NASA has successfully developed a new and innovative Heatshield for Extreme Entry Environments Technology, or HEEET, which, at a Technology Readiness Level (TRL) of 6, is ready for use in Ice Giant missions. HEEET is not just a replacement for the legacy full-density carbon-phenolic (FDCP) material, which was used in NASA's Pioneer-Venus and Galileo missions; it is also a more mass efficient and robust alternative, and a technology that has a sustainable manufacturing base. HEEET is a dual-layer, 3-dimensionally woven material. It has a dense outer layer, made of pure carbon fibers, that comes into contact with and protects against extreme entry environments. Below this layer is an integrally woven, lower density insulating layer, made of a blend of carbon and phenolic yarn, that reduces heat-conduction to the carrier structure. The present paper describes development of this material, its thermal, structural, and aerothermal testing, production of an engineering test unit at flight scale, and maturation for infusion into missions to various planetary destinations, with a focus on Ice Giant in situ missions. Finally, for representative entry velocities at Uranus and Neptune, and a range of entry masses and flight path angles, margined thicknesses of HEEET are computed. When the limits of heat fluxes and pressures that can be achieved in ground-test facilities, and loom limits, are imposed on these thickness estimates, it is shown that several atmospheric entry missions are possible at the two destinations.

Starting in 2013 and completing in 2019, the Heatshield for Extreme Entry Environment Technology (HEEET) project has been working to mature a 3-D Woven Thermal Protection System (TPS) to Technical Readiness Level (TRL) 6 to support future NASA missions to destinations with extreme entry environments such as Venus, Saturn, Uranus, Neptune and high-speed sample return missions to Earth. A key aspect of the project has been the building and testing of a 1-meter base diameter Engineering Test Unit (ETU) representative of what could be used for a Saturn probe. This paper provides a high-level overview of the HEEET project including 1) manufacturing and testing of the ETU for structural model verification, 2) establish system capability and 3) verify manufacturing workmanship.