Printable Heat Shield Form-ulations Advance Spacecraft Construction
Materials and Coatings
Printable Heat Shield Form-ulations Advance Spacecraft Construction (MSC-TOPS-137)
Novel material formulations speed production and save cost
Overview
Innovators at NASA Johnson Space Center have developed an additively manufactured thermal protection system (AMTPS) comprised of two printable heat shield material formulations. These formulations are directly applied by 3-D printer or other robotic extrusion system, and bonded to a spacecraft to devise a heat shield suitable for atmospheric entry. This technology could significantly decrease heat shield or thermal protection system (TPS) fabrication cost and time.
Current state of the art TPS manufacturing and application methods are expensive, labor-intensive, and complex. These drawbacks are primarily due to the amount of skilled, manual labor needed for form fitting and bonding individual TPS tiles across a spacecraft’s forebody – each tile comprised of differing thermal properties and layers – and includes filling the gaps in-between the tiles with an additional component formulation.
This AMTPS technology can solve these challenges and may represent a game changing innovation in TPS manufacturing – away from convention-al labor-intensive, costly, long-schedule techniques and towards automa-tion. It reduces the complexity of TPS integration, and eases the produc-tion of large and specially contoured heat shields. Additionally, this tech-nology allows heat shields to be created as a single mold and prevents the need to treat the tile gaps of current heat shields, thus eliminating numerous potential failure points.
The Technology
One inner insulative layer, and one outer robust ablative layer comprise the AMTPS technology. When applying the heat shield to the surface of a spacecraft, the insulative layer is printed first and primarily functions to reduce the amount of heat soak into the vehicle. The formulation of the insulative layer has a slightly lower density (as compared to the robust layer) and is adjusted using a differing constituent ratio of phenolic and/or glass microballoon material. Both formulations combine a phenolic resin with various fillers to control pre- and post-cure properties that can be adjusted by varying the carbon and/or glass fiber content along with rheology modifiers to enhance the fluid flow for deposition systems.
The robust layer is applied next and functions as the ablative layer that ablates away or vaporizes when subjected to extremely high temperatures such as those achieved during atmospheric entry. The formulation of the robust layer produces a gas layer as it vaporizes in the extreme heat that acts as a boundary layer. This boundary prevents heat from further penetrating the remaining robust material by pushing away the even hotter shock layer. The shock layer is a region of super-heated compressed gas, positioned in front of the Earth-facing bottom of the spacecraft during atmospheric entry, that results from the supersonic shockwave generated.
Commercial space applications for this AMTPS technology include use on any spacecraft that transits a planetary or lunar atmosphere such as Mars or Saturn’s moon Titan. Additionally, the invention may be useful for launch system rockets to provide heat shielding from atmospheric reentry or to protect ground equipment on the launch pad from rocket exhaust plumes. As the number of government and commercial space missions to primary Earth orbits, the Moon, and the Solar System increase, there will be a growing need for cost-effective, on-demand, and timely fabrication of heat shields for space-related activities.
AMTPS Formulations – Insulative and Robust Variation is at a technology readiness level (TRL) 5 (component and/or breadboard validation in laboratory environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.
Benefits
- Facilitates single molded heat shield fabrication with embedded instrumentation
- Eliminates numerous potential failure points due to seamless heat shield construction
- Supplants current labor-intensive fabrication processes for a TPS with faster, more accurate 3D automation
- Reduces fabrication costs
- Reduces fabrication time from months to weeks
- Allows fabrication of more complex forms over current state of the art
- Reduces complexity of TPS component integration
- Enables production of larger heat shields via direct application
- Allows tunable material characteristics by varying thermal protection and cure rates
- Enables tunable material flow characteristics for adaptation to different extrusion applications
Applications
- 3-D printed Heat Shields for Earth reentry spacecraft
- 3-D printed Heat Shields for solar system exploration and atmospheric entry spacecraft – TPS formulation can be tuned to varying payload and planetary/lunar atmosphere (Titan)
- Single mold insulative coatings for terrestrial passive fire protection such as rocket launching sites
Technology Details
Materials and Coatings
MSC-TOPS-137
MSC-27453-1
Similar Results
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.
Woven Thermal Protection System
Going farther, faster and hotter in space means innovating how NASA constructs the materials used for heat shields. For HEEET, this results in the use of dual-layer, three-dimensional, woven materials capable of reducing entry loads and lowering the mass of heat shields by up to 40%. The outer layer, exposed to a harsh environment during atmospheric entry, consists of a fine, dense weave using carbon yarns. The inner layer is a low-density, thermally insulating weave consisting of a special yarn that blends together carbon and flame-resistant phenolic materials. Heat shield designers can adjust the thickness of the inner layer to keep temperatures low enough to protect against the extreme heat of entering an atmosphere, allowing the heat shield to be bonded onto the structure of the spacecraft itself. The outer and inner layers are woven together in three dimensions, mechanically interlocking them so they cannot come apart. To create this material, manufacturers employ a 3-D weaving process that is similar to that used to weave a 2-D cloth or a rug. For HEEET, computer-controlled looms precisely place the yarns to make this kind of complex three-dimensional weave possible. The materials are woven into flat panels that are formed to fit the shape of the capsule forebody. Then the panels are infused with a low-density version of phenolic material that holds the yarns together and fills the space between them in the weave, resulting in a sturdy final structure. As the size of each finished piece of HEEET material is limited by the size of the loom used to weave the material, the HEEET heat shield is made out of a series of tiles. At the points where each tile connects, the gaps are filled through inventive designs to bond the tiles together.
Multilayered Fire Protection System
The Multilayered Fire Protection system uses technology from the space craft flexible heat shield for future planetary missions. By optimizing this material for the fire environment, utilizing heat shield test methods, and experimenting with different materials, the NASA team developed a multilayered fire protection system. This system includes an outer textile layer which reflects over 90 percent of the radiant heat, an insulated layer which protects against convective heat and hot gases, and a non-porous film layer which is a gas barrier layer.
Thin Film Sensor for Ultra High-Temp Measurement
The thin film sensor’s principal advantage lies in its potential to take high frequency temperature measurements from the surface of a reentering spacecraft while simultaneously withstanding the high temperature and oxidizing environment encountered. This data provides engineers with operational phase measurements used to refine the spacecraft’s operational envelope and track flight hardware behavior in addition to providing high frequency temperature measurements that can inform the physics of a boundary layer.
Mismatches in coefficients of thermal expansion (CTE) are expected in TPS-based sensor applications because the metallic materials used for temperature sensing have thermal expansion rates that differ from the rates of the substrate and coating materials in the TPS. At high temperatures during reentry, this mismatch in CTE can create a significant strain differential between the metallic sensor, sensor leads, and the materials to which the sensor and leads are bonded.
High frequency response temperature measurements on the surface of entry spacecraft are not currently possible above ~700 F with existing measurement capabilities. This shortcoming is primarily due to the need for robust sensor behavior at temperatures of several thousand degrees F. The sensor design of this technology preserves the integrity of sensor components while enhancing its high temperature functionality.
The thin film temperature sensor has a technology readiness level (TRL) 5 (Component and/or breadboard validation in relevant environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.
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.
