The U.S. military likes to be a little sneaky with its robotic space planes. Unlike typical spacecraft, these vehicles can shift their orbits, frustrating the global network of skywatchers who keep track of just about every man-made object rotating the planet.

But the sleuths have their tricks, too. They’ve tracked down the X-37B on its second secret mission. And the information the skywatchers are finding says quite a bit about the classified operations of this mysterious spacecraft.

It took the amateur sleuths nearly a month to hunt down the first X-37B after it launched on its inaugural mission. That’s an eternity in sky-spotting time.

The second time around was easier. The U.S. space plane was discovered just four days after it blasted into orbit, earlier this month. Cape Town, South Africa’s Greg Roberts — “a pioneer in using telescopic video cameras to track spacecraft, chalking up exceptional results over the years,” according to Space.com — spotted this second secret spacecraft, just like he found the first.

The X-37B has generated intense interest, long before it ever left the ground. Boeing originally developed the 29-foot unmanned craft — a kind of miniature Space Shuttle — for NASA. Then, the military took over in 2004, and the space plane went black. Its payloads were classified, its missions hush-hush.

Depending on who you talk to, the space plane could be a prototype commando transport, an orbiting bomber or (most likely) a spy-above-the-skies. It could launch, repair or reposition U.S. satellites in low orbit. It could sneak up and disable or steal enemy satellites. Its pickup-bed-sized payload bay is particularly enticing to observers.

And now, there are observers — plural. Ontario’s Kevin Fetterof filmed the X-37B “gliding past the binary star Eta Serpentis,” according to Space.com, which has video of the flyby. Skywatchers Brad Young, Bill Young, and Alberto Rango have all reported sightings, as well.