White gaseous substance released from rockets before liftoff

[beamthegreat]

Whenever a rocket prepares for launch, they always release this white gaseous substance. Does anyone know what it is and the purpose releasing it?

You can clearly see it in this video:

https://www.youtube.com/watch?v=lbHnSu-DLR4&list=UUtI0Hodo5o5dUb67FeUjDeA
https://www.youtube.com/watch?v=lbHnSu-DLR4&list=UUtI0Hodo5o5dUb67FeUjDeA#t=662

EDIT: Not sure if the link directs you to the correct time or not. If it doesn't, skip to 3:12 and 12:23. www.youtube.com/watch?v=lbHnSu-DLR4

Thanks

 

[edward]

Whenever a rocket prepares for launch, they always release this white gaseous substance. Does anyone know what it is and the purpose releasing it?

You can clearly see it in this video:

https://www.youtube.com/watch?v=lbHnSu-DLR4&list=UUtI0Hodo5o5dUb67FeUjDeA
https://www.youtube.com/watch?v=lbHnSu-DLR4&list=UUtI0Hodo5o5dUb67FeUjDeA#t=662

EDIT: Not sure if the link directs you to the correct time or not. If it doesn't, skip to 3:12 and 12:23. www.youtube.com/watch?v=lbHnSu-DLR4

Thanks

It is liquid oxygen venting to prevent excessive pressure build up. A little bit can look like a lot because it is so cold as soon as it hits the air moisture condenses. Occasionally it will be seen coming out of the engines because the LOX is released through the engines before any fuel is.

https://www.youtube.com/watch?v=Tz9gDsGI_0c

 

[edward]

The water spray is three fold. It is a fire safety device, and it keeps the rocket blast from incinerating the launch pad and equipment. It is also used as a sound attenuator. It keeps the sound and vibration from the rocket engines from damaging the rocket's fuel and oxidizer tanks.

 

[beamthegreat]

Thanks for the response.

Do they have to vent out some liquid hydrogen as well? Wouldn't it would be pointless to have some hydrogen left over in the tank without any oxidizer? Also, doesn't this decreases the delta-v of the rocket?