In the 1960s he played an important role in the development of the Centaur upper stage rocket, which pioneered the use of liquid hydrogen as a propellant.

He subsequently studied mathematics and engineering as a graduate student at Case-Western Reserve University in Cleveland, Ohio.

The following year, he was the Project Manager of a test program that investigated the Centaur's booster pump, which increased the pressure of the propellant flowing to the engine.

He directed the design and engineering of the launch vehicles, and coordinated relations with Air Force, aerospace industry teams, and mission planners.

[3][4] Stofan became Deputy Associate Administrator for the Office of Space Science at NASA Headquarters in 1978, but returned to the Lewis Research Center as its director in 1982.

[3][4] After retiring from NASA in 1988, Stofan joined Martin Marietta Astronautics as its vice president of Advanced Launch Systems and Technical Operations.

In 1991 he returned to Cleveland as the president of Analex Corporation, a firm established and run by ex-NASA employees who provided engineering and management expertise to US agencies.

[4][11] His daughter, Ellen Stofan, served as Chief Scientist at NASA, assistant director of the National Air and Space Museum and Under Secretary for Science and Research at The Smithsonian.