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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

An analysis of the Voyager 2 Ultraviolet Spectrometer occultation data at Uranus - Inferring heat sources and model atmospheres

Heat source information is derived here from the Voyager 2 Ultraviolet Spectrometer occultation data of Uranus. Analytic functions for the local heat dependence on altitude are used to obtain a temperature profile by solving the heat equation. The stellar entrance and exit occultation and a solar occultation are used to infer the thermal and density structure of the atmosphere. The least squares fit solution to the solar occultation data gives one source located at 1.8 x 10 exp -5 microbar with a strength of 0.056 +/- 0.01 erg/sq cm/s. Latitudinal temperature gradients are obtained.

Stevens, Michael H.↗
DOE OSTI2024

Large-scale Structure of the Heliospheric Current Sheets within the Heliosheath Inferred from Voyager 2 Observations

In this paper, we conducted an analysis of the heliospheric current sheets (HCSs) in the heliosheath (HS), utilizing observations by Voyager 2 between 2008 and 2018. Employing rigorous criteria, we identified a total of 34 HCSs that indicate significant changes in magnetic polarity. These occurrences were more prevalent during solar maximum periods when the HCS expanded to higher latitudes, coinciding with the spacecraft positioned at an average latitude of –31° from the solar equator. We determined certain features of the large-scale structures of the identified HCSs. Most importantly, employing two distinct methods indicates that the thickness of the HCSs within the HS ranges from ~0.003 to ~0.4 au with an average thickness of ~0.03 to ~0.1 au, depending on methods of event selection and fitting techniques. This thickness surpasses that known near 1 au or other heliospheric distances. It is also notably thicker than the typical proton inertial length, implying unfavorable conditions for magnetic reconnection. Additionally, our analysis reveals a frequent tilt of HCS planes relative to the solar equatorial plane by a varying angle up to several tens of degrees, likely implying a common occurrence of a warped structure of the HCS within the HS. Longitudinally, the HCS planes closely align with the Parker spiral field direction expected in the HS. Finally, for a large fraction of the identified HCS events, the HCS planes are likely characterized by a rotational discontinuity. These findings are valid within the limits of the 1 hr resolution data used in this study.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Plasma observations near Uranus - Initial results from Voyager 2

The results of observations of the spatial distribution and physical properties of the space plasma near Uranus with instrumentation on board Voyager 2 are described. The data revealed the existence of a magnetosphere that held a warm component with a temperature of 4-50 eV and a peak density of 2 protons/cu cm and a hot component with a temperature of a few electron volts and a density of about 0.1 proton/cu cm. Only the warm component was observed within the L shell. The numerous crossings made of the plasma sheet in the magnetotail were at locations which suggested that the magnetotail has a geometric structure similar to that of the earth magnetotail. Finally, possible sources of the magnetospheric plasma particles are discussed.

Bridge, H. S.↗
NASA NTRS1987

Uranian ring photometry - Results from Voyager 2

The rings of Uranus are characterized on the basis of an analysis of seven images obtained with a clear filter by Voyager 2 during its encounter with Uranus in January 1986. The data are presented graphically and compared with the predictions of theoretical models with different particle size distributions. Parameters determined include average particle Bond albedo 0.014 + or - 0.004, fractional area of the main rings in dust-size particles 0.002 or less, and average dust-particle size 1.0 + or - 0.3 microns for a Hansen-Hovenier (1974) distribution and a power-law distribution of spherical particles with spectral index 2.5 + or - 0.5.

Ockert, Maureen E.↗
NASA NTRS1987

Voyager 2 plasma ion observations in the magnetosphere of Uranus

Positive ion measurements in the magnetosphere of Uranus have been made by the Voyager 2 plasma science experiment. The paper presents an overview of the entire data set and a detailed analysis of the observations from the inner magnetosphere which complements and extends results reported elsewhere. Densities and temperatures are obtained from an analysis which incorporates details of the instrumental response. These results are then used to calculate flux tube particle and energy content to support the hypothesis that the plasma transport is controlled by a solar wind-driven magnetospheric convection system. Variations in the flux tube content suggest both a local source of plasma, produced from the neutral hydrogen corona of Uranus, and a nonlocal source, convected inwared and heated by adiabatic compression. In each case a proton composition is inferred. Sharp boundaries in the high-energy (approximately 1 keV) plasma population are interpreted in terms of the spatial extent of the magnetospheric convection, with significant shielding of the convection electric field. The convection theory is also used in a simulation of the low-energy (approximately 10 eV) ion component using the neutral hydrogen source, resulting in distribution functions which qualitatively agree with the observations.

