From May 20, the X-37B spy mission will be on a new mission. Operated by the US Air Force, the spy plane looks like a smaller version of the retired Space Shuttle. Mission details remain a secret.

Phantom Works division of Boeing has designed the plane, which is a 29-foot spacecraft having a wingspan of 15-foot and also has a cargo bay measuring 7 feet in length and 4 feet in width.

The fourth test flight of the spy plane aboard an Atlas 5 rocket plane will take place between 10.45 am and 2.45pm EDT. Mission engineers will be able to tell the exact time of the launch on the day of the mission. Until now, it is said that there is a 60% chance of favorable conditions for liftoff.

In the first three test flight, a pair of spacecraft was used and they logged 1,368 days in space. After their flights, they landed at Vandenberg Air Force Base in California. It is said that these three flights have spent more time in space in comparison to combined total of 135 flights over three decades.

“We are excited about our fourth X-37B mission. With the demonstrated success of the first three missions, we're able to shift our focus from initial checkouts of the vehicle to testing of experimental payloads”, said Randy Walden, director of the Air Force Rapid Capabilities Office.

During the fourth test flight, Air Force officials are going to test many systems present aboard the X-37B. Among the systems to be checked is an advanced form of electrical propulsion. The launch will also carry the LightSail project being managed by The Planetary Society.

This test flight will reveal how well new technologies work in a small spacecraft that will operate like a sailboat in space. In 2016, the first operational flight of the LightSail spacecraft design will take place.