[amsat-bb] Re: Explain Photo?

Sil - ZL2CIA zl2cia at amsat.org
Sat Dec 15 15:04:31 PST 2007

jkelly at home wrote:
> Can someone explain to me what actually is happening in this photo?
> http://www.eanet.com/kodama/astro/2007/1110a/7.htm
> Jeff
> KT2K
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Hi Jeff,

you probably want to know more than this..

What I understand is happening is that the excess 
fuel  (propellant and oxidizer) is vented from the 
rocket. This is fuel that was unused by the rocket 
and remained in the tanks. The rocket motor was 
shut down before all the fuel was used because the 
rocket had reached a sufficient velocity to attain 
the required orbit.

I think the fuel is dumped into space because it 
is considered a safety risk to leave it in the 
rocket's fuel tanks.

When the fuel is dumped, it does not burn. The 
fuel is visible because it reflects sunlight 
before it becomes dispersed. I imagine that the 
fuel is released in liquid form. Surface tension 
probably forms it into small droplets which 
quickly evaporate.

While it looks as though the fuel is being 
squirted out of the rocket in a jet of fluid, it 
is not and this is an illusion. The fuel is vented 
and the cloud of fuel immediately starts expanding 
into the vacuum around the craft. In this photo, 
the rocket is moving from left to right. It is 
orbiting and not being propelled by it's motor any 
more. The fuel on the left of the picture has had 
more time to expand into space, while the fuel on 
the right has only just been released. This 
creates a nice illusion of a jet from the rocket 
but that is not what is happening in this photo.

There must be more to the story that this. Even 
dumping the fuel could alter the orbit of the 
craft, so it would have to be done in a very 
managed way. I have read that the Apollo 13 flight 
suffered an error because the Lunar Module (used 
as a lifeboat) vented waste gases unevenly.

It you are interested, I found a story about 
another space fuel dump here:


And a story about some on watching it here:


And here:


It would be a cool thing to see.

Best wishes.


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