 Both the four-stage Juno I and three-stage Jupiter-C launch vehicles were the same height (21.2 meters), with the added fourth-stage booster of the Juno I being enclosed inside the nose cone of the third stage.Following the successful launch of Explorer 1 on January 31, 1958, the first U.S. satellite, Juno I made five more launches before being retired in favor of Juno II.Although Juno I's launch of the Explorer 1 satellite was a huge success for the U.S. space program, only two of its remaining five flights were successful, Explorer 3 and Explorer 4, giving the Juno I vehicle a mission total success ratio of 50%.