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  • Comparison of theoretical and experimental attitude data for the Dodge spacecraft

    Paper ID



    • J. M. Whisnant
    • V. L. Pisacane


    The Johns Hopkins University, Applied Physics Laboratory






    The DODGE (Department of Defense Gravity Experiment) satellite1 was designed and built for the Department of Defense by the Johns Hopkins University, Applied Physics Laboratory. It had two objectives, first to demonstrate gravity-gradient stabilization near synchronous altitudes and secondly to determine the adequacy of theoretical analyses by correlation between simulation results and experimental data. On July 1, 1967 DODGE was launched into a near synchronous orbit. Gravity-gradient stabilization was achieved July 15 and as of September 1969 the spacecraft continues to operate. To date, papers written on post-launch DODGE attitude stabilization have been primarily concerned with presenting the flight results.2’^ Here the flight data is compared with the results of the digital simulation and possible reasons for discrepancies are discussed. DODGE was equipped with ten extendible booms with end masses so that its configuration could be varied in orbit to obtain either two axis or three axis stabilization. The “plus”, the “times”, the “dumbbell”, and the “dumbbell with rotor” configurations are illustrated in Fig. 1. These are the configurations most frequently discussed for gravity-gradient stabilization near synchronous altitudes. A constant speed rotor and a magnetic dipole were included to augment yaw stabilization. Four damping systems are available to dissipate librational energy: an enhanced magnetic hysteresis damper, an eddy current gimballed-boom damper, a magnetic hysteresis gimballed-boom damper and a time-lag magnetic damper. The availability of multiple control systems provides a high degree of reliability and the opportunity to perform many experiments. To provide for a thorough evaluation of the times configuration and each damper, the mass properties of the spacecraft can be changed by individually varying the length of each boom. A detailed list of the physical characteristics of the spacecraft is given in Ref. 4.