Charles E. Bartley, 74, who invented rubber-based solid propellants used in solid rocket fuels. Bartley did his initial work on solid fuels as a scientist at the Jet Propulsion Laboratory in the 1940s. He put his knowledge to commercial use in 1952 when he founded Grand Central Rocket Co. in Redlands. Six years later, his company provided the fuel for the third stage of Explorer I, America's first satellite. Bartley eventually sold Grand Central and founded two other solid propellant rocket companies specializing in weather rockets and ejection seats for jets--Rocket Power, which he formed in Mesa, Ariz., in 1959, and Universal Propulsion Co., which he established in Phoenix in 1963. He was elected to the American Rocket Society (now the American Institute of Aeronautics and Astronautics) in 1951. On Wednesday in Scottsdale, Ariz., of cancer.