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The satellite 1963 22A was successfully captured into a condition of passive, gravity-gradient stabilization. All elements of the stabilization system, including magnetic dispin, magnetic orientation devices, the extendible boom, the damping spring, and the attitude detection system performed satisfactorily. An unexpected high frequency oscillation of the boom and satellite system was observed which was most probably a dynamic effect resulting from thermal bending. This has caused the satellite to stabilize with a maximum deviation off the vertical of approximately 10 degrees. The objective of the gravity-gradient stabilization for the 22A satellite was to have the antennas directed downward within 20 degrees of the local vertical at all times. This objective has been successfully accomplished by the satellite's passive gravity-gradient attitude stabilization system. (Author).
The possibility of using the earth's gravity field for vertical stabilization of near-earth satellites has intrigued theoreticians for many years. The very small stabilizing torque available and the lack of a natural damping mechanism have been recognized as the major problems. The satellite 1963-22A, launched in June 1963, was the first orbiting vehicle to achieve passive gravity-gradient stabilization. A 100-foot extendible boom was used to develop gravity-gradient stabilizing torque. A combination of a lossy spring and magnetic hysteresis rods provided damping. By June 1964 four other satellites had achieved gravity-gradient stabilization. The satellite 1964-26A was similar to 1963-22A except that good damping was achieved with magnetic hysteresis rods alone. The discovery that several slender rods of magnetic material, weighing only 0.6 pounds and entirely passive, would damp gravity-gradient librations by interaction with the earth's magnetic field was a major advance in space technology. The accuracy of vertical stabilization has typically been better than 10 degrees. (Author).
Applied Mathematics and Mechanics, Volume 7: Torques and Attitude Sensing in Earth Satellites focuses on the possible torques that can affect the angular momentum of an Earth satellite. This book provides an understanding of the environment in which a satellite operates. Organized into 16 chapters, this volume starts with an overview of the application of force-free motion to space programs. This text then discusses the torque effects of a gravitational field, particularly with its gradient. Other chapters consider a particular method of gravity-gradient stabilization that utilizes a passive device to damp librations and thereby attain a vertical orientation. This book discusses as well the effects of the geomagnetic field on the angular motion of a satellite. The reader is also introduced to the method of magnetic attitude control employed in the Tiros satellite. The final chapter deals with the problem of horizon sensing, which is important for satellites requiring Earth stabilization. Astrophysicists will find this book useful.
Method for predicting attitude of passive gravity stabilized satellite.
Satellite attitude stabilization systems utilizing the gradient of the earth's gravitational field have the advantage of being completely passive (i.e., no power is required). However, the stabilizing moments developed are extremely small and as a result such systems are subject to attitude perturbations from sources which would ordinarily be neglected in the evaluation of an active stabilization system. This memorandum investigates certain of these sources of attitude perturbation including micro-meteoroid impact, solar radiation pressure, stationkeeping propulsion, orbital eccentricity, and on-board rotating machinery. In the analysis, formulas are developed which determine the magnitude of the pitch, roll and yaw perturbations resulting from each of the above sources. Application of these results to an assumed vehicle configuration shows that the resulting attitude perturbations can be of the order of several degrees. While these perturbations do not necessarily rule out gravity gradient stabilization, their magnitudes for a given vehicle configuration should be considered for their compatibility with the mission requirements. (Author).