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SpaceX Falcon 9 FT - NROL 76 (classified) - LC-39A

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Remember, there's no noise in vacuum, and there's very little noise in partial vacuum.
Noise needs molecules to propagate through. The thinner then air, the less noise can get places.
Anyhow, I truly doubt cold gas thrusters (N2) are anywhere that noisy (at sea level).
Its probably less than the noise of a tire air nozzle when it discharges directly to the air.

Wikipedia gives cold gas thruster ISP=73 s. So gas comes out 716 m/s. Slower in atmosphere. Supersonic gas makes lot of noise. I don't know pressure used. Perhaps it is 100*pressure of a car tire.

Atmosphere seems to have surprisingly large effect on rocket exhaust from entry burn at 60 km altitude. There is not much air.
 
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Wikipedia gives cold gas thruster ISP=73 s. So gas comes out 716 m/s. Slower in atmosphere. Supersonic gas makes lot of noise. I don't know pressure used. Perhaps it is 100*pressure of a car tire.

Atmosphere seems to have surprisingly large effect on rocket exhaust from entry burn at 60 km altitude. There is not much air.
If we need someone to go up there and check it out, am happy to volunteer.