LightSail-B will steer in Earth's orbit using nothing more than radiation from the sun. Made up of three miniature CubeSats, it will launch aboard SpaceX's Falcon Heavy rocket, which has yet to be flown. The four sails will ride inside the CubeSats until they're ready to be unfurled, several weeks after liftoff.
LightSail-B will be boosted to medium-Earth orbit inside another spacecraft called Prox-1, a Georgia Institute of Technology project. Prox-1 will spit LightSail out and remain nearby to watch the spacecraft unfurl. (LightSail-A, meanwhile, would only reach low-Earth orbit in a mission designed to show how well the craft operates in space.)