X-37B OTV-4 landing
The X-37B on the Shuttle Landing Facility runway at NASA's Kennedy Space Center after a May 7, 2017, landing that ended a 718-day mission. Credit: U.S. Air Force

WASHINGTON — A secretive U.S. Air Force spaceplane landed in Florida early May 7 after spending nearly two years in orbit on a classified mission.

The X-37B landed at the Shuttle Landing Facility at NASA’s Kennedy Space Center, a runway four and a half kilometers long previously used for landings by the space shuttle. The Air Force did not disclose the exact landing time, but announced the landing in a tweet shortly before 8 a.m. Eastern.

The X-37B had been in orbit on a mission designated Orbital Test Vehicle (OTV) 4 since a launch on an Atlas 5 from Cape Canaveral Air Force Station, Florida, on May 20, 2015. The Air Force disclosed prior to the launch that the OTV-4 mission would carry a Hall effect electric thruster developed by Aerojet Rocketdyne and a materials science experiment provided by NASA, but did not disclose other plans for the mission.

Project officials offered no new details about the OTV-4 mission after landing, but called the mission the success. “We are incredibly pleased with the performance of the space vehicle and are excited about the data gathered to support the scientific and space communities,” said Air Force Lt. Col. Ron Fehlen, X-37B program manager, in a May 7 Air Force statement after the landing.

The landing was the first time that the X-37B has landed at the KSC runway. The first three X-37B missions, also launched on Atlas 5 rockets at Cape Canaveral, landed at Vandenberg Air Force Base in California.

“Our team has been preparing for this event for several years, and I am extremely proud to see our hard work and dedication culminate in today’s safe and successful landing of the X-37B,” said Air Force Brig. Gen. Wayne Monteith, commander of the 45th Space Wing, in the statement. The wing operates the Cape Canaveral launch sites and had responsibility for the landing.

The 718 days the X-37B spent in space set an endurance record. Each X-37B mission has flown longer than the previous one, from a 224-day flight of the first X-37B, launched in April 2010, to the 674 days spent in space on the third X-37B mission, launched in December 2012.

A fifth X-37B mission is scheduled for launch later this year, again from Cape Canaveral, the Air Force said in its statement about the landing.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...