Exactly when the space plane will land is unknown.
The previous X-37B mission touched down at KSC's Shuttle Landing Facility on May 7, 2017 — a first for the program. All prior missions had ended with a tarmac touchdown at Vandenberg Air Force Base in California.
Several website postings say that the Air Force aims to launch the sixth X-37B mission, OTV-6, sometime this year aboard a United Launch Alliance Atlas V (501) rocket. The liftoff would be from Cape Canaveral Air Force Station’s Space Launch Complex-41.
The classified X-37B program "fleet" consists of two known reusable vehicles, both of which were built by Boeing.
The Orbital Test Vehicles were 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 measuring 7 feet (2.1 m) by 4 feet (1.2 m) that can be outfitted with a robotic arm. Each 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.
Milestone for the program
Prior to the 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," Walden said.
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.
Ted Molczan, a Toronto-based satellite analyst, told Inside Outer Space that OTV-5 began September 2018 in an orbit about 243 miles (391 kilometers) high, inclined 54.5 degrees to the equator. Its ground track repeated every three days, after 46 revolutions.
"In mid-September, it lowered its altitude to 214 miles (344 km), which caused its ground track to repeat every two days, after 31 revolutions," Molczan said. "It appeared to still be in approximately that orbit when last observed, on January 26, by Alberto Rango, from Rome, Italy."
Repeating ground tracks are very common, Molczan said, especially for spacecraft that observe the Earth. "I do not know why OTV has repeating ground tracks," he said.
Kevin Fetter, an amateur Canadian satellite spotter in Brockville, Ontario, caught the OTV-5 craft zip by above a bright star.
X-37B Military Space Plane's Latest Mystery Mission Passes 600 Days
Exactly what it's doing up there is unclear.
The U.S. Air Force's X-37B space plane has now been circling Earth for more than 600 days on its latest mystery mission.
The reusable robotic vehicle, which looks like a miniature version of NASA's space shuttle orbiters, launched atop a SpaceX Falcon 9 rocket from NASA's Kennedy Space Center in Florida on Sept. 7, 2017.
As of today (April 30), the space plane has been aloft for 601 days, on a mission known as Orbital Test Vehicle 5 (OTV-5) because it's the fifth flight of the X-37B program.
Related: The X-37B Space Plane: 6 Surprising Facts
It's unclear what exactly the spacecraft is doing up there. X-37B missions are classified, and Air Force officials tend to speak of project goals in general terms, as this excerpt from the X-37B fact sheet shows: "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."
Still, the Air Force does divulge some payloads flying on X-37B missions. For example, we know that OTV-5 includes the Advanced Structurally Embedded Thermal Spreader experiment (ASETS-II), which is measuring the performance of electronics and oscillating heat pipes in the space environment.
The Air Force has at least two X-37B vehicles, both of which were built by Boeing. Each space plane is 29 feet (8.8 meters) long and 9.6 feet (2.9 m) tall, with a wingspan of almost 15 feet (4.6 m). The solar-powered spacecraft have payload bays about the size of a pickup-truck bed.
The X-37B launches vertically and lands horizontally on a runway, like the space shuttle orbiters did.
OTV-5 is not, so far, the longest-duration X-37B mission, though the outing will earn that distinction if the established pattern holds: Each OTV flight has lasted longer than its predecessors:
Mysterious X-37B Military Space Plane Caught on Camera (Photo)
We still don't know what the X-37B is doing up there, however.
The U.S. Air Force's X-37B robotic space plane in orbit, as photographed by satellite tracker Ralf Vandebergh.
(Image: © Ralf Vandebergh)
Skywatcher and satellite tracker Ralf Vandebergh of the Netherlands recently caught a rare glimpse of the U.S. Air Force's secretive X-37B space plane.
Vandebergh said he'd been hunting for the robotic spacecraft for months and finally managed to track it down in May. But it took a bit longer to get photos of the vehicle.
"When I tried to observe it again [in] mid-June, it didn't meet the predicted time and path," Vandebergh explained. "It turned out to have maneuvered to another orbit. Thanks to the amateur satellite observers' network, it was rapidly found in orbit again, and I was able to take some images on June 30 and July 2."
The X-37B's recent passes were almost overhead, Vandebergh added.
The X-37B, also known as the Orbital Test Vehicle (OTV), looks like a miniature version of NASA's retired space shuttle.
"It is really a small object, even at only 300 kilometers [186 miles] altitude, so don't expect the detail level of ground-based images of the real space shuttle," Vandebergh said.
Taking this into consideration, the newly captured imagery far exceeded Vandebergh's expectations.
"We can recognize a bit of the nose, payload bay and tail of this mini-shuttle, with even a sign of some smaller detail," he said.
Vandebergh captured the photos using a 10-inch F/4,8 aperture Newtonian telescope with an Astrolumina ALccd 5L-11 mono CMOS camera. Tracking was fully manual through a 6×30 finderscope, he said.
The X-37B has winged past 666 days of flight on this latest mission, which is called OTV-5 because it's the fifth flight for the program.
OTV-5 began on Sept. 7, 2017, with a launch atop a SpaceX Falcon 9 boosterfrom NASA's Kennedy Space Center (KSC) in Florida.
X-37B missions are carried out under the auspices of the Air Force Rapid Capabilities Office, and mission control for OTV flights is handled by the 3rd Space Experimentation Squadron at Schriever Air Force Base in Colorado. This squadron oversees operations of the X-37B and 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.
And that may be a signal as to what the robotic craft is doing — both looking down at Earth and upward.
Related: US Air Force's Secretive X-37B Space Plane (Infographic)
Each X-37B mission has set a new flight-duration record for the program:
Most X-37B payloads are classified, and the Air Force releases few details about the spacecraft's orbit and activities. The only OTV-5 payload that Air Force officials have revealed 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 initial on-orbit thermal performance, to measure long duration thermal performance, and to assess any lifetime degradation.