Recommend reading TFA:

>Think of it as a large pingpong ball with computers and cameras pointing in different directions. The big advantage? The spherical shape, coupled with a "hollow" laser beam that's stronger toward its outside edge, could be naturally centered on the beam throughout the acceleration.

>"Imagine blowing a piece of paper straight up. It's going to fly off the beam unless it's perfectly aligned," says Zac Manchester, a Stanford professor and Starshot engineer who's researched the subject and already launched a 1.4-inch square spacecraft into Earth's orbit.