Abstract: In this paper,the special themes which include effect ofdegradation of material properties on the dynamic response of largespace structures(LSS)and damage assessment for LSS have been dealtwith.This damage is usually observed in fibrous composite media.Delicatestudies implemented on representative space truss structures indicate thatdegradation of material properties will result in a reduction of naturalfrequencies and may have important effects on the mode shapes.A theoryfor assessing the occurrence,location,and extent of potential damageusing on-orbit response measurements is presented.A MAST truss is usedas an example.The damages to the structural system for the sampleproblem have been identified and the extent of the damage quantified.