Juno II rocket. Unsuccessful launch of an American Juno II rocket just before it exploded. This rocket was launched on 16 July 1959 with the Explorer S1 satellite aboard. The four-stage rocket was ordered to self-destruct by the launch site's safety officer when it veered off-course on take-off. This was the third Juno II mission, and the first to fail during launch. The Juno II rocket was developed for lifting comparatively heavy payloads. There were a total of 10 spacecraft launches aboard Juno II rockets between 6 December 1958 and 24 May 1961. Five of these missions failed due to rocket malfunctions during launch.