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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.

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Louisiana braces for 3rd hurricane in 2 months as Zeta closes in

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Zeta strengthened into a hurricane again early Wednesday and was on track to make landfall in southeastern Louisiana by the afternoon, per the National Hurricane Center.

The state of play: Louisiana Gov. John Bel Edwards (D) requested a pre-landfall Federal Declaration of Emergency in a letter to President Trump on Tuesday.

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The Pennsylvania National Guard was mobilized Tuesday during a tense second night of protests in Philadelphia over the fatal police shooting of Walter Wallace, a 27-year-old Black man.

Driving the news: Philadelphia Mayor Jim Kenney (D) and Police Commissioner Danielle Outlaw said in a joint statement a "full investigation" would be launched to answer questions that arose from video that captured part of Monday's incident.

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Illustration: Sarah Grillo/Axios

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