A former orbital analyst said previous reports of U. S. military's X-37B space plane spying on a prototype space module are extremely unlikely to be true.

According to Brian Weeden, a technical adviser with the Secure World Foundation and a former orbital analyst with the U. S. Air Force, the robotic X-37B space place could not possibly be surveilling China's Tiangcong 1 space laboratory as they have different orbits.

"I would go as far as to say, 'no chance,'" said Weeden. "It's not practical."

The experimental X-37B was launched for the first time by the U.S. Air Force on a classified mission in March 2011. The spacecraft is known as the Orbital Test Vehicle 2, or OTV-2. Meanwhile, China launched its unmanned Tiangong 1 space lab in September and is using the vessel to carry out orbital docking tests.

Observers have speculated that that the X-37B and Tiangong 1 have broadly similar orbits since both are currently about 180 miles (300 kilometers) above the Earth, with an inclination of roughly 43 degrees with respect to the equator.

However, Weeden said the orbits of the X-37B and Tiangong 1 differ by about 100 degrees in a parameter, called right ascension. This describes where a craft crosses the equator, he explained, such that the two satellites actually take disparate paths around the globe, with their orbits intersecting just twice per circuit.

Theoretically, the X-37B and Tiangong 1 could approach each other a maximum of two times per orbit, that is, is if timing works out perfectly, but with the very high speeds, it is not exact the best condition for a spy mission, Weeden said.

The X-37B, which looks like a smaller version of NASA's recently retired space shuttle, is about 29 feet long and 15 feet wide, with a payload bay about the size of a pickup truck bed. The U. S. Air Force has repeatedly said that the space plane's primary mission is to test out new technologies.

The space plane's orbit can also explain its activities, Weeden said. The craft, which is flying repeatedly over the stretch from 43 degrees north latitude to 43 degrees south, could be using new technology to observe the Middle East and Afghanistan, he said.

Weeden also speculated that with the current mission aloft for more than 10 months, the military may be putting the vehicle through something of an endurance test.

But with regards to observations that it is conducting surveillance on China, Weeden said the the government has better information-gathering tools at its disposal than the X-37B for the job.

"The U.S. has this whole network of ground-based telescopes and radars, several of which can do imaging - either radar or optical imaging of space objects - that are better suited for this," he said.