Why was ramjet fuel used as hydraulic fluid during Saturn V checkout?es Tk7C8 w 06m HqDL.ln2nd01 B50 Jtlb t 6zba H45 9
Fuel is also used within the engine as a lubricant and as a hydraulic working fluid, though before launch, RJ-1 ramjet fuel is supplied from the ground, it being more suited for this purpose.
https://history.nasa.gov/afj/ap11fj/01launch.html
I can't seem to find any more background on why this was done. What properties made RP-1 unsuitable for ground use?
1 Answer
What a fascinating question!
Turns out it's less flammable.
Ground Supply Fluid—Because the flash point of RP-1 fuel, which supplies the system in flight, is 110 to 139° F, it is classified as a Class Ill flammable liquid, not suitable for ground operations. A study was made to find substitute fluids with properties similar to RP-1 that could be used in the laboratory and in ground operations.
Such a fluid was found in RJ-1, a ramjet fuel. It has properties very similar to RP-1, but a flashpoint ranging from 190 to 208° F. If purchased with a specified flashpoint exceeding 200° F, it is not classed as a flammable liquid by the National Code and would not have the same stringent handling requirements of RP-1 fuels. Therefore, the RJ-1 fuel can be used in the laboratories or in GSE with the same precautions as taken with MIL-H-5606
GSE = Ground Support Equipment
Source - The December 1963 issue of Hydraulics and Pneumatics magazine
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1$\\begingroup$ It seems ironic to use jet fuel because it's the less flammable option! $\\endgroup$ – corsiKa 2 hours ago