US Air Force's Secret X37-B Space Plane Prepares for Launch
U.S. Air Force's space plane is set to begin its fourth mission this week.
— -- A secretive space plane owned by the United States Air Force is set to launch on its fourth out-of-this-world mission on Wednesday.
While little is known about the X-37B space plane and what it will be doing in space, here are five things we do know about the plane.
Size
Measuring 29 feet in length and having a 15-foot wingspan, the unmanned re-usable orbital test vehicle looks like a miniature version of NASA's now retired space shuttles.
Last Mission
After 674 consecutive days in space, the plane touched down last October at Vandenberg Air Force Base in California, marking the end of its third mission.
Landing
Like the space shuttle, the X-37B lands on runways, though it does so without pilots at the helm.
This Mission
While it is not known how long the plane's fourth mission will last, Wright-Patterson Air Force Base said last month the plane will be testing a Hall thruster, a type of propulsion system that could one day be used to power spacecraft on long-haul missions.
The Rocket
The launch is set for Wednesday morning. The X-37B plane will be carried into space on the back of an Atlas V rocket from Cape Canaveral Air Force Station in Florida.