Flexible Phenolic Intermingled Carbon Ablators (PICA-Flex)
Materials and Coatings
Flexible Phenolic Intermingled Carbon Ablators (PICA-Flex) (TOP2-331)
Materials Engineered for Re-entry using Innovative Needling Operations (MERINO)
Overview
For the past three decades, phenolic impregnated carbon ablators (PICAs) have been the state of the art in ablative entry materials for heat shields for Mars and Earth sample return missions for entry conditions. Traditional rigid PICAs have very low density and highly efficient ablative capability to provide mass efficiency for these heating regimes. Non-rigid variants of PICA provide additional benefits beyond traditional rigid PICA, offering reduced density variants with increased strain to failure. However, all three materials require lengthy infusion processes involving complex equipment and infrastructure, yield toxic byproducts, and the rigid thermal protection system (TPS) produced requires complex and costly integration processes. NASA Ames has developed a family of materials called Materials Engineered for Re-entry using Innovative Needling Operations (MERINO), a flexible PICA material based on felting and fiber intermingling techniques that can create a blanket of thermal protection material to install onto spacecraft.
The Technology
Flexible PICAs combine both carbon and phenolic fiber constituents during a felting process rather than introducing a phenolic through infusion processes that also uses harsh chemicals. MERINO PICA-Flex materials drastically reduces integration complexities when compared to traditional phenolic infused rigid tiles, and can eliminate the costly and time intensive phenolic infusion process, resulting in a thermal protection system (TPS) material more akin to a “blanket” than a rigid TPS. PICA-Flex encompasses a range of configurations, including a dual layer PICA-Flex material with a higher density outer layer(s) to minimize recession, a lower density PICA-Flex material with applicability to aftbody TPS, and a single piece PICA-Flex forebody. PICA-Flex is fabricated by combining by intermingling both carbon and phenolic fiber constituents during a needle punch felting process during which the fibers are made into battings, and the battings are needled together layer-by-layer to build up thickness.
Benefits
- Drastically reduces integration complexities when compared to traditional phenolic infused rigid tiles, which require precision machining and integration steps
- Eliminates the lengthy phenolic infusion process, resulting in a TPS material more akin to a blanket than a rigid TPS
- Blanket-like felted material TPS drastically reduces integration complexity when compared to traditional phenolic infused rigid tiles, resulting in significant cost and schedule savings (e.g., can be produced in a week or two as opposed to six months or more) when compared to traditional rigid TPS materials
- Helps the emerging commercial space market by meeting low to moderate heat flux requirements that are orders of magnitude less expensive but just as capable as, if not better than, previous TPS materials
- Relatively large areas of PICA-Flex can be produced and installed on the spacecraft without significant direct or touch labor hours, thus reducing installation time and increasing safety
- Due to its flexibility, PICA-Flex may allow differently shaped and potentially larger spacecraft to be produced with limited gaps and seams
Applications
- Spacecraft that undergo atmospheric entry (e.g., forebody and aftbody TPS)
- Space exploration
- Systems engineering
- Thermal Protection Systems
- Materials engineering
- Mechanical engineering
Technology Details
Materials and Coatings
TOP2-331
ARC-19046-1
Similar Results
Surface Densification Of Phenolic Impregnated Carbon Ablator (PICA)
The graded Thermal Protection System (TPS) offers a lower density than comparable state-of-the-art TPS systems operating at similar maximum heating conditions. This approach is straight forward in terms of processing and surface-treatment application and can be applied to machine PICA materials without having an effect on the final tolerance. The process results in increased usability and handling since standard uncoated PICA is relatively weak. Surface-densified PICA provides an approach for improvements in the robustness for the baseline CEV heat shield. A graded approach eliminates the need for joints and/or bonding agents between material plies. PICA surface densification offers robust mechanical protection against transit damage, handling damage, and in-flight object damage.
