Past Event: Oden Institute Seminar

Tutorial on Ablative Thermal Protection Systems (TPS)

Dr. Bernard Laub, NASA Ames Research Center

Abstract

Ablative materials have been designed to protect structures from intense heating since the earliest days of space exploration, almost 50 years ago. The manned Mercury, Gemini and Apollo reentry capsules all used ablative materials for TPS. These materials are also used as nozzles for solid propellant rocket motors and as heat shields on strategic reentry vehicles (e.g., Minuteman, Trident). All scientific probes to planets and moons with atmospheres employ ablative heat shields. Given th criticality of this technology to both DoD and NASA, it is surprising that no courses are taught at any university in the USA nor is there even one text. The seminar describes the early approaches employed to model the thermal and ablation response of these materials and how these models evolved through the mid-late 60s. Modeling improvements since then have been incremental. Focus will be on the development of thermochemical ablation models and how such models are used to describe the performance of complex organic resin composites. Understanding the performance of these materials requires experiments at flight-representative conditions. Arc plasma facilities provide the best simulations of flight environments yet, typically, are unable to simultaneously simulate actual flight parameters (heat flux, pressure, enthalpy, shear, \u00e2\u0080\u00a6). Flight experiments are rarely conducted due to cost. Consequently, traceability between ground and flight can only be accomplished with models that accurately represent materials response phenomenology. Conducting ground tests of ablative materials in arc plasma facilities is also costly and defining the actual test conditions is, in itself, a challenge. The data that are critical to model development and validation will be discussed. In conclusion, the status of existing ablative materials is described with particular emphasis on the classes of materials appropriate for specific planetary exploration missions. The requirement for new TPS materials will be discussed.