The R-7 would go on to become one of the most successful rockets in history.
It was used to place Sputnik in orbit and Yuri Gagarin in space.
A heavily modernized version of the R-7 is still used as the launch vehicle for the Russian Soyuz spacecraft.
The trouble with early Soviet missiles was the use of liquid oxygen as the oxidizer for the fuel.
These propellants were hypergolic, meaning they spontaneously ignited upon contact, eliminating the need for external ignition sources.
The downside was that both UDMH and nitric acid are extremely corrosive and toxic.
They were so dangerous that Soviet engineers called them devils venom.
The initial checks at the launch pad were apparently uneventful and were completed successfully by October 23.
On the same day the missile was fueled for launch.
Nedelin reportedly set up a chair on the pad to observe and direct operations.
Around 150 other nonessential people, including military and civilian, also remained on the pad.
Shortly after the fueling process was finished, the rocket developed a fuel leak.
Consequently, the launch team had no alternative but to proceed or abort the mission.
The following day, October 24th, was the day of launch.
Meanwhile, mounting technical problems and lack of time were pushing the technicians to the wall.
In seconds, a giant fireball, up to 120 meters in diameter engulfed the launch pad.
A video camera that had been set up to record the launch captured these terrible moments instead.
Rescue workers arriving on the scene attempted to help the people who had run to them.
They flung them to the ground and threw sand on them.
A thick stream of fire unexpectedly burst forth, covering everyone around.
The temperature at the center of the fire was about 3,000 degrees.
Those who had run away tried while moving to tear off their burning clothing, their coats and overalls.
Alas, many did not succeed in doing this.
It’s all my fault.
At least seventy-four people died that day and approximately fifty more died later of their injuries.
Details of the disaster remained a secret for nearly three decades.
Nedelin’s death was officially listed as having occurred in a plane crash.
Details about the disaster did not become public until 1989 when the Soviet Union acknowledged the events.
The memorial at the site of the disaster.
