[amsat-bb] Re: Explain Photo?

jkelly@home jkelly at bellatlantic.net
Sat Dec 15 15:22:12 PST 2007

Thank you Sil - excellent explanation.


----- Original Message ----- 
From: "Sil - ZL2CIA" <zl2cia at amsat.org>
To: "jkelly at home" <jkelly at bellatlantic.net>; "AMSAT" <amsat-bb at amsat.org>
Sent: Saturday, December 15, 2007 6:04 PM
Subject: Re: [amsat-bb] Explain Photo?

> 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:
> www.space.com/spacewatch/mystery_cloud_040901.html
> And a story about some on watching it here:
> http://www.satobs.org/seesat/Nov-1997/0141.html
> And here:
> http://www.allaboutastro.com/Delta4.html
> It would be a cool thing to see.
> Best wishes.
> Sil

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