The US Air Force is about to launch a secret spacecraft

The US Air Force is about to launch the fourth X-37B flight, the unmanned spacecraft to join a secret program of this force.

The US Air Force is about to launch the X-37B spacecraft

The Atlas V 501 space rocket will put the X-27B into orbit on a mission called Orbital Test Vehicle 4 (OTV-4) on May 20 . The US Air Force will join other partners, including the US Aerospace Agency (NASA), to test a number of space technologies.

The secret spacecraft X-27B will be launched on May 20.(Photo: US Air Force)

The flight will test the propulsion system, developed by the US Air Force Research Laboratory and the Center for Missile and Space Systems. In addition, X-37B will carry out an advanced testing of NASA materials.

"We are very pleased with the experiments arranged for OTV-4. We will continue to evaluate improvements in the space vehicle's operability, but it is also an honor to organize appropriate experiments This work, which helps promote the most advanced space technology, " said Randy Walden, director of the US Air Force's Rapid Response Agency.

The X-37B is the UAV 's unmanned space aircraft (UAV) . The spaceship looks similar to a NASA space shuttle, with a length of 8.8 m, height of 2.9 m and a span of 4.6 m. The secret about X-37B has raised many assumptions around its purpose for the past time.

The X-37B program completed the latest mission on October 17 last year, landing after 674 days in orbit. Its first mission began on April 22, 2010, lasting 224 days . The two flights were then carried out in 2011 and 2012.