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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The atmosphere of Uranus - Results of radio occultation measurements with Voyager 2

The Uranian atmosphere is investigated on the basis of S-band and X-band occultation observations (including measurements of Doppler frequency perturbations) obtained during the Voyager 2 encounter with Uranus in January 1986. The data are presented in extensive tables and graphs and characterized in detail. The atmosphere is assumed to have an H2/He abundance ratio of about 85/15, but also to contain small amounts of CH4 at above-cloud relative humidity 30 percent, cloud-base relative humidity 78 percent, and below-cloud mixing ratio 2.3 percent by number density. Other parameters estimated include magnetic-field rotation period 17.24 h, 1-bar equatorial radius 25,559 + or - 4 km, polar radius 24,973 + or - 20 km, equatorial acceleration of gravity 8.69 + or - 0.01 m/sec sq, and atmospheric temperature 76 + or - 2 K (assuming 85 + or - 3 percent H2).

Lindal, G. F.↗
NASA NTRS1990

A post-Pioneer Venus reassessment of the Martian dayside ionosphere as observed by radio occultation methods

Global characteristics of the dayside ionosphere of Mars were investigated by reanalyzing the electron-density dayside altitude profiles obtained by Mariners 4, 6, 7, and 9 and the Viking 1 and 2. The properties of both the electron density peaks and the topside profiles with the behavior expected for a Chapman layer in the Mars ionosphere were compared with those observed at Venus with the Pioneer Venus. The results yield an improved picture of the solar zenith angle dependences of both the peaks and the scale heights of the ionosphere of Mars, and their comparison with Venus at solar minimum. It is shown that, under similar conditions where the incident solar wind dynamic pressure exceeds the peak ionospheric thermal pressure, the Martian dayside ionosphere peaks at higher altitudes in the flanks and has a greater scale height. Thus, Martian and Venusian ionospheres would present different obstacles to solar wind.

Zhang, M. H. G.↗
NASA NTRS1990

Voyager radio occultation by the Uranian rings: Structure, dynamics, and particle sizes

Diffraction of Voyager 2's 3.6 and 13 cm wavelength microwaves by the Uranian rings is removed through an inverse Fresnel transform filtering procedure that accommodates the significant eccentricity of the rings. Resulting 50 m resolution profiles at two observation longitudes: (1) reveal remarkably detailed and longitudinally varying structure, (2) provide eccentricity gradient profiles of Rings alpha, beta, and epsilon which bring into question current theoretical models for observed rigid precession, and (3) suggest that two possible unseen satellites may confine some of the very sharp edges observed via resonant interactions.

Gresh, Donna Leigh↗
NASA NTRS1991

Resonance structures in Saturn's rings probed by radio occultation. I - Methods and examples

Individual and comparative analyses are conducted for 29 of the wavelike features revealed by optical depth profiles of Saturn's rings; of these, 18 are in Ring A, one is in Ring B, and 10 are in Ring C. Only 20 of these were identifiable with known resonances, and all eight of the unexplained wave features are in Ring C. For 14 weak density waves in Ring A, a linear density wave theory modeling of the waveform near resonance yields independent estimates of the surface mass density together with reliable estimates of resonance location.

Rosen, Paul A.↗
NASA NTRS1992

The atmosphere of Neptune - An analysis of radio occultation data acquired with Voyager 2

The vertical structure of Neptune's atmosphere is studied on the basis of recordings of the tracking signals received from Voyager 2 during its occultation by Neptune. The measurements began at a planetographic latitude of 62 deg north and ended near 45 deg south, and cover an altitude interval of about 5000 km. The 1-bar isobaric surface has equatorial and polar radii of 24,766 +/-15 km and 24,342 +/-30 km, respectively, and a corresponding oblateness of 0.0171 +/-0.0014. At this pressure, the temperature was 72 +/-2 K. The tropopause was detected approximately 40 km above the 1-bar level at a pressure of about 100 mbar. A comparison with IR observations indicates that the gas at the tropopause consists of 78-84-percent hydrogen by number density with the rest being mostly helium. The temperature in this region was 52 +/-2 K.

Lindal, Gunnar F.↗