But for the past 24 years, he has had an extraordinary hobby. He has carefully re-created detailed designs of America's very first nuclear weapons: Little Boy, the bomb that was dropped on Hiroshima, and Fat Man, the one that fell on Nagasaki.
It would be easy to write him off as an eccentric, but experts do not. "He knows a lot," says Johnpierre Paglione, a physics professor at the University of Maryland who recently invited Coster-Mullen to give a lecture about the bomb as part of his class on the Manhattan Project.
"The impressive thing about the work, to me, is how much information he was able to curate over time," says Jeffrey Lewis, a scholar at the Middlebury Institute of International Studies at Monterey.
It all began in 1993 with a scheme to make a little money.
"The 50th anniversary of the bombs was coming up, and I thought I could make little replicas of the bombs and sell them," Coster-Mullen recalls.
Sunday, December 31, 2017
"Coster-Mullen is an unlikely judge of North Korea's nuclear progress. He works nights for a major trucking firm, delivering merchandise to big box stores"