Small, windowless and bearing a classified payload, the U.S. Air Force’s unmanned space plane—the X-37B Orbital Test Vehicle (OTV)–has been shrouded in mystery since its first flight in December of 2010. Over the weekend the mysterious craft completed its third—and longest—space mission, prompting renewed speculations as to what it does and why: Is it collecting surveillance? Is it a weapon of some kind? Why has it changed hands so many times—from NASA to the Pentagon to the secretive Air Force Rapid Capabilities Office? The Air Force is so far keeping quiet about the OTV’s cargo and the purpose of its 15-month mission in orbit, but has somewhat cryptically stated that plane’s primary objectives are twofold: “Reusable spacecraft technologies for America’s future in space and operating experiments which can be returned to, and examined, on Earth.”
The robotic spacecraft, which resembles a diminutive space shuttle, is only 9 feet tall and 29 feet long. Relatively light-weight with a wingspan of 15 feet, it lands horizontally like an airplane and is considered much less risky than space shuttles.
Joan Johnson-Freese, professor of national security affairs at the Naval War College, told the Associated Press that the craft quickly could give the U.S. “eyes” over conflict regions.
Last year, space analyst John Pike of the think tank and online forum GlobalSecurity.org told TIME that the OTV might have no practical use at all. “When we ask what secret mission [the OTV] is performing, that may assume greater rationality than it deserves,” he said. “It may just be that this program got up a head of steam and was too big to fail.”