The United States Air Force X37-B Space Plane (one of two) takes off into orbit above Earth in its fourth secretive mission. The craft itself is not a secret - we know what it's capable of. The contents of the craft are not entirely secret - we know MOST of what's inside. What the United States Air Force is doing on this mission with the cargo they carry - that's the question here. With one of two X-37B space planes headed to space with, amongst other cargo, 10 minuscule "cubesats" and a real deal Solar Sail, we'll be interested to see what becomes of their testing and action.