Discussion:
Impulse Drive Exhaust Temperature?
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nuny@bid.nes
2014-06-11 18:11:53 UTC
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According to the ST:TNGTM, impulse engines are basically fusion reactors that feed hot plasma through warp coils just strong enough to reduce ship mass without generating a warp field, and the resulting "depleted" plasma is exhausted through usually red or red-orange glowing ports that point aft.

OK, so it would seem that much of the plasma's energy goes into generating the subspace field that reduces ship mass, and the red color indicates a fairly cool exhaust temperature.

Any idea how cool? I don't *think* the exact color is consistent from ship to ship, nor even from one shot to another of the same ship, so "color temperature" doesn't seem to be a valid approach.

Any ideas at all? Do I have this completely sideways, even allowing for the TNGTM's known departures from earlier canon?

For that matter, is there anything in earlier canon that would give a hint about exhaust temperature?


Mark L. Fergerson
Piotr Karocki
2014-06-12 12:28:00 UTC
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Post by ***@bid.nes
According to the ST:TNGTM, impulse engines are basically fusion
reactors that feed hot plasma through warp coils just strong enough
to reduce ship mass without generating a warp field, and the
resulting "depleted" plasma is exhausted through usually red or
red-orange glowing ports that point aft.
By the way, IRC "is a armored sphere six meters in diameter", but its
"wall thickness of 674 cm" seems to contradict it :)
nuny@bid.nes
2014-06-22 22:17:06 UTC
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Post by Piotr Karocki
Post by ***@bid.nes
According to the ST:TNGTM, impulse engines are basically fusion
reactors that feed hot plasma through warp coils just strong enough
to reduce ship mass without generating a warp field, and the
resulting "depleted" plasma is exhausted through usually red or
red-orange glowing ports that point aft.
By the way, IRC "is a armored sphere six meters in diameter", but its
"wall thickness of 674 cm" seems to contradict it :)
I was more concerned with departures from previous ST canon, not from reality.

Good point though.

So, is the color of the exhaust plasma related to its temperature, is it due to some sort of redshift phenomenon as it exits the local sub-warp subspace field, does it just look cool to the producers, or what?


Mark L. Fergerson
Piotr Karocki
2014-06-24 10:50:34 UTC
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Post by ***@bid.nes
I was more concerned with departures from previous ST canon, not from reality.
It is inconsistence, not departure from reality (maybe, from possibility
:) )
Post by ***@bid.nes
Good point though.
Thanks.
Post by ***@bid.nes
So, is the color of the exhaust plasma related to its temperature,
is it due to some sort of redshift phenomenon as it exits the local
sub-warp subspace field, does it just look cool to the producers, or
what?
Flame color is related to 'ingrediens', plasma color should be also, at
least in some way, related to plasma-of-what (plasma-from-what). Deuterium,
but maybe not pure, some trace elements may be present when Bussard
collectors are in use.
Also, color maybe related to contens of interstellar space - not empty
space. Interstellar dust, gas, etc., heated by plasma, also emit light.
nuny@bid.nes
2014-06-24 20:48:16 UTC
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Post by Piotr Karocki
Post by ***@bid.nes
I was more concerned with departures from previous ST canon, not from reality.
It is inconsistence, not departure from reality (maybe, from possibility
:) )
Now that I think about it, there have been Star Trek/Dr. Who crossover stories. Maybe the IRC's are "bigger on the inside"?

Here's a smiley back at you. ;>)
Post by Piotr Karocki
Post by ***@bid.nes
Good point though.
Thanks.
Post by ***@bid.nes
So, is the color of the exhaust plasma related to its temperature,
is it due to some sort of redshift phenomenon as it exits the local
sub-warp subspace field, does it just look cool to the producers, or
what?
Flame color is related to 'ingrediens', plasma color should be also, at
least in some way, related to plasma-of-what (plasma-from-what). Deuterium,
but maybe not pure, some trace elements may be present when Bussard
collectors are in use.
Also, color maybe related to contens of interstellar space - not empty
space. Interstellar dust, gas, etc., heated by plasma, also emit light.
Those are all good points, but the hotter the plasma, the bluer its color no matter its composition.

The IRCs are stated to burn protons at a max output of 10^11 megawatts, meaning they must run at several hundred billion K. That gives a blackbody color in the high gamma range before the (presumably mostly Helium) plasma even leaves the reactor.

To make the plasma look visually red as it comes out the exhaust ports its temperature must be at most a couple of hundred K. It must therefore lose the energy difference to the field coils and/or the accelerator/generator sections.

