A US military space plane sets off on another secret mission expected to last years

The US military's X-37B spaceplane lifted off on Thursday on another secret mission expected to last at least two years.

Like previous missions, the reusable aircraft, which resembles a small space shuttle, carried secret experiments. There is no one on board.

The spaceplane aboard a SpaceX Falcon Heavy rocket took off from NASA's Kennedy Space Center overnight, more than two weeks late due to technical problems.

This is the seventh flight of the X-37B, which has logged more than 10 years in orbit since its debut in 2010.

The final flight, the longest to date, took two and a half years before ending on the runway at Kennedy Airport a year ago.

Space Force officials have not said how long this orbital test vehicle will remain aloft or what is on board other than a NASA experiment to measure the effects of radiation on materials.

The X-37B, built by Boeing, resembles retired NASA space shuttles. But it is only a quarter of the size and is 29 feet (9 meters) long. No astronauts are needed; The X-37B has an independent landing system.

They take off vertically like rockets but land horizontally like airplanes, and are designed to orbit between 150 miles and 500 miles (240 kilometers to 800 kilometers) high. There are two X-37B aircraft stationed in the former shuttle hangar at Kennedy.

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