The mysterious spaceplane is built by Boeing and operated by the Air Force Rapid Capabilities Office and the Space Force. Its last mission ended a little over a year ago after spending 2.5 years in low-Earth orbit. 

"The X-37B continues to equip the United States with the knowledge to enhance current and future space operations," Chief of Space Operations Gen. B. Chance Saltzman said in a statement. 

Saltzman continued: "X-37B Mission 7 demonstrates the USSF's commitment to innovation and defining the art-of-the-possible in the space domain."