Selesnick, Richard S.↗
NASA NTRS1988

Observations of energetic ion enhancements and fast neutrals upstream and downstream of Uranus' bow shock by the Voyager 2 spacecraft

Measurements of energetic ions and electrons upstream and downstream from Uranus obtained during the low energy charged particle experiment on Voyager 2 are discussed. The results indicate that energetic ions were present upstream of Uranus' bow shock and that their charcteristics, in terms of anisotropies and energy spectra, are consistent with an Uranian magnetospheric origin and are inconsistent with predictions of in situ acceleration via the Fermi mechanism. An upper limit to the flux of energetic neutrals escaping the magnetosphere is established, and the volume-averaged neutral hydrogen density inside 5 Uranian radii is constrained.

Krimigis, S. M.↗
NASA NTRS1993

Voyager 2 Test Of The Radar Time-Delay Effect

Report presents analysis of radio range measurements generated during superior solar conjunction of Voyager 2 spacecraft in December 1985. One in continuing series of studies directed toward verifying prediction, according to theory of general relativity, that electromagnetic signal propagating near Sun is delayed by solar gravitational field.

Krisher, Timothy P.↗
NASA NTRS1986

Voyager 2 radio science observations of the Uranian system Atmosphere, rings, and satellites

The results of preliminary analyses of radio occultation data obtained by Voyager 2 as it passed Uranus are described. The occultations took place between 2-7 deg S latitude and yielded atmospheric temperature profiles between pressure levels of 10-900 mbar, an altitude range of 100 km. The mole fractions of hydrogen and helium in the tropopause were estimated, in conjunction with IR data, to about 0.85 and 0.10-0.20, respectively. Radio signal intensity data indicated the presence of a cloud deck of CH4 ice at a pressure level of 1300 mbar and a temperature of 81 K, implying a CH4 mole fraction of 0.02 at very low altitudes. The ionosphere extended upward, in two levels, to more than 10,000 km altitude. The ring system was different than the one around Saturn and possessed cylindrical substructures. The radio data also permitted mass density estimates for the five major moons, i.e., about 1.40 gr/cu cm, a value which rules out cometary origins.

Tyler, G. L.↗
NASA NTRS1991

Micron-sized particles detected near Neptune by the Voyager 2 plasma wave instrument

Observations and an analysis are presented of the micron-sized-particle impacts observed by the plasma-wave instrument aboard the Voyager 2. After a detailed description of signals produced by the dust impacts, the impact noise is interpreted in terms of the number density and mass of the particles. The likely sources of the particles are discussed.

Gurnett, D. A.↗
NASA NTRS1979

An empirical polytrope law for solar wind thermal electrons between 0.45 and 4.76 AU: Voyager 2 and Mariner 10

Empirical evidence is presented that solar wind thermal electrons obey a polytrope law with polytrope index gamma = 1.175 plus or minus 0.03. The Voyager 2 and Mariner 10 data used as evidence are compared and discussed. The theoretical predictions that solar wind thermal electrons in the asymptotic solar wind should obey a polytrope law with polytrope index gamma = 1.16 plus or minus. The widespread impressions in the literature that solar wind electrons behave more like an isothermal than adiabatic gas, and the arguments that Coulomb collisions are the dominant stochastic process shaping observed electron distribution functions in the solar wind are reexamined, reviewed and evaluated. The assignment of the interplanetary potential as equal to approximately seven times the temperature of the thermal electrons is discussed.

Sittler, E. C., Jr.↗
NASA NTRS1986

Pointing calibration of the MKIVA DSN antennas Voyager 2 Uranus encounter operations support

The MKIVA DSN introduced significant changes to the pointing systems of the 34-meter and 64-meter diameter antennas. To support the Voyager 2 Uranus Encounter, the systems had to be accurately calibrated. Reliable techniques for use of the calibrations during intense mission support activity had to be provided. This article describes the techniques used to make the antenna pointing calibrations and to demonstrate their operational use. The results of the calibrations are summarized.

Stevens, R.↗
NASA NTRS1987

The upper atmosphere of Uranus - EUV occultations observed by Voyager 2

EUV (52-170 nm) solar and stellar occultation observations of the Uranian atmosphere from 500 microbar to about 1 pbar, obtained with the UV spectrometer on Voyager 2 during its encounter with Uranus in January 1986, are reported. The data are presented in extensive tables and graphs and characterized in detail. The atmosphere is found to be dominated by H2 (with very small hydrocarbon mixing ratios) out to about 1.25 Uranian radii, where atomic H becomes important. Also noted are a small (relative to Jupiter and Saturn) homopause eddy-diffusion coefficient, little difference between the atmospheres of the day and night hemispheres, high temperatures (800 + or - 100 K) above about 1-10 nbar, and number densities of several hundred H/cu cm at 2 Uranian radii. The implications of the latter finding for ring dynamics and plasma populations are explored.

