The Match That Lights a Soyuz Rocket

NASA fires their rockets with an electronic ignition system. The Russians use giant wooden matches to fire up their rockets. The device, invented in the 1950s for intercontinental ballistic missiles, is called a PZU, which stands for a Russian phrase meaning “pyrotechnic ignition device.” In other words, a match. But they are huge, and a bit more complicated than a sulphur match that you’d strike against rough surface.

After the Soyuz is installed onto the launch pad, technicians working from an access bridge under the pad manually insert wooden sticks in a shape of a T-bar into each combustion chamber. Twenty big sticks go into the main chambers and 12 smaller ones go into the steering engines. At the top of each stick you'll find a pair of pyro-charges, and between pyro-charges there is a spring-loaded brass wire that acts as an ignition sensor. Wires from pyrotechnics and from the sensor run down the stick to an outlet where they are plugged into the launch control network.

When those charges fire inside the combustion chamber, their flame cuts the brass wire and the spring pulls the lose end away, breaking the electric circuit. That's what generates the ignition signal at launch control. Because the firing nozzles of the pyro-charges face each other, the ignition of only one of them ensures that the second one would light up as well (imagine two matches right next to each other). Only after the launch control has confirmed ignition inside of each and every one of the 32 chambers will they open the valves on propellant supply lines, initiating the full combustion. The flimsy wooden rig and a few wires are instantly and harmlessly incinerated in the ensuing inferno.

It may seem like a terribly old fashioned method, but look who is actually sending people into space in rockets now, and who isn’t. Read more about the PZU at Popular Mechanics. -via Metafilter