Design of a Hierarchical Health Monitoring System for Detection of Multilevel Damage in Bolted Thermal Protection Panels: A Preliminary Study

Abstract

Space vehicles perform in the temperature range from - 160°C in space to 1650°C reached during reentry. As a result, space vehicles require high performance thermal protection systems (TPS) that provide high temperature insulation capability with lower weight, high strength, and reliable integration with the existing system. Carbon-carbon panels mounted with bracket joints are potential future thermal protection systems with light weight, low creep, and high stiffness at high temperature. However, the thermal protection system experiences a very harsh high temperature and aerodynamic environment in addition to foreign object impacts. Damage of failure of panels without being detected can lead to catastrophe. Therefore, knowledge of the integrity of the thermal protection system before each launch and reentry is essential to the success of the mission. Currently, the maintenance procedure of TPS is extremely time consuming and expensive due to its heavy reliance on human labor, which is also the largest obstacle in shortening the downtime of space vehicles after a mission. The objective of the study is to develop a built-in diagnostic system to assess the integrity of TPS panels as well as to lower inspection and maintenance time and costs. An integrated structural health monitoring system is being developed to monitor the TPS panels. The technology includes hierarchical investigation of the damages from loosening of bolts which connects TPS panels to the supporting structure, to potentially, identifying the location of damage on the panel caused by external impacts from micrometeorites and other objects. A prototype was manufactured and tested in an acoustic chamber which simulated a reentry environment to investigate the feasibility of the health monitoring system focusing on its survivability and sensitivity. The preliminary results were promising.