GOLDEN, Colo. — As the U.S. Air Force’s unmanned X-37B spaceplane surpasses 430 days in orbit, its Boeing-built twin is being prepared to return to space this fall.

The X-37B that has been circuiting Earth since early 2011 is the second spacecraft of its kind built for the Air Force by Boeing’s Phantom Works. Known as the Orbital Test Vehicle 2, or OTV-2, the spaceplane’s classified mission is being carried out by the Air Force Rapid Capabilities Office.

The robotic X-37B space plane is a reusable spacecraft that resembles a miniature space shuttle. The Air Force launched the OTV-2 mission March 5, 2011, with an unmanned Atlas 5 rocket lofting the spaceplane into orbit from the Cape Canaveral Air Force Station in Florida.

Gen. William Shelton, commander of Air Force Space Command, briefly saluted the high-flying X-37B space plane April 17 during his remarks at the 28th National Space Symposium in Colorado Springs, Colo.

“Our second X-37 test vehicle has been on orbit for 409 days now” — much longer than the 270-day baseline design specifications, Shelton said. “Although I can’t talk about mission specifics, suffice it to say this mission has been a spectacular success.”

In a follow-up meeting with reporters, Shelton said: “It’s doing wonderful.” When asked specifically about when the craft will be brought back down to Earth, his response was guarded.

“When we’re through with it … it’s going great,” Shelton said.

U.S. Air Force Maj. Tracy Bunko, spokeswoman for the X-37B project, said that the spaceplane’s current mission “is still on track … and still ongoing.”

Bunko said that a third flight of an X-37B spacecraft — slated for liftoff this October atop a United Launch Alliance Atlas 5 rocket — will use the same craft that flew the first test flight, the OTV-1 mission, in 2010. That maiden voyage of the X-37B spaceplane lasted 225 days. It launched into orbit April 22, 2010, and landed Dec. 3, zooming in on autopilot over the Pacific Ocean and gliding down onto a specially prepared runway at Vandenberg Air Force Base in California.

Each X-37B spaceplane is about 8.8 meters long and 4.5 meters wide. It has a payload bay about the size of a pickup truck bed and is outfitted with a deployable solar array power system.

What is not known about these space vehicles is the nature of the payloads they carry. What purposes they serve is classified.

Last March in a Washington briefing with reporters, Shelton advised that the winged, reusable robot plane is a vehicle the Air Force wants to keep using. But there is currently no go-ahead to add spaceplanes (beyond the two already built) that would increase the fleet size, he said.

When the second X-37B cruised by its one-year milestone in orbit in March, Lt. Col. Tom McIntyre of the Air Force Rapid Capabilities Office lauded the spacecraft’s endurance run.

“We are very pleased with the results of ongoing X-37B experiments. The X-37B program is setting the standard for a reusable spaceplane and, on this one-year orbital milestone, has returned great value on the experimental investment,” McIntyre said. “Upon completion of all objectives, we look forward to bringing the mission to a safe, successful conclusion.”

According to Ted Molczan, a Toronto-based leader in a network of amateur skywatchers who keep an eye on the whereabouts of spacecraft, the X-37B/OTV-2 has maintained its orbit since mid-August of last year.

Last observed on April 22 by fellow skywatcher Greg Roberts of South Africa, the craft was in a 42.8 degree, 332 kilometer by 341 kilometer orbit, Molczan said.

“It makes frequent small maneuvers to maintain that altitude against the significant atmospheric drag that is present. That orbit causes its ground track to repeat nearly precisely every two days,” Molczan added.

“Ground tracks that repeat at intervals of two, three or four days, have long been favored for U.S. imagery intelligence satellites, so this may be a clue to the mission of OTV-2,” he said.

An intriguing sidelight to the X-37 program is whether Boeing’s Phantom Works is keen on using the spacecraft for other, nonmilitary missions, or even upgrading the X-37 spaceplane concept for human spaceflight.

Last year at Space 2011, a conference organized by the American Institute of Aeronautics and Astronautics (AIAA), an X-37B derivatives plan was sketched out by Arthur Grantz, chief engineer for Experimental Systems Group at Boeing Space and Intelligence Systems in Seal Beach, Calif.

Grantz detailed a vision for the spacecraft and scaled-up versions to support space station cargo deliveries and even carry astronauts into orbit.

In March, Boeing declined to offer any more details about potential new roles for X-37B. “That AIAA presentation was a one-time event and we are not saying anything more publicly about the X-37B,” said Boeing spokeswoman Diana Ball. “Sorry we cannot help you out this time.”



Boeing-built X-37B Approaches Predecessor’s Flight Distance Record

X-37B Wraps Up 7-month Mission Shrouded in Secrecy

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...