Are you suggesting NASA somehow rejected using this material as a replacement on the existing shuttle.
Both quoted articles claim this. - Here's what the inventors themselves write on the properties of their material:
Nose Cap of the CRV Experimental X-38
st.dlr.de
The basic material of the nose cap is a ceramic matrix composite (C/C-SiC), which consists of carbon fibres embedded in carbon and silicon carbide. The main shell structure was made with a netshape technology using a liquid silicon infiltration process (LSI). Special in situ joining techniques made it possible to manufacture this part de facto in one shot, integrating even complex mounting flanges. Our (in-house developed) material was already successfully proof-tested on several Soviet reentry capsules (Foton) and the EXPRESS mission, a German-Japanese cooperative project.
The connection of the nose cap to the vehicle is done via eight single fittings made of C/C-SiC and - where temperatures are not so extremely high - of high-temperature metal alloys. The specific arrangemant and design of the lever like attachment system enable high mechanical loads as well as an unimpeded thermal expansion of the components. This can grow up to 3 mm, related to the average dish diameter of 700 mm. With a stiff joint, the dish would be destroyed due to the thermally generated stresses.
An additional element of the nose cap system is the so called hard sealing which is fixed at the edge of the dish and (under)laps the following thermal protection system. In conjunction with a flexible sealing package, this hard sealing prevents hot gases getting in the inside of the nose cap.
Also integrated in the nose cap system is a pressure measurement system, used for position control of the vehicle. At nine holes, distributed over the nose cap, the static air pressure is detected and carried in a high temperature resistant duct system to the pressure sensors inside the vehicle.
The thermal insulation between nose cap and substructure is managed by a multi-layered flexible fleece insulation mat, made of oxidic ceramic fibres like aluminum oxide. The up to 45 mm thick mat achieves the maximum temperature of the aluminum substructure to be only about 100 °C.
Fabrication of Ceramic Matrix Composites (C/C-SiC)
st.dlr.de
The Institute of Structures and Design has been developing fibre reinforced ceramic matrix composites via the Liquid Silicon Infiltration process (LSI process) for over a decade. The materials manufactured using this processing technique are suitable for a broad range of applications. The advantages of these SILCA materials are the short, simple and economical manufacturing method and the variety of variable material properties. In general, SILCA materials exhibit excellent thermal shock resistance, high mass specific values and possess a dense matrix.
The basic principle of processing has three steps:
* Production of an ordinary composite made of carbon fibres (e.g. fabric) and polymer.
* Pyrolisation of this composite in an inert atmosphere forms a 3-D net of interconnected capillaries.
* Infiltration of this "crack net" with liquid silicon and chemical reaction: C + Si -> SiC
The final product is a high temperature structural hybrid material with an inherent oxidation resistance.
Literature:
Krenkel, W.; Gern, F. H.: Microstructure and Characteristics of CMC Manufactured via the Liquid Phase Route, Proceedings ICCM-9, Madrid, Spain, 12-16 July, 1993
Gern, F. H.; Krenkel, W.: Morphology and Infiltration Dynamics of Liquid Silconized Carbon/Carbon, ICCM-10, Whistler, B.C., Canada, 14.-18. August 1995
Krenkel, W.; Fabig, J.: Tailoring of Microstructure in C/C-SiC Composite s, ICCM-10, Whistler, B.C., Canada, 14.-18. August 1995
Gern, F.; Kochendörfer, R.: Liquid Silicon Infiltration: Description of Infiltration Dynamics and Silicon Carbide Formation. Composites: Part A Applied Science and Manufacturing, 28A No. 4 1997, 335-364.
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Aside from weight issues and the monsterous issues of stripping off tiles and replacing with an alternative material, would this material stand up to a hit of sheded foam any better than the existing tiles.
Stripping off the tiles and replacing them would be feasible with the space shuttle launch budget of about one billion USD. |