Herbert, Floyd↗
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 NTRS1982

Jovian winds from Voyager 2. I - Zonal mean circulation

Independent measurements of Jovian cloud motions confirm previously published results on the general structure of Jupiter's zonal mean circulation. The new results are based on Voyager 2 images and measurement techniques which are different from those used in previous studies. The latitudes of the zonal jets agree with previous results, but there are some differences in the measured speed of the jets which exceed uncertainty estimates. These differences may be due to differences in sampling strategies. The structure of the zonal mean meridional velocity profile has still not been clearly resolved: mean meridional velocities generally differ from zero by no more than their estimated uncertainty. An analysis of successive measurements of the same cloud targets shows that most of the variance of individual velocity measurements is due to true variability of the winds.

Limaye, S. S.↗
NASA NTRS1980

Detection of energetic hydrogen molecules in Jupiter's magnetosphere by Voyager 2 - Evidence for an ionospheric plasma source

The discovery of energetic (approximately 1 MeV/nuc) H3 and H2 molecules in Jupiter's magnetosphere is reported. The data, obtained with the LECP instrument on Voyager 2, showed these molecules to be present throughout the magnetosphere and as far as 180 Jupiter radii from the planet, in the 'magnetospheric wind' region. Although the relative abundances of H3 and H2 do not show a monotonic trend with distance from Jupiter, the intervals of highest abundance were found in the outer magnetosphere. As an example, in the radial range 51-56 Jupiter radii, of the dayside magnetosphere, the abundances of H3 and H2 (0.60-0.95 MeV/nuc) were about 20 and 13-25% that of He, respectively, and the He abundance was about 1-2% that of H. Since H3(+) is expected to be an important constituent of Jupiter's ionosphere, the data provide strong evidence that, in addition to Io, the ionosphere may be an important local plasma source for the Jovian energetic particles. The measurements reported may represent the first detection in nature of molecules at energies as high as 1 MeV/nucleon.

Hamilton, D. C.↗
NASA NTRS1986

Voyager 2 in the Uranian system - Imaging science results

Details of the characteristics of the Uranian atmosphere and the surface features and projected formation processes of the Uranian moons are surveyed on the basis of 7000 images obtained by Voyager 2. Brightness distribution curves are provided for the CH4 Uranian atmosphere, and various anomalies, e.g., banding, that are apparent are discussed. Attention is given to the detectable cloud structure, circulation patterns and wind effects, noting that at certain latitudes the wind speeds exceed the planetary rotational velocity. The physical dimensions, orientations and compositions of the nine rings are described, along with the locations and sizes of the 10 shepherd satellites discovered between Miranda and Uranus. Finally, the large database accumulated on the visual characteristics of the five major satellites is examined in detail, particularly in relation to the orbits, origins, formation processes and surface features.

Smith, B. A.↗
NASA NTRS1988

C-smithing of Voyager 2 non-imaging instrument pointing information at Uranus

The development of a family of techniques, collectively called C-smithing, for improving spacecraft nonimaging instrument pointing knowledge is discussed. C-smithing studies using data from the Voyager 2 Uranus Encounter show that significant improvements in pointing knowledge for nonimaging instruments can be achieved with these techniques. This improved pointing information can be used to regenerate instrument viewing geometry parameters for the encounter, which can then be made available to science investigators.

Wang, Tseng-Chan↗
NASA NTRS1987

Voyager 2 photopolarimeter observations of the Uranian satellites

The surfaces of the principal Uranian satellites are characterized on the basis of UV and IR geometric albedos, phase curves, and phase coefficients obtained in full-disk photopolarimetric observations during the Voyager 2 encounter with Uranus in January 1986. The data are presented in tables and graphs and found to be consistent with a heavily cratered terrain and loosely packed regolith. The Bond albedos are calculated as 0.22 + or - 0.1 for Ariel, 0.07 + or - 0.05 for Umbriel, 0.16 + or - 0.12 for Titania, and 0.19 + or - 0.22 for Oberon. The characteristics of the Uranian satellites indicate compositions (and probably formation conditions and surface-modification mechanisms) distinct from those of the Saturnian and Jovian satellites.

Nelson, Robert M.↗