The LightSail is a special spacecraft, developed by the non-profit Planetary Society, that consists of a CubeSat about the size of a shoebox. It was designed by California-based Stellar Exploration.
The craft is named as such because once it is deployed, it will harness the pressure from sunlight to push itself along in a phenomenon referred to as solar sailing. The satellite is being designed to be light enough to be pushed by sunlight yet sturdy enough to move along and maintain its shape without collapsing. The satellite's design will be tested over the course of a four week stint.
The second LightSail flight is scheduled for 2016, at which time solar sailing will be demonstrated in the Earth's orbit.