An unmanned US space plane landed at the Air Force base on the coast of Southern California after a top secret two-year mission. The aircraft known as orbital test vehicle X-37B resembles a mini space shuttle and has spent 674 days orbiting the Earth on a classified mission.

The plane which took off in December 2012, touched down at the Vandenberg Air Force Base at 9.24am on Friday. This was the third such mission with first two missions lasting 225 and 469 days respectively. Boeing, the manufacturer of X-37B, says that the space plane orbits at a lower level of around 110 to 500 miles above the earth. The International Space Station orbits at about 220 miles.

Here’s the infrared view of the X-37B landing at the Vandenberg Air Force Base:

US Space Plane -1

There has been a lot of speculation as to what the plane was doing in space for so long. Many experts say that it carried spy gear while some theories are rather bizarre saying that the spacecraft could capture other countries’ satellites or shadow the space lab of China. However, in a written statement, the US Air Force merely said that it had been conducting “on-orbit experiments.”

The space plane X-37B that looks like a mini shuttle is blasted into the orbit also like a shuttle, by a rocket, but it lands on the runway like a normal plane. It is a small plane and cannot carry people aboard but has a cargo bay that is big enough to hold a small satellite.

US Space Plane -2

Col. Keith Balts, commander of the 30th Space Wing at Vandenberg said in a statement, “I’m extremely proud of our team for coming together to execute this third safe and successful landing. Everyone from our on-console space operators to our airfield managers and civil engineers take pride in this unique mission and exemplify excellence during its execution.