SEP 2018


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85 HEEET: A Broader Mission Illustration / Karl Reque HEEET Woven Thermal Protection System Heatshield › Dual-layer, 3D design's generally lower density reaps a weight reduction of 40-50% vs. the legacy carbon fiber/ phenolic system from the 1990s. › 3D woven fabric mechanically interlocks the two layers, providing higher interlaminar strength and temperature resistance vs. an adhesive bonding. › Standard system is tailorable for small to large (1-3m) space probes and provides robust perform- ance in steep and shallow entry conditions, enabling wider spacecraft application and mission flexibility. enable a range of entry conditions, what NASA terms "a larger entry corridor." Legacy carbon fiber-reinforced phenolic at high density performs well at steep, quick entries that generate high heat flux, but some missions require a shallow approach, flying longer at higher altitude to reduce the G loads on sensitive instru- ments. "HEEET offers this robust performance and can be adapted to enable scientific probe missions to Venus, Saturn, Uranus, Neptune and sample return missions from Mars, asteroids, comets, Europa and Enceladus," says Venkatapathy. "It's not just a one-shot development. It's a broader technology." Evolving TPS to a 3D woven system HEEET began with efforts to find new TPS materials in the early 2000s. "With the Galileo probe to Jupiter in 1995-1996, we used a 2D carbon fiber fabric system impregnated with phenolic resin," recalls Venkatapathy. It was capable, but the source material was no longer available. erefore, a search began for alternative materials. Around this time, the Adaptive Deployable Entry system ProjecT (ADEPT) — which used carbon fiber (CF) fabric in a deployable, umbrella-type heatshield — required a vendor to manufacture and support the development. Bally Ribbon Mills (BRM, Bally, PA, US) responded to a NASA request for information. "We started working with BRM for ADEPT and this led, eventually, to exploring a new way of making rigid and flexible TPS," says Venkatapathy. e next project, "3D Multifunctional Ablative TPS (3D-MAT) for Orion Compression Pad," began in 2012. "We chose quartz fiber because it has low thermal conductivity and is a resilient fiber, not as brittle as carbon," he explains. NASA and BRM worked to produce a 3D woven fabric that was infused with resin to form the compression pads now flying on the Orion spacecraft (see Learn More p. 86). From there, the objective shifted to a heatshield system design that could be tailored and applied across many missions. For that, notes Venkatapathy, "carbon fiber is good at handling heat flux, but it is highly conductive, and we needed a system that was insu- lative as well. Dual-layer, 3D woven carbon fiber and phenolic fiber fabric 1M-DIAMETER ENGINEERING TEST UNIT Lower-density recession layer Higher- density recession layer Phenolic resin-infused composite tile Spacecraft structure

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