Platinum as a Metallic Material
Examples of Applications in Satellite Rocket Engines
Applications for platinum materials in space transportation are combustion chambers and expansion sections for rocket engines or “thrusters” in satellites.
- Rocket engines
Satellites are usually equipped with an apogee engine. This has the function of propelling the satellite to its final operating altitude after it has been launched by a rocket or the Space Shuttle. For this purpose, it is normal to use a bipropellant apogee engine with a thrust of 400 N powered by monomethylhydrazine (MMH) and mixed oxides of nitrogen (MON, mainly N2O4).
The figure shows an apogee engine in which the highly stressed parts have been manufactured from platinum materials. The combustion chamber and the throat of the nozzle are exposed to very high temperatures of > 1,400 for several hours. High mechanical loadings arise in this region as a result of the thrust. Furthermore, high alternating loads occur around the throat as a result of the low frequency vibrations during the launch of the carrier rocket. A third type of loading ensues from the large variations in temperature and thus differences in thermal expansion over the height of the expansion part. The alloy PtIr70/30 has proved itself in the critical region of the combustion chamber and the throat. However, it was found that it was not possible to achieve a satisfactory weld joint between this material and the nickel alloy used in the cooler regions. This problem was overcome by using transition pieces made of the alloy PtRh80/20.
- Control thrusters
Control thrusters for satellites represent a further example in the field of engines for space flight. To control the orbit and orientation of satellites, they are normally equipped with between 8 and 16 small bipropellant rocket engines which typically have a thrust of 10 and are also powered by MMH1)/MON2). In this case, the combustion chamber and expansion part are machined from a single blank. As the thrusters are used for small corrections and fine adjustments to the position and orientation of the satellite, they are normally operated in a pulsed mode which leads to very rapid temperature changes between low temperatures and 1,400 . In addition to the requirement of sufficiently high strength and corrosion resistance at the maximum operating temperature, a very high degree of resistance to thermal fatigue is essential for this application. This combination of properties is offered by the alloy PtRh90/10. The figure shows an engine for satellite control having a thrust of 10 . The combustion chamber and expansion part are made of PtRh90/10.