[UCANSEE2]

One question... where is the beam located ?

[ProtectOurFreedom]

Where is the beam located?

Sheesh, didn’t read the article? The beam hits the sail to make it go.

[ctdonath2]

That's what I'm wondering. Putting it almost anywhere involves more movement and noise. Then there's sheer distance necessitating an incredibly narrow angle, with any angle wider than the craft at distance is wasted energy - and we're talking a scale of one meter spread at one light year distance, 10^−16 degrees.

[LibWhacker]

The beam is a laser beam fired from earth at a "starchip," and that beam provides the propulsion for the miniature spacecraft. Yes, there are huge engineering challenges associated with this method of interstellar propulsion, but nothing in principle that can't be overcome -- at least no showstoppers have been identified yet.

This article explains it far better than I ever could. There's also a pretty interesting article about it on Wikipedia.