SK-100 Credit - © Mark Wade

In 1962 Yangel produced his first design for a large clustered rocket. The SK-100 would have clustered seven R-16 ICBM first stages in order to put 100 metric tons into earth orbit. The concept was abandoned for the simpler R-56 design.

The SK-100 first stage was to consist of six R-16 first stages, clustered around a single R-16 first stage as the second stage / vehicle core. The third stage would be derived from the R-16 second stage. Lift-off mass would have been 2,000 metric tons.

While superficially attractive, this cluster concept would have resulted in 24 first stage engine chambers firing simultaneously (4 chambers per stage x 6 stages). Failure of a single chamber could be catastrophic. Furthermore the clustered stages presented complex dynamic interaction and resonance problems. Another new technical challenge was zero-G start-up of the second stage. Propellant settling prior to engine ignition was solved by using ullage motors. These liquid fuel engines were pressure-fed using diaphragm-contained propellants. This 'low thrust system' would find application in later Yangel missile designs.

Work on the SK-100 reached the point of testing of a sub-scale dynamic model, and detailed design of the inter-stage structural elements and engine feed plumbing. But Yangel, noting the 'gigantomania' that was driving Korolev, Chelomei, and Glushko to propose ever more complex super-booster designs, decided to 'go back to the drawing board' with a clean sheet of paper. The result would be the R-56, a third way to large booster design between that of Chelomei's UR-700 and Korolev's N1.

Manufacturer: Yuzhnoye. LEO Payload: 100,000 kg (220,000 lb). to: 200 km Orbit. at: 52.00 degrees. Total Mass: 2,000,000 kg (4,400,000 lb). Core Diameter: 30.00 m (98.00 ft). Total Length: 55.00 m (180.00 ft).