"Unlike conventional chemical rockets which use Newton's third law of motion, solar sails take advantage of radiation pressure from stars. Kaku believes that after sending a gigantic solar sail into orbit, one could install lasers on the moon, which would hit the sail and give it extra momentum. Another alternative is to send thousands of nanoships, of which only a few would reach their destination. "Once arriving on a nearby moon, they could create a factory to make unlimited copies of themselves," says Kaku. Nanoships would require very little fuel to accelerate. They could visit the stellar neighborhood by floating on the magnetic fields of other planets."