[ExI] Mining the Sky SL Talk I gave today

spike spike66 at att.net
Wed Apr 28 22:44:16 UTC 2010

On Behalf Of Adrian Tymes
> --- On Tue, 4/27/10, spike <spike66 at att.net> wrote:
> > OK this seems convincing enough.
> Thanks.
> > If my scheme is successful, we could use it to haul the 
> platinum from 3 AU down to about a 5000 NM HEO...

Hey cool, check this:


I recognized a flaw in my reasoning from yesterday.  Platinum is a good
reflector in the shorter wavelength end of the solar spectrum, if you
measure it as a function of layer thickness.  But layer thickness isn't what
matters.  Rather once one takes into account reflectivity per unit mass, the
crazy high density of platinum makes it not as good as plain old common
aluminum.  It takes more energy to vapor deposit a given mass of aluminum,
but the final product of aluminized mylar would be likely a better solar
sail than a platinum mylar reflector, since it would be lighter.

We already have plenty of experience with aluminized mylar: those toy helium
balloons so common today are made from that.  

I have found only one material that works better than aluminum in this
specific reflectivity: lithium.  I just don't know how much lithium is
available in a typical asteroid.  Another thing I don't know is if there
exists a multilayer solution that would be better than lithium in specific
reflectivity, such as mylar aluminum gold chromium.

Stay tuned.


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