Control parameters transition during deploying operations of a space flexible structure via multi-body approach

The need to model very complex spacecraft has induced many researchers to develop different methodologies for their study, depending on the type of analysis to be performed. In the ease of structural analysis a classical finite element approach is used to describe in detail each component. In the case of flight mechanics a simple rigid spacecraft can be used for studying guidance, navigation and control laws. On the contrary for studying deploying mechanisms it is necessary to define models of joints and actuators. The necessity to reduce time and cost of the development of new space platforms requires the integration of these different design models and processes. In recent years new methodologies, based on the so-called multibody approach, have been introduced for modeling mechanical systems. Complex space structures are divided into sub-elements (rigid or flexible) connected to each other through joints. With this approach, a very detailed multibody model of a spacecraft can be easily adapted to face different disciplines. Unfortunately, when dealing with elastic bodies the number of degrees of freedom (DOFs) drastically increases. The approach here suggested to keep the number of DOF low is to employ a hybrid approach where a limited number of bodies is chosen, depending on the values of their inertial and elastic properties. In the present work a very large flexible satellite is modeled via multibody technique. In particular the deployable solar arrays and the bus are represented with only three elastic bodies. The deployment phase of the solar panels is simulated through a time sequence of panels models with different geometries. For each configuration the inertial and modal properties are evaluated, and eventually these parameters are interpolated in order to determine their values when a continuous movement of the panels is simulated. On account of the geometry variation we can observe not only a variation on the values of the natural frequencies, but also an exchange on the ranking of the relevant modal shapes and hence on the relevant modal participation factors. A re-ordering of the modal shapes is mandatory before doing any interpolation. A robust and easy to implement re-ordering criteria is presented in the paper together with a number of numerical simulations showing that the proposed hybrid approach can be considered as a valid alternative to simulate a deployable structure with a reduced number of elements and hence of a reduced computational cost. Copyright © (2012) by the International Astronautical Federation.