Umm... Orbiting ships are far higher then the stratosphere... We're talking several thousand kilometers here. No volcano is going to throw debris that high. Not even a supervolcano will do it. This is way beyond the stratosphere. Is this out in SPACE. Theres not even a single atmospheric atom anywhere NEAR the craft. (Except what gets "lost", but even that is very little). Whats happening in the intro, is they are showing asteroid fregments hitting the planet. Those arn't volcanoes (They actually state this verbally). The reason for leaving, is that when an asteroid breaks up, whether it be by weapons or naturally, it leaves a lot of debris spread out in the area. Dust, and small pieces of rock that broke off the main mass will linger for quite some time. It'll even spread out in the system. Its quite possible for that debris to even assume orbit around the sun, and if there is enough of it, to significantly reduce the amount of light getting to the planet (Ice age x 2!), but the asteroid would have to be gigantic for that to happen. It'd also have to shatter into a giant cloud of dust for it to work, and be pretty close to the sun.
