A prototype spaceplane developed for the US military has been launched into orbit from Florida.
The X-37B, which has been likened to a scaled-down space shuttle, blasted off from Cape Canaveral Air Force Station at 1952 EDT (2352 GMT) on Thursday.
The military vehicle is unpiloted and will carry out the first autonomous re-entry and landing in the history of the US space programme.
The spacecraft can return experiments to Earth for inspection and analysis.
At 9m (29ft) long and with a 4.5m (15ft) wingspan, the reusable spaceplane is about one-quarter the size of the shuttle, with a large engine mounted at the rear of the ship for orbit changing.
The project could lead to the military's first operational spaceplane
"It might be at this point in time that [the Air Force is] going to roll the dice and see if something good happens." Dr Joan Johnson-Freese US Naval War College
And while the space shuttle uses a fuel-cell power-system, the military vehicle is powered by a solar array and lithium-ion batteries.
The precise objectives and cost of the programme are secret, but the first few flights will allow officials to evaluate the vehicle's performance and ensure components and systems work the way they are supposed to.
"The top priority technology demonstration on this first flight is the vehicle itself," Gary Payton, the US Air Force's deputy under secretary for space programs, told journalists on a teleconference this week.
"Getting it into orbit, getting the payload bay doors open, the solar array deployed, learning about on-orbit attitude control and bringing it all back."
The X-37B was launched vertically atop an Atlas V rocket. The Air Force (USAF) says the vehicle will be used to test advanced guidance, navigation and control, thermal protection systems, avionics and high temperature structures and seals.
The Pentagon has not specified a duration for this mission, but the X-37B is designed to operate on orbit for up to 270 days: "In all honesty, we don't know when it's coming back for sure. It depends on the progress that we make with the on-orbit experiments, the on-orbit demonstrations," said Mr Payton.
Once the mission is complete, a command will be sent from the ground prompting the 5,000kg (11,000lb) spaceplane to fire its engine to re-enter the atmosphere - reportedly for landing at Vandenberg AFB in California.
