From: Michael M. Butler (butler@comp-lib.org)
Date: Wed Feb 28 2001 - 18:43:30 MST
Of course. What Dr. Minsky was unsuccessfully trying to debunk was what
is sometimes called "lightsailing" (a subcategory of solar sailing),
where a "lightsail" is built and payloaded so "light" (yes, a pun) that
it can hang in sunlight at zero orbital velocity. I seem to recall 60
tons per square mile of aluminum as a figure close to that.
The terrific advantage of a lightsail over a heavier solar sail is that
it can assume positions and take trajectories which are _not_ orbits.
One could in principle hang a lightsail in geostationary position over
New Jersey (five no-prize points to the first person to identify the
obscure reference).
Lightsail is to solar sail as sailplane is to glider. Gliders are
sturdy, and they work, but sailplanes have significant advantages re
maneuverability, catching thermals, etc.
hal@finney.org wrote:
>
> Spike wrote:
> > Eliezer, Minsky was the same guy who was the dinner speaking at
> > the first west coast Foresight Nanocon, which was in about 1990 or
> > 91. He dismissed solar sailing by claiming that even if nanotech
> > could produce a sheet of aluminum a single atom thick, then the
> > gravitational force of the sun would be greater than the light
> > pressure from the sun, and that since both fields fall off as the
> > inverse square of the distance, solar gravity is greater than
> > solar light pressure everywhere.
>
> Even if this were true, solar sailing would still work, right? You would
> use the sail at an angle to speed up or slow down your orbital speed,
> thereby enlarging or shrinking the orbital radius. In this way you
> could maneuver to any orbit in the solar system, eventually (watch out
> for those planets though).
>
> Hal
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