ATTITUDE-CONTROL OF SPACE PLATFORM BASED TETHERED SATELLITE SYSTEM

Using an order N Lagrangian formulation, the paper studies attitude co ntrol of a rigid platform supporting a flexible tether connected to a rigid satellite. The system, in an arbitrary orbit, is free to undergo three-dimensional motion in both rigid and flexible degrees of freedo m. As can be expected, the governing equations of motion, in general, are highly nonlinear, nonautonomous, and coupled, and are amenable onl y to numerical integration, The control is achieved through time depen dent offset of the tether attachment point, as determined through the Liapunov method, thus providing regulated amount of tether tension ind uced damping moment. Results suggest that the controller is quite succ essful in stabilizing the platform about its nominal equilibrium posit ion in a few orbits, even in the presence of relatively large disturba nces, Furthermore, extensive parametric study suggests that the contro ller is quite versatile in imparting any desired orientation to the pl atform. This would enable the system to undertake diverse missions aim ed at communications, launch and retrieval of spacecraft, monitoring t he Earth's environment, planetary and galactic observations, etc.