[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?
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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
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:
It would be a cool thing to see.
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