Mission Type: Orbiter
Launch Vehicle: N1 (no. 15007)
Launch Site: NIIP-5 / launch site 110L
Spacecraft Mass: about 9500 kg
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

This was the fourth test launch of the giant Soviet N1 booster. The first two, launched in 1969, attempted to send rigged-up 7K-L1 ("Zond") spacecraft to lunar orbit. The third booster carried a payload mockup for tests in Earth orbit. All three failed.

This fourth launch was intended to send a fully equipped 7K-LOK spacecraft (similar to a beefed-up Soyuz) on a robotic lunar orbiting mission during which the spacecraft would spend 3.7 days circling the Moon (over 42 orbits), taking photographs of future landing sites for piloted missions.

The booster lifted off without problems, but a few seconds prior to first-stage cutoff, at T+107 seconds, a powerful explosion ripped apart the bottom of the first stage, destroying Soviet hopes of ever sending cosmonauts to the Moon. There was never a conclusive reason for the explosion; some suggested that there had been an engine failure, and others were convinced that the scheduled shutdown of six central engines had caused a structural shock wave that eventually caused the explosion.