Air Force personnel in self-contained atmospheric protective ensemble suits conduct initial checks on the USAF's unmanned X-37B spaceplane. [US Air Force]

X-37B OTV

X-37B is an American unmanned, reusable orbital test vehicle (OTV). It is boosted into space by a rocket, then re-enters Earth's atmosphere and lands as a spaceplane.

On Oct. 17, 2014, X-37B successfully landed at Vandenberg Air Force Base in California after a 675-day-long spaceflight mission, the third and the longest one by far.

The X-37B spacecraft is 29 feet, 3 inches long and 9 feet, 6 inches high with a wingspan of 14 feet and 11 inches. It weighs about 5.5 tons. It resembles NASA's famous space shuttle but is much smaller.

X-37B can perform outerspace cruises and strike missions in the Earth's atmosphere. It has great spying and attack potential, which can assist U.S. forces in the "Prompt Global Strike" program.