Timmons, son of a railroad shop machinist, grew up in Indianapolis. He enlisted in the Army on 29 February 1944, earning two bronze stars in World War II. After the war he went to college, graduating from the University of Washington in 1950, and entered the aerospace industry. In the 1960's he was in charge of Apollo Applications projects at Martin Marietta. This finally materialized in a scaled-back form as Skylab, and he became the company's Project Manager for the Multiple Docking Adapter portion of that space station. In 1971 he conceived of the idea of flying student payloads aboard NASA missions.
After Skylab he was put in charge of Martin Marietta's contract to produce the expendable external tank for the space shuttle. By 1979 he had been made Vice President and General Manager Martin Marietta, Denver Aerospace, Michoud Division. Hating to see the company's external tanks being simply jettisoned to burn up in the atmosphere after each shuttle launch, during the 1980's he advocated leaving the tanks in orbit and using them as space stations. He retired to Santa Rosa, California.
Birth Place: Indianapolis, Indiana.