Wrapping up a classified 469-day mission, an unmanned Air Force space plane dropped out of orbit and returned to Earth on Saturday, executing an automated landing to close out the program's second test flight.
Built by Boeing's Experimental Systems Group, the X-37B is equipped with twin tail fins, stubby wings and an advanced heat shield. It is about one quarter the size of NASA's now-retired space shuttle, measuring 29 feet long. It has a wingspan of just 14 feet and weighs about 11,000 pounds when loaded with propellants.
"With OTV-1, we proved that unmanned space vehicles can be sent into orbit and safely recovered," Paul Rusnock, Boeing vice president of Government Space Systems, said in a company statement. "With OTV-2, we tested the vehicle design even further by extending the...mission duration of the first vehicle and testing additional capabilities.
"We look forward to the second launch of OTV-1 later this year and the opportunity to demonstrate that the X-37B is an affordable space vehicle that can be repeatedly reused."
The spacecraft was originally developed by Boeing for NASA and the Defense Advanced Research Projects Agency, or DARPA, but it eventually was turned over to the Orbital Test Vehicle program operated by the Rapid Capabilities Office of the Air Force.
The unmanned orbiter is based on the same lifting body design used for the space shuttle and flies a similar re-entry trajectory. But the X-37B features more lightweight composite materials, improved wing leading edge insulation and tougher heat-shield tiles that "are significantly more durable than the first generation tiles used by the space shuttle," according to a Boeing Web site description. "All avionics on the X-37B are designed to automate all de-orbit and landing functions."
The X-37B features a scaled-down 4-foot by 7-foot payload bay. But unlike NASA's manned orbiter, which relied on fuel cells for electrical power, the Air Force space plane is equipped with a deployable solar array that permits it to remain in orbit for long-duration missions.
What else might have been carried aloft during the OTV program's second mission is not known. The possibilities include reconnaissance cameras or other spy sensors; test gear to precisely measure the craft's performance over the course of a long-duration mission; and space exposure experiments to help researchers learn more about the long-term effects of the space environment on sensitive materials or instruments.
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