Space Vehicle Heat Shield Having Edgewise Strips of Ablative Material

Langley Research Center, Hampton, Virginia

An alternate heat shield concept for the Orion space vehicle is to use interlocking blocks of Phenolic Impregnated Carbon Ablator (PICA). The blocks are independent from one another and there is a defined gap inches between the blocks. That gap poses serious problems to the vehicle and crew if gases flow between the PICA blocks. This invention is a simple yet robust invention for PICA block gap filler. Strips of preconditioned PICA blocks are positioned edgewise to fill gaps between PICA blocks to provide a gap filler substance that allows thermal expansion, and satisfies mechanical strain between the PICA tiles and substructure.

PICA is a low-density, low-strength material that generally must be isolated from mechanically and thermally induced deformations and strains of the underlying heat shield carrier structure. One type of PICA configuration consists of discrete blocks of PICA material bonded to a fibrous strain isolation pad (SIP) that is then bonded to the underlying carrier structure. The PICA blocks, SIP, and gaps between blocks must be designed to accommodate all carrier structure deformations without overstressing and damaging the PICA material. Open gaps between blocks of PICA could prevent overstressing the material, but could lead to damaging hot gas flow in the gaps, catastrophic damage to the underlying carrier structure, and even loss of crew. Thus, the gaps must be filled with a material.

Different approaches have been proposed, such as Room Temperature Vulcanizing (RTV) adhesives and fibrous gap fillers. This invention uses edgewise strips of PICA to completely eliminate the gaps between tiles. The strips are preconditioned and installed between the tiles to fill the gap, yet are compliant enough to accommodate thermal expansion and mechanical strain mismatch between the PICA tiles and substructure.

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