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  • Earth Resources and Remote Sensing; Instrumentation and Photography; Meteorology and Climatology  (1)
  • Mechanical Engineering  (1)
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  • 1
    Publication Date: 2016-06-07
    Description: Early in 1993, a servo motor within one of three Fine Guidance Sensors (FGS) aboard the Hubble Space Telescope (HST) reached stall torque levels on several occasions. Little time was left to plan replacement during the first servicing mission, scheduled at the end of '93. Accelerated bearing life tests confirmed that a small angle rocking motion, known as Coarse Track (CT), accelerated bearing degradation. Saturation torque levels were reached after approximately 20 million test cycles, similar to the flight bearings. Reduction in CT operation, implemented in flight software, extended FGS life well beyond the first servicing mission. However in recent years, bearing torques have resumed upward trends and together with a second, recent bearing torque anomaly has necessitated a scheduled FGS replacement during the upcoming second servicing mission in '97. The results from two series of life tests to quantify FGS bearing remaining life, discussion of bearing on-orbit performance, and future plans to service the FGS servos are presented in this paper.
    Keywords: Mechanical Engineering
    Type: 30th Aerospace Mechanisms Symposium; 13-29; NASA-CP-3328
    Format: application/pdf
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  • 2
    Publication Date: 2019-08-13
    Description: Cloud ice properties and processes play fundamental roles in atmospheric radiation and precipitation. Limited knowledge and poor representation of clouds in global climate models have led to large uncertainties about cloud feedback processes under climate change. Ice clouds have been used as a tuning parameter in the models to force agreement with observations of the radiation budget at the top of the atmosphere, and precipitation at the bottom. The lack of ice cloud measurements has left the cloud processes at intermediate altitudes unconstrained. Millimeter (mm) and submillimeter (submm)-wave radiometry is widely recognized for its potential to fill the cloud measurement gap in the middle and upper troposphere. Analyses have shown that channels from 183900 GHz offer good sensitivity to ice cloud scattering and can provide ice water path (IWP) products to an accuracy of 25 by simultaneously retrieving ice particle size (Dme) and IWP. Therefore, it is highly desirable to develop a cost-effective, compact mm/submm-wave instrument for cloud observations that can be deployed on future small satellites.This paper presents a conceptual study for a mm/submm-wave instrument for multispectral measurements of ice clouds. It discusses previous work at these frequencies by NASA Goddard Space Flight Center (GSFC) and the current instrument study, as well as receiver architectures and their anticipated performance. And finally, it describes a microsatellite prototype intended for use with this mm/submm-wave instrument.
    Keywords: Earth Resources and Remote Sensing; Instrumentation and Photography; Meteorology and Climatology
    Type: GSFC-E-DAA-TN15865 , Canadian Symposium on Remote Sensing (CSRS); Jul 13, 2014 - Jul 18, 2014; Quebec, QC; Canada|International Geoscience Remote Sensing Symposium (IGARSS); Jul 13, 2014 - Jul 18, 2014; Quebec, QC; Canada
    Format: application/pdf
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