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  • 1
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    Magellan aerobrake navigation (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Magellan spacecraft has been aerobraked into a 197 x 541 km near-circular orbit around Venus from which it is conducting a high-resolution gravity mapping mission. This was the first interplanetary aerobrake maneuver and involved flying the spacecraft through the upper reaches of the Venusian atmosphere 730 times over a 70 day period. Round-trip light-time varied from 9.57 to 18.83 minutes during this period. Navigation for this dynamic phase of the Magellan mission was planned and executed in the face of budget-driven down-sizing with all spacecraft safe modes disabled and a flight-team one-third the size of comparable interplanetary missions. Successful execution of this manuever using spacecraft hardware not designed to operate in a planetary atmosphere, demonstrated a practical cost-saving technique for both large and small future interplanetary missions.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: British Interplanetary Society, Journal (ISSN 0007-094X); 48; 3; p. 111-122
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  • 2
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    A gravity field to support Magellan navigation and science at Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The development and validation of the revised JPL Venus Gravity Model are described with attention given to the incorporation of data regarding the longitudinal coverage. The motivation for the JPL Venus Gravity Model 1B (VGM1B) is related to the determination of orbit-support requirements for the Magellan mission. Existing gravity models for Venus are reviewed, and the present model is based on orbit-prediction data taken from Doppler tracking data from the Pioneer Venus Orbiter (PVO). Revised information arrays are developed incorporating more complete data describing the longitudinal conditions of the gravity field. Improvements are noted in the Doppler residual statistics taken from field-validation fits to the PVO and Magellan tracking data by using the VGM1B harmonic field. The VGM1B gravity field is also shown to reduce the trajectory errors from PVO and Magellan navigation.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 40; 107-134
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  • 3
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    Martian mass and earth-moon mass ratio from coherent S-band tracking of Mariners 6 and 7 (1970)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: Mariners 6 and 7 range and Doppler tracking data for studying Martian mass and earth-moon mass ratio
    Keywords: SPACE SCIENCES
    Type: ; ADEMIE DES SCIENCES
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  • 4
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    Gravity field of Mars from Mariner 9 tracking data. (1973)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the earth or the moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The value obtained for the inverse mass of Mars is in good agreement with prior determinations from Mariner fly by trajectories. The direction found for the rotational pole of Mars is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (1) the dynamical flattening, (2) the maximum principal moment of inertia, and (3) the period of precession of Mars' pole.
    Keywords: SPACE SCIENCES
    Type: Icarus; 18; Feb. 197
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  • 5
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    Earth-moon mass ratio from Mariner 9 radio tracking data. (1973)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The phase-coherent range and Doppler tracking data obtained as a basis for the navigation of the Mariner 9 spacecraft from earth to Mars determine also the earth-moon mass ratio. As the earth revolves about the center of mass of the earth-moon system, a sinusoidal curve is impressed on the range and Doppler tracking data with a frequency equal to the sidereal mean motion of the moon. The mass ratio was determined from range and Doppler data obtained over a period of 15 weeks. The results from the Mariner Mars 1971 data are presented in a table together with previous results obtained in connection with other spacecraft.
    Keywords: SPACE SCIENCES
    Type: Nature; 241; Jan. 12
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  • 6
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    A mixed formulation finite element for linear thin shell analysis (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: An eight node curved thin shell slement was tested. The element is based on the degenerate solid concept and the mixed formulation with the independent inplane and transverse shear strains. The number of unknown parameters in the assumed strains is chosen to alleviate the spurious constaining or locking effect. It is indicated that for a pinched cylindrical shell with diaphragmed ends and fixed ends the present element shows good performance.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center Res. in Struct. and Solid Mech., 1982; p 219-228
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  • 7
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    The liquid crystal light valve, an optical-to-optical interface device (1972)
    In:  Other Sources
    Details
    Publication Date: 2016-06-07
    Description: A photoactivated liquid crystal light valve is described as an optical-to-optical interface device (OTTO) which is designed to transfer an optical image from a noncoherent light beam to a spatially coherent beam of light, in real time. Schematics of OTTO in use, the liquid cyrstal cell, and the liquid crystal structure are presented. Sensitivity characteristics and the principles of operation are discussed.
    Keywords: PHYSICS, GENERAL
    Type: NASA. Goddard Space Flight Center Proc. of the Conf. of Parallel Image Process. for Earth Observation Systems; p 103-113
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  • 8
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    Navigating the Magellan Aerobrake (1993)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: The Magellan spacecraft has been aerobraked into a 197 x 541 km near-circular orbit around Venus from which it is conducting a high-resolution gravity mapping mission. This was the first interplanetary aerobrake maneuver and involved flying the spacecraft through the upper reaches of the Venusian atmosphere 730 times over a 70 day period.
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  • 9
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    Determination and prediction of Magellan's orbit (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Magellan spacecraft has been systematically mapping the surface of Venus since September 15, 1990, using a synthetic aperture radar. The spacecraft orbit about Venus is nearly polar, with an orbital period of 3.26 hours and periapsis altitude of 295 km. The radiometric measurements and the data reduction method used to determine and predict the spacecraft state are described. Orbit determination and prediction results are given for the first 146 days of mapping (through February 8, 1991, 60 percent of the first rotation of Venus). Orbit accuracy requirements of 150 meters in the radial position, and 1 km in the along-track and cross-track positions are shown to be met, but with exceptions. All error requirements were exceeded during a combined period of limited in-plane orbit observability due to earth-orbit relative geometry, and increased measurement noise due to superior conjunction.
    Keywords: ASTRODYNAMICS
    Type: AAS PAPER 91-180 , In: Spaceflight mechanics 1991; Proceedings of the 1st AAS(AIAA Annual Spaceflight Mechanics Meeting, Houston, TX, Feb. 11-13, 1991. Pt. 2 (A93-17901 05-13); p. 1143-1160.
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  • 10
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    Principle Component Analysis of the Evolution of the Saharan Air Layer and Dust Transport: Comparisons between a Model Simulation and MODIS Retrievals (2006)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: The onset and evolution of Saharan Air Layer (SAL) episodes during June-September 2002 are diagnosed by applying principal component analysis to the NCEP reanalysis temperature anomalies at 850 hPa, where the largest SAL-induced temperature anomalies are located. The first principal component (PC) represents the onset of SAL episodes, which are associated with large warm anomalies located at the west coast of Africa. The second PC represents two opposite phases of the evolution of the SAL. The positive phase of the second PC corresponds to the southwestward extension of the warm anomalies into the tropical-subtropical North Atlantic Ocean, and the negative phase corresponds to the northwestward extension into the subtropical to mid-latitude North Atlantic Ocean and the southwest Europe. A dust transport model (CARMA) and the MODIS retrievals are used to study the associated effects on dust distribution and deposition. The positive (negative) phase of the second PC corresponds to a strengthening (weakening) of the offshore flows in the lower troposphere around 10deg - 20degN, causing more (less) dust being transported along the tropical to subtropical North Atlantic Ocean. The variation of the offshore flow indicates that the subseasonal variation of African Easterly Jet is associated with the evolution of the SAL. Significant correlation is found between the second PC time series and the daily West African monsoon index, implying a dynamical linkage between West African monsoon and the evolution of the SAL and Saharan dust transport.
    Keywords: Geophysics
    Format: application/pdf
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