posted 09-20-2010 04:01 PM               

Right before space shuttle main engine (SSME) ignition, close-up videos of the area show what appear to be several fountains of sparks shooting and arching toward the area immediately under the engine bells.

posted 09-20-2010 05:02 PM               

Those sparks are called our hydrogen burn-off igniters and they are intended to burn free hydrogen. When we start up the engines, there is a little bit of hydrogen that comes out that hasn't ignited yet when combined with the oxygen in the system. Also, if we do have an on-pad engine shutdown after we've started the engines and have to turn them off for some reason, we shut down fuel rich as well meaning that the last bit of fuel that comes out of the engines will be hydrogen. So, those sparklers, that we like to call them, will burn off free hydrogen in the atmosphere rather than let it ignite on its own as it travels up the side of the ship. That's a safety consideration. It burns hydrogen before it causes us any trouble.