Skywatcher Ralf Vandebergh of the Netherlands recently snapped an impressive photo of the US Air Force's most secretive space plane orbiting Earth.

The Boeing X-37, also known as the Orbital Test Vehicle (OTV), is a reusable robotic space plane, was conducting a top-secret mission in low Earth orbit when Vandenbergh recorded the image.

"When I tried to observe it again [in] mid-June, it didn't meet the predicted time and path," Vandebergh explained. "It turned out to have maneuvered to another orbit. Thanks to the amateur satellite observers' network, it was rapidly found in orbit again, and I was able to take some images on June 30 and July 2."

The X-37B resembles a smaller version of NASA's retired Space Shuttle orbiter.

"It is a small object, even at only 300 kilometers [186 miles] altitude, so don't expect the detail level of ground-based images of the real space shuttle," Vandebergh said.

Vandebergh said the newly captured images exceeded his wildest expectations.

"We can recognize a bit of the nose, payload bay and tail of this mini-shuttle, with even a sign of some smaller detail," he said.

Vandebergh noted that he used a 10-inch F/4,8 aperture Newtonian telescope with an Astrolumina ALccd 5L-11 mono CMOS camera (both can be bought over the internet under $10,000).

Space.com said the X-37B had achieved 666 days of flight on OTV-5 mission.

Notice how each OTV mission has a longer duration in space...

OTV-1 launched on April 22, 2010, and ended on December 3, 2010 (224 days in space).

OTV-2 began March 5, 2011, and landed on June 16, 2012 (468 days).

OTV-3 launched on December 11, 2012, and came down on October 17, 2014 (675 days).

OTV-4 lifted off on May 20, 2015, and landed May 7, 2017 (718 days).

OTV-5 began on September 2017 atop a SpaceX Falcon 9 rocket, with experimental cargo: electronics and oscillating heat pipes for long-duration stints in the space environment. The payload's top science objectives are to measure the thermal performance of extended space travel to asses any lifetime degradation.

The 3rd Space Experimentation Squadron oversees OTV-5 at the Schriever Air Force Base, has sparked suspicion that the space plane's payload could be carrying intelligence-gathering sensors to spy on China and or Russia.