The rocket is due to launch at 11:50 pm (0450 GMT on Friday), according to SpaceX, which said a backup window is available at the same time the following day.

The US Space Force has said the drone's mission will include "a wide range of test and experimentation objectives."

"These operational demonstrations and experiments comprise of next-generation technologies including laser communications and the highest performing quantum inertial sensor ever tested in space," the service said in a statement last month.

"Mission 8 will contribute to improving the resilience, efficiency and security of U.S. space based communications architectures," it added.

About the size of a small bus, the X-37B US space drone looks like a mini version of the manned space shuttles retired in 2011. On previous missions, the X-37B has carried out tests for US space agency NASA.

In operation since 2010, the X-37B Orbital Test Vehicle was designed for the Air Force by United Launch Alliance by Boeing.

It is 30 feet (nine meters) long, has a 15-foot wingspan and is powered by solar panels.