For the past year, it's been hard not to get caught up in the hype surrounding the 'impossible' EM Drive - the fuel-less propulsion system that defies Newton's third law, and yet continues to produce a small but unexplained amount of thrust in test after test.

Things got particularly interesting in December, when the Chinese government claimed they were already testing an EM Drive in space, and an anonymous source told the IB Times that the US was doing the same thing on board the military's mysterious space plane, X-37B. Five months later and those rumours are still circulating on blogs and news sites. So what's going on?

In case you've missed it, X-37B, or Boeing X-37, is a solar-powered, unmanned space plane that's been orbiting Earth for more than a record-breaking 678 daysstraight... but we still don't really know what it's doing up there.

Launched by the US Air Force in May 2015, the government has remained relatively tight-lipped about how long the plane will stay in space, and exactly what its purpose is.