Leonard David's INSIDE OUTER SPACE

The first X-37B Orbital Test Vehicle waits in the encapsulation cell of the Evolved Expendable Launch vehicle on April 5, 2010 at the Astrotech facility in Titusville, Fla. Half of the Atlas V five-meter fairing is visible in the background.
Credit: U.S. Air Force

The secretive mission of the United States Air Force’s X-37B space plane has cruised by 500 days of operation in Earth orbit.

The robotic mini-space plane was sent spaceward on the program’s fourth flight on May 20, 2015, orbited by a United Launch Alliance Atlas V rocket from Florida’s Cape Canaveral Air Force Station, kicking off a mission dubbed OTV-4 (short for Orbital Test Vehicle-4).

What the winged space plane’s on-orbit duties are continue to remain a tight-lipped affair, and how long the vehicle will remain in orbit has not been detailed.

Track record

The first OTV mission began April 22, 2010, and concluded on Dec. 3, 2010, after 224 days in orbit. The second OTV mission began March 5, 2011, and concluded on June 16, 2012, after 468 days on orbit. The OTV-3 mission chalked up nearly 675 days in orbit.

A third mission of the Boeing-built X-37B Orbital Test Vehicle was completed on Oct. 17, 2014, when it landed and was recovered at Vandenberg Air Force Base in California following a successful 674-day space mission. The upcoming space plane flight – on the program’s fourth mission — may land at the Kennedy Space Center in Florida.
Credit: Boeing

There is no word on where the craft will wheel to a full-stop. In the past, all three X-37B missions ended at Vandenberg Air Force Base in California, gliding to a landing strip on auto-pilot.

New landing site?

Progress has been made, however, to consolidate its space plane operations, including use of NASA’s Kennedy Space Center (KSC) in Florida as a landing site for the X-37B. A former KSC space-shuttle facility known as Orbiter Processing Facility (OPF-1) was converted into a structure that will enable the Air Force “to efficiently land, recover, refurbish and relaunch the X-37B Orbital Test Vehicle (OTV),” according to Boeing.

Recovery crew members process the X-37B Orbital Test Vehicle at Vandenberg Air Force Base after the program’s third mission complete.
Credit: Boeing

The X-37B vehicle development falls under the Boeing Space and Intelligence Systems in El Segundo, California, the firm’s center for all space and experimental systems and government and commercial satellites.

The Air Force Rapid Capabilities Office is leading the Department of Defense’s OTV initiative, by direction of the Under Secretary of Defense for Acquisition, Technology and Logistics and the Secretary of the Air Force.

Fleet size

Only two reusable X-37B vehicles have been confirmed as constituting the fleet. This current OTV-4 trek is the second flight of the second X-37B vehicle built for the Air Force by Boeing.

Looking like a miniature adaptation of NASA’s now-retired space shuttle orbiter, the reusable military space plane is 29 feet (8.8 meters) long and 9.6 feet (2.9 meters) tall, and has a wingspan of nearly 15 feet (4.6 meters).

The space drone has a payload bay about the size of a pickup truck bed. It has a launch weight of 11,000 pounds (4,990 kilograms) and is powered on orbit gallium arsenide solar cells with lithium-ion batteries.

Air Force X-37B robotic space plane is shown after Vandenberg AFB landing. Third mission of the program is now being flown in Earth orbit – the longest duration flight of the winged spacecraft.
Credit: USAF/Boeing

Onboard payloads

A few payloads onboard the OTV-4 craft have been identified.

Aerojet Rocketdyne has announced that its XR-5A Hall Thruster had completed initial on-orbit validation testing onboard the X-37B space plane.

It is also known that the vehicle carries a NASA advanced materials investigation, as well as an experimental propulsion system developed by the Air Force.

Former shuttle processing area at the Kennedy Space Center has been overhauled by Boeing to prep the military’s secretive X-37B space plane.
Credit: Malcolm Glenn

“It remains a very useful way to test out things,” Winston Beauchamp, deputy undersecretary of the Air Force for Space told Inside Outer Space during last month’s American Institute of Aeronautics and Astronautics (AIAA) meeting in Long Beach, California.

Asked about any interest in increasing the X-37B fleet size, Beauchamp said that the number of vehicles in use is fine due to the pace of experiments it conducts.

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