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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 325 records · Page 18
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NASA NTRSDate not supplied

Thermal Control Coating Charging Tests for the Europa Clipper Mission

Thermal control coatings are an essential part of spacecraft systems. Typically, these coatings are directly exposed to the space environment, which means they must be designed and applied in a manner that can withstand exposure to radiation, ultra-violet light, thermal cycles, etc. In the case of the Europa Clipper mission, the thermal control coatings must also have relatively low resistivity in order to minimize electrostatic charging (and discharging) due to the abundant low-energy plasma populations in the Jovian environment. This paper will present the results of a test campaign led by NASA’s Jet Propulsion Laboratory (JPL) to find thermal control coating solutions that minimized the occurrence of electrostatic discharges – even at cryogenic temperature conditions. The customized laboratory test system at NASA’s Marshall Space Flight Center will be described, along with the test requirements and conditions. Finally, a summary of the coatings with the best electrostatic characteristics will be provided.

Thermal Control Coatings↗
NASA NTRS2025

Sealing Europa’s Vents By Vapor Deposition: An Order-of-Magnitude Study

Fractures and vents in the ice crust of Europa, exposing the sub-surface ocean or liquid-water inclusions to the vacuum, might be responsible for the generation of planetary-scale water-vapor plumes. During its passage through the ice, the plume vapor is expected to partially condense on the cold ice walls. Together with other effects (water spillage, compression forces, etc.) this mechanism likely contributes to sealing the vent. In this work, we develop a lumped-parameter model to analyze the sealing timescales associated to water-vapor deposition alone. Neglecting all other possible mechanisms, we find shutting-off times roughly compatible with the 7-hour plume observed in 2012 by the Hubble Space Telescope, suggesting that vapor deposition might have played a major role in sealing the vent. A map of sealing times vs. plume density, mass flow rate and aperture areas is given. Plume quantities from the literature are analyzed and compared to our results. For a given plume density/mass flow rate, small apertures would be sealed quickly by vapor deposition and are thus incompatible with observations.

Europa↗
DOE OSTI2021

Europa Lander Aseptic Integration Facilities Survey

The following trade study was done to answer the following task from the Sandia JPL Collaboration for Europa Lander Statement of Work: Survey facility infrastructure SNL may have for performing aseptic assembly and integration of S/C and assess its suitability for PP applications.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Photometric radii of Io and Europa.

Simultaneous two-color photoelectric photometry of Io and Europa performed during their eclipse by Jupiter on the night of April 5/6, 1971, is reported and discussed. The results are compared with satellite radii obtained using other observational techniques. It is concluded that the eclipse technique can be used to infer satellite radii accurate to plus or minus 10 per cent. In principle the eclipse technique can also be applied to the satellites of Saturn, Uranus, and Neptune for early objective determinations of their radii.

Price, M. J.↗
NASA NTRS1974

A low resolution map of Europa from four occultations by Io

Analysis of three occultations of JII (Europa) by JI (Io) has resulted in a preliminary reflectivity map of JII for the hemisphere centered on longitude 324 deg, a measurement of 1483 plus or minus 20 km for the radius of JII, estimates of the event impact parameters, determination of the midevent times, and a visual geometric albedo of 0.74, for JII. A fourth occultation light curve was used after derivation of the results to confirm their validity.

Vermilion, J. R.↗
NASA NTRS1975

Temperature dependence of the water-ice spectrum between 1 and 4 microns - Application to Europa, Ganymede and Saturn's rings

Reflection spectra of water ice from 1 to 4 microns are presented as a function of temperature. It is found that a feature at 6056 reciprocal cm changes its intensity sufficiently so that it can be used as a spectroscopic measurement of the ice temperature. A temperature calibration curve of this feature down to 55 K is developed and used to determine ice temperatures for the Galilean satellites Europa (95 + or -10 K), Ganymede (103 + or -10 K), and the rings of Saturn (80 + or -5 K). The ice temperatures for the Galilean satellites are lower than their measured brightness temperatures, which can be explained by a higher albedo of the ice-covered regions relative to the rest of the satellite and possibly a concentration of the ice near the polar caps.

