Jupiter-C

Description

The Jupiter-C used a modified Redstone missile as its first stage, with the propellant tanks extended by eight feet and a lighter, smaller instrument section. The upper two stages were housed in a rotating assembly, or tub, mounted on top. The second stage consisted of eleven smaller Sergeant rocket engines arranged in an outer ring, while the third stage was a cluster of three similar engines inside that ring. Bulkheads and rings secured these engines, and a cylindrical shell enclosed them.

The shell’s webbed base plate sat on a ball bearing shaft attached to the first stage’s instrument section. Two electric motors spun the tub between 450 and 750 revolutions per minute to counteract thrust imbalances when the clustered engines ignited. A programmer varied the spin rate to prevent it from resonating with the first stage’s changing frequency during flight. The tub’s spin was visible before launch.

During the first stage’s burn, a gyro-controlled autopilot steered the vehicle using air vanes and jet vanes. The rocket launched vertically from a simple steel table and, at first-stage burnout 157 seconds later, was angled 40 degrees from horizontal. Explosive bolts and springs then separated the instrument section from the first-stage tanks, and four air jets at the base of the instrument section slowly tilted the instrument section and spinning tub to a horizontal position.

After a coasting phase lasting about 247 seconds, a ground radio signal ignited the second-stage cluster, detaching the tub from the instrument section. The third stage then fired to raise the apogee. This design, created by Wernher von Braun in 1956 for his Project Orbiter, allowed the Jupiter-C to operate without a guidance system in its upper stages.

Encrypted serial number

Because the Jupiter-C was part of the IRBM project, the sequence of rocket manufacture was considered a military secret, and the designation painted on the side was not a clear serial number. Instead, a simple transformation cipher was used, with the key taken from the name of the design and test base: Huntsville, Alabama, giving HUNTSVILE (duplicated letters dropped). H stood for 1, U for 2, N for 3, T for 4, S for 5, V for 6, I for 7, L for 8, E for 9, and X for 0. For example, the Jupiter-C modified to launch Explorer 1 had "UE" painted on the side, indicating serial number 29 (U→2, E→9).

Derivatives

The Juno I was a satellite launch vehicle based on the Jupiter-C, with the addition of a fourth stage atop the third-stage tub and the use of Hydyne as fuel. Von Braun chose the name Juno to make the satellite launch appear as peaceable as the Vanguard rocket, which was derived from a weather study rocket rather than a weapon. Although the Juno I was the same height as the Jupiter-C (21.2 meters), with the fourth stage hidden inside the shell, this vehicle that launched the first U.S. orbital satellite is often incorrectly referred to as a Jupiter-C.