A mysterious spacecraft has been orbiting the Earth for the past 720 days, and only the US Air Force knows why.
This is the fifth mission of the X-37B space plane, an uncrewed and solar-powered military drone. The Orbital Test Vehicle 5 (OTV-5) mission launched way back on September 7, 2017, with the help of a SpaceX Falcon 9 rocket.
On the fourth mission – Orbital Test Vehicle 4 (OTV-4) – it remained in orbit for 717 days, 20 hours, and 42 minutes, which it has now surpassed, with no details yet on when the mission may end.
The fourth flight of the vehicle, landing smoothly.
The mission objectives of the space plane – similar in design to NASA's space shuttles – have remained a closely guarded secret. The Air Force is tight-lipped about the plane, leaving people to speculate it's doing anything from putting spy satellites into orbit to testing out an EmDrive in space.
Don't get your hopes up too much on that EmDrive by the way.
When the craft launched, conspiracy theorists suggested it could be a "space bomber", a full seven years before Trump even created Space Force. The theory was quickly quashed by experts, who pointed out how changing a spacecraft's orbital plane requires a lot of thrust that would eat up its limited fuel supply extremely quickly. Essentially it would be useless at hitting any targets that didn't happen to already be on its flight path.
Another theory from Spaceflight magazine is that it's a spy plane.
"Space-to-space surveillance is a whole new ball game made possible by a finessed group of sensors and sensor suites, which we think the X-37B may be using to maintain a close watch on China's nascent space station," Spaceflight Editor Dr David Baker told BBC News back in 2012, though this too was deemed unlikely based on the ship's orbital path.
As fun as those explanations are, they are unlikely. The Air Force's official explanation doesn't give away too much, either.
"The X-37B Orbital Test Vehicle, or OTV, is an experimental test program to demonstrate technologies for a reliable, reusable, unmanned space test platform for the US Air Force," the Air Force said in a statement.
"The primary objectives of the X-37B are twofold; reusable spacecraft technologies for America’s future in space and operating experiments which can be returned to, and examined, on Earth.
"Technologies being tested in the program include advanced guidance, navigation and control, thermal protection systems, avionics, high-temperature structures and seals, conformal reusable insulation, lightweight electromechanical flight systems, advanced propulsion systems, advanced materials and autonomous orbital flight, reentry and landing."
For now, you'll either have to accept the official explanation, or just get comfortable with the knowledge that there's a mysterious space drone flying high above our heads, and only the US military knows why.