Juno I was the rocket that placed the first U.S. artificial
satellite, Explorer I, into orbit on Jan. 31, 1958. The 29,030-kg
(64,000-lb) four-stage rocket stood 24.7 m (81.3 ft) tall and had a lift-off thrust of about 369,000 newtons, or 37,648 kg (83,000 lb). The rocket was a development of the Jupiter C rocket, which in turn had been based on the Redstone medium-range
ballistic missile built under the direction of Wernher von Braun at the Army Ballistic Missile Agency. So that Juno I could be used as a
satellite launcher, a fourth-stage Baby Sergeant motor was added to Jupiter C; this allowed the rocket to achieve an orbital velocity of 28,157 km/h (17,500 mph).Juno II was a four-stage satellite and space-probe launcher based on a Jupiter intermediate-range ballistic missile (IRBM) that had its body lengthened by 0.91 m (3 ft) to allow enough propellant for 20 seconds extra burning time. It carried an arrangement of Baby Sergeant upper stages similar to the Jupiter IRBM. The weight was about 64,856 kg (121,000 lb).