A vessel that ride through the sky powered solely by heavenly breeze made true; that's Lightsail 2. In a 1610 letter to Galileo Galilei (Conversation with the Star Messenger), Johannes Kepler already wrote that the humans might one day use the technology to set a course for the stars: “Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void.” The solar sails (also called light sails or photon sails) are a way of propelling a probe through space using radiation pressure exerted by sunlight photons on a mirror-like reflective surface (in this case 4 triangular Mylar sails that are just 4.5 microns thick), without the current chemical rockets that burn fuel that the spacecraft carries on board. As The Planetary Society explained “With solar sails, a spacecraft can continue accelerating as long as there is light pushing on it. Within a solar system, sunlight can continuously push on the sail, accelerating the spacecraft throughout its entire voyage. This means that solar sail-propelled spacecraft can reach speeds that would be practically impossible for chemical rockets to achieve.”