Effect of model error on sensor placement for on-orbit modal identification of large space structures

A theory is presented for the effect of errors in large space structure prelaunch finite element models on sensor placement for the on-orbit independent identification of a set of selected target modes. The idea of positive net information is introduced. If the net information matrix remains positive definite as sensor locations are deleted from an initial candidate set, the analytical model provides useful information for the identification of the real target modes. If the net information matrix becomes indefinite, the sensor placement analysis based on the prelaunch analytical model will actually detract from the independent identification of the target modes. A bound is presented that can be easily checked after each iteration during which a sensor was deleted to determine positive definiteness of the net information matrix. Numerical examples are used to illustrate the ideas that are presented.