The lunar race demanded the impossible of Soviet engineers: build a superheavy rocket to outrun time, and launch it to the Moon, skipping the critical stage of ground testing.
From the early 1960s, the OKB-1 design bureau developed the superheavy N-1 rocket as part of the N1-L3 lunar program; the decree creating the complex was issued in September 1962. The machine was a colossus 105 meters tall with a launch mass of 2750 tons. The first stage, designated Block A, had to haul this weight off the Earth, generating 45400 kN of thrust. To achieve such figures, engineers installed a cluster of 30 oxygen-kerosene NK-15 engines on the stage. The multi-engine design was a forced measure: Soviet industry couldn't produce a single-unit engine of comparable power in time. Synchronizing this roaring ensemble was the job of the analog KORD system, which monitored the parameters of each engine and automatically shut down those that exceeded normal limits. Each engine and numerous components underwent ground testing individually, proving their reliability. The analog logic of the KORD system was designed for isolated failures, not cascading faults across an entire cluster.
The cardinal engineering sin that sealed the project's fate was the absence of full-scale static fire tests of Block A as a single unit. The USSR never built a test stand for simultaneously firing the entire stage in its flight configuration. The reasons lay in a severe shortage of resources, the pressure of the lunar race timeline, and the colossal complexity of building infrastructure capable of diverting the flame and acoustic load from thirty nozzles at once. At that moment, the Soviet space program operated like a factory where a racing engine is cobbled together, tested at idle, and then sent straight to the track. The first flight was simultaneously the first ignition of all engines together. Without a single test stand, engineers incorporated ideal models into their calculations—models that didn't account for the acoustic resonances and vibrations that arise only when thousands of tons of fuel burn simultaneously in an enclosed volume.
The first attempt to break through to the Moon came on 21 February 1969 with the launch of the 3L rocket. In the first seconds after liftoff, a voltage spike caused by the firing of pyrotechnic charges made KORD shut down engine No. 12, followed by its symmetric counterpart No. 24. Longitudinal oscillations of the airframe tore the oxidizer and fuel feed lines, a fire broke out, and on the 69th second the automated systems shut down the entire first stage; the rocket exploded at an altitude of 12.2 kilometers. A few months later, on 3 July 1969, the 5L rocket rolled out to launch pad 110. At liftoff, peripheral engine No. 8 failed: within twelve seconds, the automated systems shut down all the others except one, and the surviving engine began rotating the rocket around its transverse axis. The machine crashed flat, nearly on top of the launch complex. The explosion destroyed the launch pad and dealt a catastrophic blow to the program's schedule: repairs to the second launch facility dragged on until 1972, and the next launch took place almost two years after the accident.
The resumption of testing showed that the problems ran deeper than the designers had assumed. The launch of 6L on 27 June 1971 ended in loss of roll control: an unexpected torque sent the rocket spinning around its longitudinal axis, the steering nozzles couldn't cope, and the stages began breaking apart in mid-flight. The last, fourth launch of 7L took place on 23 November 1972. On the 107th second of flight, the oxidizer pump of engine No. 4 disintegrated—the explosion pierced the tail section, a fire started, and the stage broke apart seven seconds before the planned separation. The KORD system could shut down engines when parameters deviated, but it could neither predict a pump's destruction nor stop the instantaneous breakup of the stage.
In 1974, when Valentin Glushko took over the industry, work on the N-1 was halted—officially the program was closed two years later, in 1976, with about six billion rubles written off in expenses. Two already completed N1F boosters were scrapped. The multi-engine design was not a death sentence in itself: the NK-33 engines created for the N1F modification turned out to be so successful that they outlived their creators by decades. Years later, these engines were integrated into the American Antares rocket under the designation AJ-26 and were used in the Russian Soyuz-2.1v. The engines built for a rocket that never reached the Moon sat in storage until the collapse of the USSR, and then made successful commercial launches on another continent.