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OT for some groups, Teflon that works some of the time. mm 04-05-2007
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Posted by Max Hauser on May 2, 2007, 3:17 pm


Codicil about those ion drives (since you too encountered Teflon
volatilization in space-related projects, Jerry):

I handled such a drive in the 1970s at a space laboratory, but did not work
on it. In conventional chemical rocket fuels, a classic objective is
concentrated energy, formally "specific impulse" (SI). Also known as oomph.

High-performance chemical fuels deliver SI circa 200 or 300 seconds or more.
(For any unfamiliar reader, the number has practical meaning, it's the time
a fuel can produce thrust equal to its own weight -- so to speak, lift
itself off the ground.) Chemicals with higher SI tend also to be harder to
handle.

In the 1970s, ion drives were said to deliver 40,000 seconds or more of SI.
They actually got their energy from electricity. If you have a space probe
that is well away from any planet, a long gentle thrust can get you going
very fast. You burn a Teflon "candle" hot enough to make a plasma, which
will take an electrical charge. Then you use your solar panels as a source
of electric field to accelerate the ions and send them out the back.
Inevitably if they go one way, you go the other. I understand it produced
low accelerations (much less than earth gravity) so not useful for launching
a craft from the ground, but very useful in interplanetary space where also
the sun is much brighter, and electricity is "free."

Think of this, next time you marvel at the nonstick properties of your
properly used Teflon cookware!


-- Max



AppliancePartsPros.com, Inc.
Posted by Jerry Avins on May 2, 2007, 3:43 pm


Max Hauser wrote:
> Codicil about those ion drives (since you too encountered Teflon
> volatilization in space-related projects, Jerry):
>
> I handled such a drive in the 1970s at a space laboratory, but did not work
> on it. In conventional chemical rocket fuels, a classic objective is
> concentrated energy, formally "specific impulse" (SI). Also known as oomph.
>
> High-performance chemical fuels deliver SI circa 200 or 300 seconds or more.
> (For any unfamiliar reader, the number has practical meaning, it's the time
> a fuel can produce thrust equal to its own weight -- so to speak, lift
> itself off the ground.) Chemicals with higher SI tend also to be harder to
> handle.
>
> In the 1970s, ion drives were said to deliver 40,000 seconds or more of SI.
> They actually got their energy from electricity. If you have a space probe
> that is well away from any planet, a long gentle thrust can get you going
> very fast. You burn a Teflon "candle" hot enough to make a plasma, which
> will take an electrical charge. Then you use your solar panels as a source
> of electric field to accelerate the ions and send them out the back.
> Inevitably if they go one way, you go the other. I understand it produced
> low accelerations (much less than earth gravity) so not useful for launching
> a craft from the ground, but very useful in interplanetary space where also
> the sun is much brighter, and electricity is "free."
>
> Think of this, next time you marvel at the nonstick properties of your
> properly used Teflon cookware!

Well, this is a cooking and chat newsgroup, so I guess it's OK so chat
about my feeling that the ion-drive SI numbers were cooked. :-) Other
fuels were taxed with bringing their own energy to the game. Ion drives
use an external energy source not weighed into the accounting. It's
rather like concluding that electric motors are far lighter than
internal-combustion engines of the peak same power without accounting
for the weight of the battery. Do you remember when the term "prime
mover" had more prominence than it does now?

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Posted by Max Hauser on May 2, 2007, 6:44 pm


>
> ... Well, this is a cooking and chat newsgroup, so I guess it's OK so chat
> about my feeling that the ion-drive SI numbers were cooked. :-)

You could almost say it was nothing but hot air. (Forgive me, bad company
lately. Physicians discussing research related to liver damage, after which
one of them said, three times, that Web-based medical advice must be viewed
with a jaundiced eye ...)

> Other fuels were taxed with bringing their own energy to the game.

Yes, I suppose, Jerry: That would be important to contenders at the Rocket
Fuel Olympics, for fairness. Much as air-breathing engines (including
SCRamjets) have advantages over rockets because they poach part of their
supplies en-route. The SI number is just cited for drama. I can't think of
many situations where one could actually use a rocket in place of an ion
engine or vice versa. People have tried hard, on the other hand, to develop
air-breathing transatmospheric craft [translation: space shuttles]. One of
those people told me (at the dFVLR) in 1985 that this could potentially
replace the huge rockets the US space shuttles needed to get into orbit. A
dangerous configuration, with that big external oxygen tank. "Don't be
surprised if you wake up one morning and hear that one of the space shuttles
has exploded." (When that happened exactly, a few months later, I sent a
telegram right away, regretting that he was right. He wrote back
predicting that the disaster would be traced to some minor component, taken
for granted: "a clevis pin, or an O-ring.")



Posted by Chuck on May 2, 2007, 11:41 pm


Aside from being tiresome, this applies to cooking how?



Posted by Jerry Avins on May 3, 2007, 9:36 pm


Chuck wrote:
> Aside from being tiresome, this applies to cooking how?

Since you quoted nothing, I can only go by the subject of the thread.
People cook in Teflon. It scares some of them. We think it needn't.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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