Nedelin catastrophe
The Nedelin catastrophe or Nedelin disaster was a launch pad accident that occurred on 24 October 1960 at Baikonur test range (of which Baikonur Cosmodrome is a part), during the development of the Soviet R-16 ICBM. As a prototype of the missile was being prepared for a test flight, an explosion occurred when the second stage engine ignited accidentally, killing an unknown number of military and technical personnel working on the preparations. Despite the magnitude of the disaster, news of it was suppressed for many years and the Soviet government did not acknowledge the event until 1989. The  disaster is named after Chief marshal of Artillery Mitrofan Ivanovich Nedelin, who was killed in the explosion. As commanding officer of the Soviet Union's Strategic Rocket Forces, Nedelin was the head of the R-16 development program. Launch preparations. On 23 October 1960, the prototype R-16 had been installed on launching pad 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 the hypergolic pair of UDMH as fuel and a saturated solution of in nitric acid as the oxidizer —nicknamed "Devil's venom"—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 achieving a test launch ahead of the 7 November 1960 anniversary of the Bolshevik Revolution resulted in extreme schedule pressure, in a context of substantial emerging engineering difficulties. Ultimately pre-launch tests began to overlap with launch preparations. Accident. A short circuit in the replaced main sequencer caused the second-stage engine to fire while being  tested before launch. This detonated the first stage fuel tanks directly below, destroying the missile in an enormous explosion. Before seeking refuge, the camera operator 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 engine 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 explosion  incinerated or asphyxiated Nedelin, a top aide, the USSR's top missile-guidance designer, and over 70 other officers and engineers. Others died later of burns or poisoning. Missile designer Mikhail Yangel and the test range commanding officer survived only because they had left to smoke a cigarette behind a bunker a few hundred metres away, but nonetheless suffered burn injuries. Casualties. The exact death toll of the explosion is not known. The first Western reporting of the accident via the Italian Continentale News Agency in December said that 100 people were killed, while "The Guardian" reported in 1965, citing  information from spy Oleg Penkovsky who had passed information to the West, that as many as 300 had died. The Soviet Union said only that a "significant number" had died when it first acknowledged the incident in a 1989 "Ogoniok" article, but later in the year, the government put the number of dead at 54. The most recent estimated death toll, released by Roscosmos on the 50th anniversary of the accident and originating with agency engineer Boris Chertok, was that 126 people had died, but the agency qualified the number by saying that the actual number could be anywhere from  60 to 150 dead. Aftermath. Complete secrecy was immediately imposed on the events of 24 October 1960 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. When Brezhnev arrived at  the firing range on 25 October 1960, he said: "Comrades! We do not intend to put anyone on trial; we are going to investigate the causes and take actions to recover from the disaster and continue operations". Despite this, I. A. Doroshenko was held accountable for the event. Afterwards, when Nikita Khrushchev asked Yangel, "But why have you remained alive?", Yangel answered in a trembling voice, "Walked away for a smoke. It's all my fault". Yangel later suffered a heart attack and was off work for months. After the committee presented its report, the R-16 program resumed in January  1961 with first successful flight on 2 February 1961. The delay to the R-16 spurred the USSR toward the development of more effective ICBMs and sparked Khrushchev's decision to install Intermediate-range ballistic missile (IRBM)s 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 to the victims of the test was erected in the first half of the 1960s in the Park of Baikonur and is still visited by RKA officials before any manned launch. Another fatal accident , with the R-9 missile, occurred at Baikonur exactly three years after the Nedelin catastrophe, causing October 24 to be referred to as Baikonur's "Black Day." No launches have been attempted on that date at Baikonur ever since. 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 8 December 1960, from undisclosed sources, that Marshal Nedelin and 100 people had been killed in a rocket explosion. "The Guardian" reported on 16 October 1965 that captured spy Oleg Penkovsky had confirmed details of  the missile accident, and exiled scientist and Soviet dissident Zhores Medvedev provided further details in 1976 in the British weekly magazine "New Scientist". However, it was not until 16 April 1989 that the Soviet Union acknowledged the events, with a report appearing in the weekly newsmagazine "Ogoniok".