The X-37B looks a bit like NASA's recently retired space shuttle, but it's far smaller. The X-37B is about 29 feet (8.8 meters) long and 15 feet (4.5 m) wide, with a payload bay about the size of a pickup truck bed. Two X-37B vehicles could fit inside the payload bay of a space shuttle.
The spacecraft's orbital longevity is enabled by its solar array, which generates power after deploying from its payload bay.
Cargo and crew carrier? While the X-37B currently flies only hush-hush missions for the Defense Department, its spaceflight role may be expanded in the future.
In its current state, the vehicle could fly cargo missions to the International Space Station, docking to the orbiting outpost's common berthing port, Boeing officials have said.
Boeing is also looking into building a larger variant of the spacecraft called the X-37C, which could ferry up to six astronauts to the space station. The X-37C would be 65 to 80 percent bigger than the X-37B.