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

I think Robert Forward has adequately covered the subject of tacking solar
sails, it is possible, it does work like a boat, and it isn't necessarily
dependent upon having water and a keel, even to go "upwind".

Lee Parker

> -----Original Message-----
> From: owner-starship-design@lists.uoregon.edu
> [mailto:owner-starship-design@lists.uoregon.edu]On Behalf Of Steve
> VanDevender
> Sent: Wednesday, September 01, 1999 1:33 PM
> To: starship-design@lists.uoregon.edu
> Subject: Re: starship-design: Mini-Magnetosphere and Star-Travel
> 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.