A Hybrid FEM-Continuous Approach for Modeling Large Space Structures for Attitude Control Synthesis

In the last decade space agencies and industries have focused their attention on proposing and developing a new class of large space structures (LSS). LSS have potentially broad applications in space including low-stiffness precision shaped antennas for mobile communications satellites, narrow-band broadcast services and remote sensing, low-stiffness planar structures for large solar arrays. A lightweight design responding to the low gravity environment and live loads due to gravity gradients, extreme thermal variations, and solar wind create new and challenging problems in dynamic analysis of LSS. Since LSS will be designed for minimum weight and be quite flexible a significant problem will also arise on developing the capability to suppress and control flexible modes of vibration, some of which are closely packed with their frequencies that in turn could be very close to the ones of the attitude controller. On account of this it is necessary to have a very accurate model of the LSS. In the present work a hybrid FEM-continuous formulation, based on the classical modal reduction of a LSS under gravity and gravity gradient forces, will be presented. Analyses will be also performed to evaluate the effects of modal truncation on the robustness of attitude control laws.