Photos: Air Force's 2nd Secretive X-37B Space Plane Flight

Aft and Mid APAS X-37B Configurations

These designs from a Boeing study show configuration for a crewed space plane (X-37C) derived from the unmanned X-37B spacecraft. The designs could carry up to six astronauts to low-Earth orbit and include autonomous and piloted flight capabilities.

X-37B Size Comparison

This size chart shows how the Boeing-built X-37B robot space plane compares to NASA's space shuttle, a larger version of the spacecraft called the X-37C and an Atlas 5 rocket.

X-37B Derivatives

This Boeing graphic depicts the steady evolution of the robotic X-37B space plane design into a larger vehicle that could potentially carry astronauts. The process incrementally retires risk as capabilities increase, according to Boeing officials.