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In this picture from the AsiaSat 6 launch by Falcon 9 on 8th September 2014, the part of the rocket between the fairing and the engine appears to be surrounded by dust, water droplets or debris:

Falcon9 launch

And another launch:

Falcon9 launch

There is smoke but many fewer particles in launches of other rockets. Saturn V:

SaturnV

Atlas:

Atlas

These particles are particularly prominent in Falcon 9. What are they?

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    $\begingroup$ cute how the OP uses a picture of Apollo 4, yet calls it "many fewer particles". That rocket is shedding like crazy. $\endgroup$
    – CuteKItty_pleaseStopBArking
    Jul 10, 2021 at 19:24

1 Answer 1

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Ice. All these rockets use oxygen as the oxidizer component of their propellant. The Saturn 5 also used hydrogen in some of its engines (upper stages). They are stored in liquid state, which requires very low temperatures (below -183c for oxygen, below -253c for hydrogen). Despite insulation, some of the outside surfaces can get cold enough to condense and freeze moisture out of the air, so there will be accumulations of ice. When the vehicle launches, acceleration and vibration shakes it loose so it falls away.

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  • $\begingroup$ Actually, no matter the pressure, it would be impossible to keep oxygen liquid at room temperature, because that is above its critical temperature. $\endgroup$
    – Rikki-Tikki-Tavi
    Nov 10, 2014 at 0:38
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    $\begingroup$ Not just moisture. With launchers using liquid hydrogen (LH2), its temperature is low enough to condense and freeze surrounding atmospheric air on contact. This is usually referred to as cryo-pumping. Insulation can help with that but since you'd want it light, it's commonly a spray-on foam that can also soak in boiled-off propellants and purging nitrogen (cryo-ingestion) and get heavier and/or crack with acoustic shock during liftoff. Some launchers would use removable thermal shroud over some of their stages to reduce this and/or boil-off. $\endgroup$
    – TildalWave
    Nov 10, 2014 at 5:31
  • $\begingroup$ It's worth also pointing out that ice coming off the external tank and damaging the ceramic heat shield on the space shuttle was the cause of the Space Shuttle Columbia disaster. $\endgroup$
    – pbristow
    Jan 11, 2015 at 14:53
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    $\begingroup$ @Pbarranis: A piece of foam from the external tank, not ice, was the cause of damage to the ceramic heat shield ultimately causing the shuttle's demise. $\endgroup$
    – user8235
    Jan 14, 2015 at 20:16
  • $\begingroup$ It should be noted that ice was a significant concern for the space shuttle TPS - the LOX beanie cap was added to prevent any such buildup. $\endgroup$
    – 0xDBFB7
    Nov 16, 2020 at 21:02