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Comment by alex_hitchins | Hacker News Reader

What would the substances have been on the glass? I assume it would be something nasty but my chemistry is poor. Also, do workers wear haz-mat suits when working in the area? I'd guess there is a lot of the same stuff on the ground/atmosphere that could be inhaled. The ecological damage of launches is something I should really look more in to.

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HTPB, unburnt ammonium perchlorate, aluminum powder.

https://en.wikipedia.org/wiki/Hydroxyl-terminated_polybutadi...

And the combustion products include lots of water and hydrogen chloride, which combine to form hydrochloric acid. The gritty aluminum oxide (another combustion product) is probably a pretty good particulate sponge for holding acid as it cools below HCl's condensation point.

Thanks both for the reply. Is the Aluminimum oxide forming part of a thermite style reaction then?

Somewhat yes. Iron oxide is included, but considered a catalyst.

The rubbery plastic binder is a fuel. The Aluminum is a high-energy fuel. The "ammonium" part of ammonium perchlorate is a fuel, and the "perchlorate" part is an oxidizer.

The amount of aluminum is limited to prevent the temperature from getting too high and because it makes low-energy exhaust particles. Good exhaust particles are low-mass gasses with few degrees of freedom in the molecular shape. Aluminum oxide forms solid particles consisting of many atoms stuck together, which is pretty useless.

only to the extend that the Al powder in the motor is burning in the O2 released from the perchlorate, it'[s not an exchange like a traditional thermite

Essentially they add Al because it burns well and has a high mass which ups the mass of the exhaust gasses and as a result gives you more thrust

My understanding is post-shuttle launch, the ponds around the launch pad end up with a pH of ~1, due to the hydrochloride acid released.

Not of any life form that can survive that.

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