Redstone Jupiter-C

Two changes separated the Jupiter-C from a production Redstone: propellant tanks lengthened by some 2.4 metres for a longer burn, and a smaller, lighter instrument compartment. On top sat a spinning tub carrying the upper stages — an outer ring of eleven scaled-down Sergeant motors as the second stage, a cluster of three more inside as the third. Electric motors spun the tub at between 450 and 750 revolutions per minute before release to cancel out any thrust asymmetry when the clustered motors lit.

The arrangement, worked out by Wernher von Braun for his Project Orbiter proposal, spared the upper stages any guidance system at all: spinning kept them pointed. During first-stage flight a gyro autopilot worked air vanes and jet vanes; at burnout, explosive bolts released the instrument section and four air jets tipped it slowly to the horizontal. At the top of the arc a radio command from the ground fired the eleven-motor cluster, and the third stage followed.

The first Jupiter-C flew on 20 September 1956 and reached an altitude of 1,100 kilometres. The second, in May 1957, carried an ablative cone. The third, on 8 August 1957, flew a one-third-scale Jupiter nose cone and recovered it — the first object returned from space. President Eisenhower displayed that cone in the Oval Office during his televised address in November of the same year.

Given a fourth stage hidden inside the third-stage shell and Hydyne for fuel, the same vehicle became the Juno I that orbited Explorer 1; because both stood the same height, the two are still confused with each other. The stretched first stage, fitted with the operational Redstone's A-7 engine, also became the starting point for the Mercury-Redstone.