Surface Densification Of Phenolic Impregnated Carbon Ablator (PICA)

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.

Microorganisms are unique from the standpoint that they can be employed as self-replicating bio-factories to produce both native and engineered mission relevant bio-products. Methane (CH4) usage in In-Space Manufacturing (ISM) platforms has been discussed previously for human exploration and has been proposed to be used in physicochemical systems as a propulsion fuel, supply gas, and in fuel cells. Carbon Dioxide (CO2) is abundant on Mars and manned spacecraft. On the International Space Station (ISS), NASA reacts excess CO2 with Hydrogen (H2) to generate CH4 and Water (H2O) using the Sabatier System (Figure 1). The resulting water is recovered in the ISS, but the methane is vented to space. Recapturing this methane and using it for microbial manufacturing could provide a unique approach in development of in-space bio-manufacturing. Thus, there is a capability need for systems that convert methane into valuable materials. Methane (CH4) is a potential carbon substrate for methanotrophic microorganisms which are able to metabolize CH4 into biomass. The innovative technology from NASA Ames Research Center ports Soluble Methane Monooxygenase (sMMO) to Pichia, that is, it moves the methane metabolism into a robust microbial factory (Pichia pastoris) (Figure 2). The yeast Pichia pastoris is a refined microbial factory that is used widely by industry because it efficiently secretes products. Pichia could produce a variety of useful products in space. Pichia does not consume methane but robustly consumes methanol, which is one enzymatic step removed from methane. This novel innovation engineers Pichia to consume methane thereby creating a powerful methane-consuming microbial factory and utilizing methane in a robust and flexible synthetic biology platform.

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.

The fine-grained targets are a matrix of a prismatic edge natural flake graphite that produces strong structural pi bonds when pressed at room temperature. The targets have an approximate grain size of 2 microns. The graphite provides a carbon source that is combined with a metal catalyst made of powder forge nickel and powder forge cobalt. Previously used targets involved pressing and binding targets with Dylon carbon cement. These particles had an approximate 200-micron particle size, which led to large regions of uncatalyzed target. The new metal powders are small (~0.5 microns), highly dispersible, and two orders of magnitude less expensive. The powders are mixed in appropriate quantities and subjected to low-energy ball-milling to ensure mingling. Targets undergo additional preparatory steps, including high pressure processing. The targets are then subjected to a series of ultrafast infrared laser light pulses at a high repetition rate to vaporize the layers of the spinning targets and create a plume of nanotubes.

The low-temperature oxidation catalyst technology employs a novel catalyst formulation, termed platinized tin oxide (Pt/SnOx). The catalysts can be used on silica gel and cordierite catalyst supports, and the latest developments provide sprayable formulations for use on a range of support types and shapes. Originally developed for removal of CO, the catalyst has also proven effective for removal of formaldehyde and other lightweight hydrocarbons. NASA researchers have also extended the capability to include reduction of NOx as well as developed advanced chemistries that stabilized the catalyst for automotive catalytic converters via the engineered addition of other functional components. These catalyst formulations operate at elevated temperatures and have performed above the EPA exhaust standards for well beyond 25,000 miles. In addition, the catalyst can be used in diesel engines because of its ability to operate over an increased temperature range. For use as a gas sensor, the technology takes advantage of the exothermic nature of the catalytic reaction to detect formaldehyde, CO, or hydrocarbons, with the heat being produced proportional to the amount of analyte present.