Advanced sandwich structures for thermal protection systems in hypersonic vehicles: A review

A heat shield called the thermal protection system (TPS) is an important structure in hypersonic vehicles as it prevents hot air from entering vehicles and potential impacts from space debris. With the increase in demand for low-cost reusable launch vehicles as well as for searching and exploration of new planets in both unmanned and manned missions, the need for developing an effective TPS has increased across many countries. The structural design of TPSs has become more prominent in the early stage of hypersonic vehicle development. Sandwich structures that have the advantages of low density and high performance are integrated into the structural design of an effective TPS. This paper provides a comprehensive review of recent research efforts on sandwich structures for TPSs. The topics discussed in this paper include aspects of structural and material design, mechanical and thermomechanical performances, and manufacturing methods. In particular, we review and discuss the structural design as well as the material design of sandwich structures for different TPS types with various configurations, including corrugated cores, lattice cores, multilayer cores, foams, honeycomb cores, bio-inspired cores. The materials used for the sandwich structures, such as various types of laminated composite, ceramic matrix composite, and metals, are included. We also discuss the performance of the TPS sandwich structures in terms of temperature gradients, deformation limits, and mechanical strengths and provide a discussion on the manufacturing methods of TPS sandwich structures for hypersonic vehicles. Finally, further research directions and challenges of sandwich structures for TPSs are presented.