"The return capability allows the Air Force to test new technologies without the same risk commitment faced by other programs. We're proud of the entire team's successful efforts to bring this mission to an outstanding conclusion," he said.
The military won't say what OTV-2 was doing during its 15 months in orbit, but a third mission already is on the calendar for launch this fall. OTV-2 blasted off aboard an unmanned Atlas 5 rocket from Cape Canaveral Air Force Station on March 5, 2010.
Boeing Phantom Works built two of the robotic space planes, which resemble diminutive space shuttle orbiters, as test vehicles. The military, which took over the program from NASA, says it is using them to learn how to quickly and inexpensively refurbish reusable spaceships for flight.
The X-37Bs also serve as orbital testbeds for instruments that could be incorporated into future satellites.
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The vehicles look like miniature versions of NASA's now-retired space shuttle orbiters, with a similar shape and a payload bay for cargo and experiments. They are 29 feet (8.9 meters) long, compared to the shuttle's 122-foot (37-meter) length, and have a wingspan of 15-feet (4.5 meters),compared to the shuttle's wingspan of 78 feet (23.7 meters).
Rather than hydrogen-oxygen fuel cells like the orbiters, the X-37Bs are powered by gallium arsenide solar cells with lithium-ion batteries. The vehicles were designed to stay in orbit for up to 270 days.
OTV-2 surpassed that milestone by 199 days.
The X-37B due to fly this fall is the vehicle that inaugurated the program in 2010.
Image: Infrared photograph of the U.S. Air Force's second X-37B robotic space plane as it landed at Vandenberg Air Force Base, Calif. on June 16, 2012. Credit: USAF/Vandenberg Air Force Base