in the nighttime, topside ionosphere. At auroral latitudes, precipitating magnetospheric electrons frequently drove the satellite to such strongly negative potentials that the ambient electrons were shielded from instruments. In such cases, simultaneous measurements can be used to calculate the vehicle potential. Potentials of up to -40 volts were observed during impulsive precipitation events. Within the plasma trough, vehicle potentials varied between -1.5 and -4 volts, as compared with the -0.5 to -1 volt observed in the polar cap. The source of this vehicle potential enhancement was ascribed to fluxes of photoelectrons that have escaped from the sunlit conjugate ionosphere.

Sagalyn, R. C.↗

NASA NTRS1994

Monitoring Mars with the Hubble Space Telescope: 1990-1991 observations

Images of Mars obtained using the Planetary Camera on the Hubble Space Telescope during 1990 and 1991 are described and analyzed. Multispectral images of Mars record the martian season between L(sub s) = 348 deg and 60 deg corresponding to late winter and spring in the northern hemisphere. The wavelengths of these observations varied between 230 nm in the ultraviolet and 890 nm in the near infrared. We use these images to discuss atmospheric and polar phenomena, to constrain the aerosols and ozone in the martian atmosphere, and to compare surface albedo features within this data set as well as with previous observations. Two methods are used to constrain the opacity of the martian atmosphere: comparisons of ultraviolet images with atmospheric scattering models and examination of contrast changes of surface features observed at visible wavelengths. Our observations are consistent with a Mars which was quite different from the planet when it was viewed by Viking; we estimate an upper limit of 0.1 for equatorial dust opacity near vernal equinox, compared to values of 0.4 to 0.5 measured in Chryse by Viking Lander 1. Later, at L(sub s) = 60 deg, and upper limit of 0.2 was found for dust in the southern hemisphere. Except for suggestions of local dust activity near the north polar cap in late spring, there was no visual evidence of dust storms on the planet. The Hartley band of ozone is within the F230W filter bandpass, and the 230W/336W ratio is therefore sensitive to ozone. High latitude ozone is observed at a concentration similar to that observed by Mariner 9; a seasonal dependence in ozone concentration was observed with concentration decreasing at northern arctic latitudes and increasing at southern midlatitudes as L(sub s) increases from 350 deg to 60 deg. Despite the difference in dust loading, the behavior of condensate clouds and the recession of the north polar cap are consistent with those observed during Viking years. Late winter images of the north polar region reveal an active north polar hood with a maximum (UV) opacity of about 0.25 near 50 deg latitude; the hood seems to have an annular form, with the central, polar regions having smaller opacity. Clouds observed in the northern hemisphere to the south of the hood boundary are suggestive of fronts similar to those observed during the Mariner 9 mission. A diurnal variation in the hood clouds which is (anti) correlated with the amount of water vapor in the atmosphere is noted. Images were deconvolved using the Richardson-Lucy iterative algorithm to remove the defocussing effects of the spherical aberration of the HST primary. Even when Mars subtended less than 5 arcsec, in May 1991, the images were scientifically useful and comparable to photographic images obtained at opposition. Although the data are subject to the solar pointing constraint for HST, the relatively slow movement of the allowed observation window, which is more than one half martian year, with respect to the martian seasons will permit us to address the question of major variations in the martian atmosphere.

James, Philip B.↗

NASA NTRS2013

Vertical Distribution of Dust and Water Ice Aerosols from CRISM Limb-geometry Observations

[1] Near-infrared spectra taken in a limb-viewing geometry by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter provide a useful tool for probing atmospheric structure. Specifically, the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved. More than a dozen sets of CRISM limb observations have been taken so far providing pole-to-pole cross sections, spanning more than a full Martian year. Radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations. Both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well-mixed or Conrath-v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes. Significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season. Dust typically extends to higher altitudes (approx. 40-50km) during the perihelion season than during the aphelion season (<20km), and the Hellas region consistently shows more dust mixed to higher altitudes than other locations. Detached water ice clouds are common, and water ice aerosols are observed to cap the dust layer in all seasons.

