From: scerir (scerir@libero.it)
Date: Thu Jul 03 2003 - 10:20:15 MDT
'The solar sail and the mirror'
by Thomas Gold (Center for Radiophysics and Space Research, Cornell
University)
-3 pages, no figures-
http://arxiv.org/abs/physics/0306050
The radiation pressure exerted by incoherent light on diverse surfaces is
examined. The thermodynamic rule, first given by Carnot in 1824, describes
the limitation to the amount of free energy that can be obtained from a
source of thermal energy, and he gave the compelling reason for this rule,
that if more free energy than he had prescribed could ever be extracted,
then a heat pump could use that free energy and re-create all the heat
energy that had been consumed. A perpetual motion machine could then be
constructed. Now, 179 years later, it is proposed to fly a spacecraft that
is expected to gain velocity from the radiation pressure the sunlight is
expected to exert on solar sails, panels of thin plastic sheets, mirror
surfaced on the side facing the sun. However a detailed examination of this
proposal shows it to be in direct conflict with Carnot's rule, and no such
pressure can be expected. Either Carnot's accepted rule is in error, or the
solar sail proposal will not work at all.
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