Finite element design of manipulator-coupled spacecraft for a research testbed

This paper describes the design and analysis of a research testbed developed to study the control of manipulator-coupled spacecraft with independent attitude control systems. This scenario could present itself in the assembly of Space Station Freedom (SSF). SSF assembly calls for a rendezvous of the Space Shuttle (SS) with SSF. Part of the assembly process requires that both spacecraft be coupled via the Space Shuttle Remote Manipulator System. An additional criterion that poses increased complexity is that the Space Shuttle controls and Space Station controls can not communicate. The technical issue involved is unwanted vibrations of the coupled-configuration that occur retraction and the complications due to non-interacting control systems. To understand these vibrations and possible complications, a research testbed has been built at the Marshall Space Flight Center in Huntsville, AL.To build the testbed, the manipulator links joints, and vehicles that represent the Space Shuttle and Space Station had to be designed. Pre-design simulation studies using ANSYS [1] (a Finite Element Computer Code) is used to size and design the manipulator links for the experimental facility. The ANSYS results were verified by the development of the Lagrangian Equations of motion. The Harmonic drives used as joints for the two link, three joint manipulator have been dissected into free body diagrams to ensure proper load paths in the ANSYS models. Accurate simulation of manipulator-coupled spacecraft is an important technology for NASA to understand. This paper outlines the methodology behind the preliminary design of a research testbed developed to help NASA gain knowledge in this area.