Recovery crew members process the X-37B Orbital Test Vehicle at Vandenberg Air Force Base after completing 674 days in space.image courtesy:Universe Today

The U.S. military’s experimental X-37B space plane landed on Sunday at NASA’s Kennedy Space Center in Florida, completing a classified mission that lasted nearly two years, the Air Force said.It was the first Florida landing of a returning spacecraft since Atlantis flew home in the program’s final mission in 2011.

The Boeing-built space plane blasted off in May 2015 from nearby Cape Canaveral Air Force Station aboard an Atlas 5 rocket built by United Launch Alliance, a partnership between Lockheed Martin Corp and Boeing Co.

The X-37B, one of two in the Air Force fleet, conducted unspecified experiments for more than 700 days while in orbit. It was the fourth and lengthiest mission so far for the secretive program, managed by the Air Force Rapid Capabilities Office.

The X-37 program started in 1999 with NASA, which initially planned to construct two vehicles: an Approach and Landing Test Vehicle (ALTV) and an Orbital Vehicle.

NASA transferred the project to the U.S. military in 2004,specifically, the Defense Advanced Research Projects Agency (DARPA). At that point, X-37 became a classified project.

DARPA finished the ALTV part of the program in 2006, conducting a series of captive-carry and free-flight tests. NASA’s envisioned Orbital Vehicle was never built, but it served as the inspiration for the space plane that came to be called the X-37B.

The X-37B program is run by the Air Force’s Rapid Capabilities Office, with mission control for orbital flights based at the 3rd Space Experimentation Squadron at Schriever Air Force Base in Colorado. The space planes are built by Boeing’s Phantom Works division.

“The primary objectives of the X-37B are twofold: reusable spacecraft technologies for America’s future in space and operating experiments which can be returned to, and examined, on Earth,” states an X-37B fact sheet produced by the Air Force.

The Air Force states that this includes testing avionics,flight systems, guidance and navigation, thermal protection, insulation, propulsion, and re-entry systems.

General characteristics

Crew: none,Length: 29 ft 3 in (8.92 m),Wingspan: 14 ft 11 in (4.55 m),Height: 9 ft 6 in (2.90 m),Max takeoff weight: 11,000 lb (4,990 kg),Electrical power: Gallium arsenide solar cells with lithium-ion batteries,Payload bay: 7 × 4 ft (2.1 × 1.2 m).

Performance

Orbital speed: 28,044 km/h (17,426 mph),Orbit: Low Earth orbit,Orbital time: 270 days (design).

On 17 November 2006, the U.S. Air Force announced that it would develop its own variant from NASA’s X-37A. The Air Force version was designated the X-37B Orbital Test Vehicle (OTV). The OTV program was built on earlier industry and government efforts by Defense Advanced Research Projects Agency(DARPA), NASA and the Air Force, and was by the U.S.Air Force Rapid Capabilities Office,in partnership with NASA and the Air Force Research Laboratory.Boeing was the prime contractor for the OTV program. The X-37B was designed to remain in orbit for up to 270 days at a time.

The Secretary of the Air Force stated that the OTV program would focus on “risk reduction, experimentation, and operational concept development for reusable space vehicle technologies, in support of long-term developmental space objectives”.

Sunday’s landing was the X-37B’s first in Florida. The three previous landings took place at Vandenberg Air Force Base in California. The Air Force relocated the program in 2014, taking over two of NASA’s former shuttle-processing hangars.

The Air Force intends to launch the fifth X-37B mission from Cape Canaveral Air Force Station, located just south of the Kennedy Space Center, later this year.

The X-37B features more lightweight composite materials, improved wing insulation and tougher heat-shield tiles that “are significantly more durable than the first generation tiles used by the space shuttle,” according to a Boeing website description. “All avionics on the X-37B are designed to automate all de-orbit and landing functions.”

The X-37B is equipped with a scaled-down 4-foot-by-7-foot payload bay. But unlike the space shuttle, which relied on fuel cells for electrical power, the Air Force spaceplane is equipped with a deployable solar array that permits it to remain in orbit for long-duration missions.

“This mission once again set an on-orbit endurance record and marks the vehicle’s first landing in the state of Florida,” Lt. Col. Ron Fehlen, X-37B program manager, said in the Air Force statement. “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.”

The Secure World Foundation, a nonprofit group promoting the peaceful exploration of space, says the secrecy surrounding the X-37B suggests the presence of intelligence-related hardware being tested or evaluated aboard the craft.