This approach is starting to look better the more I think about it. As I review some episodes I see that when the impulse drive is "revved up" the exhaust seems to get yellower (have a hotter color temperature).

Also, consider that the Ent NX-01 had blue impulse exhausts, which could be explained as it not having the driver coils needed by the later much more massive Enterprises, hence the plasma wouldn't lose all that energy on the way from the reactor to the exhaust.

Yeah, I'm definitely liking this.

Thanks for letting me bounce this off you.


Mark L. Fergerson
Piotr Karocki
2014-06-29 16:31:08 UTC
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Post by ***@bid.nes
The IRCs are stated to burn protons at a max output of 10^11
megawatts, meaning they must run at several hundred billion K. That
Too much, million K would be OK, but billion?
Post by ***@bid.nes
To make the plasma look visually red as it comes out the exhaust
Why: "plasma"?
Maybe light is not from plasma itself, but from hot starship components?
nuny@bid.nes
2014-06-30 08:58:04 UTC
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Post by Piotr Karocki
Post by ***@bid.nes
The IRCs are stated to burn protons at a max output of 10^11
megawatts, meaning they must run at several hundred billion K. That
Too much, million K would be OK, but billion?
(Sorry, I meant deuterium not protons even though the TNGTM directly mentions proton-proton fusion at one point)

I know billions of Kelvin sounds ridiculously high, but to get 10^11 MW out of deuterium (which the Next Gen Tech Manual specifies), that's what the numbers say.

The minimum temperature per the Lawson criterion for the D-D reaction is a mere 40 million Kelvin or so, but to get maximum power you want to maximize the reaction rate. For D-D, the hotter the better:

http://en.wikipedia.org/wiki/Nuclear_fusion#mediaviewer/File:Fusion_rxnrate.svg

Also, D-D yields He-3 plus a neutron or H-3 plus a proton. All those except the neutron can also be fused to give more power (but the minimum temperatures are higher for some of them), and why waste it? Again, the hotter, the better.
Post by Piotr Karocki
Post by ***@bid.nes
To make the plasma look visually red as it comes out the exhaust
Why: "plasma"?
Because the end product helium-4 is still ionized. It's fully ionized in the reactor (at those temperatures it has to be), it's still fully ionized when it passes through the accelerator/generator (or the A/G couldn't work), and when it passes through the subspace driver coils (or they wouldn't work). At no point is adding electrons to neutralize it mentioned so it's still ionized when it passes through the exhaust vectoring thingy.
Post by Piotr Karocki
Maybe light is not from plasma itself, but from hot starship components?
If the red-orange color is strictly due to the temperature of whatever we're looking at, whether the exhaust mechanism or the plasma blowing out of it, it still has to be no hotter than 1000 Kelvin. That's true whether it's helium plasma, the mythical ceramics and alloys of starship hulls, or cast iron.


Mark L. Fergerson
Piotr Karocki
2014-07-01 15:39:30 UTC
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Post by ***@bid.nes
If the red-orange color is strictly due to the temperature of
whatever we're looking at, whether the exhaust mechanism or the
plasma blowing out of it, it still has to be no hotter than 1000
Kelvin. That's true whether it's helium plasma, the mythical
ceramics and alloys of starship hulls, or cast iron.
Maybe plasma is hot enough to emit ultraviolet light, so it couldn't be
seen; and we can only see these ceramics and alloys you mention.
nuny@bid.nes
2014-07-02 17:29:45 UTC
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Post by Piotr Karocki
Post by ***@bid.nes
If the red-orange color is strictly due to the temperature of
whatever we're looking at, whether the exhaust mechanism or the
plasma blowing out of it, it still has to be no hotter than 1000
Kelvin. That's true whether it's helium plasma, the mythical
ceramics and alloys of starship hulls, or cast iron.
Maybe plasma is hot enough to emit ultraviolet light, so it couldn't be
seen; and we can only see these ceramics and alloys you mention.
Possibly, but the plasma would have to be in the neighborhood of a million Kelvin. Why wouldn't the exhaust director absorb heat from the plasma and get hotter, thus bluer?


Mark L. Fergerson
Piotr Karocki
2014-07-03 09:57:49 UTC
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Post by ***@bid.nes
Possibly, but the plasma would have to be in the neighborhood of a
million Kelvin. Why wouldn't the exhaust director absorb heat from
the plasma and get hotter, thus bluer?
Because it would be inappriopriate for ship :)

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