Short answers, pulled from the story.
The Interplanetary Monitoring Platform was a NASA program managed by the Goddard Space Flight Center in Greenbelt, Maryland, as part of the Explorers program. It consisted of eleven satellites designed to study interplanetary plasma, solar wind, cosmic rays, and magnetic fields in interplanetary and cislunar space. The program also supported the Apollo Moon landing missions by collecting space radiation data.
Explorer 18, designated IMP-A, was the first spacecraft to carry integrated circuit chips when it launched on the 27th of November 1963. This predates the use of integrated circuits in the Apollo Guidance Computer used for the Moon missions.
Explorer 33, designated IMP-D, was the first spacecraft to use MOSFET integrated circuits when it launched on the 1st of July 1966. The MOSFET blocks were manufactured by General Microelectronics, which had commercialized MOS technology in 1964 and held NASA as its first MOS contract customer.
IMP-D carried 2,000 transistors and 256 communication channels, up from 1,200 transistors and 175 channels on the first three IMP satellites. At the same time, IMP-D required only 1,000 non-resistor electrical parts compared to 3,000 on IMP-A, despite being twice as electrically complex.
Explorer 50, designated IMP-J and the eighth IMP satellite, launched on the 26th of October 1973 and remained in service until 2006. It was the final satellite in the IMP-I, IMP-H, and IMP-J design series.
The IMP satellites collected data on space radiation, solar wind, cosmic rays, and magnetic fields along the routes between Earth and the Moon. This data supported mission planning and safety assessment for human spaceflights, contributing to the success of the Apollo 11 mission and the first human Moon landing in 1969.