A methodology is presented for the flutter analysis of the seal of thermal protection system (TPS) panel of X-33 Advanced Technology Demonstrator test vehicle. The seal is simulated as a two-dimensional cantilevered panel with an elastic stopper, which is modeled as an equivalent spring. This cantilever beam-spring model under the aerodynamic pressure at supersonic speeds turns out to be an impact nonlinear dynamic system. The flutter analysis of the seal is thus carried out using, time domain numerical simulation with a displacement stability criterion. The flutter boundary of the seal is further verified with a family of three traditional and one nontraditional panel flutter models. The frequency domain method that applies eigenanalysis on the traditional panel flutter problem was used. The results showed that the critical dynamic pressure could be more than doubled with properly chosen material for the base stopper. The proposed methodology can be easily extended to three-dimensional panel seals with flow angularity.Mei, Chuh and Cheng, GuangfengLangley Research CenterACOUSTIC FATIGUE; BOUNDARIES; DISPLACEMENT; FLUTTER ANALYSIS; PANEL FLUTTER; SUPERSONIC SPEED; THERMAL PROTECTION; CANTILEVER BEAMS; CRITERIA; CRITICAL PRESSURE; FLUTTER; FREQUENCY DOMAIN ANALYSIS; NONLINEAR SYSTEMS; PROTECTION; PROVING; SIMULATION; STABILITY; TEST VEHICLES; X-33 REUSABLE LAUNCH VEHICLE...