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The above photograph shows a close-up of an early transistor approximately ½ inch in diameter. Transistors were invented in 1948 and were applied to the needs of guided missile electronics in the early 1950's. Transistors had major advantages over vacuum tubes because they required less power to operate, they could withstand the vibration and stress of missile launches, and they were smaller. The major disadvantage was the significantly lower level of signal output, which demanded concurrent development in encoding or signal conditioning for successful ground-based receipt of signals.

In an Archives oral history interview, a JPL employee recalled that in about 1955 some boxes were received from the Army with a letter saying, "These things are called transistors; see what you can do with them." The first transistors that JPL worked with were valued at about $40,000 each. By 1957, when they were used for Explorer 1, the price decreased to $2,000 - $4,000 each. The use of transistors increased as the invention became smaller and more powerful. Many were grouped together into integrated circuits and became the electronic heart of the satellites and spacecraft JPL would later design and build.