Thermal and Structural Analysis of BOLT-1B Flight Geometry Including Joint Step Estimates

The Boundary Layer Transition (BOLT) series of flight experiments was designed to study hypersonic boundary-layer transition and turbulence on a geometry with low-curvature concave surfaces and highly swept leading edges. A refly of the BOLT-1A flight experiment, named BOLT-1B, was designed, fabricated, and tested in preparation for flight from Andøya Space in Norway. BOLT-1B was successfully launched on 2 September 2024 at 0941 hrs Coordinated Universal Time. A comprehensive CFD++ database was generated to calculate aerothermal heating on the BOLT-1B payload. A finite element analysis model was developed to analyze the thermomechanical response of the payload during the hypersonic flight experiment. Thermal contact resistance across the payload nosetip joints was analyzed and validated against thermocouple data. The step heights across the joints resulting from differential thermal expansion during the flight were estimated. The analysis indicates that the steps on the primary experiment side on the BOLT-1B flight geometry remained rear-facing during the flight, which was desired to minimize roughness effects. The roughness effects with intended greater step heights on the secondary side were successfully achieved. A delayed step-height response following time-dependent aerothermal heating was observed. The analysis in this paper provides a reasonable estimate of joint step magnitudes during the BOLT-1B flight.