...a year later on 23 July 1981 after a second disaster of the same cause was narrowly avoided it was discovered that a design flaw in the fuel filters of the r

...a year later on 23 July 1981 after a second disaster of the same cause was narrowly avoided it was discovered that a design flaw in the fuel filters of the rocket were likely the cause of the 1980 disaster, although it was impossible to confirm which type of filters were used in the rocket that exploded. The catalytically active lead solder on the filters would cause an explosion upon contact with hydrogen peroxide. Cover-up The disaster was not reported in Soviet media at the time and only reached western media outlets in 1989 upon declassification. Pravda reported that the launch of the rocket was a success and did not say anything about the explosion.