Mike Hughes, a go-it-alone daredevil, limousine stunt driver and self-taught astronaut who professed to believe that the Earth was flat and who was known to supporters as Mad Mike, died in a rocket launch in the California desert on Saturday. He was 64.

Darren Shuster, Mr. Hughes’s publicist, confirmed his death. Mr. Shuster, who was not at the launch on Saturday, said his client’s last message to him that morning asked, “Is the media going to be there?”

Around 2 p.m. on Saturday, San Bernardino County sheriff’s deputies were called to a rocket launch on private property in Barstow, Calif., about 120 miles northeast of Los Angeles. “A man was pronounced deceased after the rocket crashed in the open desert,” the sheriff’s office said in a statement.

A video of the launch posted by Justin Chapman, a freelance journalist, shows Mr. Hughes’s steam-powered rocket shooting off into the sky and a parachute falling down to the earth. Moments later, the rocket plummets and crashes near the launch site.