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This image is from the first launch attempt of spaceX's IFT-8.

First Launch Attempt of SpaceX IFT-8 (https://www.teslaoracle.com/2025/03/03/live-updates-starship-flight-8-watch-the-live-stream/)

During propellant loading, I understand that the process requires significant venting, my question is the following:

Why does SpaceX vent from the circled location in the picture?

I can't think of any particular benefit, so I wondered if it might have been an aesthetic choice due to the lovely plume.

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  • $\begingroup$ The wind direction is quite important for the picture as well. As long as there are no ventilators installed to blow in the direction of the rocket I'd say it was a lucky shot. $\endgroup$ Commented Mar 19 at 14:15
  • $\begingroup$ @Arsenal This is a good point! Though prevailing wind directions can be quite consistent. And it is my experience that coastal locations often have prevailing winds coming from the water's direction. $\endgroup$ Commented Mar 19 at 14:40
  • $\begingroup$ I feel like I've seen a similar cloud of exhaust from basically every space launch ever, whether SpaceX, NASA, Boeing, Blue Origin, ESA, RSA, etc. Maybe it didn't look so pretty from some of the older launches, though that may be partly due to improvements in the cameras getting the footage too. $\endgroup$ Commented Mar 19 at 21:14

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tl;dr summary: this is not venting, it is condensation coming from the liquid oxygen retention pond.

Starship uses cryogenic liquid propellants, meaning, propellants which are stored well below ambient temperature. Starship uses liquid methane as fuel and liquid oxygen as oxidizer. In order to be liquid at the pressures they are being stored, the liquid methane needs to be cooled down to 111.66 K (−161.49°C; −258.68°F) and the liquid oxygen even further to 90.19 K (−182.96°C; −297.33°F). (Technically, those are the temperatures at atmospheric pressure, inside the tanks, the temperatures can be slightly higher since the pressure is higher, but it's still hundreds of degrees below ambient.)

In fact, SpaceX sub-cools the propellants, making them more dense, which allows them to squeeze more propellant mass into the same tank volume. This means they are probably even colder than those temperatures listed above.

Having those cryogenic propellants meet the plumbing at ambient temperatures without preparation can lead to problems: the pipes and valves can get damaged by being "shock frozen", but even worse, the propellants will flash-boil and expand, thus rupturing the pipes. In order to avoid that, the lines are "conditioned" by first carefully trickling just a little bit of propellant through them, then slowly increasing that flow.

Methane is a potent greenhouse gas and also obviously highly flammable, so that gets captured. But the liquid oxygen that is used for the conditioning typically just gets dumped overboard. However, Starship is so big and the amount of liquid oxygen that gets dumped is so large that the FAA, the EPA, and Texas Fish and Wildlife Service asked SpaceX to install a retention pond where the liquid oxygen gets collected in one place and can boil off.

Warm air can hold more water than cold air. The oxygen that is boiling off in that pond is still extremely cold, which cools down the air above the pond. As a result, the air cannot hold the water anymore, and the water vapor condenses into mist.

So, what you are seeing there is water condensing to mist because of the warm, humid air coming into contact with the extremely cold oxygen above the liquid oxygen retention pond.

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    $\begingroup$ I realize there are no sources cited in my answer. The liquid oxygen retention pond is described in one of the environmental documents on the FAA website, but I'm not sure which one. If anybody fancies a stroll through the FAA archives, feel free to edit. $\endgroup$ Commented Mar 17 at 14:31
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    $\begingroup$ There are of course lots of other sources of vapors, condensation, and venting, but the big source at the location you circled is the pond. It is just an above-ground pond. You can see it on Google Maps, even though there is still some construction going on when this photo was taken: maps.app.goo.gl/CJ6qk97dgNB4ZHbW7 $\endgroup$ Commented Mar 17 at 14:46
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    $\begingroup$ Even if the regulatory agencies hadn't asked for it for environmental reasons, somebody would probably have eventually pointed out that large quantities of liquid oxygen flowing everywhere willy-nilly is dangerous. Pretty much any porous, combustible material that is soaked in liquid oxygen is a bomb waiting to happen. Controlling where the flow goes definitely reduces the risk of setting the wrong things on fire. $\endgroup$ Commented Mar 17 at 21:54
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    $\begingroup$ @Perkins I am not certain that that would have motivated SpaceX action before a significant incident $\endgroup$ Commented Mar 18 at 11:45
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    $\begingroup$ @QuestionablePresence Hard to say. They probably would have been reluctant to build anything this elaborate, but a couple hours with a trencher to make sure it flows in a defined path so there's none of it lurking around threatening to unexpectedly destroy expensive equipment after launch would be cheap and just being able to predict where the stuff will be is most of the battle from a safety point of view. Of course, we don't know how it was flowing before... Quite possibly it was already behaving predictably. $\endgroup$ Commented Mar 18 at 17:59

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