In the area of thermal protection systems (TPS) design, MR&D has been heavily involved in the analysis and design of C-C and ceramic matrix composites for wing leading edges, hot structure control surfaces, and acreage regions of hypersonic and re-entry vehicles.
Leading Edge Designs
For leading edges, we have assessed both passively cooled and actively cooled design concepts for AFRL for the sharp leading edges of scramjet components. The passively cooled designs have investigated both dovetail and tab/pin concepts for short spanwise direction leading edge segments. Actively cooled designs have investigated the use of high conductivity plugs to move heat to the cooler fuel source.
Dovetail and tab/pin design concepts for segmented sharp leading edge sections.
As mentioned elsewhere on this website, MR&D performed the design of the C-C material architecture for the sharp nose leading edges for the X-43A hypersonic vehicle.
Other efforts in leading edge work include the analysis and design of heat pipe cooled refractory composites for the blunt nose leading edges of re-entry vehicles. These designs predicted significantly lower temperatures for the entire leading edge component, thus enhancing the durability and lifetime of the refractory composite leading edges.
MR&D has also performed trade studies for AFRL to assess the mass, thermal and structural efficiency of a variety of passively cooled blunt leading edge designs for proposed AFRL re-entry vehicles. As with most of the work performed under government contract, these results have been presented in ITAR-restricted conferences, including the Annual Conference on Composites, Materials and Structures in Daytona Beach, FL and at the National Space and Missile Materials Symposium.
Examples of re-entry vehicle blunt wing leading edge design concepts.
Hot Structure Control Surfaces
MR&D’s most prominent work in the area of hot structure control surfaces is in connection with the NASA X-37 orbiter vehicle.
Artist’s concept of X-37 vehicle during re-entry from earth orbit.
The X-37 hot structure control surface effort was conducted under contract to GE Power Systems Composites, where Boeing-Phantom Works was the prime contractor. The complete effort involved the design, analysis, manufacture, and testing of two hot structure control surfaces, i.e. the flaperon and the ruddervator for the X-37 reentry vehicle. MR&D completed preliminary designs and detailed thermo-structural analyses of the full scale CVI C/SiC flaperon and ruddervator for the NASA/Boeing X-37 next generation RLV technology demonstrator. Finite element models of these hot structure control surfaces are shown in the figure below.
Finite element models of full scale hot structure control surfaces for NASA/Boeing X-37.
All subelements and a portion of the subcomponent test articles manufacturing and testing in support of this program has been completed. Vibration, acoustic, and combined thermal and mechanical testing of the CVI C/SiC flaperon subcompent test article, shown on the left in the figure below, have been successfully completed. The CVI C/SiC flaperon subcomponent test article successfully endured representative design vibration loads, acoustic loads, thermal loads, mechanical loads, and combined thermal & mechanical loads. This test article was designed and analyzed by MR&D; was fabricated by GE Energy Composites of Newark, DE; and was tested by NASA Dryden Flight Research Center (DFRC). This test article was very successful in that it ultimately failed at 169.5% of the design limit load. Pre-test predictions of failure were at 162% design limit load.
Fabrication of the CVI C/SiC ruddervator subcomponent test article, shown on the right in the below, has also been completed. Testing of this article, including vibration, acoustic, mechanical and thermal tests, is currently in progress. MR&D is under contract with NASA DFRC to provide pre-test predictions, on-site test support, and post-test data correlation for all of these tests.
Photographs of CVI C/SiC X-37 Hot Structure Flaperon (left) and
Ruddervator (right) Control Surface Subcomponent Test Articles.
The CMC X-37 control surface structural analyses consisted of transient heat transfer analysis to find the temperature distributions followed by a thermal and mechanical stress analysis. The transient thermal analysis included all of the effects of radiation to the atmosphere and radiation interaction within the structure. The resulting temperature distributions were subsequently used to calculated thermal stresses. The component stresses were calculated and compared to allowable stresses. These numbers were combined with required factors of safety to compute the margins of safety. When all margins of safety were positive, the design was considered acceptable.
Acreage Region TPS Designs
In the area of TPS designs for hypersonic and re-entry vehicle acreage regions, MR&D has performed analysis, design, pre-test predictions and post-test data correlation efforts on oxide-oxide designs for ATK Ceramics of San Diego, CA. We have also designed SiC-C acreage region TPS designs for Lockheed Martin of Palmdale, CA. Trade study efforts focused on designing the largest TPS acreage region panels of the lowest areal weight design have been performed for AFRL under contracts with the University of Dayton Research Institute and for the Southern Research Institute. All of these efforts were performed for so-called “parasitic” TPS designs, in which the primary function of the TPS components were to shield the internal structure from the high heat flux experienced at the outer mold line of the vehicle.
Photograph of SiC-C acreage TPS rib-stiffened sandwich structure panel including corner standoffs.
Subsequent recent efforts, performed for both AFRL and NASA, have focused on the development of material and structural designs for acreage region TPS in which the load carrying capability of the TPS designs acts to reduce the structural mass of the space operating vehicle. This is a significant challenge since the thermal strain experienced by the TPS designs, resulting from the large temperature differences between the outer mold line and cooler internal structure, is not relieved by means of isolated segmented TPS panels.
Truss core manufacturing demonstration articles for load bearing acreage TPS panel designs.