Atmosphere↗

NASA NTRS2006

Techniques for Surface-Temperature Measurements and Transition Detection on Projectiles at Hypersonic Velocities--Status Report No. 2

The latest developments in a research effort to advance techniques for measuring surface temperatures and heat fluxes and determining transition locations on projectiles in hypersonic free flight in a ballistic range are described. Spherical and hemispherical titanium projectiles were launched at muzzle velocities of 4.6-5.8 km/sec into air and nitrogen at pressures of 95-380 Torr. Hemisphere models with diameters of 2.22 cm had maximum pitch and yaw angles of 5.5-8 degrees and 4.7-7 degrees, depending on whether they were launched using an evacuated launch tube or not. Hemisphere models with diameters of 2.86 cm had maximum pitch and yaw angles of 2.0-2.5 degrees. Three intensified-charge-coupled-device (ICCD) cameras with wavelength sensitivity ranges of 480-870 nm (as well as one infrared camera with a wavelength sensitivity range of 3 to 5 microns), were used to obtain images of the projectiles in flight. Helium plumes were used to remove the radiating gas cap around the projectiles at the locations where ICCD camera images were taken. ICCD and infrared (IR) camera images of titanium hemisphere projectiles at velocities of 4.0-4.4 km/sec are presented as well as preliminary temperature data for these projectiles. Comparisons were made of normalized temperature data for shots at approx.190 Torr in air and nitrogen and with and without the launch tube evacuated. Shots into nitrogen had temperatures ~6% lower than those into air. Evacuation of the launch tube was also found to lower the projectile temperatures by approx.6%.

Bogdanoff, D. W.↗

NASA NTRS1998

The Atmospheric Structure of Triton and Pluto

The goal of this research was to better determine the atmospheric structures of Triton and Pluto through further analysis of three occultation data sets obtained with the Kuiper Airborne Observatory (KAO.) As the research progressed, we concentrated our efforts on the Triton data, as this appeared to be the most fruitful. Three papers have been prepared as a result of this research. The first paper presents new results about Triton's atmospheric structure from the analysis of all ground-based stellar occultation data recorded to date, including one single-chord occultation recorded on 1993 July 10 and nine occultation lightcurves from the double-star event on 1995 August 14. These stellar occultation observations made both in the visible and in the infrared have good spatial coverage of Triton, including the first Triton central-flash observations, and are the first data to probe the altitude level 20-100 km on Triton. The small-planet lightcurve model of J. L. Elliot and L. A. Young was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude, indicating that Triton's atmosphere is spherically symmetric at approximately 50 km altitude to within the error of the measurements; however, asymmetry observed in the central flash indicates the atmosphere is not homogenous at the lowest levels probed (approximately 20 km altitude). From the average of the 1995 occultation data, the equivalent isothermal temperature of the atmosphere is 47 plus or minus 1 K and the atmospheric pressure at 1400 km radius (approximately 50 km altitude) is 1.4 plus or minus 0.1 microbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989. The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model. In our opinion, the disagreement in temperature and pressure is probably due to modeling problems at the microbar level, since measurements at this level have not previously been made. Alternatively, the difference could be due to seasonal change in Triton's atmospheric structure. The second paper reports observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. The most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years -- significantly faster than predicted by published frost model for Triton. Our results suggests that permanent polar caps on Triton play a dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto. A third paper 'Global Warming on Triton' will appear in a the January 1999 issue of Sky and Telescope.

Elliot, James L.↗

NASA NTRS2005

Tumbleweed Rovers

Tumbleweed rovers, now undergoing development, are lightweight, inflatable, approximately spherical exploratory robotic vehicles designed to roll across terrain, using only wind for propulsion. Tumbleweed rovers share many features with beach-ball rovers, which were discussed in several prior NASA Tech Briefs articles. Conceived for use in exploring remote planets, tumbleweed rovers could also be used for exploring relatively inaccessible terrain on Earth. A fully developed tumbleweed rover would consist of an instrumentation package suspended in an inflated twolayer (nylon/polypropylene) ball. The total mass of the rover would be of the order of 10 kg, the diameter of the ball when inflated would be 2 meters, and the minimum wind speed needed for propulsion would be about 5 m/s. The instrumentation package would contain a battery power supply, sensors, a Global Positioning System (GPS) receiver, and a radio transmitter that would send the sensor readings and the GPS position and time readings to a monitoring station via a satellite communication system. Depending on the specific exploratory mission, the sensors could include a thermometer, a barometer, a magnetometer (for studying the terrestrial magnetic field and/or detecting buried meteorites), a subsurface radar system (for measuring ice thickness and/or detecting buried meteorites), and/or one or two diametrally opposed cameras that would take the part of sending two side-looking images out. In the planned Antarctic field test, a prototype tumbleweed rover was released at a location near the South Pole. Using the global Iridium satellite network to send information about its position, the rover transmitted temperature, pressure, humidity, and light intensity data to NASA s Jet Propulsion Laboratory. The rover reached speeds of 30 km per hour over the Antarctic ice cap, and traveled at an average speed of about 6 km per hour. The test was designed to confirm the rover s long-term durability in an extremely cold environment, with the goal being eventual use of the device to explore the Martian polar caps and other planets in the solar system. On future Antarctic exploratory missions, tumbleweed rovers might be used to acquire sensor data for studies of global warming, ozone depletion, and impacts of meteorites.

Behar, Alberto↗