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UPDATE: Liftoff window has been delayed to 3:45 p.m. ET.

On Tuesday afternoon, a rocket the size of a 20-story building, containing 27 engines and a cherry-red Tesla Roadster as its payload, is slated to lift off from NASA’s Kennedy Space Center in Florida. It will be the maiden flight of Space X’s Falcon Heavy, the most powerful rocket to launch in 45 years, since NASA’s Saturn V, which last flew in 1973.