Modeling and control of active gravity off-loading for deployable space structures

The mechanics of deployable space structures are examined through ground based testing to predict the structures' deployment in a microgravity environment. In order to simulate the microgravity conditions a test article would experience in space, a method of counteracting the loads and deflections induced by gravity is required. This accomplished through various gravity off-loading methods, which forces opposite and equal to the force of gravity acting upon a test article throughout its deployment. Current gravity off-loading methods are passive rail-cart systems with their movement forced due to their physical coupling with a test article; this introduces unwanted boundary conditions, such as inertia and side-loading from a test article's transverse movement. Therefore, an active gravity off-loading method is being developed that will deploy simultaneously with a test article. This method employs motorized carts with active position control based upon the lead angle of the off-loading cable. The maximum allowable lead angle is designed to be +/- 5 degrees, with the intention of minimizing the forcing of the carts' longitudinal deployment. System dynamics and kinematics analytical modeling is derived. Simulated system results from the analytical system model and preliminary results from the prototype are presented.