World's biggest aircraft to begin testing

The Stratolaunch carrier, built by Microsoft billionaire Paul Allen's Stratolaunch Systems, has the longest wingspan of any aircraft ever built — and it just rolled out of its supersized hangar for the first time to begin its first fueling, engine, and taxi tests before its first flight test later this year, per Popular Mechanics.

Put in perspective: The 500,000-pound, six-engined Stratolaunch carrier's wingspan is 385 feet. That's 25 feet longer than the length of a football field.

Its purpose: The aircraft is designed to carry rockets into the stratosphere, where it'll drop them before they fire and launch into space. It's could improve the reliability and cost-effectiveness of orbital spaceflight, but the aircraft's first launch test isn't scheduled until 2019.