Predicting the dynamics of flexible space payloads under different boundary conditions through substructure decoupling

Flexible space payloads, such as solar panels or array antennas for space applications, can be attached to the body of the satellite using different types of joints. To predict the dynamic behaviour of such structures under different boundary conditions, it is convenient to start from their dynamic behaviour in free-free conditions. In fact, the effect of different boundary conditions, such as additional constraints or appended structures, can be taken into account starting from the frequency response functions in free-free conditions. In this situation, they would exhibit rigid body modes at zero frequency. To experimentally simulate free-free boundary conditions, flexible supports such as soft springs are typically used: with such arrangement, rigid body modes occur at low non-zero frequencies. Since flexible space payloads exhibit the first flexible modes at very low frequencies, the two sets of modes become coupled and the low frequency dynamics of the free-free structure cannot be estimated directly from measurements. To overcome this problem, substructure decoupling can be used, that allows to identify the dynamics of a substructure (i.e. the free-free panel) after measuring the FRFs on the complete structure (i.e. the panel with the supports) and from a dynamic model of the residual substructure (i.e. the supporting structure). Subsequently, the effect of additional boundary conditions can be predicted using an FRF condensation procedure. The procedure is tested on a reduced scale model of a space solar panel.