Guided waves generated in a structure can propagate large distances with very little loss of energy and therefore have very high potential in detection of damages in structures. Typical spacecraft structure is majorly composed of honeycomb sandwich panels, which are load carrying members and have embedded inserts for payload mounting and structural connections. Typical failures like disbond of face skin from the core and insert damage influence the structural integrity and load carrying ability of the structural panel. Guided wave method of damage detection and quantification using piezo actuators / sensors is the ideal candidate for implementation of on board structural health monitoring of spacecraft structure. This work aim to study the wave propagation charactrestics in honeycomb sandwich panels and to identify a suitable technique to detect and quantify the damage by experiments and numerical simulations. Preliminary studies through experimental and numerical simulations using piezo actuators and sensors are done on propagation, scattering and mode conversion of guided waves in presence of asymmetrically located damage. The fundamental antisymmetric (Ao) mode is more suitable in localization and quantification of the damage. It is shown that the mode converted guided wave could be advantageously used for damage identification, localization and quantification.