WASHINGTON — The U.S. Air Force says its unmanned X-37B spaceplane — which has been orbiting Earth on a classified mission for 672 days and counting — will land soon at Vandenberg Air Force Base, California.

The exact time and date of the landing will depend on weather and technical considerations, according to an Oct. 10 Air Force press release.

Built by Boeing Space & Intelligence Systems of El Segundo, California, the X-37B is a reusable unmanned orbital maneuvering vehicle that launches atop a rocket and returns to Earth much like NASA’s now-retired space shuttle, gliding in for a runway landing. Its three missions to date are classified.

“Team Vandenberg stands ready to implement safe landing operations for the X-37B Orbital Test Vehicle, the third time for this unique mission” Air Force Col. Keith Balts, commander of the 30th Space Wing at Vandenberg, said in the Oct. 10 release.

The X-37B launched Dec. 11, 2012, from Cape Canaveral Air Force Station, Florida, atop a United Launch Alliance Atlas 5 rocket.

Construction is underway to convert a former space shuttle hangar at NASA’s Kennedy Space Center into a maintenance facility for the spaceplane. The facility will allow the Air Force to land, recover, refurbish and relaunch the X-37B, the Boeing officials have said.

All three X-37B missions to date were launched from Cape Canaveral Air Force Station, which is co-located with Kennedy. The first two missions ended with landings at Vandenberg.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.