Explorer 2 was an American unmanned space mission within the Explorer program. Intended to be a repetition of the previous Explorer 1 mission, which placed a satellite into medium Earth orbit, the spacecraft was unable to reach orbit due to a failure in the launch vehicle during launch. Explorer 2 was launched from Cape Canaveral Missile Test Center of the Atlantic Missile Range (AMR), LC-26A in Florida on 5 March 1958 at 18:27:57 GMT by a Juno I launch vehicle. The Juno I had its origins in the United States Army's Project Orbiter in 1954. The project was canceled in 1955 when the decision was made to proceed with Project Vanguard. Background Following the launch of the Soviet Sputnik 1 on 4 October 1957, the Army Ballistic Missile Agency (ABMA) was directed to proceed with the launching of a satellite using the Juno I four-stage variant of the three-stage Jupiter-C, which had already been flight-tested in nose-cone re-entry tests for the Jupiter IRBM (intermediate-range ballistic missile). Working closely together, ABMA and Jet Propulsion Laboratory (JPL) completed the job of modifying the Jupiter-C and building Explorer 1 in 84 days. Spacecraft Explorer 2 was identical to Explorer 1 except for the addition of a tape recorder designed to enable playback of data. The satellite was a long, diameter cylinder and nosecone that comprised the fourth stage of the Jupiter-C launch vehicle. With a mass of , it was about heavier than Explorer 1. The spacecraft body was made of stainless AISI-410 steel, thick. The case was heat-oxidized to a gold color and eight alternate stripes of white Rokide A (flame sprayed aluminum oxide) were used for temperature control. The base of the cylinder held the Sergeant solid-fuel rocket motor. The sub-carrier oscillators and Mallory mercury batteries for the low power transmitter were in the upper part of the nose cone. Below these was the low power (10 mW, 108.00 MHz) transmitter for the carrier and sub-carrier signals, which used the stainless steel satellite skin as a dipole antenna. Below the nose cone was the detector deck, holding the Geiger-Mueller counter tube for the cosmic ray experiment, the command receiver, for recorder interrogations, high power playback transmitter (60 mW, 108.03 MHz) for interrogation response, cosmic ray experiment electronics, Mallory mercury batteries for the high power transmitter, and a , diameter magnetic tape recorder. An acoustic micrometeorite detector was mounted to the inside