The US Air Force will today launch its second X-37B spaceplane from Cape Canveral to intesnse interest from Russia and China, which are suspicious about its secret payload.
Built by Boeing, the unmanned X-37B Orbital Test Vehicle, or OTV, is designed for vertical launch to low Earth orbit altitudes, where it can stay for up to 270 days.
When commanded, it autonomously re-enters the atmosphere, descends and lands horizontally on a runway. Looking rather like a miniature version of the Space Shuttle, it's 29 feet long and powered by solar panels. Today's flight will see it lifted to orbit by an Atlas V rocket.
The Air Force says that today's flight is intended to test advanced guidance, navigation and control, thermal protection systems, avionics, high temperature structures and seals, conformal reusable insulation, lightweight electromechanical flight systems, and autonomous orbital flight, re-entry and landing.
But it's cagy about the long-term purpose of the spaceplane, with many observers suggesting that it could be the foundation for a weapons system. One Chinese professor has suggested that it might be intended as a way of attacking other satellites and spacecraft.
But Laura Grego, a senior scientist with the Union of Concerned Scientists, says the spaceplane is unlikely to be much use for such missions because of its weight and lack of maneuverability.
"For example, it would have a harder time carrying payloads into orbit, maneuvering in space, rendezvousing with satellites, and releasing multiple payloads," she says.
"Yes, the space plane may offer more flexibility and is potentially reusable, but that comes at a very high price compared with the alternatives. We have not seen an analysis that shows why it is worth that high price."
The Air Force's first X-37B, OTV-1, launched from Cape Canaveral last April, landing at Vandenberg Air Force Base in December, after traveling 91 million miles over 224 days.