LOS ANGELES (AP) — Billionaire Paul G. Allen's Stratolaunch, a massive aircraft designed to launch rockets into space from high altitude, has been rolled out of its hangar for the first time in preparation for testing.

Here are things to know about the program that has been underway since 2011:

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GIGANTIC

The Stratolaunch aircraft is enormous, with a wingspan totaling 385 feet (117 meters), longer than the wingspan of any other aircraft and greater than the length of an American football field. Its twin fuselages stretch 238 feet.

By comparison, the H-4 flying boat — nicknamed Spruce Goose a...