On the Development of Control Laws for an Orbiting Tethered Antenna / Reflector System Test Scale Model

Abstract

Tethered systems can be used to change the geometry and inertial characteristics of space structural systems to meet the gravity gradient stability requirements. The control law design for an orbiting shallow spherical shell (antenna/reflector) system connected by a massive and flexible tether to a subsatellite is investigated in this article. The subsatellite is nominally deployed below the antenna along the yaw axis at a sufficient distance to provide a favorable composite moment of inertia ratio for gravitational stabilization. It is assumed that the tether would be deployed through the end of a rigid boom attached to the shell apex. The tension control strategy is used for stationkeeping and deployment and the control gains are obtained based on the structural data for a future proposed real space antenna/reflector. In order to prove the feasibility of this concept, a test scale model for an in-orbit experiment is also studied. The scale model should be small enough so that it could be accommodated within the volume and size limitations of the space shuttle cargo bay. Since the or bital angular velocity (determined by the orbital altitude of the space shuttle), tether diameter, etc. may not be directly scaled, the control gains will be adjusted to fit the requirements for the scale model. Furthermore, during the deployment, the real control gains will be adjusted to the change of the length of the tether and the deployed tether mass. Therefore, the control law gains for the pro posed in-orbit experiment scale model would be synthesized in a piece-wise adaptive manner. Nu merical results are presented both for the real antenna as well as for the proposed in-orbit (test) scale model.