Fink, U.↗
NASA NTRS1979

Jovian longitudinal asymmetry in Io-related and Europa-related auroral hot spots

Auroral emissions generated by the Jovian moons Io and Europa, originating at the foot of the magnetic flux tubes of the satellites, may be largely limited to longitudes where the planet's ionospheric conductivity is enhanced. The enhanced conductivity is produced by trapped energetic electrons that drift into the Jovian atmosphere in regions where the planet's magnetic field is anomalously weak. The most active auroral hot-spot emissions lie in a sector of the northern hemisphere defined by decametric radio emission. Weaker auroral hot spots are found in the southern hemisphere along a magnetic conjugate trace. The brightness and the longitude of the Jovian hot spots predicted in this paper are in agreement with observations reported by Atreya et al. (1977).

Dessler, A. J.↗
NASA NTRS1981

Lineament and polygon patterns on Europa

A classification scheme is presented for the lineaments and associated polygonal patterns observed on the surface of Europa, and the frequency distribution of the polygons is discussed in terms of the stress-relief fracturing of the surface. The lineaments are divided on the basis of albedo, morphology, orientation and characteristic geometry into eight groups based on Voyager 2 images taken at a best resolution of 4 km. The lineaments in turn define a system of polygons varying in size from small reticulate patterns the limit of resolution to 1,000,000 sq km individuals. Preliminary analysis of polygon side frequency distributions reveals a class of polygons with statistics similar to those found in complex terrestrial terrains, particularly in areas of well-oriented stresses, a class with similar statistics around the antijovian point, and a class with a distribution similar to those seen in terrestrial tensional fracture patterns. Speculations concerning the processes giving rise to the lineament patterns are presented.

Pieri, D. C.↗
NASA NTRS1981

Is Europa surface cracking due to thermal evolution

It is proposed that some of the surface features of Europa may be due to processes occurring within a planet in which hydrated silicates are stable. Based on considerations of the mechanical properties of hydrated silicates and ice and the likely thickness of the ice crust (less than 24 km), models are developed for the long, relatively dark lineaments that lie on great and small circles and frequently possess bright medial stripes, and for the complex network of fractures surrounded by cuspate ridges in the antijovian region. The global-scale lineaments are explained in terms of planetary expansion brought about by positive volume changes resulting from the dehydration of the hydrated silicates. The apparently tensile features in the antijovian region are attributed to a region of upwelling in the convecting anhydrous silicate interior surrounded by a region of return flow beneath the hydrated silicate mantle.

Finnerty, A. A.↗
NASA NTRS1981

Evidence for sulphur implantation in Europa's UV absorption band

The UV spectral characteristics of the Galilean satellites are investigated (using data from the International Ultraviolet Explorer (IUE) spacecraft) as a function of the orbital position, large-scale areal variability, and temporal dynamics. The discovery of an absorption feature at 280 nm in Europa's reflection spectrum is reported and observations show that the absorption is strongest on the trailing hemisphere (central longitude 270 degrees). The feature resembles SO2 and seems to result from S-O bond formation between deeply implanted sulphur atoms and the adjacent damaged water-ice-lattice. The sulphur supposedly comes from energetic (hundreds of keV) sulphur ions that are present in the Jovian magnetosphere. An appropriate equilibrium condition can be found to match the observed spectral data if sputtering erosion occurs at no greater than approximately 20 meters per one billion years.

Lane, A. L.↗
NASA NTRS1980

Fractures on Europa - Possible response of an ice crust to tidal deformation

The surface of Europa contains a planetwide system of low albedo lineaments which have been interpreted as fractures in an icy crust. The pattern of fractures on the surface consists of radial and concentric fractures having the general appearance of tension cracks within a region near the antipode of the sub-Jupiter point. Outside this region, linear fractures intersect at angles near 60 deg, suggesting that they are conjugate shear fractures. The orientation of this pattern on the surface suggests that a principal axis of the deformation that produced the fractures was approximately radial to Jupiter. Fracturing may thus be consistent with an origin due to cyclical tidal deformation resulting from orbital eccentricity. Orbital eccentricity related to a relatively recent establishment of orbital resonance among the Galilean satellites may explain the presence of fractures in a relatively young, lightly cratered planetary surface.

