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Rockets on the launchpad often need to release liquids or gases before launch. For example, cryogenic liquids boil off; the vapors need to be released to prevent tanks from bursting. It seems that such fluids are typically removed from the rocket through an umbilical. For the shuttle, boiled-off oxygen was removed at the "beanie cap", and boiled-off hydrogen came out through the hydrogen vent arm.

Are there any examples where fluids were released from a rocket directly to the air or surroundings, instead of through an umbilical?

The question is about rockets on the launchpad. Rocket exhaust and urine dumps in space might technically be direct releases of fluids, but such things are not the scope of this question.

(I suspect that releasing cryogenic vapors would caused undesired condensation and icing on the rocket, but releases of other fluids seem plausible.)

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    $\begingroup$ You probably want to exclude unintended leaks. ;) $\endgroup$
    – AJN
    Jun 25 at 15:28
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Saturn V vented GOX directly to the atmosphere during countdown. Watch any Apollo countdown video such as Apollo 11.

The Apollo 12 SA507 reference manual mentions propellant venting on pages 4-12 (S-IC "Prior to launch, boil off in the lox tank may be harmlessly vented overboard"), 5-15 (S-II "The tanks are vented by opening the tank vent valves, two per propellant tank, to allow ullage gas to escape from the tanks"), 6-13 (S-IV "The lox tank is vented through its propulsive vent duct, located in the aft skirt, during loading").

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The payload fairings (containing the payload) are supplied with cool dry air while the rocket is on the launch pad. I doubt whether two hoses are ever provided; one for the air to enter and the other for the air to leave the fairing. There doesn't seem to be any reason why the air couldn't just vent through vent holes in the fairing.

I went through a few user guides.

  1. DeltaII

Air-conditioning is supplied to the spacecraft via an umbilical after the payload fairing is mated to the launch vehicle. The payload air-distribution system (Figure 4-1) provides air at the required temperature, ... The air flows downward around the spacecraft and is discharged below the second stage through vents in the interstage.

  1. Long March 3A. This one has a diagram with two arrows leaving the fairing hinting that the air pumped in for air conditioning is just vented out.
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  • $\begingroup$ Nothing exotic about this answer :) Just plain air (or nitrogen). $\endgroup$
    – AJN
    Jun 25 at 15:49

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