From: ederd@bcstec.ca.boeing.com (Dani Eder)
Subject: Re: Interstellar travel (magsails, solar sails, whatever)
Date: Jun 08 1995
Newsgroups: sci.space.tech

bderksen@gpu3.srv.ualberta.ca (Bryan Derksen) writes:

>Steven J. Johnson (sjj9289@aw101.iasl.ca.boeing.com) wrote:
>: mcvos@cs.vu.nl (Vos MC) writes:

>: >I've been thinking about several other ways to do this. For example:
>: >a huge railgun that uses electromagnetic pulses to launch ships at
>: >incedibly high speeds. To get anywhere near lightspeed, you'd need

>: Great!  And since all your passengers are now a thin layer of red
>: jam on the back walls, you can save on oxygen, water, legroom . . .

>: If you were to accelerate at one gravity, you'd need a railgun
>: longer than the solar system to get to any significant fraction 
>: of lightspeed.

Here's how you do it:  You build a series of coils that are physically
independant, each having a solar sail for positioning and to concentrate
sunlight on the power supply (an array of solar cells).  You spread them
out over the solar system in a straight line pointing at your target,
with the sails used to maintain position.

You start firing a series of fuel tanks first, at high g's.  The
crew is launched last, at a tolerable acceleration.  They come out
of the accelerator fast enough to catch up with the first fuel tank,
which is launched slowest.  This fuel is used to accelerate and catch
up with the next fuel tank, etc.  This way the manned vehicle has
a reasonable g level, and you get around mass-ratio problems.

Since firing the accelerator will move the coils opposite the direction
of firing, the coils carry enough extra sail to re-position themsleves
after each shot.  Coil alignment can be by laser pointing up the
line of the accelerator.  I would use big coils with lots of clearance
for the vehicle.

Dani Eder