A New Family of Low-Density, Flexible Ablators
The invention provides a family of low density, flexible ablators comprising of a flexible fibrous substrate and a polymer resin. The flexible ablators can withstand a wide range of heating rates (40-540 Watts/cm2) with the upper limit of survivable heat flux being comparable to the survivable heat flux for rigid ablators, such as PICA and Avcoat. The amount and composition of polymer resin can be readily tailored to specific mission requirements. The material can be manufactured via a monolithic approach using versatile manufacturing methods to produce large area heat shields, which provides a material with fewer seams or gaps. The goals of the work are primarily twofold: (i) to develop flexible, ablative Thermal Protection System (TPS) material on a large, blunt shape body which provides aerodynamic drag during hypervelocity atmospheric entry or re-entry, without perishing from heating by the bow shock wave that envelopes the body; and (ii) to provide a relatively inexpensive TPS material that can be bonded to a substrate, that is unaffected by deflections, by differences in thermal expansion or by contraction of a TPS shield, and that is suitable for windward and leeward surfaces of conventional robotic and human entry vehicles that would otherwise employ a rigid TPS shield. This technology produces large areas of heat shields that can be relatively easily attached on the exterior of spacecraft.
Creating Low Density Flexible Ablative Materials
The low density flexible ablator can be deployed by mechanical mechanisms or by inflation and is comparable in performance to its rigid counterparts of the same density and composition. Recent testing in excess of 400W/cm2 demonstrated that the TPS char has good structural integrity and retains similar flexibility to the virgin material, there by eliminating potential failure due to fluttering and internal stress buildup as a result of pyrolysis and shrinkage of the system. These flexible ablators can operate at heating regimes where state of the art flexible TPS (non-ablative) will not survive. Flexible ablators enable and improve many missions including (1) hypersonic inflatable aerodynamic decelerators or other deployed concepts delivering large payload to Mars and (2) replacing rigid TPS materials there by reducing design complexity associated with rigid TPS materials resulting in reduced TPS costs.
Thermal protection supplement for reducing interface thermal mismatch
The invention includes an exposed surface cap with a specially formulated coating, an insulator base adjacent to the cap with another specially formulated coating, and one or more pins that extend from the cap through the insulator base to tie the cap and base together through ceramic bonding and mechanical attachment. The cap and insulator base have corresponding depressions and projections that mate and allow for differences in thermal expansion of the cap and base. The cap includes a high-temperature, low density, carbonaceous, fibrous material whose surface is optionally treated with a High Efficiency Tantalum-based Ceramic Composite (HETC) formulation, the fibrous material being drawn from the group consisting of silicon carbide foam and similar porous, high temperature materials. The insulator base and pin(s) contain similar material. The mechanical design is arranged so that thermal expansion differences in the component materials (e.g., cap and insulator base) are easily tolerated. It is applicable to both sharp and blunt leading edge vehicles. This extends the possible application of fibrous insulation to the wing leading edge and/or nose cap on a hypersonic vehicle. The lightweight system comprises a treated carbonaceous cap composed of Refractory Oxidation-resistant Ceramic Carbon Insulation (ROCCI), which provides dimensional stability to the outer mold line, while the fibrous base material provides maximum thermal insulation for the vehicle structure. The composite has graded surface treatments applied by impregnation to both the cap and base. These treatments enable it to survive in an aero-convectively heated environment of high-speed planetary entry. The exact cap and base materials are chosen in combination with modified surface treatments and a specially formulated surface coating, taking into account the duration of exposure and expected surface temperatures for the particular application.
New Resin Systems for Thermal Protection Materials
This method produces a low density ablator similar to Phenolic Impregnated Carbon Ablator (PICA) using a cyanate ester and phthalonitrile resin system, rather than the heritage phenolic resin. Cyanate ester resin systems can be cured in a carbon matrix and generate high surface area structure within the carbon fibers. This helps to reduce the thermal conductivity of the material which is one of the key requirements of thermal protection system (TPS) materials. The material has densities ranging from 0.2 to .35 grams per cubic centimeter. NASA has successfully processed the cyanate ester and phthalonitrile resins with a morphology similar to that of the phenolic phase in PICA, but with more advanced properties such as high char stability, high char yield, and high thermal stability. This new generation of TPS materials has the same microstructure as heritage PICA, but improved characteristics of PICA such as increased char yield, increased char stability, increased thermal stability and increased glass transition temperature.
