Soyuz 7K-OK No.1

Soyuz 7K-OK No.1 was an unmanned spacecraft of the Soyuz program, originally intended to perform a rendezvous maneouver with Kosmos 133 (Soyuz 7K-OK No.2). After the Kosmos 133 mission failed, the rocket was moved to the launch pad on December 12, 1966 and scheduled to launch on December 14, 1966, 4 PM local time.

However, once the Soyuz rocket's engines ignited, they did not operate at full power and didn't produce enough force to lift the rocket up, causing it to stay on the launch pad. The cause was later found to be a faulty oxygen valve. After 30 minutes, personnel attempted to secure and defuel the rocket. Suddenly, the launch escape system started and pushed the Soyuz spacecraft 600 meters into the air. It landed 300 meters away from the rocket.

The launch of the spacecraft caused the rocket to catch fire. The personnel immediately ran for safety, and after 2 minutes the rocket exploded as the fire ignited the first stage. The launch pad was completely destroyed for months and all personnel were killed; even buildings a kilometer away were damaged by the blast.

The cause was later found to be an unintended safety feature of the spacecraft. There were only thought to be three ways to trigger the LES, but there was in fact a fourth, which was triggered by disconnecting the rocket from external power and receiving a launch signal (which the system interpreted as the start of a vertical launch without any other signals by the inertial system), but the rotation of the earth causing a deviance of more than eight degrees from the initial starting orientation, which was an abort criterion. This poorly-planned security measure caused the explosion of the rocket and the death of the personnel.