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The wingspan in metres of the world’s largest aircraft, which recently hit an important milestone in its path to the skies with its first high-speed taxi test.

Called the Stratolaunch, the plane is the brainchild of Microsoft co-founder Paul Allen and has been in development since 2011. It is nearly double the width of a Boeing 747 (60m), weighs 580 tons, and carries six engines on 28 wheels.

At its runway test in Mojave, California, last month, it hit a top speed of 74km/h.

The mission is to have it be used as a launch vehicle for space rockets and the developers hope it will be airborne some time next year.