History's worst rocket tragedy actually occurred on the ground, in 1960, when the Soviets were experimenting with a dangerous new fuel. Piers Bizony chronicles it in his upcoming book, How To Build Your Own Spaceship:
On August 3, 1957, the Soviet Russian R-7 Semyorka missile, called "Little Seven" by the men who worked around it, flew a simulated nuclear strike trajectory, then became a space launcher just two months later, on October 4, by launching Sputnik. A great international triumph, then, but in missile terms, not necessarily the military advantage that Russia wanted.
The Semyorka used kerosene and LOX. Who in their right mind wants a nuclear missile that takes three or four hours to prime with LOX before you can launch it? Not the Soviet Red Army, for sure. So they commissioned an even more secret missile, the R-16, which, in theory, could be fueled and primed several days, or even weeks, before it was needed, with no loss of oxidizer, because its engineers had abandoned super-cold LOX and kerosene in favor of nitric acid and hydrazine: hypergolic fuels... a fuel and oxidizer combination that can be stored indefinitely at normal pressures and temperatures.
Hypergolic chemicals are efficient too. They ignite spontaneously on contact with each other and deliver a pretty good bang for your buck. Of course there's a downside. Hypergolics are among the nastiest and most toxic substances in the rocket business. Did we mention that they can be stored? Well, sort of. They are so corrosive they will play havoc with any part of your rocket (or your people) that they come into contact with that they shouldn't....
In October 1960, the R-16 was hoisted upright for launch at Baikonur, Russia's ultrasecret equivalent of Cape Kennedy, based deep in the deserts of Kazakhstan. And so began the single greatest rocket disaster in history.
The R-16's "storable" fuels wouldn't store. They were viciously corrosive and leaky as hell, oozing from dozens of pipe joints and tank seams. On October 23, the surrounding launch gantries were crowded with young technicians trying to fix a dozen different problems. As zero hour approached, the rocket began to drip nitric acid from its base. At this point, launch director Mitrofan Nedelin should have ordered the entire gantry to be evacuated, but he didn't seem to care about the risks. He sent yet more ground staff into the pad area straightaway, to see if they could tighten up some valves and stop the leaks and get the rocket up in the air.
Suddenly, the rocket exploded, instantly killing everyone on the gantry. With nothing to support it, the upper stage crashed to the ground, spilling fuel and flame. The new tarmac aprons and roadways around the gantry melted in the heat, then caught fire. Ground staff fleeing for their lives were trapped in the viscous tar as it burned all around them. The conflagration spread for thousands of yards, a wave of fire engulfing everything and everyone in its path. More than 190 people were killed, including Nedelin, perched on his chair near the gantry as a surge of blazing chemicals swept toward him.
From Piers Bizony's How To Build Your Own Spaceship, due out this August for $15. Excerpted with permission of Plume, an imprint of the Penguin Group.
Video of the disaster:
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Haunting details and quotes from the event, curated by Jacqueline Sly in a space history project