System modes and dynamics of the proposed space station type configurations

Abstract

The paper studies libration/vibration interaction dynamics of the space station Freedom during its evolutionary phases. To that end, a relatively general nonlinear formulation, applicable to a system of interconnected plate and beam-type structural members forming a tree topology is developed. System modes, obtained through a finite element analysis, are employed in the discretization process and the response study is purposely confined to the orbital plane to emphasize interactions between librational dynamics and flexibility. Finally, an approximate closed-form nonlinear solution of the problem is attempted using the variation of parameters method. Its validity is assessed through comparison with the numerically obtained results over a range of system parameters and initial conditions. Results provide information pertaining to the levels of librational and vibrational response and the associated acceleration tield, which may prove helpful in appropriately locating experiments and monitoring instruments. It may also aid in the planning of the control system. The analytical approach provides surprisingly close correlation with the more elaborate numerical procedure, thus promising better physical appreciation of the complex interactions as well as a considerable saving in the computational cost.