Stofan joined the Lewis Flight Propulsion Laboratory in 1958, shortly before it became part of the newly formed
National Aeronautics and Space Administration (NASA) as the
Lewis Research Center. He became a research engineer in the Propulsion Aerodynamics Division, where he researched the use of
ejector nozzles in supersonic aircraft. These nozzles subsequently found use in the
Lockheed SR-71 Blackbird. As NASA switched its focus from aviation to space-related technologies, he joined the Chemical Rocket Systems Branch in the new Rocket and Aerodynamics Division, where he studied
slosh dynamics, the manner in which fuel sloshed about in the
propellant tanks of
liquid-fuel rockets. Fuel could slosh for many different reasons, and understanding these and their effects was crucial to mitigating them in order to ensure that the fuel could be pumped into the engine. Stofan's expertise with sloshing was called upon in 1962 when Lewis took on the development of the
Centaur upper-stage vehicle, which was fueled with
liquid hydrogen and
liquid oxygen. Liquid hydrogen was a
cryogenic fuel about which there was little empirical knowledge at the time. He played a key role in understanding its behavior: he helped develop internal baffles to control propellant sloshing, gauges to measure the boiling of cryogenic propellants, and a propellant utilization system that ensured that the liquid hydrogen and liquid oxygen would run out at precisely the same time, thereby ensuring that neither was wasted. Centaur upper stages were used atop
Atlas-Centaur rockets by the
Surveyor program, which sent
robotic spacecraft to the Moon. He went back to NASA headquarters in 1986 to head the Space Station Office, directing the design of the
Space Station Freedom. He retired from NASA on April 1, 1988. For his services, he had received the
NASA Exceptional Service Medal in 1975 and the
NASA Distinguished Service Medal in 1981. He also received the
Presidential Rank Awards of Meritorious Executive in 1982 and Distinguished Executive in 1985. ==Later life and death==