London: The US Air Force`s highly secret unmanned space plane is set to land in June, after circling the Earth for a year at 17,000 miles per hour.
The experimental Boeing X37-B was due to land in California in December, but is now expected to land in mid to late June.
At launch, the space plane was accompanied by staff in biohazard suits, leading to speculation that there were radioactive components on board.
“The men and women of Team Vandenberg are ready to execute safe landing operations anytime and at a moment`s notice,” the Daily Mail quoted Colonel Nina Armagno of the US Air Force`s Space Wing as saying.
The plane resembles a mini space shuttle and is the second to fly in space.
It was meant to land in March, but the mission of the X-37B orbital test vehicle was extended – for unknown reasons.
The first one landed last December at Vandenberg Air Force Base in California after more than seven months in orbit.
The 29-foot, solar-powered craft had an original mission of 270 days.
The Air Force said the second mission was to further test the technology but the ultimate purpose has largely remained a mystery.
“We initially planned for a nine-month mission. Keeping the X-37 in orbit will provide us with additional experimentation opportunities and allow us to extract the maximum value out of the mission,” the vehicle`s systems program director, Lieutenant-colonel Tom McIntyre, told the Los Angeles Times in December.
However, many sceptics think that the vehicle`s mission is defence or spy-related.
There are rumours circulating that the craft has been kept in space to spy on the new Chinese space station, Tiangong.
However, analysts have pointed out that surveillance would be tricky, since the spacecraft would rush past each other at thousands of metres per second.
“If the U.S. really wanted to observe Tiangong, it has enough assets to do that without using X-37B,” Brian Weeden, from the Secure World Foundation, told the BBC.
Last May, amateur astronomers were able to detect the orbital pattern of the first X-37B which included flyovers of North Korea, Iraq, Iran, Pakistan and Afghanistan, heightening the suspicion that the vehicle was being used for surveillance.
Other industry analysts have speculated that the Air Force is just making use of the X-37B`s amazing fuel efficiency and keeping it in space for as long as possible to show off its credentials and protect it from budget cuts.