1967

Apollo 1

Sometimes engineers make mistakes. Sometimes those mistakes are disastrous. The Apollo 1 tragedy demonstrates one of those mistakes. It also shows how engineers learn from their mistakes, correct things, and move forward.

The initial design for the Apollo space capsule called for a pure oxygen atmosphere at higher than normal pressure. There were a number of good, rational reasons for this design decision. One reason is because that is the way NASA had done it on the Mercury and Gemini missions.

Having a single gas in the capsule, rather than a nitrogen/oxygen mix as on Earth, is lighter. There is only one gas to carry, meaning only one tank to hold the gas and no mixing/monitoring equipment to keep two gases in the right proportions. Also, the capsule pressure can be reduced to 5 psi (34 kPa) once in space, which is the same pressure used in a spacesuit. Low pressure is especially helpful in a spacesuit because it maximizes flexibility.

On the launch pad, however, the problem with a pure oxygen atmosphere is that it must be maintained at slightly higher than ambient pressure to keep outside gases from entering: 16 psi (110 kPa). With pure oxygen at this pressure, materials we think of as flammable become incendiary. They burn far faster and hotter. And Apollo was full of flammable material, particularly nylon, which is a plastic that burns readily. Even the flight suits were made of nylon.

During a routine ground test, the three astronauts were locked in the capsule with 16-psi oxygen. A spark started a fire. And then the fire spread with stunning speed. All three astronauts died. The last intelligible words out of the capsule were “I’m burning up!” and they came just 17 seconds after ignition.

A twenty-month review and redesign process followed the tragedy. The biggest change: a mixed nitrogen/oxygen atmosphere on the launch pad. Another was the replacement of nylon with a non-flammable material in the flight suits.

Engineers do make mistakes. The key thing is that they learn from them and make things better in the future.

SEE ALSO Plastic (1856), Saturn V Rocket (1967), Lunar Landing (1969), Apollo 13 (1970).

Crew prepares to enter their spacecraft.