For two years now, we’ve been following the progress of the Defense Advanced Research Project Agency’s "XS-1" project, a continuing mission to build a reusable vehicle for launching small payloads into orbit. Unlike the Space Shuttle operated by NASA from 1981 to 2011, DARPA calls its project a "space plane."
Here’s the crucial difference: Unlike the Space Shuttle, which launched like a rocket, orbited like a space ship, and then returned to Earth to land like an airplane, XS-1 will never actually enter orbit itself. Instead, it will rocket "to the edge of space," and once there, boost a payload the rest of the way into low Earth orbit.
After releasing the payload, XS-1 will land like an airplane, refuel, and be ready to launch again the next day. Ideally, DARPA wants its space shuttle to be so reliable and so reusable that it can fly "10 times in 10 days." Also, XS-1 will have no pilot. It will be a drone.