Helfenstein, P.↗
NASA NTRS1982

Structures on Europa

Four classes of lineation patterns have been identified on Europa in the area covered by high-resolution Voyager 2 images. These include dark, wedge-shaped bands in the west-central part of the area; triple bands associated with diagonally trending, global lineations; gray concentric curvilinear bands in the southeastern part; and ridges near the terminator. The major structures appear to have been formed by tidal forces centered on the axis pointing toward Jupiter, but variations in the detail of the structural patterns may have been caused by internal forces. The older strain patterns tend to be rejuvenated by younger fractures. The most persistent rejuvenated strain patterns are the global diagonal fractures, probably formed by conjugate shear, and the straight and curvilinear fractures that apparently caused an early dichotomy in fracture patterns.

Lucchitta, B. K.↗
NASA NTRS1982

Radar properties of Europa, Ganymede, and Callisto

The radar properties of Europa, Ganymede, and Callisto are summarized and present understanding of these properties is documented. The radar techniques are described, observational results reviewed, and salient aspects of the radar data set discussed. Theoretical interpretation of the satellites' anomalous radar properties is addressed, including aspects such as external scattering and double reflection from hemispherical craters, the random-facet model, total internal reflection, multiple total internal reflection, the high radar geometric albedos, the tenous upper layer, the two-component regolith, and compositional effects. It is concluded that multiple total internal reflection from randomly oriented subsurface facets can explain the anomalous circular polarization inversion in the radar echoes from the three satellites. Several refinements of the Goldstein-Green (1980) scattering model are suggested.

Ostro, S. J.↗
NASA NTRS1984

Comparison of Hapke's photometric theory with Voyager observations of Europa, Enceladus, Rhea and Mimas

Voyager imaging observations of the satellites of Jupiter and Saturn provide an excellent test for various photometric theories that were proposed to describe the scattering properties of planetary and satellite surfaces. Not only does the Voyager data set include observations of surfaces ranging widely in albedo, but it provides measurements (in both disc-integrated and disc-resolved forms) over a wide range of phase angles. A detailed comparison of the above models with Voyager data for Europa, Enceladus, Rhea, and Mimas was described. These satellites were selected because they cover a range of reflectances from 0.65 to 1.0 and because for them the Voyager photometric data sets are most complete.

Buratti, B.↗
NASA NTRS1985

Patterns of fracture and tidal stresses due to nonsynchronous rotation - Implications for fracturing on Europa

This study considers the global patterns of fracture that would result from nonsynchronous rotation of a tidally distorted planetary body. The incremental horizontal stresses in a thin elastic or viscous shell due to a small displacement of the axis of maximum tidal elongation are derived, and the resulting stress distributions are applied to interpret the observed pattern of fracture lineaments on Europa. The observed pattern of lineaments can be explained by nonsynchronous rotation if these features formed by tension fracturing and dike emplacement. Tension fracturing can occur for a small displacement of the tidal axis, so that the resulting lineaments may be consistent with other evidence suggesting a young age for the surface.

Helfenstein, P.↗
NASA NTRS1986

Europa - Characterization and interpretation of global spectral surface units

In the present analysis of the Voyager global multispectral mosaic of the Galilean satellite Europa, which was conducted to map surface units with similar optical properties, color assignments are indicative of the spectral nature of the given unit. The unit maps are noted to exhibit a marked hemispheric asymmetry which is most clearly seen in the UV/violet albedo ratio image. It appears as if the surface has been most darkened at the center of the trailing hemisphere, with a gradual decrease to a minimum at the center of the leading hemisphere as the cosine of the angle from the antapex of motion; this cosine pattern suggests that the darkening is exogenic in origin, and is interpreted as evidence of surface alteration by in bombardment from the Jovian magnetosphere.

Nelson, M. L.↗
NASA NTRS1986

Diatoms on earth, comets, Europa and in interstellar space

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 A, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. The observational data are reviewed, and the known properties of diatoms and bacteria are considered. It is suggested that these characteristics are consistent with the concept of a cosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.

Hoover, R. B.↗