According to observations published in Spaceflight Magazine, the United States Air Force may be spying on Tiangong-1 — China's first space station — from orbit. Seems reasonable: China is steadily advancing towards and the US may want to know what they're doing.
According to the magazine, the mini-space shuttle X-37B may be near the Chinese station, following it in close orbit. The Air Force launched this X-37B on March 2011 on a Atlas V rocket, after her sister ship landed at Vandenberg AFB in California following a highly successful 225-day mision.
Like that mission, this one is also classified and nobody knows what the spaceship is doing up there. Experts believe the USAF uses the X-37B as a testbed for surveillance technology. Now, a dedicated group of space object trackers have noticed that the X-37B is following an orbit that is nearly identical to Tiangong-1. According to Spaceflight editor Dr David Baker, there's no doubt the X-37B is following China's space station:
The parallels with X-37B are clear. With a period differential of about 19 seconds, the two vehicles will migrate toward or against each other, converging or diverging, roughly every 170 orbits.
The article in Spaceflight, a reputable magazine published by the British Interplanetary Society, says that X-37B is now flying at an altitude of 300km with an orbital inclination of 42.79°. Tiangong-1 — which launched later — is flying with an orbital inclination of 42.78°. The distance is close enough for X-37B to clearly see China's station.
But according to Brian Weeden at the Secure World Foundation, it may all be a coincidence. Talking to the BBC, the former USAF orbital analyst said that X-37B's orbit indicates that it may be monitoring the Middle East and Afghanistan. Well, Brian, that's what you believe. I want to believe there's some pew-pew going up there. [Spaceflight Magazine via BBC]