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This article indicates that a faclon 9 launch is being delayed due to an issue with the "payload fairing pressurization system".

Are launch fairings pressurized to 1 atmosphere for the benefit of the cargo? And why produce a pressurized environment for a satellite?

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    $\begingroup$ The pressure outside should be equal the pressure inside the fairing to avoid the huge forces caused by a pressure difference and the large area of the fairing. $\endgroup$ – Uwe Feb 24 '18 at 22:39
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Are launch fairings pressurized to 1 atmosphere for the benefit of the cargo?

No, pressure within the fairing will drop gradually during the launch. The reason for the pressurization system is to control the pressure change, to protect the cargo from sudden changes. The Falcon 9 User's Manual has a section on "Fairing Internal Pressure", which describes pressure falling not more than 0.35 psi/sec, with a wider variation allowed around the time it breaks the sound barrier.

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While I have no specific knowledge of Falcon 9's fairing, it is common for compartments of space vehicles to be purged or pressurized slightly above ambient while on the pad to keep contamination out of the vehicle.

After launch, vents allow the pressure in the compartments to drop in a controlled fashion as ambient pressure drops.

To get a feel for how this operates, you can read about the shuttle's comparable systems here. Some excerpts:

Three purge circuits are connected by the T-0 umbilical to ground equipment before launch during the preflight countdown and postlanding phases. Purge gas (cool, dry air and gaseous nitrogen) is provided to three sets of distribution plumbing: the forward fuselage, orbital maneuvering system/reaction control system pods, wings and vertical stabilizer; the midfuselage; and the aft fuselage. The purge gas makes all the unpressurized volumes inert, maintains constant humidity and temperature, forces out any hazardous gases and ensures that external contaminants cannot enter.

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At T plus 10 seconds, all vent doors are commanded open. At T plus 80 seconds, vent doors 8 and 9 are commanded closed to prevent hazardous gases from entering the aft fuselage; at T plus 122 seconds, vents 8 and 9 are commanded open. All vent doors remain open during the remainder of ascent and on-orbit operations.

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The article is rather vague, but this could be a reference to the pressurized separation system that is used to deploy the fairing after launch. SpaceX uses pneumatic locks and pistons to separate the two fairing halves and kick them away from the 2nd stage. An issue with this system could prevent the fairing from separating cleanly, which would most likely result in total mission failure.

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