A Transistor Museum Interview with Dr. George Ludwig The First Transistors in Space - Personal Reflections by the Designer of the Cosmic Ray Instrumentation Package for the Explorer I Satellite
Copyright © 1957 by George Ludwig Shown above is a photo of one of the pulse counting decks (scalers) designed by Dr. Ludwig for the Explorer III.  Note use of the TI 900 series silicon transistors, which are different from the 2N33X series of TI transistors used on Explorer I and IV.
Shown at right (above) are two TI type 905 silicon grown junction transistors, date code 723 (1957 week 23).  At left is a TI 600 series silicon diode, which was also used on the early Explorers.  The TI 900 series of transistors was the first commercial line of silicon transistor and became available originally in 1954.
	As noted in this Oral History, transistor technology was evolving rapidly during the mid 1950s, when the instrumentation for the Explorer satellites was designed.  Commercial silicon devices were just becoming available, so circuits originally designed by Dr. Ludwig with germanium transistors were quickly re-designed to use the new silicon transistors.  TI was the first to market with silicon transistors and so it isn’t surprising to see the widespread use of TI silicon transistors in the early space program.  As shown above, in this Feb 13 1959 ad in Electronics magazine, TI was proud to document the importance of their silicon transistors to the success of the Explorer satellite program. Go To Ludwig Oral History, Page 12
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