Editor's Note: This story was first published in April.
Washington (CNN) -- Mystery surrounds the U.S. military's Orbital Test Vehicle, the X-37B OTV, which launched into space in April from the Cape Canaveral Air Station in Florida.
Is it an aircraft? Is it the next generation space shuttle? How much does it cost? And why is it such a secret?
The X-37B OTV is a classified Air Force project that has never been fully explained by the Pentagon.
Some worry it may be the start of military operations in space -- that the plane might some day carry weapons to shoot down enemy satellites.
Some are concerned it may be used as a quick-response vehicle that could be sent very quickly with weapons to a danger spot, said Victoria Samson of the Secure World Foundation.
The private group says it is "dedicated to maintaining the secure and sustainable use of space for the benefit of Earth and all its peoples."
In a recent meeting with reporters, a top Air Force official rejected those types of suggestions. "I don't know how this could be called weaponization of space," said Gary Payton, deputy undersecretary for space programs. "Fundamentally, it's an updated version of the space shuttle."
Unlike the re-usable space shuttle, the X-37B is unmanned and much smaller. It is controlled from ground stations.
It can stay in space for 270 days, but the Air Force won't say how long it's staying up this time or what exactly it will be doing other than testing out its high tech guidance and navigation.
The Air Force won't even say how many billions of dollars it's spending on the program.
Military officials have said some of the things they hope will come from the X-37B. "The OTV has the potential to revolutionize how the Air Force operates in space by making space operations more aircraft like," said David Hamilton Jr., the Air Force Rapid Capabilities office director.
The OTV "will provide a flexible space test platform to conduct various experiments and allow satellite sensors, subsystems, components and associated technology to be efficiently transported to and from the space environment where it will need to function," the Air Force said in a news release.
The OTV is the first vehicle since NASA's shuttle orbiter that has the ability to return experiments to Earth for further inspection and analysis, the Air force said.
It "will be used to test technologies including advanced guidance, navigation and control, thermal protection systems, avionics and high temperature structures and seals," the news release said.
"The X-37B is an important step in the effort to make space access more routine, affordable, and responsive," said Hamilton in the news release. "The technologies and concepts of employment that are proven by the Orbital Test Vehicle will be folded into development programs that will provide capabilities for our warfighters in the future."