WASHINGTON – Rocket scientist and retired Navy Capt. Robert Truax collaborated with physicist Robert Goddard in the 1940s and helped design some of the military’s most advanced ballistic missiles during the Cold War.

He spent part of his retirement from the Navy designing a steam-powered rocket to propel daredevil Evel Knievel over Snake River Canyon in Idaho. It might have worked, but a parachute malfunctioned.

“Old Evel crawled up out of the river and said, ‘Bob, now what have you got up your sleeve?”‘ Truax told Popular Mechanics in 1981. “I told him I could make him the world’s first private astronaut.”

Truax, who died of prostate cancer Sept. 17 at age 93 in Valley Center, Calif., was an engineer with unorthodox ideas and grand ambitions. Inspired by an enthusiasm for private space flight, he took out a classified advertisement in The Wall Street Journal:

“Wanted: risky capital for risky project. Man or woman interested in becoming the world’s first private astronaut — must be in reasonably good health and able to produce 100,000 in spendable money.”

So began his work on the X-3, which cannibalized many parts from the 1974 Knievel escapade.

Truax received more than 2,000 requests to fly it, including from a pilot in the Royal Australian Air Force, a millionaire tortilla magnate and a Beach Boys roadie.

But many of the would-be space travelers bowed out when they learned just how dangerous Truax’s rocket was. Because of budget constraints and weight, the spaceship was not equipped with an emergency oxygen supply or escape pod.