 They were able to determine Sputnik's orbit by analyzing the Doppler shift of its radio signals during a single pass.Discussing the way forward for their research, their director Frank McClure, the chairman of APL's Research Center, suggested in March 1958 that if the satellite's position were known and predictable, the Doppler shift could be used to locate a receiver on Earth, and proposed a satellite system to implement this principle.Development of the Transit system began in 1958, and a prototype satellite, Transit 1A, was launched in September 1959.