The Air Force launched a secretive space plane into orbit Thursday night from Cape Canaveral, Florida. And they're not sure when it's returning to Earth.

Perched atop an Atlas V rocket, the Air Force's unmanned and reusable X-37B made its first flight after a decade in development shrouded in mystery; most of the mission goals remain unknown to the public.

The Air Force has fended off statements calling the X-37B a space weapon, or a space-based drone to be used for spying or delivering weapons from orbit. In a conference call with reporters, deputy undersecretary for the Air Force for space programs Gary Payton acknowledged much of the current mission is classified. But perhaps the most intriguing answer came when he was asked by a reporter wanting to cover the landing as to when the X-37B would be making its way back to the planet.

"In all honesty, we don't know when it's coming back for sure," Payton said.

Payton went on to say that the timing depends on how the experiments and testing progress during the flight. Though he declined to elaborate on the details. The vague answer did little to quell questions about the ultimate purpose of the X-37B test program.

At only 29 feet long, the X-37B is roughly one fourth the size of the space shuttle. It's onboard batteries and solar arrays (pictured at left from its NASA days) can keep it operating for up to nine months according to the Air Force. It is similar to the shuttle with payload doors exposing a cargo area, and uses a similar reentry procedure before gliding to a runway. In the case of the X-37B, the vehicle will autonomously return to earth and land itself using an onboard autopilot. The primary landing spot is Vandenberg Air Force Base in California.

In his conference call, Gary Payton told reporters the primary goal is to see if the system is a viable option for the Air Force.

"Top priority is an inexpensive turn around," Payton said. "Do we have to do a lot of servicing? If that's the case, it makes this kind of vehicle less attractive to us in the future."

Payton described an ideal turn around to be similar to a large airplane.

"I would like to see this X-37 handled much more like an airplane, maybe an SR-71" he said referring to the legendary spy plane. "Handled more like that than what we see with other space launch mechanisms, space launch vehicles."

The military has been looking into the idea of an orbital space platform for decades. And the X-37 program itself has been around for quite a while. Built by Boeing's Phantom Works division in the mid 1990s, it was first developed for NASA as a reusable space vehicle that could be carried to orbit either inside the space shuttle or using a booster rocket. The unmanned X-37 would then orbit for a period of time before launching or retrieving a payload and return to earth.

The program was transferred to the Department of Defense in 2004. Since that time the X-37 has become a classified program, raising questions as to whether or not it would become the first operational military space plane. During the 1960s, the Air Force and Boeing conducted research on the X-20 Dyna-Soar space plane. After initial development, much of it with then test pilot Neil Armstrong, the Dyna-Soar was canceled in 1963.

A vehicle such as the X-37 could be a valuable platform for intelligence gathering with the advantage of a satellite's point of view, but the flexibility of an aircraft that can be launched relatively quickly and maneuvered in orbit much easier than a traditional satellite.

With the lack of specificity expected from a classified program, and without a translator, the Air Force described the X-37B program as "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. This service directly supports the Defense Department’s technology risk-reduction efforts for new satellite systems. By providing an ‘on-orbit laboratory’ test environment, it will prove new technology and components before those technologies are committed to operational satellite programs.”

Once the current mission is over, the miniature unmanned space shuttle will be inspected to determine if it is a truly reusable vehicle. A new generation of protective tiles, similar to those that plagued early shuttle flights will be examined as well as the autonomous flight control systems that pilot the space craft. The other key component to the program, the overall time needed to prepare the X-37 for another flight, will also be closely watched. The goal is to have it flight ready again in 15 days.

A second X-37B is in the works and the Air Force said it could be ready for a 2011 launch.

[Photos: Air Force, Boeing]