On the Stability and Pointing of an Attached Double-gimbal Experiment Package
The pointing capability of a double gimbal experiment isolation and control system of the Apollo telescope mount (ATM) type was investigated. Three composite structural models of an experiment package connected through frictionless gimbals to a carrier vehicle (including a rigid package-rigid carrier model, a rigid package-flexible carrier model, and a flexible package-flexible carrier model) were used, and a linear model of the nominal ATM gimbal control system is considered. A linear stability analysis was performed to verify stability of the control system with nominal gains. Transform techniques were used to compute pointing errors onboard the experiment package due to random crew motions input into the carrier vehicle. Results of the investigation indicate that there is no stability problem due to flexible coupling of the experiment package and the carrier, and that the ATM-type system is capable of pointing accuracies better than 0.1 arc second.
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0.1 arc second activities APPENDIX array assumed ATM modes ATM package ATM-type axis base block calculation carrier modes carrier vehicle center-of-mass offset Compressive walking computed considered consists continuous control system convolution coordinates correspond coupled system Crew motion crew-motion filters defined described developed diagonal matrix discrete Fourier transform distribution disturbances domain double-gimbal experiment effects elements equation experiment isolation experiment package experiment package connected experiment-package Figure fine-sun-sensor location flexible flexible model flexible-body folding frequency gain gimbal gimbal control given included input Langley Research Center Laplace transform limitations linear loop mass matrix method modal NASA natural frequencies nominal obtained parameters performed periodic pointing accuracy pointing error presented random rate-gyro referred represents respectively rigid sampled sequence sequence f^(k Skylab Space stability structural models TABLE telescope telescope modes torque transfer function vector vibration modes zero