starship-design: Sail types

[Steve VanDevender <stevev@efn.org>]

Lindberg writes:
 > I have a question about starships using some kind of sail for
 > propulsion.  All of the sail proposals i have seen rely on direct
 > pressure for their drive.  Although i realize that what i'm about to ask
 > wouldn't work for light, could a directed relatavistic particle beam (or
 > solar wind) be used to create an "aerodynamic" form of thrust?  This has
 > several advantages, at least at sea on earth, which is where i'm taking
 > this from.  A modern sailboat sails fastest when the wind is on its
 > beam.  It will sail much faster than a square rigged boat of similar
 > hull, sail area, and waterline length running before the wind.
 > Furthermore it is easier to control. Also, modern sailboats can sail up
 > to 45 degrees (appx) into the wind.  If this could be translated to
 > space it could help fix the "return" problem for star sail trips. 
 > Anyway, all this is very nice, but i have no idea if it is even
 > theoretically possible in space using charged particles instead of air.

Much of the capability of sailboats to sail into the wind depends
on them being hydrodynamically inclined to move more easily
forwards and backwards than sideways because they have long
hulls.

In space, there's no water to move through and no intrinsic
preferred directions of motion for a ship in response to an
impulse.

Some light sail or particle sail designs take advantage of
gravity as a force to "tack" against in interplanetary space; for
example, a sail ship can lower or raise its orbit by reflecting
sunlight along or against its direction of motion to decrease or
increase its orbital velocity.  In deep space you would have
little to work with, though; the ship would pretty much have to
go in the direction the beam pushed it, with a little flexibility
to maneuver perpendicular to the beam.