Solid rocket fuel or liquid rocket fuel? I was at KSC when the Hubble went up. It was curious to me that after the launch, the announcement came that we had to leave the area because a sulpher dioxide cloud was approaching our area. I thought the same thing that if it's O2 & H, how could there be sulpher dioxide?



The shuttle's main engines burn hydrogen and oxygen, so the product is water (in gaseous form, of course), which is why the plumes are barely visible.

The solid rocket boosters, on the other hand, use Ammonium perchlorate composite propellant, which is nasty stuff and by comparison generates lots of pollutants.