The X-37B returns from its third flight. Credit: Boeing

WASHINGTON — The U.S. Air Force’s unmanned X-37B spaceplane — which had been orbiting Earth on a classified mission for 22 months — landed Oct. 17 at Vandenberg Air Force Base, California.

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

The X-37B touched down at 9:24 a.m. local time, wrapping up its third classified trip to orbit since 2010.

A fourth mission is planned for 2015, the Air Force announced after the landing.

“We’re pleased with the incremental progress we’ve seen in our testing of the reusable space plane,” Col. Keith Balts, 30th Space Wing commander, said in an Oct. 17 press release.

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

Since then, the Air Force has been tight-lipped about the program’s mission. In the press release, officials said only that the spaceplane is managed by the Air Force Rapid Capabilities Office and the program performs “risk reduction, experimentation and concept of operations development for reusable space vehicle technologies.”

Experts have suggested the spaceplane’s mission was reconnaissance-related and may also have included surveillance of spacecraft in low Earth orbit. Others have suggested an intelligence, surveillance and reconnaissance mission for the National Reconnaissance Office to test out new sensor technologies.

Brian Weeden, a former Air Force officer specializing in space surveillance who now works as a technical adviser at the Secure World Foundation think tank, said the spaceplane likely is used both for reconnaissance and testing guidance and thermal protection systems for reusable spacecraft.

Weeden said that the spaceplane likely was not collecting data over Russia, which is north of the orbit where the X-37B was flying. Instead, X-37B’s reconnaissance targets were more likely in the Middle East, Afghanistan, Africa, Southeast Asia and Latin America.

Weeden said he thought it unlikely the spaceplane was used to perform orbital inspection, repair or retrieval.

Construction is underway to convert a former space shuttle hangar at NASA’s Kennedy Space Center near Cape Canaveral 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 and landed at Vandenberg. The fourth mission will also launch from Cape Canaveral. The Air Force did not say where the spaceplane will land.

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.