World's largest airplane is rolled out (photo)

Stratolaunch -- which is designed to release rockets that will carry satellites into space -- has a 385-foot wingspan, features six engines used by the Boeing 747, stands 50 feet tall and can carry more than 500,000 pounds of payload. And it has those 28 wheels.

The twin-fuselage aircraft, the baby of Microsoft co-founder Paul Allen, was pulled out of its Mojave Air and Space Port hangar in California to begin fueling tests -- the first of many ground tests.

Jean Floyd, Stratolaunch's chief executive officer, said the goal is to have a launch demonstration as early as 2019.