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  • 1
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    Drag-free satellite control system technology (1971)
    In:  CASI
    Details
    Publication Date: 2005-11-30
    Description: Some of the technology developed in building a drag-free satellite simulator for laboratory use is described. The design decisions made in order to achieve a 10 to the -11th power g perturbation level for the navigation satellite is discussed. The control system development that will make possible drag-free operation of spinning satellites to reduce perturbation levels by averaging is described.
    Keywords: NAVIGATION
    Type: JPL Proc. of the Conf. on Exptl. Tests of Gravitation Theories; p 190-196
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Comments on the drag-free control of a solar probe relativity mission (1978)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: A spacecraft going within 4 solar radii of the Sun experiences an acceleration up to .00005 g from solar radiation pressure, and significant (though smaller) accelerations from the solar wind. To obtain satisfactory information about relativistic effects and the Sun's quadrupole mass coefficient, these non-gravitational accelerations are either measured or compensated out by making the spacecraft drag free. A proof mass inside the spacecraft structure is shielded from the external forces, so that it follows a nearly ideal gravitational orbit, and a control system activates gas jets (or other translational forcers) to make the vehicle follow the mass. The problems are mechanizing the control laws and minimizing extraneous effects such as the self gravitational pull of the spacecraft. The extraneous forces can be averaged in one plane by having a spinning vehicle.
    Keywords: SOLAR PHYSICS
    Type: JPL A Close-up of the Sun; p 60-68
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    NASA TECHNICAL REPORTS
  • 3
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    A proposed lunar orbiting gravity gradiometer experiment. (1972)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Analysis of the gravity gradiometer developed by Forward and Bell (1970) suggest that an accuracy, in the range 0.1 to 0.5 EU can be expected in a lunar orbiter application. This accuracy will allow gradient anomalies associated with mascons to be mapped with 1% accuracy and should reveal a great deal of new information about the lunar gravity field. The proposed experiment calls for putting such a gradiometer into a closely circular polar orbit at an average height of about 30 km above the lunar surface. This orbit allows the entire lunar surface to be covered in fourteen days, the gradiometer to be checked twice per revolution and results in successive passes above the lunar surface being spaced at about the resolution limit of about 30 km set both by the satellite altitude and instrumental integration time.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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    NASA TECHNICAL REPORTS
  • 4
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    A simple microgravity table for the Orbiter or Space Station (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Methods of limiting perturbations in microgravity experiments are proposed. An acceleration level below 10 to the -4th m/s-squared is necessary to maintain an undisturbed microgravity environment. Machinery vibrations, crew motion, and the firing of vernier thrusters produce acceleration levels greate than 10 to the -4th m/s-squared. The use of a weak spring system or simple electromagnets to isolate an experimental table from these factors is described. The manners in which crew motion and vernier firing are countered by the springs are examined. The steady acceleration caused by atmospheric drag, gravity gradient force, and steady rotation can be maintained below 10 to the -th m/s-squared; however, the springs can protect the table from these accelerations if required.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Earth-Oriented Applications of Space Technology (ISSN 0277-4488); 5; 3, 19
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  • 5
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    Caging Mechanism for a drag-free satellite position sensor (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A disturbance compensation system for satellites based on the drag-free concept was mechanized and flown, using a spherical proof mass and a cam-guided caging mechanism. The caging mechanism controls the location of the proof mass for testing and constrains it during launch. Design requirements, design details, and hardware are described.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: JPL 10th Aerospace Mech. Symp.; p 125-132
    Format: application/pdf
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  • 6
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    A precision, active, table leveling system. (1966)
    In:  Other Sources
    Details
    Publication Date: 2019-05-30
    Description: Automatic feedback table leveling system, noting tilt to simulate aerodynamic drag
    Keywords: FACILITIES, RESEARCH, AND SUPPORT
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    NASA TECHNICAL REPORTS
  • 7
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    Elastic suspension of a wind tunnel test section (1982)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Experimental verification of the theory describing arbitrary motions of an airfoil is reported. The experimental apparatus is described. A mechanism was designed to provide two separate degrees of freedom without friction or backlash to mask the small but important aerodynamic effects of interest.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: NASA. Kennedy Space Center The 16th Aerospace Mech. Symp.; p 277-297
    Format: application/pdf
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  • 8
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    A preliminary design of a drag-free satellite and its application to geodesy (1969)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The design of a drag-free satellite and its application to measuring tidal interaction of the earth and tesseral harmonics are discussed. Principle areas of discussion are: (1) the feasibility of making geophysical measurements which are not possible with conventional satellites, and (2) design of attitude and translation control systems for spinning vehicle and possible coupling of attitude and translation control for gravity stabilized vehicles.
    Keywords: SPACE VEHICLES
    Type: NASA-CR-125606
    Format: application/pdf
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  • 9
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    Propulsion requirements for drag-free satellites (1970)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Drag-free satellite design and propulsion requirements, noting orbit perturbation mechanisms
    Keywords: SPACE VEHICLES
    Type: AIAA PAPER 70-1145
    Format: text
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  • 10
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    Exospheric density measurements from the drag-free satellite Triad (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The Triad satellite is maintained within 1 mm of its proof mass (a small metal ball) in a purely gravitational orbit, using a drag-free control system, named Discos, as the disturbance compensation system. The Discos proof mass is surrounded by an outer shell which holds fuel tanks and cold gas jets. The shell shields the proof mass from such nongravitational forces as radiation pressure, atmospheric drag, and micrometeorite impact. Whenever these forces displace the outer shell relative to the proof mass, an error signal is generated by a capacitive bridge sensor, and the satellite is propelled by gas jets to remain centered on the proof mass when the error reaches 1 mm. Local atmospheric densities near 800 km were measured, using ball position data, and the observed accelerations were corrected for the effects of solar radiation pressure. The measured densities reveal a greater dependence on latitude than that indicated by balloon satellites, and also a dependence on longitude. Only a small dependence on Kp, however, was observed in the region where the measurements were made.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 81; Aug. 1
    Format: text
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