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  • LUNAR AND PLANETARY EXPLORATION  (4)
  • SPACECRAFT DESIGN, TESTING AND PERFORMANCE  (3)
  • 1990-1994  (7)
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  • 1
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    Europa's phase curve - Implications for surface structure (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The surface of the Jovian satellite Europa is characterized on the basis of an analysis of ground photoelectric photometry at 470 and 550 nm and Voyager images. The data are presented in extensive tables and graphs and discussed in detail. At 550 nm, Europa has single-scattering albedo 0.964, opposition-effect amplitude 0.5, opposition-effect width 0.0016, double-lobed Henyey-Greenstein factors b = -0.429 and c = 0.113, and mean roughness angle 10 deg (much lower than on other solar-system objects). From the small roughness and the 96-percent porosity implied by the narrow opposition peak, it is concluded that the surface was formed mainly by endogenic processes. It is also noted that only one of three observational criteria for preferential ion bombardment of the trailing hemisphere are met in Europa.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 90; 30-42
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    NASA TECHNICAL REPORTS
  • 2
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    Recent observations of high voltage spacecraft-environment interaction at LEO altitudes using sounding rockets (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The paper addresses the subject of the interaction of positively and negatively charged bodies with the terrestrial ionosphere at low earth orbit altitudes. Data from two recent sounding rocket flights are used to establish that the current collected by exposed conductors biassed positively at up to 45kV relative to the ionospheric plasma generally follow predictions which account for strong control of electron flow by the geomagnetic field. If the biased structure is in the vicinity of disturbing influences such as an emitted charged particle beam, or locally enhanced gas pressure, then large deviations from the space-charge-limited return currents occur.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 90-0635
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    NASA TECHNICAL REPORTS
  • 3
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    Recent experimental measurements of space platform charging at LEO altitudes (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The paper discusses some of the results of vehicle electrical potential from recent sounding rocket experiments involving charging of a space platform by both electron beam emission and by the application of differential bias between elements of the platform. Conclusions are presented that are applicable to the experimental parameters of the CHARGE-2 and SPEAR-1 payloads. The currents collected by HV biased collectors in the sphere show strong magnetic limiting and are close to the values predicted by Parker and Murphy (1967). No volume breakdown was observed above 100 km altitude by exposing voltages up to 45 kV to the ionosphere in the SPEAR-1 payload. The release of gas at flow rates typical of ACS systems can provide sufficient plasma to electronically neutralize space platforms biased at either positive or negative potentials.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Advances in Space Research (ISSN 0273-1177); 12; 12 D
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  • 4
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    An atmospheric outburst on Neptune from 1986 through 1989 (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Visual photometry and methane-band imaging indicate that Neptune underwent a period of atmospheric activity in the 1986-1989 period with an enhancement of 8900 A CH4-band brightness and an increased standard deviation of the mean yearly magnitudes at visual and near-IR wavelengths. These observations are presently interpreted as due to a localized upwelling source that could be similar to the 'great white spots' that have been periodically observed on Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 2; p. 363-367.
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  • 5
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    TSS-1 - Orbiter current and voltage experiments (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Although the deployment distance of the TSS-1 tethered satellite was only about 1 percent of nominal, experiments to study the current collection and vehicle charging effects at low voltages were performed. We present measurements of Orbiter charging resulting from electron beam emission from the Orbiter, currents in the TSS system with and without electron beam emissions, and the effects of Orbiter thrusters on charging and currents. Generally, charging induced by beam emission was limited to a few volts, though during times with low ambient plasma density the Orbiter was charged up to 80 V. Thrusters are seen to enhance Orbiter charging during beam emission, and reduce ion current collection at other times.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 93-0702 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 10 p.
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  • 6
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    Neptune's cloud structure in 1989 - Photometric variations and correlation with ground-based images (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Ground-based photoelectric photometry in b, y, and the 6190 and 7250 A methane-bands, as well as spectrum scans of the methane 6190 A band and CCD images at 6190 and 8900 A, were obtained for Neptune during Voyager 2's approach of that planet on August 24, 1989. Photometric variations are presently correlated with the disk transit of bright planetary features, and the changes in feature distribution and brightness noted in the results are evaluated for implications bearing on long-term variability. It is suggested that the long-term secular variation is related to a slow change in a size of location of both the bright companion and the Great Dark Spot.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 90; 299-307
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  • 7
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    The brightness, albedo, and temporal variability of Neptune (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Sine 1972, the brightness of Neptune at 4720 and 5510 A has slowly varied with an amplitude of 4 percent, apparently anticorrelated with cyclic solar activity. In addition, there is a secular trend towards redder color. The night-to-night variation of brightness tends to be greater in seasons when the planet is relatively bright. From annual spectrophotometric observations at 8 A resolution, 3295-8880 A, the geometrical albedo spectrum was computed for 1982, when the planet was relatively faint, and for 1987, when it was relatively bright. The two spectra do not differ substantially from each other, but yield a significantly higher albedo in the ultraviolet compared with the values published by Neff et al. based on 1981 observations and a different solar irradiance spectrum.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 368; 287-297
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