Jupiter is the name given to two different rockets. One (Jupiter C) was the basis for the Juno I satellite launches. The
other was an intermediate-range ballistic missile (IRBM) later developed into Juno II. Both were under the control of the U.S. Army Ballistic Missile Agency. The Jupiter C, first launched on Sept. 20, 1956, to test nose-cone materials for the Jupiter IRBM, was a Redstone rocket lengthened to a total of 20 m (65.6 ft). Its original
liquid oxygen/ethyl alcohol propellants were changed to liquid oxygen and Hydyne, a mixture of 60% unsymmetrical dimethylhydrazine and 40% diethylene triamine. Two solid-
propellant stages were clustered in a spinning "tub" on the separable nose. Stage 2 had an outer ring of 11 solid-propellant rocket motors; stage 3 had 3 of these motors (Baby Sergeants) inside. Juno I consisted of a fourth-stage Baby Sergeant motor added to the Jupiter C. This allowed the rocket to achieve orbital velocity. The 29,000-kg (64,000-lb) four-stage rocket, which stood 21.7 m (71.2 ft) tall and had a lift-off thrust of about 369,000 newtons, or 37,600 kg (83,000 lb), placed the first U.S. artificial satellite, Explorer I, into orbit in 1958. The Jupiter IRBM, first test-launched at Cape Canaveral on Mar. 1, 1957, was a liquid-propellant (liquid oxygen/kerosene) rocket. It stood 18.4 m (60.3 ft) tall and had a launch weight of approximately 49,900 kg (110,000 lb). Maximum design range was 2,575 km (1,600 mi). The later development of lightweight thermonuclear warheads and the desire to place missiles in nuclear submarines resulted in the more compact solid-propellant Polaris missile, and Jupiter production was terminated. Juno II, a four-stage launcher, was a Jupiter IRBM lengthened by 0.9 m (3 ft) to allow enough propellant for 20 seconds of extra burning time. It carried an arrangement of Baby Sergeant upper stages similar to the Jupiter IRBM. The weight was about 55,340 kg (122,000 lb).