Thermal protection systems

Fig. 2. A simplified material thermal performance analysis for a reentry vehicle thermal protection system where = density x surface recession thickness = total aerodynamic heat/heat of ablation ...

The practice of employing reusable thermal protection systems for reentry is becoming more common. These are essentially ablative materials exposed to environments where veryHtde ablation actually occurs. Examples iuclude the space shuttle tiles and leading edges, exhaust no22le flaps for advanced engines, and the proposed stmctural surface skin for the National Aerospace plane. 

The thermal protection system of the space shutde is composed mainly of subliming or melting ablators that are used below their fusion or vaporization reaction temperatures (42). In addition to the carbon-carbon systems discussed above, a flexible reusable surface insulation composed of Nomex felt substrate, a Du Pont polyamide fiber material, is used on a large portion of the upper surface. High and low temperature reusable surface insulation composed of siHca-based low density tiles are used on the bottom surface of the vehicle, which sees a more severe reentry heating environment than does the upper surface of the vehicle (43). 

C. WiUiams and L. RonquiUo, Thermal Protection System for the Space Shuttle External Tanks, 6th SPI Inti., Tech. /Mark. Conf, 1983, pp. 90—100. 

Fig. 13. Shingle from C/SiC for thermal protection systems of reentry vehicles... 

Figure 1.9. C/SiC component for HERMES thermal protection system [46]...

Calculations and tests in a high pressure cooling rig shortly will demonstrate the reduction of cooling air using the all-oxide CMC WHIPOX as thermal protection system in combustion chambers. 

TPS thermal protection system UHMW ultrahigh molecular weight... 

With re-entry vehicles and spaceplanes, the material resistance to extremes of temperature becomes a matter of major concern. When spacecraft dive into the Earth s atmosphere, aerodynamic surfaces are exposed to high thermal and mechanical loads maximum heat fluxes of the order of MW/nr, dynamic pressure, shear stress, acoustic vibrations and material degradation put the vehicles structures to a hard test. Payload and passenger survival is committed to the efficiency of the thermal protection system (TPS) which has to maintain the internal temperature within appropriate limits through various energy dissipating mechanisms. 

The properties and characteristics of ablative composites are greatly influenced by the presence of a plastic component. The inherently wide range of material properties available in these plastic containing composites has led to broad use in a variety of entry thermal protection systems. 

It is important to realize that mechanical properties can also be critical in non-structural applications. For example, in the design of the thermal protection system of the space shuttle, highly porous, fibrous silica tiles are used. The microstructure of these materials, shown in Fig. 1.1, consists of a bonded array of fibers, usually based on silica glass. Clearly, the prime reason for using these materials was their low thermal conductivity but the resistance to thermal and structural stresses was a key item in the final design. In some non-structural applications, mechanical properties can be important in determining the lifetime... 

There are also numerous semi-structural applications that may be good applications for all-oxide composites [16, 17]. Thermal Protection Systems (TPS) are combinations of... 

Grant TL, Crown EM. Electrostatic properties of thermal-protective systems. Part I simulation of garment-layer separation. J Textil Inst 2001 92(3/3) 395 02. 

A.L. Chamberlain, W.G. Fahrenholtz, G.E. Hilmas and D.T. Ellerby, Characterization of Zirconium Diboride for Thermal Protection Systems, Key Engineering Materials. 264-268 493-496 (2004)... 

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