 Philco's SBDT improved surface-barrier transistor, was used in the early prototype design of the 10-milliwatt Minitrack satellite transistorized (radio beacon) transmitter, for the United States Navy Vanguard I satellite project program.On January 31, 1958, the United States first artificial Earth satellite was launched by the Army Ballistic Missile Agency at Cape Canaveral in Florida, which was called Explorer 1, and was developed by the California Institute of Technology Jet Propulsion Laboratory (JPL).The Explorer 1 satellite's payload, consisted of a low-power Microlock transistorized (radio beacon) 108.00 MHz transmitter, which was used for tracking and telemetry, and had consisted of a Philco high-frequency surface-barrier transistor in its original circuitry designs.