Acta Astronautica 62 (2008) 592 – 604 www.elsevier.com/locate/actaastro Damage assessment of large space structures through the approach Leonardo D. Chiwiacowsky a , Paolo Gasbarri b , Haroldo F. de Campos Velho c,∗ a Programa Interdisciplinar de Pós-Graduação em Computação Aplicada (PIPCA), Universidade do Vale do Rio dos Sinos (UNISINOS), Av. Unisinos, 950,93022-000 São Leopoldo, RS,Brazil b Dipartimento di Ingegneria Aerospaziale e Astronautica, Università Degli Studidi Roma - “La Sapienza”, Via Eudossiana, 18,00184 Rome, Italy c Laboratório Associado de Computação e Matemática Aplicada (LAC), Instituto Nacional de Pesquisas Espaciais (INPE), Av.dos Astronautas, 1758,P.O.Box 515, 12245-970, São José dos Campos, SP,Brazil Received 2 February 2006; received in revised form 8 January 2007; accepted 10 January 2008 Available online 11 April 2008 Abstract The present investigation is focused on the solution of a dynamic inverse problem which is concerned with the of damage in large space structures by means of measured vibration data. This inverse problem has been presented as an optimization problem and has been solved through the use of the conjugate gradient method with the adjoint equation, also called the variational approach. When a high number of damaged elements has to be found and these element damaged, it is shown that the use of an additional method is necessary in order to provide a better initial gues gradient method. A stochastic method, represented by the genetic algorithm method, has been chosen becaus search in complex spaces and also reduces the chance of converging to local optima. The application of this hybrid approach showed that better results can be achieved, although the computational time for the application analyzed here could increas The damage estimation has been evaluated using noiseless and noisy synthetic experimental data,and the reported results are concerned with a space truss structure. © 2008 Elsevier Ltd. All rights reserved. Keywords: Large space structure; Damage assessment; Inverse vibration problems; Structural dynamics 1. Introduction Future space missions will involve the use of large and light weight structures such as antennas, sunshields, solararrays, etc.One of the main characteristics of large flexible space structures is the large uncertainty in the knowledge of its structural dynamic behaviour. Models of flexible appendages, for instance, are partly ∗ Corresponding author. Fax:+55 12 3945 6375. E-mailaddress: haroldo@lac.inpe.br (H.F. de Campos Velho). 0094-5765/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2008.01.017 representative of the true space dynamics and of ot characteristics such as damping factor, couplings be- tween axes, number of flexible modes. As far as con design is concerned, for example, the number of fle modes and the uncertainties in the knowledge of th characteristics such as natural frequencies and/or d ing factors motivate the evolution of sophisticated a dedicated control strategies. Generally the study of physical characteristics of large space structure com nents indicates that the dynamic modeling is an app imation to the actual system and can only be verified