An unmanned Atlas rocket carrying a miniature space shuttle has blasted off from Cape Canaveral, Florida on a test flight that could last as long as nine months.

The 20-storey rocket, built under a joint venture of Lockheed Martin and Boeing, had a picture perfect lift-off and soared over the Atlantic Ocean, heading toward orbit.

The point of the military project is to test a next-generation space shuttle, which is due to retire in mid-September.

Unlike the current Space Shuttle, the X-37B is not meant to carry people and is designed to spend as long as nine months in space, then land autonomously on a runway.

If the flight of the X-37B is successful, the Air Force plans to launch a second vehicle in 2011.

The aircraft's stated mission is to examine safer and less costly re-entry possibilities, although there is speculation among military and security insiders that the X-37B will be used to position satellites and other types of surveillance.

The Air Force spacecraft's launch has been delayed several times, and was most recently postponed earlier this week to accommodate Discovery's return.