The fire in the capsule of the Apollo 1 mission, in 1967, ended the lives of its three crew members.

On January 27, 1967, just fifty years ago, NASA suffered its first tragedy: the fire in Apollo 1, which involved the death of the three men who should have manned it and almost derailed the entire American lunar program.

It was a Friday afternoon at Cape Kennedy. The rocket that a few weeks later was to take the first manned Apollo ship to space was already installed on the launch pad. Inside the capsule, the three astronauts – Virgil Grissom, a veteran of the Mercury program, Ed White, the first American to do a spacewalk and the rookie, Roger Chaffee – were simulating the pre-launch operations for the umpteenth time.

But all was not well. Communications between the ship and the control room were interrupted and interfered with. An exasperated Grissom came to complain. “How are we supposed to communicate with the Moon if we cannot manage it just three buildings away?” True, that capsule was an obsolete model, called Block 1, suitable only for orbital flights. But it was the only one available. Model 2, the one that would go to the Moon, was still under construction.

NASA planned to launch that capsule to test most of the equipment without leaving Earth’s orbit. In the previous weeks, dozens of technicians had entered and left it, installing and modifying one device after another. In fact, the floor beneath the pilots’ seats was a jumble of disordered cables.

In order to try to reproduce the actual conditions of the mission, the interior of the capsule had been filled with pure oxygen at a slightly higher pressure than atmospheric pressure. In the vacuum of space, the pressure would be only one-third of the atmosphere, but for a test at sea level, those conditions had to be simulated by applying a pressure somewhat higher than that of the outside.

Why then an atmosphere of pure oxygen and not a mixture of oxygen and nitrogen as the Russians did? Essentially, to purge all the dissolved nitrogen in the blood of the astronauts and thus, avoid the danger of gas embolism when they went outside the ship with their suits under reduced pressure. That had always been the policy of NASA and had worked well since the early days of the Mercury program.