Until now the only space vehicle capable of returning to Earth - in a controlled manner anyway - was the Space Shuttle. With that craft scheduled to be retired from service next year the U.S. Air Force's Boeing X-37 program is focused on demonstrating a next generation unmanned reusable spaceplane. On April 22 this year the X-37B Orbital Test Vehicle (OTV) was launched from Cape Canaveral Air Force Station in Florida. On December 3, after an experimental test mission lasting over 220 days, the craft successfully de-orbited and landed safely at Vandenberg Air Force Base, making it the United States' first unmanned vehicle to return from space and land on its own.
The objectives of the X-37B test platform include space exploration, risk reduction, and concept-of-operations development for reusable space vehicle technologies that could enable future space missions. The craft is designed to operate in low-earth orbit, 110 to 500 miles (177 to 805 km) above the Earth at a nominal speed of about 17,500 mph (28,164 km/h). Although its design borrows heavily from the Space Shuttle, with the same lifting body design and a similar landing profile, the X-37B is just one-fourth the size of the Shuttle, coming in at 29 ft 3 in (8.9 m) long with a wing span of 14 ft 11 in (4.5 m).
Instead of the traditional aluminum, it was built using lighter composite structures and the carbon-carbon wing leading-edge tiles, which were the cause of the Columbia disaster, have been replaced with a new generation of high-temperature wing leading-edge tiles made from toughened uni-piece fibrous refractory oxidation-resistant ceramic (TUFROC). The craft also uses toughened uni-piece fibrous insulation (TUFI) impregnated silica tiles, which are significantly more durable than the first generation tiles used by the Space Shuttle.
There are no hydraulics onboard the X-37B with flight controls and brakes instead using electromechanical actuation. Additionally, all the craft's avionics are designed to automate all de-orbit and landing functions. Boeing says the success of the X-37B's inaugural mission demonstrates that unmanned space vehicles can be sent into orbit and safely recovered. The long duration of the test flight was to prove that the X-37B is capable of long-duration operations and to understand the long-term effects on system components, such as structure and future payloads.
"This marks a new era in space exploration, and we look forward to the launch of the second vehicle in 2011. By combining the best of aircraft and spacecraft into an affordable, responsive unmanned vehicle, Boeing has delivered an unprecedented capability to the RCO (Air Force Rapid Capabilities Office)," said Paul Rusnock, Boeing vice president of Experimental Systems and program director for the X-37B.
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