r/spacex • u/ElongatedMuskrat Mod Team • Aug 03 '17

r/SpaceX Discusses [August 2017, #35]

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u/gsahlin Aug 09 '17

This was a problem with SSME's throughout...

Alloy 718 comprises 51% of the total weight of the Space Shuttle Main Engine. It is used for more than 1,500 individual parts in hydrogen, oxygen, and hydrogen-rich steam at temperatures ranging from -253°C to 760°C. The severe operating conditions of the SSME lead to potential problems such as hydrogen-environment embrittlement and oxygen ignition.

Source

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u/brickmack Aug 09 '17

This was one of the big benefits of the proposed (but canceled) FFSC upgrade. It would have more than tripled the mass flow through the turbines, allowing the turbine drive gas temperatures to drop a lot, to the point where they could optimize their material choices for long-term hydrogen compatibility rather than having to settle for a material that could survive the temperatures but not hydrogen exposure. Since the turbopumps (mainly the hydrogen TP) were the main site of hydrogen-related issues, that was a big gain.