SpaceX Launching X-37B Space Plane between 9:50 am and 2:55 pm ET

SpaceX is counting down to launch the U.S. Air Force's X-37B space plane today, Sept. 7, sometime between 9:50 a.m. EDT and 2:55 p.m. EDT (1350-1855 GMT) from Pad 39A of NASA's Kennedy Space Center in Cape Canaveral, Florida. You can watch it live here, courtesy of SpaceX.

SpaceX will also attempt to land the first stage of its Falcon 9 rocket at the company's Landing Zone 1 at the nearby Cape Canaveral Air Force Base.

The classified mission, called OTV-5, will be the fifth secret flight of an X-37B space plane for the U.S. Air Force. Weather is forecast to be 50 percent go for today's launch. SpaceX has a backup launch day of Friday, Sept. 8, if needed.

The fifth OTV mission continues to advance the X-37B's performance and flexibility as a space technology demonstrator and host platform for experimental payloads," Air Force officials said in a statement. "This mission carries small satellite ride shares and will demonstrate greater opportunities for rapid space access and on-orbit testing of emerging space technologies."

The X-37B looks like a miniature version of NASA's space shuttles, though two of the small robotic military space planes could fit inside a NASA shuttle payload bay. The X-37B is 29 feet (8.8 meters) long and 9.6 feet (2.9 m) tall, and has a wing span of nearly 15 feet (4.6 m).

Here's a look at the past flights:

• The first OTV mission began April 22, 2010, and concluded Dec. 3, 2010, after 224 days in orbit.
• The second OTV mission began March 5, 2011, and concluded June 16, 2012, after 468 days in orbit.
• The OTV-3 mission chalked up nearly 675 days in orbit when it landed Oct. 17, 2014. That mission also was the first to reuse an X-37B space plane.
• On May 7, 2017, OTV-4 landed at NASA's Kennedy Space Center Shuttle Landing Facility — a first for the program, as all previous OTV missions ended with a tarmac touchdown at Vandenberg Air Force Base in California.
• The OTV-4 mission conducted in-orbit experiments for 718 days during its mission, extending the total time spent in orbit for the OTV program to 2,085 days.