The Air Force is known to possess two X-37B vehicles, each of which was built by Boeing. The 29-foot-long space planes launch vertically and land horizontally, just like the space shuttle used to do.

The US X-37B and China's Shenlong are competing unmanned space planes whose covert missions are getting more complex. See how the spacecraft compare.

Boeing's X-37B, an unmanned and highly advanced space plane, just completed a nearly-two-long year Air Force mission whose purpose is still not currently known. Whatever its mission, the plane ...

The U.S. Air Force's unmanned X-37B space plane has now circled Earth for more than 400 days on a hush-hush mission that is creeping closer and closer to the vehicle's orbital longevity record.

The X-37 Orbital Test Vehicle (OTV) began life under the umbrella of NASA, but was passed to the US military, which created the X-37B variant. That model first flew in orbit in 2010 and the two ...

X-37B sits on the runway following the successful completion of the OTV-6 mission, which lasted a record 908 days. [Courtesy: U.S. Space Force] Yet X-37B is only one-fourth as large, about the ...

The X-37B has winged past 666 days of flight on this latest mission, which is called OTV-5 because it's the fifth flight for the program. ... model rockets, drones and more.

The US X-37B and China's Shenlong are competing unmanned space planes whose covert missions are getting more complex. See how the spacecraft compare.