The Soviet Union, locked in a space race with the United States, was developing an intercontinental ballistic missile known as the R-16, and on October 24, 1960 was scheduled to launch a prototype rocket when it exploded on the launch pad.
"People died in horrific pain, essentially burning alive, but the country and the rest of the world practically never learnt anything about that terrible catastrophe and its heroes-victims," Russian space agency Roscosmos said.
"To this day it is considered the most horrific (tragedy) in the history of space exploration," the agency said ahead of Sunday's anniversary.
In the West, the tragedy is referred to as the Nedelin disaster, after the commander of the Russian Strategic Missile Forces Mitrofan Nedelin, who oversaw the rocket programme and died along with designers and testers.
Soviet authorities led by Nikita Khrushchev imposed total secrecy over the accident. The files on the launch failure were only declassified in the 1990s.
By coincidence, on the same day three years later a fire at a launch pad killed another seven testers.
In the wake of the two accidents, October 24 is known as "a black day" for space exploration on which Russian officials commemorate the memory of all those who dedicated their lives to the space programme.
Sending the first man into space in 1961 and launching the first sputnik satellite four years earlier are among key accomplishments of the Soviet space programme and remain a major source of national pride in Russia.
The International Space Station (ISS) saw a rare hiccup in September when the return of the Russian Soyuz capsule carrying three crew back to Earth was delayed by 24 hours after their craft failed to undock from the ISS.
Their delay in landing was the first in a decade of Soyuz flights.
Source: AFP Global Edition