High Temperature Resistant Thermal Protection for Re-Entry Applications

High temperature resistant Thermal Protection System (TPS) materials are critical to the success of new reentry vehicles, hypersonic vehicle weapons and related U.S. defense modernization priorities. Once developed and implemented within a design, these materials often possess a single point of failure (SPOF) or multiple SPOF’s within a single supply chain. The DoD has identified SPOF as a significant threat to defense rated programs. One such SPOF material is Rayon Carbon. Another SPOF is the recent sale, imminent closure, and relocation of the facility which processed the Rayon Carbon into Graphite Carbon and manufactured MK-4, MK-5 reentry vehicle heat shields. We have identified three potential replacement materials: a Graphitized “Low-Fired-Stretch-Broken-PAN-Fiber” (GLFSP), Graphitized “Blended-Stretch-Broken-PAN-Fiber” (GBSP) and Graphitized “Stretch-Broken-PAN-Fiber” (GSP). Any of these potential replacement materials can readily be demonstrated and proven in a prepreg system coated with phenolic resin and graphitic filler then processed into Reentry Vehicle Heat Sheilds by tape wrapping or employed within leading edge and acreage area Hypersonic Aeroshells via carbon-carbon (C-C) processing. The TPS material currently qualified at Northrop in Hypersonic Glide-Bodies or “Aeroshells” consist of phenolic resin and a low fired, stretch broken PAN fiber (LFSP) and/or blended stretch broken PAN fiber (BSP) prepreg processed into carbon-carbon. Both LFSP and BSP fiber solutions have been found to be suitable replacements for the rayon-based carbon phenolic used in tape wrapped rocket nozzles and 2D C-C components. However, the GLFSP, GBSP and GSP prepreg materials can provide better performance with higher temperature resistance and lower surface regression rate in tape wrapped Reentry Vehicle heat shields. For use in C-C Aeroshell components, these prepregs provide faster conversion (i.e. lower cycle time in re-densification) to current C-C processes and lower internal stress in components due to the stretch-broken fiber and graphitization of fabric prior to tape wrapping and C-C fabrication. Heat treated Rayon Carbon fabrics had proven capable in TPS applications, however, possess high residual stress due to continuous filament fabrics being graphitized in tape wrapped components, and high rate of component failures in the manufacturing process, attributed to low across-ply tensile strength causing stress related cracking failures. Alkemix has demonstrated LFSP and BSP, high char yield prepreg systems for replacement of SPOF ablative Rayon Carbon. Similarly, applying the high char yield resin with the discontinuous “stretch broken” fiber in a graphitized fabric would resolve several SPOF, in-process/post-process delamination and stress crack damage, and improved Reentry Vehicle and Hypersonic TPS production rates.