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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.space
Subject: Re: Better solar sails? - (nf)
Message-ID: <3290@utzoo.UUCP>
Date: Mon, 31-Oct-83 20:52:29 EST
Article-I.D.: utzoo.3290
Posted: Mon Oct 31 20:52:29 1983
Date-Received: Mon, 31-Oct-83 20:52:29 EST
References: <532@ucbcad.UUCP>
Organization: U of Toronto Zoology
Lines: 23

Perforating a solar sail with holes smaller than the wavelength of
light not only greatly reduces the mass of the sail, it also greatly
reduces the air drag on the sail in low Earth orbit.  (This would not
work in a viscous-flow regime, like Earth-surface pressure, but at
orbital altitude the individual air molecules are moving quite
independently of each other and it works fine.)

I heard about the idea in a talk by Robert Forward, but he may have
got it from somebody else.

You would definitely make the stuff in space, because it makes little
sense to apply the perforating technique unless your sail is as light
as possible to start with.  The lightest known solid sails are Eric
Drexler's metal-foil sails:  vacuum-deposited aluminum sheet about
30 nm thick.  Sails made with this stuff must be manufactured in space,
because the stuff is too thin to be unfolded from a compact package in
a practical way.  Drexler sails already have quite spiffy performance
(by solar-sail standards!), and a 90% reduction in mass would really
make them clip along, so if the practical details of perforating can
be worked out it would be great.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry