The daredevil “Mad” Mike Hughes was killed in a rocket launch gone wrong Saturday in Barstow, Calif., two witnesses to the accident confirmed. He was 64.

It was the third launch for Hughes in one of his homemade rockets and part of his eventual plan to be able to determine for himself, up in the sky, if the Earth was as flat as he proclaimed to believe.

A steel ladder was attached to the rocket’s launch ramp to make it easier for Hughes to enter the rocket’s cockpit.