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From: KING@KESTREL@sri-unix.UUCP
Newsgroups: net.physics
Subject: Re: Sundiver Thermodynamics - (nf)
Message-ID: <3105@sri-arpa.UUCP>
Date: Thu, 14-Jul-83 12:10:00 EDT
Article-I.D.: sri-arpa.3105
Posted: Thu Jul 14 12:10:00 1983
Date-Received: Sun, 17-Jul-83 04:13:31 EDT
Lines: 42

From:  Richard M. King 

	The physics is wrong.

	The output of a laser is virtually entropyless.  It is possible to
have a heat-pumped laser at any frequency, but said laser has to dump heat 
at some lower temperature.  The best we can hope for is Qi/Qo=Ti/To, where
Qi is heat input to laser, Qo is heat output of radiator's output, Ti is
heat source temperature, and To is radiator temperature.

	HOWEVER, with one supplemental idea this would be a tremendous help.
Suppose the ship carried a supply of water.  Further suppose that the ship
went to the 1 atmosphere level of the sun.  For every calorie the laser
absorbed at 6000K it might only have to dissipate .06 calories at 373K.
This would tremendously reduce the need for water.

	The laser need not be an X-ray laser.  The output of ANY laser is
virtually entropyless (effectively at infinite temperature, like electricity
in a wire).  To convince yourself of this, remind yourself that the light
of an IR laser was frequently used to burn holes in razor blades in the early 
days of lasers (and is now used to burn holes in materials that can't easily
be cut in any other way).  The key point is that the light is coherent and
can be focussed arbitrarily tightly.  Incoherent light can only be focussed 
enough for the target to reach the temperature of the source.
	The laser might work as follows: heat the working material (CO2?)
to 6000K.  The molecules go to a high energy state.  Expand the gas
(supersonic nozzles) which cools it, so the high energy state is dis-
equilibrious and therefore there is a population inversion.  Lase.  Cool the
gas to a lower temperature and recompress it.
	There is no need for a laser.  A garden variety turbogenerator or
MHD device would do as well, and have the additional advantage that power
would be generated and that there would be no constraint on temperatures or
working fluid.  The bulk of the electricity has to be sent somewhere; a 
radio transmitter comes to mind.  (They certainly need one anyway).

	The most important points are YOU NEED THE WATER and THE X-RAY-ness
OF THE LASER or even the use of a laser AT ALL is spurious.

	Corrections welcome.

						Dick
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