US: Mysterious robotic spacecraft launched for fourth secretive mission

A mysterious US space plane has been launched for its fourth secretive mission.

The mission by the X-37B robotic plane will involve an orbital flight, the fourth in five years.

The reusable craft’s third mission went on for a record 675 days in space, following which it landed on a California air base last October.

The plane’s mission and objectives remain secret, but the US air force did reveal that it would test a new type of electric engine that “produces thrust by ionizing and accelerating a noble gas.”

Tagged as: US space plane, secretive mission, X-37B robotic plane, orbital flight, reusable craft, California air base, world news