The Interplanetary Monitoring Platform (IMP) was launched in 1963, and involved a network of eleven Explorer satellites designed to collect data on space radiation in support of the Apollo program. The IMP program was a major step forward in spacecraft electronics design, as it was the first space program to use integrated circuit (IC) chips and MOSFETs (MOS transistors). The IMP A (Explorer 18) in 1963 was the first spacecraft to use IC chips, and the IMP D (Explorer 33) in 1966 was the first to use MOSFETs.