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From: sewilco@mecc.UUCP (Scot E. Wilcoxon)
Newsgroups: net.space
Subject: Re: cheap interstellar probes
Message-ID: <133@mecc.UUCP>
Date: Tue, 28-May-85 12:44:58 EDT
Article-I.D.: mecc.133
Posted: Tue May 28 12:44:58 1985
Date-Received: Thu, 30-May-85 07:18:08 EDT
References: <1946@mordor.UUCP>
Organization: MN Ed Comp Corp, St Paul
Lines: 32

In <1946@mordor.UUCP> redford%avoid.DEC@decwrl.ARPA  (John Redford) writes:
> ...[after showing well how he calculated it]...
>For every kilogram of sail, we must apply 6 million watts for 46 years.
>That works out to 2.6 billion kW-hrs of energy per kilogram of sail, or
>(at seven cents per kilowatt-hour) 180 million dollars worth of energy
>per kg.

Maybe we need a cheaper laser.  Or lasers..several lower power ones would
have great maintenance advantages.  Could always put a bank of lasers on a
"Solar Power Satellite" (is SPS a recognized acronym?), but it would be
nice to avoid the (photon-electron-photon) middleman.

BTW, I assume these lasers would be in space.  I don't care to have that
much power going through the atmosphere we have to breathe.  I'd also feel
a bit safer if Earth's atmosphere were opaque to the laser's frequency.

If a gas laser can be triggered by photons, maybe a group of mirrors
can focus enough sunlight on the lasers.

There's also the idea (wish I remembered the source) of using mirrors to
focus sunlight on the sail.  But since non-coherent light cannot be
concentrated over long distances, this is only useful relatively near
the sun.  So to achieve significant acceleration, several (maybe even a
ring) of mirrors are put around the initial circular orbit of the sail.
As the sail starts getting too far from one mirror it is near enough to
the next one for it to focus on the sail.  When mirrors are not
focusing on the sail, they are used as sails to accelerate nearer to the
(ever expanding) orbit of the target sail.  After the target sail uses
a planet to direct itself onto the final course, lasers can be used to
continue boost.  If the mirrors can't be used to drive the lasers,
they'll find some other use..SPS reflectors, asteroid smelter, Pluto
probe...