Re: Return to No Stealth in Space

On Thu, 20 Mar 2008 01:15:20 -0000, Tim Little
<tim@[EMAIL PROTECTED]
> wrote:

>On 2008-03-18, James Nicoll <jdnicoll@[EMAIL PROTECTED]
> wrote:
>> What's the naive calculation of the temperature of a 5000 km/s jet?

>The most naive calculation is just to assume an ideal gas with thermal
>energy comparable to kinetic energy and say a few billion kelvin.
>This is obviously a gross overestimate.

In particular, if the jet actually does have a velocity of 5000 km/s,
either A: it was accelerated by some non-thermal means, leaving us
with no information about it's temperature, or B: a few billion K
worth of thermal energy was just *extracted* from the jet.

If the only thing you know about a gas is that it was just cooled
by a few billion Kelvin, yeah, it's probably a bit much to assume
that it's presently at a few billion Kelvin.


Somewhat more sophistcated estimate: So long as the stuff is still
ionized, it's possible to continue converting thermal energy to jet
energy using a magnetic nozzle.  So, it won't be allowed to exit the
nozzle until it's cool enough to no longer be ionized.  For hydrogen,
that's on the order of 10,000 K.

Correct answer: Mu.  What is this thing you call "temperature", and
how is it relevant to observing the plume of a fusion rocket?


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