Simulation of on-orbit modal tests of large space structures

This paper describes a procedure to analytically simulate a modal test of an on-orbit large space structure (LSS), extract the modal properties, and evaluate the success of the modal test. This procedure addresses some of the major challenges to performing an on-orbit modal test of an LSS including high modal density, low frequency modes, and limitations in excitation capabilities. A finite element model of the orbiting structure is used to predict acceleration responses due to thruster excitations, time-domain modal extraction methods are used to estimate the modal properties, and comparison of frequencies and cross-orthogonality values is used to evaluate the success of the modal test. Several alternative excitation patterns and sensor arrangements were evaluated using a space station model as an example. Results of the simulations indicate that the choice of excitation functions is critical to the success of the test.