The US Air Force’s (USAF) X-37B spacecraft is set to return to Earth this week, ending the service’s 22 month-long secret mission.
Also known as the Orbital Test Vehicle mission 3 (OTV-3), the plane is expected to land at Vandenberg Air Force Base, California, US, under the guidance of space professionals from the 30th Space Wing.
30th Space Wing commander colonel Keith Baits said: "Team Vandenberg stands ready to implement safe landing operations for the X-37B Orbital Test Vehicle, the third time for this unique mission."
While the USAF insists that the exact landing date and time will depend on technical and weather considerations, local media reported that the touchdown is likely to occur as early as today.
The spacecraft was launched aboard an Atlas V rocket from Cape Canaveral Air Force Station, Florida, in December 2012.
Built by Boeing Phantom Works, the X-37B is a derivative of the company’s X-40A space manoeuvre vehicle, and can operate at Mach 25 velocity range upon its re-entry.
Measuring 8.8m in length, the spacecraft resembles miniature versions of Nasa’s space shuttles, and features small payload bay about the size of a pickup truck bed.
The OTV-3 mission represents the third X-37B flight, but uses the same space plane that was launched on the programme’s first mission, OTV-1, in April 2010, as reported by SPACE.com.
While the first flight lasted 225 days, the second X-37B space plane spent 469 days in orbit following its launch in March 2011.
Two X-37B spacecraft are currently present in USAF’s fleet and have been flying on secret missions since 2010.
Last week, the USAF signed an agreement with Nasa to take over two mothballed space shuttle processing hangars at the Kennedy Space Center in Florida for X-37B programme.
The US Air Force Rapid Capabilities Office oversees all X-37B missions, while the 3rd Space Experimentation Squadron at Schriever AFB Base in Colorado Springs, Colorado, serves as mission control.
Image: The X-37B orbital test vehicle taxis on the flightline at Vandenberg Air Force Base, California, US. Photo: courtesy of US Air Force.