( CNN ) -- The U.S. Air Force 's mysterious unmanned space plane , the X-37B , is about to come back to Earth after nearly two years in orbit on a mission the military wo n't tell us much about . The X-37B is expected to land at Vandenberg Air Force Base in California , the Air Force said . The base did not give an exact time for the landing , but a notice to aviators and mariners on the Federal Aviation Administration 's website Tuesday said airspace around the Southern California base would be closed from 8 a.m. to 5 p.m. PT Wednesday . `` Team Vandenberg stands ready to implement safe landing operations for the X-37B Orbital Test Vehicle , the third time for this unique mission , '' Col. Keith Baits , commander of the 30th Space Wing , said in a statement . The X-37B , which looks like a small space shuttle , lifted off from Cape Canaveral in Florida on December 11 , 2012 . At the time , the Air Force said its mission would last about nine months . The X-37B `` is designed to demonstrate reusable spacecraft technologies for America 's future in space and operating experiments which can be returned to , and examined , on Earth , '' an Air Force statement said . `` Technologies being tested in the program include advanced guidance , navigation and control , thermal protection systems , avionics , high temperature structures and seals , conformal reusable insulation , lightweight electromechanical flight systems , and autonomous orbital flight , re-entry and landing . '' But as the spacecraft has been in orbit for more than 22 months , speculation on other uses abounds , including testing of a secret space weapon or spying activities . The previous mission of the X-37B , which landed at Vandenberg on June 16 , 2012 , lasted 469 days , according to the Air Force . That mission was flown by the second of the Air Force 's two X-37B orbiters . The current mission is the second for the first of the orbiters , which was refurbished after it spent 224 days in orbit following an April 2010 launch . When the current mission launched , the Air Force said it might not be the last . `` Officials anticipate multiple missions will be required to satisfy the test program objectives , but the exact number of missions has not been determined , '' a statement said . The X-37B spacecraft is 29 feet , 3 inches long and 9 feet , 6 inches high with a wingspan of 14 feet and 11 inches . It weighs about 5.5 tons . It is lifted into space by United Launch Alliance 's Atlas V rockets .
January : An FAA notice says airspace around the station will close as of Wednesday . Space Shuttle has been in orbit for more than 22 years . Air Force says use of X-37B is to demonstrate technologies . News abounds about secret weapons , spying .