Re: starship-design: Mini-Magnetosphere and Star-Travel

[Steve VanDevender <stevev@efn.org>]

Ben Franchuk writes:
 > So what happened to the tacking into the wind, for the return trip home.
 > A insystem ram scoop is a good idea -- 

Tacking works in water sailing because a boat is resistant to
moving sideways through the water.  When you tack the wind on the
sail produces a sideways thrust component that is strongly
resisted by the boat's orientation in the water and a forward
component that isn't, so the boat makes net forward motion
(especially if you zig-zag).  Unfortunately that isn't a property
of spaceships, so they can't tack.  There's a certain amount you
can do if the spaceship is already in orbit around the star; you
can arbitrarily raise or lower the spaceship's orbit using a sail
to produce thrust components with or against the ship's orbital
motion.  But you can't accelerate a ship towards the star with
the sail any better than just furling the sail and letting the
star's gravity pull you in.