A reusable spaceplane operated by the U.S. Space Force is expected to lift off from Florida for its eighth mission as soon as Thursday night. Built by Boeing, the X-37B Orbital Test Vehicle is an autonomous spacecraft that the U.S. military uses to test technology and conduct experiments in high and low Earth orbits. While the existence of the spaceplane is widely known, much of its activities are kept under wraps by Space Force, which doesn't announce its return to Earth until after the fact. h