Updated: 2019-08-25

X-37B handout.
Credit: Boeing/Inside Outer Space Screengrab


The classified U.S. Air Force X-37B space plane program  winged its way to a new milestone in its hush-hush current mission. The craft set a new long-duration record in circling the Earth – eclipsing a previous long-duration flight of 717 days, 20 hours and 42 minutes.

Also tagged as the Orbital Test Vehicle (OTV) – 5 mission, this currently orbiting space plane was lofted into low Earth orbit back on September 7, 2017 – speeding around the planet now for over 1 year and 11 months.

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 last and longest Air Force’s X-37B mission, OTV-4 — after 717 days of flight — touched down at NASA’s Kennedy Space Center Shuttle Landing Facility May 7, 2017 – a tarmac landing that was a first for the program. All prior missions had ended with a landing strip touchdown at Vandenberg Air Force Base in California.

The X-37B Orbital Test Vehicle mission 4 (OTV-4), the Air Force’s unmanned, reusable space plane, landed at NASA’s Kennedy Space Center Shuttle Landing Facility May 7, 2017.
Credit: USAF

The now-orbiting OTV-5 spacecraft was lofted skyward atop a SpaceX Falcon 9 booster from Launch Complex 39A at NASA’s Kennedy Space Center in Florida.



Record setting

Each X-37B/OTV mission has set a new flight-duration record for the program:

OTV-1 began April 22, 2010, and concluded on Dec. 3, 2010, after 224 days in orbit.

OTV-2 began March 5, 2011, and concluded on June 16, 2012, after 468 days on orbit.

OTV-3 chalked up nearly 675 days in orbit before finally coming down on Oct. 17, 2014.

OTV-4 flew for nearly 718 days during its mission, extending the total number of days spent in space for the OTV program at that point to 2,085 days. It was launched in May 2015 and landed in May 2017.

Skywatcher and satellite tracker, Ralf Vandebergh of the Netherlands, has released a new image of an over flight of the U.S. Air Force secretive X-37B space plane, also known as Orbital Test Vehicle – 5.
Credit: Ralf Vandebergh

Touchdown when?

Bottom line: Exactly when the OTV-5 space plane will land is unknown. Boeing told Inside Outer Space that it will not issue a statement on the record-setting flight, referring this reporter to the U.S. Air Force. Repeat emails to the Pentagon have not been answered to date.

What is know is that the last Air Force’s X-37B mission, OTV-4 — after 718 days of flight — glided into NASA’s Kennedy Space Center Shuttle Landing Facility on May 7, 2017 – a first for the program. 

Meanwhile, a tantalizing thought: Could the program shoot for two X-37B vehicles in Earth orbit at the same time?

An earlier X-37B Orbital Test Vehicle in the encapsulation cell at the Astrotech facility in April 2010, in Titusville, Fla.
Courtesy photo/USAF

According to some launch websites, a United Launch Alliance Atlas 5 rocket will rocket the AFSPC 7 mission for the U.S. Air Force this December. The mission’s primary payload is the X-37B, with liftoff from Cape Canaveral Air Force Station – SLC-41.

Prior to launch of OTV-5, Randy Walden, the director of the Air Force Rapid Capabilities Office said there were many firsts on this mission, making it a milestone for the program. “It is our goal to continue advancing the X-37B OTV so it can more fully support the growing space community.”

The Air Force also noted that the fifth OTV mission was launched into, and will be landed from, a higher inclination orbit than prior missions to further expand the X-37B’s orbital envelope.

Official SpaceX OTV-5 mission patch.
Credit: SpaceX

Space-based demonstrations

The missions of the X-37B space planes are carried out under the auspices of the Air Force Rapid Capabilities Office, and mission control for OTV flights are handled by the 3rd Space Experimentation Squadron at Schriever Air Force Base in Colorado. This squadron oversees operations of the X-37B Orbital Test Vehicle.

This Schriever Air Force Base unit is tagged as the Air Force Space Command’s premier organization for space-based demonstrations, pathfinders and experiment testing, gathering information on objects high above Earth and carrying out other intelligence-gathering duties.

Back to hangar for another flight day. U.S. Air Force X-37B/OTV-4 is rolled into facility after its May 7 landing at Kennedy Space Center.
Credit: Michael Martin/SAF

And that may be a signal as to what the robotic craft is doing — both looking down at Earth and upward.

Pushing the boundaries

In the personal view of Joan Johnson-Freese, a professor in the National Security Affairs Department at the Naval War College in Newport, Rhode Island:

“With each flight the Air Force appears to be pushing the boundaries of what the OTV can do – or what they hope it can do. What the eventual plans for the vehicle are remain unknown – maybe even by the Air Force,” Johnson-Freese told Inside Outer Space.

“But, as a test vehicle, the Air Force and Boeing are trying to determine its flexibility, capabilities, and duration. These test flights began going on 10 years ago so they’ve clearly gathered a considerable amount of information,” Johnson-Freese adds. In addressing the classified nature of the project, understandably it raises concerns in some other countries, she notes.

“When there is mystery there is speculation, and often of a worst-case basis when militaries are involved. Certainly if China were conducting these kinds of tests, there would be lots of worst-case speculation from the Pentagon,” Johnson-Freese concludes.

Credit: Boeing/Inside Outer Space Screengrab


On-orbit testing

On this latest clandestine mission of the space plane, all that’s known according to Air Force officials is that one payload flying on OTV-5 is the Advanced Structurally Embedded Thermal Spreader, or ASETS-II.

Developed by the U.S. Air Force Research Laboratory (AFRL), this cargo is testing experimental electronics and oscillating heat pipes for long duration stints in the space environment.

According to AFRL, the payload’s three primary science objectives are to measure the initial on-orbit thermal performance, to measure long duration thermal performance, and to assess any lifetime degradation.

Credit: Illustration by Giuseppe De Chiara

Boeing fleet

The classified X-37B program “fleet” consists of two known reusable vehicles, both of which were built by Boeing.

The X-37B Orbital Test Vehicle was fabricated at several Boeing locations in Southern California, including Huntington Beach, Seal Beach and El Segundo. The program transitioned to the U.S. Air Force in 2004 after earlier funded research efforts by Boeing, NASA and the Defense Advanced Research Projects Agency.

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

The X-37B space plane has a payload bay of 7 feet (2.1 meters) by 4 feet (1.2 meters), a bay that can be outfitted with a robotic arm. X-37B has a launch weight of 11,000 lbs. (4,990 kilograms) and is powered on orbit by gallium-arsenide solar cells with lithium-ion batteries.

This size chart shows how the Boeing-built X-37B robot space plane compares to NASA’s space shuttle, a larger version of the spacecraft called the X-37C and an Atlas 5 rocket.
Image: © AIAA/Grantz/Boeing/provided to Inside Outer Space via AIAA

Derivative plan

Curiously, back in late 2011, a technical paper popped up at a major aerospace conference. It outlined new plans for the spacecraft and a scaled-up version to support space station cargo deliveries or even haul astronauts into orbit.

An X-37B OTV and derivatives plan assessment sketched out a variety of scaled-up versions of the X-37B space plane.

What is not known, however, is whether such a plan advanced within Boeing or the Air Force.

For more information on this derivative plan from 2011, go to:


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