Short answers, pulled from the story.
NASA established the Interplanetary Monitoring Platform at the Goddard Space Flight Center in Greenbelt, Maryland during the early 1960s. The program operated as part of the Explorers initiative to investigate interplanetary plasma and magnetic fields.
Explorer 27 launched on the 27th of November 1963 at 02:30 UTC from Cape Canaveral LC-17B. This mission marked the beginning of a series designed to map invisible forces across space.
IMP-A became the first spacecraft to utilize integrated circuit chips in 1963. Explorer 18 carried these new components into orbit on the 30th of December 1965 before the Apollo Guidance Computer adopted similar technology.
IMP-D contained 2,000 transistors and 256 channels compared to just 1,200 transistors and 175 channels on earlier models. Non-resistor parts dropped from 3,000 on IMP-A down to 1,000 on IMP-D despite doubled electrical complexity.
Explorer 35 followed with IMP-E positioned in Selenocentric orbit after the 24th of June 1973. These units supported diverse orbital missions including lunar orbits and high elliptical paths.