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Let's imagine a UDMH/N2O4 thruster (like on a Soyuz) has an issue where the oxidizer valve/line freezes solid, blocking the flow. What happens with the fuel?

The propellants are pressure fed with a working pressure of around 1.4MPa. The chamber pressure (for the 11D428 thruster) is listed as 0.88MPa. But if ignition has not occurred, does this mean the difference in pressure is much greater than normal, so the fuel sprays out at a higher than normal rate? And if this occurs, does some system detect the incorrect flow rate and shut the thruster off?

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On shuttle the abnormally low Pc would be detected by the flight software and the jet would be shut off and a message & alarm annunciated onboard.

Reference: 2.22-12 in Shuttle Crew Operations Manual https://www.nasa.gov/centers/johnson/pdf/390651main_shuttle_crew_operations_manual.pdf

I think you are right about the flowrate, but the failure was detected very quickly.

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  • $\begingroup$ Do you know if I'm correct in assuming that the fuel flow would be greater in the misfire than under a normal firing, since there's no chamber pressure to impede the flow? $\endgroup$
    – Innovine
    Jun 8, 2022 at 13:27

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