NASA has published technical bulletin TB 26-08, dedicated to analyzing complex vibration modes in lightly damped structural systems from the perspective of two-mode interaction. The material was prepared as part of the work of the NASA Engineering and Safety Center (NESC), a division responsible for engineering safety issues in space systems. For additional information, contact Joel W. Sills from the Langley Research Center. In accompanying material, the NASA Chemical Equilibrium with Applications (CEA) software suite is also mentioned — a widely used tool for propulsion system analysis. It is used for chemical equilibrium calculations, rocket engine characteristics, and modeling of shock waves and detonation. The program is used both within NASA and in the broader aerospace community to assess the efficiency and safety of various systems. The publication of such technical bulletins is part of NESC's regular work to disseminate engineering knowledge and analysis methodologies that help improve the reliability and safety of aerospace structures and propulsion systems. The document is available for download in PDF format on NASA resources.