Air Force Delays Launch of Mystery X-37B Space Plane

This week's planned launch of a secretive U.S. Air Force space plane prototype has been delayed one day to allow NASA's shuttle Discovery a clear shot at returning to Earth Tuesday morning.

The unmanned X-37B space plane, known as the Orbital Test Vehicle, was slated to launch into space Wednesday from Cape Canaveral Air Force Station in Florida on a secretive mission of unknown duration.

But the mission will now blast off Thursday evening between 7:52 p.m. and 8:01 p.m. EDT (2352-0001 GMT) instead due to the delayed return of Discovery at the nearby Kennedy Space Center, according to officials with United Launch Alliance, which is providing space plane's Atlas 5 rocket.

The shuttle Discovery and a crew of seven astronauts were scheduled to land Monday morning at the Kennedy Space Center, but were thwarted by low clouds and rain at the NASA spaceport. The space agency will try again early Tuesday.

It's not the first delay this month for the X-37B spacecraft.

Air Force officials originally planned to launch the space plane Monday evening. They delayed the mission last week when NASA extended Discovery's current spaceflight by one day, making the shuttle's planned landing the same day.

Typically, two days between shuttle landings and rocket launches are required in order to reset the Eastern Range, which NASA shares with the nearby Cape Canaveral Air Force Station, for new space missions.

Air Force officials have shared few details of the upcoming X-37B test flight, an orbital debut for the reusable space plane. [Graphic: X-37B spacecraft revealed.]

"The first mission will emphasize proving technologies necessary for long duration reusable space vehicles with autonomous re-entry and landing capabilities," Air Force spokeswoman Angie Blair told SPACE.com recently.

The small spacecraft resembles a miniature space shuttle and is equipped with its own payload bay about the size of a pickup truck bed.

According to released specifications, the X-37B space plane weighs about 11,000-pounds and is just over 29 feet in length. It stands slightly more than 9 1/2 feet in height and has a wingspan just over 14 feet across.

The spacecraft was built by Boeing's Phantom Works division and its new mission is overseen by the Air Force Rapid Capabilities Office.

The X-37B is designed to launch into space unmanned to heights of up to 500 nautical miles, loiter in orbit for up to 270 days, and then re-enter the Earth's atmosphere to make an automated landing at Vandenberg Air Force Base in California.

The spacecraft originally began its life as a NASA X-37 project to develop a new generation of reusable spacecraft. NASA shuttered the project in 2004 when funding dried up and turned the space plane over to the Defense Advanced Research Projects Agency (DARPA).

The Air Force took control of the prototype in 2006, though exactly what the X-37B will do on its first mission ? dubbed Orbital Test Vehicle 1 (OTV-1) ? remains a mystery.

Some outside observers have said the Air Force's upcoming test launch could be seen by other countries as another push by the United States into the possible weaponization of space. Others, however, contend that the results of the X-37B's debut spaceflight could lead to better commercial space planes in the future.

Mark Sirangelo, corporate vice president of space systems for the commercial spaceflight company Sierra Nevada Corp., has said the Air Force's test flight is of great interest to his company. Sierra Nevada is developing a commercial space plane called Dream Chaser, which is also designed to launch atop an Atlas rocket.

"We expect that this [X-37B] launch experience will also help our knowledge of the Atlas's performance relative to lifting body vehicles," Sirangelo told SPACE.com in a recent interview. "The X-37 seems to be focused on military needs and is an unmanned demonstration while we are focusing primarily on a crewed civil and commercial mission profile."

• Photos of the X-37B Space Plane
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• Some Details of Secretive X-37B Space Plane Revealed

SPACE.com Space Insider Columnist Leonard David contributed to this report from Boulder, Colo.