Three months after returning from a debut spaceflight, a second prototype miniature space shuttle being tested by the U.S. military is ready for launch.

The Orbital Test Vehicle-2, one of two experimental spacecraft built by Boeing for the X-37B program, is scheduled for launch between 3:39 p.m. and 5:39 p.m. EST Friday aboard an unmanned Atlas 5 rocket from Cape Canaveral Air Force Station in Florida.

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The first ship spent 224 days in space, though what it was doing and any experiments or payloads that may have been aboard remains classified. The X-37B is a 29-foot long, 14-foot wide winged reusable spacecraft that the military is testing to see if it can fly cheaply, quickly and often. In addition to rapid-turnaround between flights, the goal of the program is to see if the vehicles are useful to test sensors and instruments that are being developed for future satellites.

The vehicles are designed to stay in orbit up to 270 days and autonomously land on a runway. Orbital Test Vehicle-1 returned to Earth on Dec. 3, touching down at Vandenberg Air Force Base. That vehicle is still being inspected, though the military says it appears to be in good shape. It will be refurbished and relaunched, though program managers have not yet said when.

“Because of the short timeframe between the OTV-1 landing in December and the launch of OTV-2 in March, focus was turned to getting OTV-2 ready for launch,” the Air Force wrote in an email to Discovery News.

“We will do a more detailed assessment after OTV-2 launch to prove the objectives for a quick, low-cost turn-around,” the Air Force said.

Among the possible missions for an operational fleet of unmanned shuttles are surveillance, in-space satellite servicing and repair, carrying spacecraft into orbit and testing technologies to clean up space debris.

About the only change the military is making for the second OTV mission is lowering the main landing gear tire pressure. The first ship blew a tire during touchdown.

The Air Force Rapid Capabilities Office manages the program.

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