• low thermal expansion Nevertheless, the maximum temperature of use of those materials is only increased of 100 or 200 degrees centigrade compared to the monolithic alloys. Otherwise, Intermetallic Compounds (i.e. Titanium aluminide) are currently being developed. MMC made with these alloys present, compared to titanium alloys matrix composites: • improve mechanical behavior at high temperature, • increased oxidation resistance • lower density • Glass matrix composites: Those materials are made with glass matrix (amourpheous) or glass ceramic (partially crystallized). Those materials present low density and good mechanical behavior at high temperature (till 870 K for glass matrix and 1270 for glass ceramic matrix) Heat Resistant Composite Materials Ceramic Matrix and carbon carbon composites have been developed during the last ten years. Those materials present a very good behavior at high temperature and a non-brittle mechanical behavior, compared to monolithic ceramic or polycrystalline graphite. Moreover, Ceramic Matrix composites such as C/SiC and SiC/SiC present, due to the characteristics of the matrix an improved oxidation resistance. Those materials present a low density (2 to 2.5) when that of super alloys (Nickel based) is about 8. Those materials offer new solution for the design of rocket engines to increase their efficiency. For instance, it is possible: - to increase the temperature of the combustion chamber, for example for bi-propellant liquid rocket engines, - to reduce or suppress the cooling system for combustion chambers of nozzle extension. For example, uncooled nozzle extension made of C/SiC as been tested on an HM7 cryogenic engine (3rd stage of Ariane 4 launcher)). Compared to the dump-cooled metallic one, this nozzle extension lead to an increase of about 60 kg for the GEO payload of this launcher. 8.6.13 Mission Applications The areas where these technologies can be applied are listed as a function of the mission application. Because the Space Solar Power Program is a very long term program, the precise technologies that would be used are not clear. Within the next 10 years, current launch systems and upper stages will be used for any demonstrations. However, technology development is difficult to project beyond the 10 year time frame. A list of potential technologies is therefore provided to summarize the options that are available and currently under consideration. As the Space Solar Power Program becomes more defined and the funding level is determined, a more focused vision of the transportation technologies can be developed. Earth to Orbit: Metallized Propellants High Energy Density Propellants Slush Hydrogen Gun Propulsion Mass Driver Laser Propulsion Orbital Transfer Lightweight Upper Stage Solar and Nuclear Electric Propulsion Nuclear Thermal Propulsion
RkJQdWJsaXNoZXIy MTU5NjU0Mg==