This top-secret plane has been in space for a year, and we don't know why

The highly classified mission of the X-37B is unknown, so speculation is rampant

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In a testing procedure, the X-37B Orbital Test Vehicle taxis on the flightline in June 2009 at Vandenberg AFB, California. Credit: U.S. Department of Defense

It has now been a year since the U.S. Air Force launched the mysterious X-37B into space, leaving many to wonder why it’s there.

At first glance, the vehicle looks just like a mini Space Shuttle. But anyone who’s tried online dating will know, looks can be deceiving.

The X-37B is part of a top-secret government program to develop reusable, unmanned spacecraft technologies and conduct experiments.

The Air Force has already successfully completed three X-37B missions starting with the first launch in April of 2010. The three missions and two X-37B craft have proved reusable flight, reentry, and landing technologies. So why was the latest vehicle even launched?

The mystery of the X-37B may not lie so much in the structure of the vehicle, but rather, in what it’s carrying, said Jonathan McDowell, an astronomer at Harvard-Smithsonian Center for Astrophysics.

The long missions are perfect for carrying sensitive cargo into space for testing, he said.

"They are filling the payload bay with various experiments," he added. "Probably different experiments each flight, probably for different customers."

The Air Force has opened up about some of the technologies being tested on the latest flight, including advanced guidance, reusable insulation, and advanced propulsion systems. But, McDowell predicts the government is also conducting some covert experiments.

"The sorts of things that you would want with something like this … you develop new technology sensors like new cameras, new listening devices, intelligence [gathering] radio antennas, and maybe a new type of antenna dish that unfolds in a new way. And you want to exercise it in space multiple times and then bring it back to earth," he said.

X-37B (1) U.S. Department of Defense

The X-37B is seen shortly after landing at Vandenberg Air Force Base in California after its first mission on December 3, 2010.

The X-37B could also be testing quick turnaround and relaunch.

McDowell points out that this is the first time the Air Force hasn’t specified which of the two X-37B’s they launched. Tt’s possible they sent out the same vehicle seven months after it landed on Oct. 17, 2014, he said.

So how long might the latest mission last? The duration of the past three missions has progressively increased, from 240 days, to 469 days, and finally 674 days. Still, McDowell predicts an earlier landing.

"What I would expect to see at some point … is that you’ll see this one land and then possibly the very same shuttle go up again after a much shorter period of time," he said.