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From: space@mit-mc
Newsgroups: net.space
Subject: Re: Light Sails
Message-ID: <942@mordor.UUCP>
Date: Tue, 5-Mar-85 12:34:47 EST
Article-I.D.: mordor.942
Posted: Tue Mar  5 12:34:47 1985
Date-Received: Sun, 10-Mar-85 06:23:46 EST
Sender: daemon@mordor.UUCP
Lines: 18

From: jrv@Mitre-Bedford

>> There are these little globes with vacuum and a paddle/pivot mechanism
>> inside which work on this principle.  The four paddles are arranged so
>> that the intersection of the two planes is the axis of rotation of the
>> pivot.  Each paddle has a black side and a silver side with radial
>> symmetry.
                                                            
> This says that the beast should rotate with the white (reflective) side
> retreating. Take a close look at one. They rotate in the other
> direction!

Those globes really have a small amount of air in them.  The black side of
each paddle gets hotter than the white side, so the air molecules that
strike the black side recoil with a higher velocity than those striking the
white side.  Those air molecules push the paddles, not the photons.

			     - Jim Van Zandt