How did the "sparkers" actually create the sparks before SSME ignition? I'm interested in the technical aspects such as what materials were used and how the sparks were "shot out".
Pyrophoric metal similar, if not identical to, the flint in a common cigarette lighter. Just a whole lot bigger.
Believe it was a wheel of some sort that ejected the metal radially outwards into the area below the nozzles. I remember a TV program about pyrophoricity that mentioned the ROFIs, and explained a bit on how they worked, and then proceeded to fall right into the common misconception that they actually ignite the engines.