All right.  Any SPACE SHIP given motion by a solar sail will NEVER get enough push to reach anything even remotely close to the speed of light.  I don't mean to beat on ya, Kat, but it just seems kinda funny.

A solar sail works by capturing the photons (the solid stuff pushed by light waves, or the stuff we actually "see") and using them as "solar wind".  This wind would be perfect for travel within the confines of our inner solar system.  Anything out beyond about Jupiter will never get enough OOMPH! to go anywhere in any reasonable length of time.

The reason has to do with a law (I forget the name) that states that light, like sound, falls off cubicly as you get farther away from it.  That is to say, take the square root cube (3) of the distance, and that will tell you how much energy you are getting, with a few other variables thrown in along the way.  So the farther you get away from a light source, the larger the solar sail would have to be, by a factor of 10^3.  That's pretty big.  If you were to start with a sail as big as your house when you left earth's orbit, to keep the same acceleration you would have to have something 100 times that size (give or take a few) by the time you reached the orbit of Mars.

And it would have to keep getting bigger.

Oh, and at 1/4th of the speed of light, your problem isn't friction.  Any solid matter you encounter (pebbles, meteorites, atoms) will punch a hole in your SPACE SHIP like rebar through a birthday cake.

ok so you mount the laser on the back of the ship, aim it at the sail, and you got all the oomph you need.

Seriously, I have no idea what this whole thread is about now, my head hurts and i think ill go lie down now.