93-187
The Hybrid Control Of An Orbiting Flexible Tethered Antenna/Reflector System*
Zhaozhi Tan** and Peter M. Bainum***
Abstract
In considering the dynamics of tethered spacecraft systems, the longitudinal vibration of the tether has been ignored by most researchers For the tethered antenna/reflector system considered here, however, the longitudinal vibration of the tether ha~ a significant effect on the tether tension and is coupled to the rest
of the motions of the system This can result in the performance of the system, under the control logic drawn from the mathematical model without consideration of the tether longitudinal vibration, to degrade, or even become unstable in some cases The frequencies of the longitudinal modes are quite high; direct measurement of the vibration is not easily implemented Therefore, a passive damper is designed for possible use The damper is mounted in the subsatellite at the end of the tether The system without the damper is neutrally stable in the gravitational field But the in-plane subsystem will be
asymptotically stable with the proper damper design parameters It is found that only the tether longitudinal vibration and the axisymmetric modes of the shell are effectively damped by the passive damper Therefore, attitude and shape control is assumed to result from the combination of active actuators, the tether tension, and the passve damper The LQR technique is employed to synthesize the control law~
*Research supported by AFOSR Grant F49620-92 J-165
**Visiting Research Associate, Department ot Mechanical Engineering, Howard Univorsity, Washington, D C 20059. Also, Senior Engineer, Beijing Institute of Control Engineering, Beijing, China
***Distinguished Professor of Aerospace Engineering, Department of Mechanical Engineering, Howard University, Washington, D C 20059 Fellow AAS Fellow AIAA