A model of the Juno-type high-speed
stages, including a model of the Explorer I
Used as the upper stages of Jupiter-C, Juno I, or Juno II, the lengthened Redstone or Jupiter missile would serve as
the first stage, while the "tub" would provide the second, third, and fourth
stages. On Juno II missions, the high-speed stages were covered with an
aerodynamic shroud that fastened to the Jupiter's instrument compartment.
All of the upper stages consisted of scaled Sergeant solid-propellant rocket
motors, each four feet long and six inches in diameter. The second stage
consisted of eleven of these motors in an outer, cylindrical ring. Fitting
within this tube were the three bundled motors comprising the third stage. A
fourth stage, consisting of a single motor, was mounted atop the third stage
(the Jupiter-C, which was not intended to place its payload in orbit, instead
mounted either a dummy fourth stage or a a scaled-down Jupiter nose
cone atop the third stage, depending upon the mission).
This entire assembly was spin-stabilized to minimize the effects of thrust
variations among the clustered motors.