On 23 October, the prototype R-16 was installed on launching pad 41 (Russian: стартовая позиция 41) awaiting final tests before launch. The missile was over 30 m long, 3.0 m in diameter and had a launch weight of 141 tons. The rocket was fueled with Devil's Venom — hypergolic UDMH as the fuel and a saturated solution of dinitrogen tetroxide in nitric acid as the oxidizer — which was used because of the high boiling temperatures and hence storability of the fuel and oxidizer despite being extremely corrosive and toxic. These risks were accounted for in the safety requirements of the launch procedures, but Nedelin's insistence on performing tests before November 7th (anniversary of the Bolshevik Revolution) resulted in extreme schedule pressure, with numerous safety procedures being ignored in order to economize time.

Accident

A short circuit in the replaced main sequencer caused the second stage engines, while being tested before launch, to fire inadvertently. This detonated the first-stage fuel tanks directly below, destroying the missile in an enormous explosion. Camera operator before attempting refuge had remotely activated automatic cameras set around the launching pad that filmed the explosion in detail. People near the rocket were instantly incinerated; those farther away were burned to death or poisoned by the toxic fuel component vapors. Andrei Sakharov described many details—as soon as the engines were fired, most of the personnel there ran to the perimeter but were trapped inside the security fence and then engulfed in the fireball of burning fuel. The resultant explosion incinerated Nedelin, a top aide, the USSR's top missile guidance designer, and seventy-one other officers and engineers. Missile designer Mikhail Yangel and test range commanding officer survived only because they had left to smoke a cigarette behind a bunker a few hundred yards away.

Aftermath

Complete secrecy was immediately imposed on the events of 24 October by Nikita Khrushchev. A news release stated that Nedelin had died in a plane crash and the families of the other engineers were advised to say their loved ones had died of the same cause. Khrushchev also ordered Leonid Brezhnev to head an investigation commission and go to the site. Among other things, the commission found that many more people were present on the launch pad than should have been — most were supposed to be safely offsite in bunkers.

According to Sergei Khrushchev, Brezhnev did insist that the commission punish none, explaining that "The guilty have already been punished".

Afterwards, Yangel was asked by Nikita Khrushchev "But why have you remained alive?". Yangel answered in a trembling voice - "Walked away for a smoke. It's all my fault". Later he suffered a heart attack and was out of work for months.

After the committee presented its report, the R-16 program resumed in January 1961 with first successful flight in November. The delay to the R-16 spurred the USSR toward the development of more effective ICBMs and sparked Khrushchev's decision to install IRBMs in Cuba. Before the disaster Yangel had ambitions to challenge Sergei Korolev as leader of the Manned Space program, but he was directed to focus on the R-16.

A memorial the victims of the testers was erected in the first half of the 60 years of the last century soldier in the Park of the Baikonur and is still visited by RKA officials before any manned launch.

Official acknowledgment

A news release stated that Nedelin had died "in a plane crash while on an undisclosed mission". The Italian news agency Continentale first reported on December 8, from undisclosed sources, that Marshal Nedelin and 100 people had been killed in a rocket explosion. The Guardian reported on October 16, 1965, that captured spy Oleg Penkovsky had confirmed details of the missile accident, and exiled scientist Zhores Medvedev provided further details in 1976 in the British weekly magazine New Scientist. However, it was not until April 16, 1989, that the Soviet Union acknowledged the events, with a report appearing in the weekly newsmagazine Ogoniok.